Stupid People Refuting MythBusters over Plane/Conveyor Belt
Posted January 31st, 2008 @ 11:13am by Erik J. Barzeski
The (in)famous "Plane on a Conveyor Belt" experiment was run last night on MythBusters and, as physics dictates, the plane takes off.
That was a terrible experiment. The whole basis for the myth was that the airplane could take off from a treadmill traveling at the same speed as the aircraft. Unfortunetly during their testing they failed to keep the aircraft and the treadmill at the same speed. It is clearly evident from the video that the aircraft is accelerating faster than the treadmill is being pulled. If they were moving at the same speed the aircraft would not be passing all the cones while on the treadmill...it would remain in a stationary position relative to the cones.
The physics are totally wrong, an aircraft doesn't fly because of a propeller, ie a glider. It flys because of the air flow over the wings creating lift. If you were to run 20 mph down a road your hair would blow in the wind stream being created. If you run 20 mph on a treadmill your hair will look just as pretty as when your standing in place. Its the same principle with a wing.
The myth is a scam. They need to retry the myth with a pilot that can keep the plane at the same speed as the treadmill.
- It's not clearly evident.
- The aircraft would still pass all the cones (just as it would if it were on ice). It most definitely would not remain stationary.
- The physics are correct. Lift is generated by airspeed. Forward motion is generated because the engine (jet or propeller) acts against the air, not the ground.
- A person running has nothing to do with it. That's the "car" problem. Strap a jet pack on a person running on a treadmill and you've got the equivalent version.
Why can't these idiots get it through their thick skulls that the plane moves relative to the ground? They seem to be basing all of their opinions on the assumption that the plane stays still due to, I dunno, magic??? Even the most basic version MythBusters ran - the actual plane on the treadmill - proves them otherwise. The propeller pulls the plane through the air.
The only shocking thing to me in the entire episode was that 400 pound planes exist and they can take off going only 25 MPH!!!
More quotes below, because, well, why not? It's like spectating a car accident. In the voice of Haley Joel Osment: "I see stupid people."
Please note: all the quotes below are incredibly stupid and WRONG. I've left the names off to protect the stupid, but they can all be found at the MythBusters forum link above.
I think they blew this one. The whole object of the conveyor belt was to keep the plane from moving. The plane still moved. Thus not busted.
I think they would have better luck tying the plane with a long rope to keep it from gaining forward motion while still allowing it to gain upward motion and trying that instead of a treadmill.
They needed to account for the forward motion of the plane. They did not measure how far it took the plane to take off while on the conveyor belt. I'm betting it was the same distance as off the belt.
Excuse me, but as the videotape proves, the planes (both scale and lifesized) were moving. As the tape clearly shows, the plane was NOT traveling at the same speed of the treadmill, as the plane was moving FORWARD in relation to the pylons that were on either side of the runway. Therefore, air WAS moving under the wings by the action of the movement, NOT THE PROPELLOR.
Do you REALLY think that the NAVY would spend BILLIONS of dollars on catapult systems for aircraft carriers, if they could have just gotten away with having a treadmill instead.
GET WITH THE PROGRAM PEOPLE. It is all physics, just like the pilot Mark said: If I move the air provides lift, if the treadmil matches my speed, then the plane will be a brick.
This has NOT been proven at all.
Presuming the 'conveyor belt' was moving at 25 mph and the plane was not powered, it would be moving backwards at 25 mph. When the prop turns sufficiently to pull the plane forward (without the tarp) at 25 mph it will have lift off, but when on the tarp, the forward speed is cancelled by the reverse speed of the 'conveyor belt'. Therefore the plane moving forward at 25 mph means the engine is revving sufficient to overcome the tarp plus 25 mph (total 50 mph) and creating lift off at its required forward speed.
The plane and the conveyor belt were NOT traveling at the same speed. If they were, the plane would be stationary. It wasnt hard to see the plane was moving forward pretty fast, obviously faster than the belt. So its ground speed was still fast enough to reach takeoff speed to produce enough lift on the wings to fly. The prop doesnt make the plane fly, the wings do. Shut an engine down during flight, what happens, you glide. Cut your wings off in flight, see what happens.
I have lost all faith in humanity. I am truly disappointed in the MythBusters on this one. This myth should never have made it past the so-called "science content" segment. A plane is able to fly because air is passing over and under the wings at a certain velocity. This myth is a question of relativity. If the plane and the conveyor belt are moving at the same speed but in different directions, the plane is still NOT moving relative to the air. The ultralight plane in the episode took off because it was moving fast enough relative to the air to create lift under the wings. The conveyor belt was not moving fast enough to keep the plane stationary relative to the air. If you can't understand this concept, I would suggest opening a physics or calculus III book. Books can usually be found in libraries. If you cannot find a library, try google searching "how a plane flies."
Is this the only way to make a formal critique of the method used to test this myth? I just want to make a point in the hopes of clarifying a few things.
First, if you watch the footage from the show you can see that the plane is moving relative to the cones on the ground which, i assume, are stationary. Therefore, the plane is moving relative the ground and the basic premise behind the myth (that the plane is not moving relative to the ground because it is traveling on the belt of the treadmill at the same speed that the belt is moving in the opposite direction) is not what is going on in the experiment. To test the myth properly, the plane must remain stationary relative to the ground.
Second, the speed of the truck pulling the treadmill being higher than the take-off speed of the plane means nothing. The take-off speed is the speed relative to the ground required to give the plane enough lift to take off. The plane's wheels could make it travel much faster than that if the plane would stay on the ground. The treadmill just increases the speed the wheels have to go to get the plane to the take-off speed relative to the ground.
The episode proved that a plane can take off with a 25 MPH tail wind. It did not prove that iit could take off if it was standing still in relationship to the ground/air.
The proper test for what they were trying to prove is almost as simple as what they did, but requires a bit more preflight testing.
What they need to determine is the propellor speed at which the plane will reach 25 MPH. (It will work because this is a fixed pitch prop)
Get the truck/tarp moving at 25 MPH and increase the airplane's throttle until the proper RPM is reached, if the plane does not take off, keep increasing the throttle until it does.
If it requires 20% or more rpm then I would say that a plane cannot take off on a conveyor belt that continues to increase its speed porportionately to the increase in power of the plane.
This guy seems to think the Mythbusters pulled the plane forward with the conveyor belt instead of in reverse:
Wow! I can't believe the Mythbusters folks messed up so bad on this episode. Air has to move over and under the wings to create lift. Newton's Third Law: For every action there is an equal and opposite re-action. There is NO air current (Action A) against the wings to push back (Action B) and create lift. Sorry guys, the truck pulled the airplane forward to create a lift.
This guy is adding words to the problem to justify his misconception. The "wheel" speed is never mentioned in the original problem, and in fact, the wheels go 2x as fast as in a normal, non-conveyor takeoff:
The Myth was, Can a plane take off on a conveyor belt when the "wheels" on the plane are going the same speed as the "conveyor belt" when both are moving the same speed in opposite directions. In that case no it cannot since both will cancel each other out and plane should stay in the same spot on the conveyor belt and the plane will have no forward movement to build airspeed to create lift. In order to the plane to take off, it will need to make up the speed that it needs to take off. So technically the wheels on the plane were going 50mph in that myth and the plane was going 25mph forward to build enough lift under the wings in order to take off. So yes, technically a plane can take off on a conveyor belt but if the conveyor belt and the plane's wheels were going to the same speed, then no it cannot. Myth is still not busted
I'm afraid the only thing they busted was my love for the show. Had they truly matched the speed of the plane (ie 25mph) to the belt and not have throttled the engine (thus prop) to more than a 25 mph pull it would have never took off. What a shame they didn't realize this in time to do a decent show.
I would just like to point out that, if in fact, the plane was indeed going as fast as the "treadmill" tarp pulled by the truck, there would be no forward motion. The plane has forward motion and is indeed going faster than the tarp is being pulled. Therefore, the plane is able to get air under its wings and thus has the ability to generate lift. When you understand that air speed generates lift than you can see that if in fact the plane and the treadmill were going at the exact same speed, there would be no forward motion, momentum or wind speed generated by the plane moving. It would be as if the plane were static, that is if they were the same speed (the "treadmill" and the plane) then the plane would have no lift generated by movement. Hence it would technically not be moving. It is impossible to lift if the plane has no forward mmotion. I know this is excruciating detail but it just not possible if the plane was static like the car in the episode. It only took off because it was going faster than the tarp. Point blank. If you watch the episode, the plane moves past the cones which would be impossible if both the plane and the tarp were going the same speed.
Ok I'm new, But it seems most of the later posts got it correct. The aircraft moved past the trafic cones (it had ground speed), the wing had lift. Had the aircraft not had foward movement, but relied only on engine thrust (coveyor and aircraft speed REALLY match); (provided thrust made enough lift over the wing). The aircraft would lift vertically before it would move foward.
An airplane's propeller pulls the plane through the air, causing lower pressure on top of the wing than under it*, which is what lifts the plane.
The propeller does not push enough air across the wing surface to cause a great enough pressure differential for the plane to overcome gravity.
If the full-size test were actually done precisely, the plane would have stood still with respect to the ground.
Instead, the plane accelerated down the runway, passing cones all the way.
The same is true of the small-scale test: if the speeds were exactly the same, the plane would have remained still with respect to both the ground and the frame of the treadmill.
If the "forward motion" of the plane exactly equaled the "backward motion" of the treadmill, there would be a net-zero wind passing over the wings, and therefore no lift. This should be true even if moved at double or triple the minimum takeoff speed because you still have a net result of no wind over the wings. Less physical strain on the hardware, but really no different than mounting the plane on a pole - the plane can not move forward through the air, therefore it can not generate any lift.
Let me try to explain this slowly: If the aircraft does not appear stationary then the speeds are not matched.
Let me try to explain it slowly: If the aircraft is stationary, it has no speed TO match.
This was a huge oversight! The ground camera clearly showed that the plane had forward motion. Anyone that knows anything about how a plane flies knows that the wings must have air flowing over them in order to produce lift. Spinning the wheels does nothing to produce lift. The experiment proved nothing. I don't know why the pilot didn't contest the validity of the test!
The plane moved forward. It was beyond the cones when it took off. The plane was accelerating faster than the treadmill was moving...thus it had airflow over the wings, which provided the lift for take-off. Most aircraft cannot accelerate straight up...they need airflow over the wings to to produce "lift". Only a few, mostly military and acrobatic aircraft...and most R/C models...can accelerate vertically...which means the thrust is overcoming the weight. Do this "busted" myth again with a camera placed 90 degrees from the plane. Keep the plane in that position and pull the conveyor belt as fast as you want...the plane won't take off. The propeller won't produce enough airflow over the wings to produce lift.
I'm a pilot, I'm solidly in the no fly group. In fact it is hard to believe there is a "fly" group. Then mythbusters says "busted". Puhleeze... All this myth proved is that the airplane( in both cases) has more than enough thrust to fly faster than its take off speed (11 and 25 MPH). In fact the yellow plane probably can fly at 80 mph. So unless the conveyor also sped up to 80 the plabne would generate lift and fly. To prove this myth the planes must be limited to ONLY their minimum take off power and speed. This can be verified by manifold pressure and tire speed. At any time that the power exceeds the minimum, clearly the plane is going to start to go forward (shown initially as tire speed increasing). If the plane is allowed to accellerate it is clearly going to generate a bit of lift. At this point the wheels will no longer be in firm contact with the conveyor, the (relative) conveyor speed will diminish (as shown by decreasing wheel speed) The (relative) aircraft speed will increase by this corresponding amount and the aircraft will IMMEDIATELY fly. Basically as soon as either plane moves forward in the frame and generates a bit of lift, then the myth is over as the conveyor and planes are no longer moving at the same speed.
There should have been a science content here, but then there would have been no show. To call it busted is just a way to generate letters and NO ONE could be that stupid.
I love the people who say "it was not supposed to move because moves at the same speed." Do they not see the blatant disregard for simple logic?
Just because you saw it on television doesn't make it true! Granted the mythbusters are pretty awesome but they're not perfect. And in this case, boy were they wrong. Anyone who has taken a physics class knows that a plane needs air passing over and under it's wings to take off. And in order for the air to pass under/over the wings it has to be moving. From what the mythbusters said the plane was not supposed to move because it was moving at the same speed that the conveyer belt was moving but in the opposite direction. I really think they need to revisit this myth or at least explain what happened and why their "busted" really wasn't.
I agree with all those who say that this myth needs to be redone. The plane and the conveyor belt weren't going the same speeds, if they were, the plane would have stayed stationary. They show the speed of the ultra-light on the practice run, but don't show it during the test and they never show the speed of the truck Jamie is driving. As a pilot (and I hope all other pilots know), you need airflow over the wings to make an airplane fly. A stationary plane with no wind will not create any lift so the plane will not fly. The plane in this myth was moving down the conveyor belt so it was able to create lift by flying faster than the conveyor belt and was able to take-off. If the idea of this myth was just to see if a plane could take-off from a conveyor belt, then yes it is busted, because all you have to do is get the planes speed up to conveyor belt speed plus take-off speed and the plane will take off. But if the myth is that a plane can take-off while matching the conveyor belt speed, this myth is far from being busted. If they decide to redo this myth, I don't see why they can't build an actual conveyor belt to place the plane on. According to the show, they were using an ultra-light aircraft that only weighed 300 lbs, are you telling me that after all the experiments that they've done, they can't build something like that. It would be able to show exactly how fast the belt is actually moving.
This guy talks (correctly) about a small issue with the host's explanation: the engine (and propeller) pulls the plane through the air, it doesn't blow air over the wings.
I think the guys got it right on the show. The plane should take off from the conveyor. However, their explanation of the physics was completely wrong. The plane does not take off because of the propeller moving air over the wings. The plane takes off because the propeller pulls the plane through the air, this movement of air over the entire wing allows the plane to fly. If the propeller were enough to keep the plane aloft, then why are the wings so large? By this theory you would only have to have enough wing directly behind the propeller. This can also be proven by testing with a "pusher" style aircraft, one with the propeller behind the wing. It would also take off with this test. To further clarify this whole thing, they should have been measuring air velocity at the wings, not ground speed at the wheels.
Donate Life
Posted 31 Jan 2008 at 1:02pm #
And by calling these people "stupid" and "idiots" you achieve what exactly?
Posted 31 Jan 2008 at 1:19pm #
Any pilot in the "no fly" camp is no pilot that I'd want flying the plane I'm in....
Posted 24 Oct 2013 at 9:13am #
I know this is old but AGAIN, any pilot that is in the "no fly" camp is assuming that the experiment posing a hypothetical universe that would allow a conveyor belt to combat forward momentum it a way that canceled out take off speed.
It is a stupid trick of wording.
One one hand the myth is so simple that anyone that takes the wording of the myth literally a face value and know instantly the the plane will take off with ease.
And on the other hand there are people that look at the simplicity of the myth and assume that the author intends the hypothetical as outlined above.
When the myth says (if a conveyor belt was able to match the take off speed) it leaves to much up to interpretation.
Does it mean that you get an aircraft and measure its takeoff speed and THEN record that speed and apply it as craft attempts to take off??
Or does it mean that LIKE MOST THOUGHT experiments it leaves parts to of the equation in the realm of theoretical expressions.
this is NOT A MYTH
this is NOT a mind experiment
This is nothing more then a silly trick of phrasing with its purpose aimed at making people argue.
If it were legitimate it would clearly spell out the test criteria.
Posted 31 Jan 2008 at 1:23pm #
[quote comment="45682"]And by calling these people "stupid" and "idiots" you achieve what exactly?[/quote]
I succeed in telling the truth? In calling a spade a spade? What would you have me call them? The word "stupid" and "idiots" mean something, and to me, the definitions pretty much line right up with what these people are doing, saying, typing, etc.
No doubt I could have used synonyms, but then you'd just be asking me what I achieve by calling people clueless, dolt-like, unintelligent, braindead, deficient, dim, dopy, dumb, foolish, mindless, moronic, obtuse, thickheaded, unthinking, slow, ignorant buffoons.
[quote comment="45685"]Any pilot in the "no fly" camp is no pilot that I'd want flying the plane I'm in....[/quote]
Indeed. I'm amazed at how many of the "no fly" people are outing themselves as pilots. Wow.
Posted 17 Dec 2011 at 6:57pm #
If you wantr to call a spade a spade then you should be pointing out that the people in the no-fly camp probably have IQs below 130. I can imagine that someone with an IQ in the 120s might fall into the no-fly camp. So these people are not necessarily stupid, but they are not gifted.
Posted 31 Jan 2008 at 7:34pm #
Maybe a good way to refute this for the nonbelievers would be with a seaplane. No wheels, just skids.
Seaplanes, obviously, can take off just fine facing upstream up a river no matter how fast the water is going. Might help them visualize how the treadmill just doesn't matter.
Posted 31 Jan 2008 at 9:34pm #
[quote comment="45682"]And by calling these people "stupid" and "idiots" you achieve what exactly?[/quote]
he made me laugh while pointing out some really obvious points that all these people would have understood if they were just more intelligent.
Posted 15 Feb 2008 at 7:45pm #
An airplane with mass M sits on a conveyor belt. The airplane's jet engine is turned OFF. The conveyor belt starts moving backward at a constant velocity V_conveyor. (note that all velocities will be quoted relative to the ground referential)
Which direction does the plane go? Backward, with velocity V_conveyor.
Intuitively it is reasonable to expect that the plane will have to overcome this backward velocity before taking off.
At time T=0, the jet engine is turned on, generating a thrust, F by pressing against (we all agree) the atmosphere. As a result, the plane experiences a forward acceleration A = F/M. Note that the conveyor belt provides no acceleration, just constant velocity. [As an aside, also note that acceleration is independent of any fixed frame of reference].
We are allowed to decompose the velocity of the plane relative to ground (V_total) into the velocity component due to the conveyor belt (V_conveyor) and the velocity resulting from thrust acceleration (V_plane):
V_total = V_plane - V_conveyor
As velocity is the integral of acceleration, at the instant in time T=0 its (forward) velocity component due to the thrust force is still V_plane = 0: the plane is still moving backward relative to earth with velocity V_conveyor - V_plane = V_conveyor.
Time, T, continues to pass. Thrust F guarantees constant acceleration A=F/M, and the equation for the velocity of the plane due to thrust is V_plane=TA.
Thus V_total = TA - V_conveyor. The plane's ground speed V_total will be zero only when
T_null = V_conveyor/A
Until this time the plane will continue to move backward. As more time passes, the plane's forward velocity component due to thrust will continue to increase linearly with time, whereas the backward velocity component due to the conveyor belt motion will remain constant, and so the plane will progressively pick up forward velocity (V_total = TA - V_conveyor > 0 ), develop lift and take off.
Thus if the conveyor belt has constant velocity the plane will, of course, teventually take off. If the conveyor belt's velocity increases linearly with time at a rate A, then the plane will not develop forward velocity and will not take off.
Posted 17 Dec 2011 at 4:00pm #
Tom. You are correct in everything you say until the last paragraph. As soon as the plane's engines overcome the friction between the wheels and the treadmill the two systems (plane and treadmill) become independent. This means that the treadmill's action no longer is communicated to the body of the plane. This means that the treadmill can be accelerating (not constant velocity) and the plane will still take off.
Posted 15 Feb 2008 at 8:16pm #
[quote comment="46011"]Which direction does the plane go? Backward, with velocity V_conveyor.[/quote]
No. If the brakes aren't on, it's quite possible that the conveyor belt could be moving backwards faster than the plane. Put a roller skate on a tablecloth and yank the tablecloth. Unless you gradually accelerate so as not to overwhelm the resting friction, the skate doesn't immediately move at the same speed as the tablecloth.
And that's without the roller skate supplying its own force opposite the direction of the table cloth (as we have with the plane).
Your math is wrong, your physics are wrong, and your methods are incorrect. V_conveyor accounts for almost no impact on the plane's velocity because the conveyor belt applies almost no force horizontally. The only force it applies is UPWARDS, to counter the weight of the plane. The "backwards" force it applies (opposite the forward direction of the plane) is supplied by the ball bearings and is, again, negligible.
You are wrong… and it's funny you'd come to a post making fun of people who get it wrong and then do as you did.
Posted 15 Feb 2008 at 8:27pm #
Erik,
This is not a frictionless world. If you wear rollerblades and setp onto a conveyor belt you may indeed not *initially* move with the conveyor belt but in a few short moments you will have the same velocity as the conveyor belt. The quality of your ball bearings has nothing much to do with it in the long run.
In other words once equilibrium is reached you will be moving at the same speed as the conveyor belt.
Once that occurs, when you turn on your jetpack the wheels and their bearings are essentially immaterial and the rest of the calculation holds.
Posted 15 Feb 2008 at 11:09pm #
Tom,
Your claim is that the rolling resistance of the ball bearings will be great enough to stop the plane from moving forward relative-to-the-air to the point of achieving lift off.
Given that claim, which is actually subtly different than the original claim, then it becomes a question of how much thrust can the plane's engine provide vs. how much rolling resistance can the wheel's bearings provide.
In general and without the bearings failing catastrophically, the answer is "a lot of thrust" vs. "very little resistance".
The quality of the bearings very much do matter simply in that your scenario would require the conveyor belt to be going at 100s or 1000s of miles per hour to provide enough rolling resistance to counteract the thrust of its engine.
Sure -- when you modify the original claim as you have, it could theoretically be possible to pull the conveyor belt "backwards" fast enough to create enough rolling resistance to prevent the plane from taking off.
More likely, at the speeds involved, the bearings would fail catastrophically and this would become a considerably more sparky experiment.
Given a powerful enough engine, the presence/absence of rolling wheels is irrelevant. It becomes entirely a question of whether or not you can achieve liftoff prior to the wheels, struts, and belly of the plane being worn through.
b.bum
Posted 16 Feb 2008 at 4:41am #
B.Bum,
I actually made no claims about bearing resistance; I'm just giving an example of one of the possible limits of the problem (plane has initial backwards velocity) and how this allows you to start thinking about the problem in simple terms that can then be built upon (first, initial velocity and momentum; only afterwards should you to start build up your model by considering friction).
Solving physics problems is all about stating your initial hypotheses.
1. If the wheels have zero friction, then the conveyor belt is a red herring because its motion will not be transmitted to the plane, ever. The plane having the advantage of acceleration will always take off.
2. If the wheels have infinite friction, then the plane won't be able to roll forward and will always have the same velocity as the conveyor belt. The plane will never accelerate and never take off.
Clearly, the real world is in between. So "solving" the riddle is a question of how your assumptions balance out. Although this was not my initial guess, I do agree that in the real world no conveyor belt would succeed in transferring its full acceleration to the plane, and that the plane will always take off.
Just to beat a dead horse:
IF the conveyor belt has constant velocity -- as was the case in the Mythbusters show -- then the plane will ALWAYS take off under ANY additional assumption (see above)
IF the conveyor belt is accelerating, things get tricky and indeed you have to get into issues of static friction etc. etc.
Posted 16 Feb 2008 at 9:49am #
Tom, no further comments from you are necessary here. Please move on.
[quote comment="46021"]I'm just giving an example of one of the possible limits of the problem[/quote]
No, you're not. We've been given a set of rules, either "reality" or the ones given in the stated problem. We're not interested in making up new versions just so that, under an unrealistic set of expectations, the conveyor belt has very much impact at all on the plane's forward progress.
The acceleration or not is a moot point, and if you think an accelerating conveyor belt somehow changes the rolling resistance, you're wrong on that count as well. Friction remains largely the same once the wheels start rolling, and by "same" I also mean "next to nothing" - nil, negligible.
[quote comment="46021"]If the wheels have zero friction, then the conveyor belt is a red herring because its motion will not be transmitted to the plane, ever. The plane having the advantage of acceleration will always take off.[/quote]
The wheel friction is so close to zero, that this is indeed how people grounded in reality choose to look at the problem.
[quote comment="46021"]If the wheels have infinite friction, then the plane won't be able to roll forward and will always have the same velocity as the conveyor belt. The plane will never accelerate and never take off.[/quote]
Actually, you'd have to lock the plane to the conveyor belt for this to be true. Otherwise I suspect that the plane would simply shred up its tires as it drug them over the pavement. Sea planes can still take off from water, after all - and they don't have wheels. So again, you're wrong.
[quote comment="46021"]Clearly, the real world is in between.[/quote]
Yet in either case, the plane takes off. In the second case - the wildly unrealistic one - it's admittedly more difficult (and the wheels may shred and blow up, and sparks may fly as bbum said), but it still takes off if it's not literally locked to the ground.
[quote comment="46021"]IF the conveyor belt is accelerating, things get tricky and indeed you have to get into issues of static friction etc. etc.[/quote]
No, they really don't get tricky at all. Acceleration's impact on the rolling resistance of ball bearings is minimal/negligible.
Really, no further comments (from anyone on either side) are necessary.
Posted 08 Dec 2008 at 8:57pm #
I think maybe the easiest way of thing about this is to consider the wheels to be like ice skates. Would a plane on big ice skates in a skating rink have trouble taking off? No. It wouldn't. Because the propeller pulls the plane through the air. No friction with the ground is necessary to move the plane.
Now consider if the ice were magically moving underneith the plane, would it cause the plane to move? No, it wouldn't, because ideally there is zero friction between skates and ice.
Since there's no friction, the movement of ice underneith plane does not change the plane's force in any significant way. Therefore when the propeller is turned on and the plane gets force forward, it will move forward and take off just like normal.
Magically moving Ice / skates, and Conveyer belt / Wheels and analoguous. It's the exact same situation.
The fact that the plane takes off just like normal, regardless of if the ground is moving underneith of it, is what busts the myth. That is exactly what the pilot commented about when he got out of the cockpit. He said "it took off just like normal!", meaning he didnt' have to gun the engine further to "outrun" the conveyer belt.
Oh well. This whole thread has been pretty amusing đ
Posted 09 Dec 2008 at 2:19am #
Yeah, except if you look at the video the "conveyor belt" is replaced by a thin plastic tarp. Do you honestly believe there is "zero friction" between the wheels of the plane and the immobile ground beneath the tarp?
Posted 09 Dec 2008 at 7:09am #
[quote comment="51337"]Yeah, except if you look at the video the "conveyor belt" is replaced by a thin plastic tarp. Do you honestly believe there is "zero friction" between the wheels of the plane and the immobile ground beneath the tarp?[/quote]
Tom, after all of the above do you really want to look this stupid?
Posted 09 Dec 2008 at 7:25am #
Listen dude, I don't know why you get off insulting people but I'm sure it helps you feel superior, and if so then great for you. I have a PhD in experimental physics and have published papers in eminent physics journals, and I've discussed this problem with OTHER researchers who have PhDs in physics -- and guess what ? The answer they give is 50-50, so its not as trivial as you may think it is, I don't care what you say or think, and frankly I'm not afraid to "look this stupid" once in a while as I am not that insecure. If it were that trivial a problem would a TV show have spent money to try to prove or disprove it?! Would hundreds of people argue about it if it were that trivial? If you can't enjoy toying with a problem or the limits it pushes then that's your issue, and if you can't discuss things with people without insulting them than I simply feel sorry for you, for all of a fraction of a nanosecond. But I guess that's why you have a blog, to feel superior and allmight. And as I said that lame plastic tarp does not do justice to the problem as it is laid out.
Posted 22 Oct 2010 at 11:02pm #
Tom, did you receive this PhD in "experimental" physics online? at what university did you study? If you're not afraid to look stupid, please link us to some of your publications... oh wait, you can't? hmmm...
It's shocking that with so much effort put into this people still cannot grasp a relatively simple concept, and may even try to use some phony-bologna physics.
Posted 09 Dec 2008 at 7:57am #
[quote comment="51341"]Listen dude, I don't know why you get off insulting people[/quote]
Let's be clear: I don't "get off" insulting people. I get off insulting incredibly stupid people. If you're even remotely as educated as you claim, then I'm ashamed for you, the schools you attended, and your friends.
[quote comment="51341"]If it were that trivial a problem would a TV show have spent money to try to prove or disprove it?![/quote]
Have you watched Mythbusters? They don't exactly limit themselves to the most complex of issues. "Can you wrap yourself around a swingset?" "Can you escape from sand when buried up to your neck?" "Will Mentos and Coke explode?" are a few of their "myths" and I'm certain there are sillier ones than those.
[quote comment="51341"]Would hundreds of people argue about it if it were that trivial?[/quote]
People argue about it because they think the thrust comes from the wheels. Once they realize that, no, the wheels are just there to spin, they get over it. Millions of people argue about it because it's a brain teaser that requires a shift in the way we normally think about propulsion.
[quote comment="51341"]If you can't enjoy toying with a problem or the limits it pushes then that's your issue, and if you can't discuss things with people without insulting them than I simply feel sorry for you, for all of a fraction of a nanosecond.[/quote]
Ooh, did you learn about nanoseconds while you were getting your Ph.D? This question pushes no limits. If it pushes yours, again, I feel sorry for the "degrees by mail" college from which you claim to have received your degree.
You've obviously subscribed to the comments here, which is why you post so quickly after someone else does. I've taken the liberty of removing you from the subscription list. As I said before, no further comments from you are necessary here. Move along.
Posted 14 Dec 2008 at 4:15pm #
Free body diagram. Force from the engines pushes the plane forward through the air, mass*gravity and the normal force cancel each other, and the wheels provide a negligible resistance to motion in the opposite direction.
end result. Plane is pushed forward, air moves over the wings, and the plane takes off. Erik is right
PLEASE NO MORE FAKE PHYSICS!
kthxbai
Posted 20 Dec 2008 at 11:39pm #
Just watched a rerun of this infamous episode and had to sound off. I am not an engineer or a pilot but its a pretty simple concept to me. Rather than reiterate the logical arguments already noted here lets propose some thought provoking comments and questions for those who don't seem to understand:
1. If you believe the wheels have any real impact on take off, what happens after flight is achieved?
2. The conveyor belt is basically only spinning the wheels faster. Thats all it is doing..
3. We have not unearthed some new way to decrease the size of runways because of this, it actually shows the plane takes off at around the same distance as it normally would (because the wheels have almost no impact on propulsion). Not because of any conspiracy or discrepancy in matching the opposing speeds.
4. Go ahead and increase the speed of the conveyor, see what happens.
Posted 22 Jan 2009 at 6:06pm #
I think the problem is that everyone interprets this problem differently.
When we are talking about the plane going the same speed as the treadmill, some people think of that as relative to the treadmill, and others think of it as relative to the ground.
If you think of it as relative to the treadmill, then you are visualizing the plane being stationary on the runway. If this is the case, then then the plane will NOT TAKE OFF.
If you think of it as relative to the ground, then you are thinking about the opposite case where the plan is providing normal forward thrust. In this case, the plane will move forward at near its normal speed, and will TAKE OFF NORMALLY.
I've never suceeded in finding the original wording of the question, but I really think everyone should stop bashing everyone else just because they have a different opinion. We've started a few too many wars that way.
Posted 22 Jan 2009 at 6:33pm #
[quote comment="52409"]When we are talking about the plane going the same speed as the treadmill, some people think of that as relative to the treadmill, and others think of it as relative to the ground.[/quote]
With all due respect, no. Since the treadmill is moving opposite the direction of the plane, the plane-to-treadmill speed will always be twice the plane-to-ground speed. There's no way for the treadmill to "match" the speed of the plane (relative to the treadmill) unless the plane's speed is 0 (in both frames of reference).
The only logical frame of reference for the plane's speed is plane-to-ground. You can't have a plane-to-treadmill speed measurement that affects the speed of the treadmill.
Posted 19 Feb 2009 at 4:37am #
Anyone wanna check my physics on this?
The instrument inside the pickup truck is a speedometer, which measures miles per hour away from a fixed point. (I know, I know...speedometers are linked to the wheels of the truck to get that measurement, unless it's a GPS based speedo, but just go with me for a minute, mmmkay?)
Now, imagine there's an instrument in the plane that's an air speed indicator. It isn't linked to the plane's wheels nor to GPS, it measures air movement through a tube mounted somewhere on the plane, and expresses the plane's speed relative to teh air around it. (I know, it's crazy, but just give me a minute, okay?) Just for simplicity's sake, let's say this instrument is also marked with "miles per hour."
That plane is going to lift off the ground when its airspeed hits 25 mph. If it was sitting still, engine off, facing into a 25 mile per hour wind, the plane would lift off the ground, right? (Yeah, someone would have to hold the tail up, in order to get the proper angle of the wings so that lift was created, and the pilot would have to monkey with flaps and such, but go with me. Yeah, I know, the plane would lift very slightly, then quite probably tumble backward, pretty much ruining the day of the guy holding up the tail....)
Conversely, if there was a 25 mph wind blowing, would the plane take off running downwind? No, not until it went 50 mph, measured from a fixed point on the ground.
I guess my point is that the treadmill is moot. My physics professor, Sister Bertrille, said, "When lift plus thrust is greater than load plus drag, anything will fly." She never got around to explaining how to hover, and she was so darn cute when she said "thrust." She never mentioned a treadmill.
What? Oh, yeah. There are four frames of reference here. Treadmill speed relative to the ground, plane speed relative to the ground, plane speed relative to the treadmill, and plane speed relative to the air. Guess what? The first three are moot. The last one is the only one that will produce lift and/or flight.
On the TV show, the model plane shot forward, off the treadmill. The full-scale plane shot forward past the cones before its wheels lost contact with the tarp. But it didn't really matter how fast the plane was moving past the cones....it only mattered that the plane had 25 mph worth of air speed. If there was a headwind that gradually increased to 25 mph, as the pilot increased engine speed to keep the plane lined up with one of the cones...viola, the plane would have lifted off the ground, and appeared to hover.....(virtually) regardless of tarp speed or truck speed.
One final thought. The plane didn't fly because it reached a ground speed of speed of 25 mph. It flew because it reached an airspeed of at least 25 mph, at which point its wings generated lift and it's engine generated forward movement. If all it took to fly was ground speed, we wouldn't even need the plane; all we'd need is a 400 pound pickup truck, right? And all we can simulate with a treadmill is ground speed, right?
And anyone who disagrees is a doodyhead, and went to a doodyhead school.
Posted 30 Mar 2009 at 11:31am #
A = wheel speed
B = Conveyor belt speed
C = speed due to plane's Thrust
Stationary
A = B (0 = 0)
Moving
If the vehicle was propelled via the wheels thenââŹÂŚ
A = B (5 = 5)
If the vehicle was propelled via an outside force thenââŹÂŚ.
A = B + C
if C is 0 then A = B
If C is any other value than 0 then A and B are both infinate.
So either the question is broken as any forward thrust breaks the simple equation OR as soon as the plane starts accelerating the wheels and treadmill will accelerate to infinity regardless of the speed of the plane as long as the plane is moving.
If the plane is stationary then the treadmill is stationary
if the plane moves then the conveyor belt and wheels will be travelling at an infinate speed.
Posted 30 Mar 2009 at 11:46am #
[quote comment="53622"]if the plane moves then the conveyor belt and wheels will be travelling at an infinate speed.[/quote]
No. The conveyor belt doesn't match the wheel speed - it matches the plane's speed relative to the ground.
Posted 07 Dec 2011 at 6:20pm #
And that is why the broadcast is a hoax, because the conveyor doesn't match the wheel speed. A properly conducted experiment would match the conveyor speed to the wheel speed, and the plane wouldn't take off.
Eric, you childish, cowardly, name-calling quivering pitiful specimen - go throttle up to full the propeller of a plane with it's wheels chocked (the analog to the velocity-matched conveyor) and wait for the plane to take off. Then see what hapens first - the plane taking off, or your fear/hatred/ineptitude becoming illuminated to you.
Posted 08 Dec 2011 at 8:46am #
[quote comment="68732"]And that is why the broadcast is a hoax, because the conveyor doesn't match the wheel speed. A properly conducted experiment would match the conveyor speed to the wheel speed, and the plane wouldn't take off.[/quote]
Hey moron: they never said wheel speed. Since the plane is moving forward the wheel speed will always be 2x the belt speed (if you're measuring on the outside of the wheel) except when both are 0.
Of course, if you measure the speed of the wheels as the center point of the axle, then the speeds did indeed match up.
People claiming the experiment was conducted in a a "wrong" way are simply trying to account for their stupid misunderstandings.
Posted 13 May 2009 at 2:54pm #
The main problem with the "no-fly" people is that they are assuming that matching the plane's speed with the treadmill means that the planes ends up not moving.
A. This is impossible, because if the plane is not moving horizontally, but the treadmill IS moving, then you have already violated the terms of the problem. Let me use a 747 as an example. The take-off speed is 180mph. People who say that if you put a plane moving forward at 180mph on a treadmill moving backwards at 180mph, the plane will not move. Well, if the plane isn't moving, then there's no speed to match. So then to keep the terms of the problem in line, the treadmill must stop.
B. Any reasonable person would agree that the reason we have wheels on plane is decrease friction against the ground as much as possible. So you have very little friction against a stationary ground while the plane propels itself through the air (guided along the horizontal plane by the ground) until it builds up sufficient speed to lift off. So why would introducing a treadmill into the equation suddenly produce enough friction to keep the plane from moving? There is SOME, but very little, friction against the ground when the plane takes off. Let's say ground friction is F*1, which obviously doesn't hinder the plane in any way. If you put the plane on a treadmill going in the opposite direction at a proportional speed, then all you get is F*2, meaning the treadmill is moving backward relative to the plane at twice the speed of a normal runway. How would that stop the plane with the massive amount of thrust it produces?
Posted 22 Jun 2009 at 6:44pm #
Lets keep this simple. A paper airplane does not need much lift to "fly" (glide). Therefore, if you're running on a tread mill with a paper airplane in hand, and just let go of the airplane, will it fly ahead of you? No, it will drop to the ground. Why? Because while there may be enough theoretical forward motion (ie: your running) for it to fly, there is no movement of air over its wings. Even on a treadmill, you are required to toss it forward. Same idea with the airplane on a treadmill. If the airplane matches the movement of the ground below it, without airflow over the wings, there is no lift. Ground speed is meaningless. Its about Airspeed. An airplane on the ground with engine turned off (or a glider) with a Vs of 50 knots will lift off the ground in a direct headwind of slightly over 50kts. Or in other words, an airplane flying at an A/S of 100kts into a headwind of 100kts will have a G/S of 0kts. But its still flying. And thats why some airplanes can fly backwards. If you're flying at 40kts in a 50kts headwind, you're going backwards (relative to the ground).
Put simply, Mythbusters got it wrong. The ultralight was clearly allowed/able to gain forward momentum (faster than the tarp was pulling)(allowing for an airflow over the wings) and therefore, lift. And the RC A/C were allowed to accelerate forwards on the conveyor belts. Jamie getting all "lecturey" about science he clearly did not fully grasp was also uncalled for.
On a side note, if the navy could develop a carrier that could do 150mph, a Super Hornet could lift off the deck vertically.
One day.
Posted 23 Jun 2009 at 7:04pm #
[quote comment="54550"]Lets keep this simple.[/quote]
It's too bad you left out the critical parts in your attempt to simplify.
[quote comment="54550"]Put simply, Mythbusters got it wrong.[/quote]
No, you did.
If you ever do realize why you got it wrong, you're going to feel pretty dumb for a few moments. It's okay. Just let it pass.
Posted 20 Jan 2011 at 7:45pm #
This is the dumbest argument I have ever heard. Holding a paper airplane while running in a conveyor belt and then just letting it go = equivalent to a plane with propeller or jets on conveyor belt? DUH.
You still can't get your head around that the wheels on an airplane are FREE SPINNING and have no power. All power is in the propellers or jets. Which acts against the AIR and not the GROUND. You running in a conveyor holding a paper airplane is causing that plane's thrust to be dependent on your legs, which act against the GROUND...you are basically same as a car on conveyor belt which cannot move!
However as you correctly pointed out (but wrongly interpreted), when you push the plane with your arm and let it go, it would still FLY. What you don't get is that the push of your harm on the paper plane is equivalent to the propellers or jets of a real plane pushing against AIR. The action of your arm pushing the plane is INDEPENDENT of the ground. So the paper plane will FLY. And that's why a real plane on a conveyor belt will fly...because the generate thrust NOT VIA WHEELS (which are free spinning like the wheels on a skateboard), but via the propellers or jets, which push on air, independent of what is going on in the ground.
All the conveyor belt does is make the wheels spin faster!
Posted 23 Jun 2009 at 7:27pm #
...sigh...
I don't think either opinion is dumb or even wrong for that matter. There are two very different questions being proposed.
Lets start with this. Put the plane on the treadmill, leave the engine off, and start the treadmill. What will happen? The plane will start to (VERY SLOWLY) move backwards, but the wheels will begin spinning FORWARDS. Can the plane take off? No. There is nothing pulling it forwards. Note however, that the plane has not gone shooting backwards, because of the wheels.
Now start the engine, there are two throttle levels we want to look at, which correspond to the two different schools of thought.
Throttle 1:
At a very, very, very low propellor speed (not one that a plane could ever take off with), the plane will stop moving backwards, and will hold still on the treadmill. The wheels will begin to spin at exactly the same speed as the treadmill. The plane will NOT take off.
Throttle 2:
If the pilot pushes the thottle up to takeoff speed, the plane will begin to move forwards, and will eventually take off.
Now supposing the treadmill speed was increased too, the plane WILL have to work harder than normal to take off, but for the treamill to actually prevent the plane from moving forward, it would have to travel at a speed that would literally sand the wheels right off the plane. In this case, the plane would probably not take off, and bad things would happen to the pilot.
So the question it comes down to is WHAT SPEED IS THE TREADMILL GOING?
If you think it is going at the plane's normal takeoff speed (say 100 km/h), the plane will certianly take off, and the wheels will just spin a little faster.
If you think the treadmill is going way faster (around 10,000km/h or something crazy like that), the friction in the wheels will hold the plane in place and it cannot take off.
Posted 03 Sep 2009 at 1:50pm #
Okay, so I'm not an avid fan of Mythbusters, nor am I of any kind of scientific accreditation at all...And to be honest, I'm not even sure if they did ANOTHER experiment to amend the problem, but I agree wholeheartedly with Erik. When they did the Segway/Paper model, the radio controlled plane accelerated faster than the paper was being pulled away, but when they interviewed the pilot...I thought FINALLY someone understands the pivotal factor in this experiment! But when the plane clearly accelerated faster than the tarp, and the pilot emerged, absolutely amazed that he was "Wrong" I had to stop my teeth from eating my brain! It was so clear that the plane had advanced forward! (Perhaps even the complete distance it takes for the plane to actually take off on a runway, give or take...) I've always respected the Mythbusters, because as men and women of science and physics, they're always thinking of things my dinky little brain could not. But you didn't need logical thought of any kind to realize that the experiment was flawed. All you needed were eyes. If the experiment HAS been developed again, and aired with a more valid/successful (In the sense of Busted or Plausible) conclusion then I don't think they should even air that episode any longer. With the fallacy being so obvious, I'd be embarrassed as a network to show it over. Sure, there are bumps and bruises in science, that's what makes the scientific method, and the development of theories so forgiving. However, if that theory is to be honored in the scientific community, then you're experiment should be a complete and accurate testing of the hypothesis at hand.
When you think about the experiment as a whole...If they were going to go through all of those resources and funding to test the myth, it was a complete waste if they weren't going to do it properly. I love the show, but in this particular instance, it seemed as if the cast were going to great lengths to prove their belief that the plane in fact could become airborne standing completely still, ignoring in it's entirety the major factor being tested.
I'm just sitting here laughing, because the more I think about it...The more I comprehend that that hour I'm never getting back! What a waste of time it was for me to respect them, and trust them to deliever the truth, rather than to go to all lengths to show their faulty logic could be proven. As a scientist, I think it's important that you can listen to reason, be observant, and overall unbiased about the experiment. I feel as if the logic delivered by the cast themselves was enough to count as a variable! Someone pushing so hard to prove they could...well...prove something!
Posted 03 Sep 2009 at 4:11pm #
the stupid, it burns.
Of course the plane moved forward.
The plane was pushed forward by the propeller.
The wheels in a plane are not powered. They do not move the plane. The wheels just give something for the plane to move upon that is less friction than, say, dragging bare metal around.
Posted 01 Jan 2010 at 5:46pm #
Assuming that there is no wind at the site of the experiment, when the airplane throttle is moved to full, the plane will accelerate and take off. This will happen regardless of how fast your treadmill is making the wheels spin. Of course, if you accelerate the treadmill to 8 gazillion miles per hour, the wheels might fall off making it a bit more difficult for the plane to take off. In that case however, the black hole created by the 8 gazillion mph treadmill will have destroyed the universe and rendered your results slightly irrelevant.
The stupid, it does indeed burn.
Posted 02 Jan 2010 at 7:04am #
When I first watched this episode I admit I thought the challenge involved an aircraft rendered stationary by a moving treadmill, and I thought the experiment was flawed when I saw the plane moving forward. True, I am NOT a pilot, nor do I claim to have a firm grasp on the laws of aerodynamics, but I should not have jumped so quickly into such an erroneous conclusion. I soon realized my mistake when I read the phrase â A treadmill CANNOT prevent a free-rolling plane from moving forward. The propellers PULL the plane through the air, thus creating lift. The plane WILL take off!â
The analogies of attaching a rope to the back of the aircraft, or holding a toy car stationary with your hand do not apply. THE PLANE WILL MOVE FORWARD AND TAKE OFF! Luckily, I realized my mistake before I posted any letters to the contrary.
I cannot call it a trick question, like the rooster laying an egg on top of a barn, but at first glance it can mislead.
Kind of reminds me of this oneâŚIf a space ship traveling at the speed of light turns on itsâ headlamps, how fast does the light from the headlamps travel!
Well, maybe not.
AnywayâŚNaysayers, for a short time I was one of you. YOU ARE INCORRECT !
Posted 03 Jan 2010 at 8:28pm #
I may have been mistaken when I stated in my previous posting that this is not a trick question, like the rooster laying an egg on top of a barn. People HEAR the word âroosterâ but ignore itsâ implication when they hear the words âlays an eggâ. They then set their mind to solving the problem of which side the egg rolls down.
In the question at hand, some people have it fixed in their mind that the âtreadmill-airplaneâ scenario has resulted in an aircraft that is âstationaryâ in relationship to itsâ surroundings. Even though the original myth makes no such determination. It only states that âAn airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.â
They ignore the fact that it doesnât matter whether the surface under the planesâ wheels is moving backwards, forwards or standing stillâŚTHE PROPELLERS ON THE PLANE ARE PULLING IT FORWARD AND THE AIRCRAFT WILL TAKE OFF WHEN IT REACHES THE PROPER AIR-SPEED. It doesnât matter if itâs a toy plane, an ultra-light, a Beechcraft, or Howard Hughesâ Spruce Goose, the result will be the same.
As I was saying, having now overlooked this, they set their minds to the other fact of fixed-wing flight. âWithout airflow there can be no liftâ. Since they now believe that this plane is âstationaryâ how can there be airflow? They have reached a correct conclusion, but to an incorrect premise.
Iâve enjoyed myself immensely reading these postings. I hope they continue!
Posted 03 Jan 2010 at 8:29pm #
âŚbut PLEASE stop comparing the airplane to cars, joggers and so on.
Picture this:
A very large airplane is flying 1000 feet above the ground. Beneath it are dangling a number of ropes. Attached to the ropes are an automobile (engine running hard), a jogger (legs pumping),a bicycler (peddling like crazy),a roller skater (well, I guess heâs just hanging there), and lastly, a smaller airplane (propellers spinning).
Letâs cut the ropes, shall we? The car, the jogger, the bicycle, and the roller skater plummet
earthward. The small plane flies off into the sunset.
The others require a surface to maintain motion. The plane is in itsâ element. The plane will always move forward even if it never takes off. It will just run off the end of that damned treadmill. It will not stay in place.
I was going to add a surfboard, but that might be a bit much
Posted 06 Jan 2010 at 2:41pm #
It appears to me that the people who are posting on this site and others fall into three catagories.
1) Those who "get it," and understand that there is a major blind spot causing some individuals to arrive at an incorrect conclusion.
2) Those who donât "get it," and stick to the premise that the plane behaves like an automoble or jogger. That is, will somehow remain in place when the speed of the plane and the treadmill are matched.
3) Those who initially began as category 2s, but later realize they are wrong. These people are most interesting because rather than outwardly "jumping ship" they stick to their original declaration, and try to convice others that there is an underlying "spirit" to the myth that substantiates their claim.
I could argue that there is a 4th group of individuals who belligerently declare that it is a stupid myth and we shouldn't even be discussing it. Evidently, the hundreds of postings we have seen disprove that position. If nothing else, it is an intriguing insight as to how people perceive and go about solving a brain teaser.
All in all, it's great fun. You might want to check out some of the videos on YOUTUBE relating to this myth. I had a few good laughs myself.
Posted 07 Jan 2010 at 8:37am #
I had a gentleman in my place of business yesterday that I happen to overhear tell one of my associates that he had flown his own aircraft down south to visit relatives over the holidays. So naturally I told him the myth.
I was astonished when he replied that the plane would NOT take off! When I asked him why it wouldn't lift off he said "I've studied aeronautical engineering and the plane would need lift to fly" When I asked why there wouldn't be lift under the conditions of the myth he said,"Because a stationary airplane would not have airflow over its' wings". "But I explained that the plane was moving forward at the same speed that the treadmill was moving backward" I replied. "Exactly" he said, "⌠so it's stationary relative to the ground"
I couldn't believe my ears. It took five more minutes of explanation before I saw the dawn of realization in his eyes. He first tried to say that I had explained it wrong, but finally gave in and sheepishly admitted I was correct.
Who says this topic isn't worthy of discussion?
Posted 09 Jul 2010 at 5:49am #
If there is still someone reading this (or just stumbling about it accidentally as I did) and still thinks the Mythbusters got it wrong, here's a thought.
1. To take off, a plane need lift. This is true.
2. To generate lift, air needs to move past the wings (or airfoil/aerofoil, google it). This is true.
3. The way the plane produces this lift, is by accelerating along the runway. This is true.
4. The way the plane ACCELERATES, (and this is the tricky part) is by applying force by the revolutions of the propeller (which is usuallo also an aerofoil, so technically, it in itself has lift).
To illustrate this, let us change the accelerating force generated by the propeller to something we are all familiar with, say, gravity. We all are familiar with the concept of gravity, yes? Good.
Now, gravity usually doesn't act on the horizontal plane, as we usually experience it. So we shall have to make another change in this thought experiment. Ge shall say that the plane is sitting on a steep, even hill, facing downhill. At this point, we make another abstraction. The wheels of the plane are the only point touching the ground, yes? Hence, the physics of a cylindrical object apply. This way, we can represent the plane with a drum.
Everyone still following for now? We have a drum, on an decline, with gravity applying. Now what happens?
The drum, will, roll. I repeat: The DRUM, WILL ROLL.
Now imagine replacing the hill with a treadmill, at the same angle as the hill previously was. What will happen? The drum will roll. It will revolve faster, yes. But it still has the inclination to go downhill.
This is essentially what happens with a plane on a treadmill. And as the plane has wings (AEROFOILS), as it speeds up, it will gain lift. Hence, it will fly.
Posted 13 Jul 2010 at 1:13am #
Sweet jesus... the explanations justifying Adam and Jaime's conclusions are laughable.
The whole point of the myth is that the velocity and acceleration of the plane are matched by the belt, such that the plane is stationary relative to the ground. Real simple concept.
The fact that the plane - while still on the ground - was moving forward relative to the ground automatically implies that it had greater velocity forward than the belt did backward, thus nullifying the experiment. It doesn't matter whether that forward velocity was generated by the propellers of the tires or the pilot farting last night's chili, or that the plane is a barrel on an incline on ice dangling by a rope in the sky, and whatever other nonsense you goofballs have come up with.
In the Mythbusters experiment, THE CORE PREMISE WAS NOT MET. PERIOD.
Myth not busted. End of discussion.
Posted 13 Jul 2010 at 7:11am #
[quote comment="62342"]Myth not busted. End of discussion.[/quote]
The whole point was not to keep the plane stationary. Not at all. You're an idiot.
Posted 13 Jul 2010 at 10:16am #
Blockhouse,
At least you are on the correct site "STUPID People Refuting Mythbusters Over Plane/Coveyor Belt"
Nowhere in the test does it state that the plane is rendered stationary in relation to it's surrounding area by the treadmill. THAT is an assumption you, and many others, are making. It is, in fact, a physical impossibility.
Let us all hope that you work in some menial occupation, such as ditch digger or window washer, and not as a scientist, teacher or, God forbid, pilot. Otherwise, the world is in bad shape.
Posted 13 Jul 2010 at 11:12am #
Nowhere in what Blockhouse said is it implied that the plane must be stationary relative to the surroundings.
So speaking of assumptions, let's hope YOU work in some menial occupation and not as a scientist, pilot, or God forbid, an English teacher.
Posted 13 Jul 2010 at 12:58pm #
[quote comment="62350"]Nowhere in what Blockhouse said is it implied that the plane must be stationary relative to the surroundings.[/quote]
Uhm, Blockhouse said "such that the plane is stationary relative to the ground." He also said that the movement relative to the ground "nullified" the experiment.
Posted 13 Jul 2010 at 1:26pm #
Oh yes, and you took him out of context...
"The whole point of the myth is that the velocity and acceleration of the plane are matched by the belt, such that the plane is stationary relative to the ground"
This is not what he is expressing is HIS belief. He is saying that the MYTH said that a plane is stationary relative to the ground while on a treadmill moving at the same speed as the plane. If the plane is stationary, then by default the treadmill, matching its speed, must be stationary too.
As he said, not a difficult concept.
The myth, as wrong as it is, is easy to understand. The truth, that the plane would, in fact, take off because it is pushing against air and not against ground is somewhat counter-intuitive to many at first.
Posted 13 Jul 2010 at 1:28pm #
"The whole point of the myth is that the velocity and acceleration of the plane are matched by the belt, such that the plane is stationary relative to the ground. Real simple concept." re: Blockhouse
Thanks, Erik. I was just about to reply. Though perhaps I was a little
brusk with Blockhouse! It just gets frustrating sometimes.
True, Blockhouse didn't use the word "ground", but I use the term "surrounding area" because someone once used the analogy
that the plane and treadmill could be on a boat, or aircraft carrier, or some such nonsense.
If the plane WERE stationary to the ground it would also be stationary to the surrounding area.
Posted 13 Jul 2010 at 1:40pm #
"True, Blockhouse didn't use the word "ground"
Sorry! I meant to write "Blockhouse used the word "ground"
Good thing I'm not a scientist, teacher, or God forbid, a proof reader!
Posted 13 Jul 2010 at 1:40pm #
[quote comment="62353"]This is not what he is expressing is HIS belief. He is saying that the MYTH said that a plane is stationary relative to the ground while on a treadmill moving at the same speed as the plane.[/quote]
The myth never said the plane was stationary relative to anything.
The myth said that the belt matched the "speed" of the plane. Whether you're measuring air speed or ground speed (they're the same when there's no head- or tail-wind), the belt moving left at 20 MPH does nothing to affect the plane moving right at 20 MPH - relative to both the GROUND and the AIR.
Posted 13 Jul 2010 at 2:18pm #
"the belt moving left at 20 MPH does nothing to affect the plane moving right at 20 MPH - relative to both the GROUND and the AIR."
I know this to be true. The myth, as I recall, is that a conveyor belt matching the plane's speed in the opposite direction would prevent the plane from taking off. if the plane's speed is being measured relative to the belt, then it can never actually match the plane's speed.
Proponents of the myth are stating that the plane would be stationary if the belt matched its speed...which cannot be the case because then the belt would be moving and the plane would not (even though this is not possible unless the method of propulsion is through the wheels of the plane), meaning that the belt is no longer matching the stationary speed of the plane.
Posted 13 Jul 2010 at 1:58pm #
You are completely correct, JC, and I understand perfectly what Blockhouse believes the myth is implying. What I, and many others are saying, is that the myth makes no such implication. It does not say that "a plane is stationary to the ground while on a treadmill moving at the same speed as the plane." Your words.
An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.
The above sentence is taken from the MythBuster web site relating to this topic. All I am saying is that this assumption, that the plane is stationary to the ground, is what is blocks them from seeing what is actually happening here.
I agree that it is counter-intuitive. That's what makes it so much fun!
Posted 13 Jul 2010 at 2:18pm #
You are completely correct, JC, and I understand perfectly what Blockhouse believes the myth is implying. What I, and many others are saying, is that the myth makes no such implication. It does not say that "a plane is stationary to the ground while on a treadmill moving at the same speed as the plane." Your words.
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
The above sentence is taken from the MythBuster web site relating to this topic. All I am saying is that this assumption, that the plane is stationary to the ground, is what blocks them from seeing what is actually happening here.
I agree that it is counter-intuitive. That's what makes it so much fun!
Posted 13 Jul 2010 at 2:22pm #
""An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.""
This was THEIR adaptation of the myth, because they realized the impossibility of the ACTUAL premise of the myth. So what they set out to do was simply see if a treadmill could keep a plane from taking off. It cannot.
Posted 13 Jul 2010 at 2:36pm #
If there was a headwind of 200mph and the plane was flying at 200mph, the ground speed would be 0. It would appear stationary to the ground, yet flying at 0 mph.
Ground speed and air speed are 2 different things.
The thrust is against the air so it doesn't matter what the conveyour belt is doing.
Depending on how the question is worded (depending where you read it), it will either take off and the conveyor can do nothing about it, or by moving it will break the rules of the question.
Posted 13 Jul 2010 at 2:49pm #
[quote comment="62360"]This was THEIR adaptation of the myth, because they realized the impossibility of the ACTUAL premise of the myth. So what they set out to do was simply see if a treadmill could keep a plane from taking off. It cannot.[/quote]
Who is "they" in "THEIR"? MythBusters? Because they didn't "change" the myth at all. They tested the myth accurately and proved that the plane can take off.
Again, with no wind, ground speed and air speed remain the same. If you didn't know the plane was on a conveyor belt, takeoff would appear perfectly normal to an observer on the ground. It'd appear normal to a person in the plane, too.
A plane can take off on ice. Wheels (bearings) and a treadmill are basically like ice - largely frictionless and thus powerless to stop a plane from pulling itself forward through the air.
MythBusters tested it properly and got the correct results.
Posted 13 Jul 2010 at 4:11pm #
"They tested the myth accurately and proved that the plane can take off."
They tested it accurately after eliminating the impossible aspect of the myth, matching the treadmill speed to the speed of the plane.
Posted 13 Jul 2010 at 4:41pm #
"This was THEIR adaptation of the myth"
This whole website is in response to the results of MythBusters testing of their adaption of the myth. No matter what the original wording of the myth, and who knows how long the question has been out there, they developed ways, as best they could, to test the dynamics involved.
The plane is the center of the controversy. The "spirit" of the myth, or the "actual premise of the myth", as you put it, does not exist because the plane CANNOT remain stationary to the ground on the treadmill. Otherwise, you might as well use a car, or a jogger, or a bicycle, and so forth, whose speed CAN be matched by the treadmill, and will remain stationary relative to the ground. Maybe if you could somehow stick a motorized propeller and wings on them they'd take off...but that's too bizarre!
That's why I don't belive there is any other version, or wording, of this myth that makes any sense. Those who do are just adding their own spin to cover up their initial snap judgement. I know because when I first saw the show I said to my wife, "Look, the plane is moving forward. The test is flawed." After I thought on it, however, I said, "Wait a minute. Of course it's moving forward. It has to."
MythBusters got it right!
Posted 13 Jul 2010 at 6:29pm #
Ok, I've been reading these posts (not all of them, but many) and my brain is exhausted from all the bickering.
So let me get this straight.
We have 2 possibilities/explanations/situations, as far as I can tell.
One, where the airplane is, in some manner, tied to the ground Preventing forward, but not vertical, motion. Under the airplane is a treadmill. The treadmill accelerates to some speed, forcing the airplane to accelerate as well or else be pushed off the treadmill like a jogger to has lost his footing. But the airplane remains stationary, no matter the speed of the treadmill; like someone holding onto the bars of a treadmill. Treadmill spins, and the legs are flapping to keep up, but at a speed equal to the treadmill.
And then theres the second scenario; where the airplane is not tethered to the ground while on the treadmill and is allowed to accelerate to any speed it can, regardless of what the treadmill is doing underneath it.
As far as I can see, in the first situation, the airplane has no airspeed, (as well as no ground speed). Therefore, no lift. Therefore no flight.
Whereas, in the second scenario, the airplane is able to freely accelerate to a greater velocity than the treadmill/conveyor is capable of. Therefore gaining forward motion, allowing for some amount of airflow over the wings and therefore, an airspeed, and incidentally, a forward ground speed. In which case, the airplane (or the people within) would not know that there is a conveyor beneath them. This forward airspeed would allow for lift/flight.
So it seems to me that for the Mythusters experiment, one would have to choose between the 2 scenarios. Where in (A) an airplane being prevented from moving is not an airplane, and therefore would be a false premise. or (B) where the airplane is free to do what it wants/can, therefore negating the premise of the myth.
So thats how I see it. If thats wrong, I'm sorry. Be nice. This isn't a forum to get snarky and mean. I don't think Adam or Jaime would appreciate seeing it.
Posted 13 Jul 2010 at 8:18pm #
[quote comment="62365"]One, where the airplane is, in some manner, tied to the ground Preventing forward, but not vertical, motion.[/quote]
That's not a possibility at all. Not one bit. It's not even worth discussing - why would a plane be tied to the ground?
[quote comment="62365"]Whereas, in the second scenario, the airplane is able to freely accelerate to a greater velocity than the treadmill/conveyor is capable of.[/quote]
Nope. The speed the treadmill is "capable of" is irrelevant. The plane takes off regardless of the speed of the treadmill - not because it's "going faster than the treadmill is capable of."
Heck, make the treadmill go twice as fast as the plane - it'll still take off. The wheels will just spin three times as fast as they normally would.
[quote comment="62365"]or (B) where the airplane is free to do what it wants/can, therefore negating the premise of the myth.[/quote]
There's no negation of anything... Where? MythBusters tested the myth properly. There's no negated premise - there's a plane on a treadmill. That's the premise. The "matching speeds" bit of the "premise" is just there to trick people who think a plane accelerates the way a car does.
[quote comment="62365"]I don't think Adam or Jaime would appreciate seeing it.[/quote]
They didn't invent the myth. They just re-popularized it.
Posted 13 Jul 2010 at 9:21pm #
Me,
Sorry! Erik is correct. The basic question is quite simple. The rest is stuff people think up to try to explain something their mind has trouble grasping.
Go to this website to see MythBusters' original statement of the myth,
and their attempt to demonstrate it. It may not be a perfect demonstration, but it is probably as close as anyone will get without building a mile long treadmill that can support an airplane.
mythbustersresults.com/episode97
Of course, you don't need a demonstration. Logic will do just fine.
Posted 19 Jul 2010 at 9:20pm #
I guess I must be one of those "stupid" people, because, I still don't get it. It may have been mentioned before, but it seems to me if the plane were on a treadmill, and thus not moving forward, there wouldn't be enough air flowing over the wings to achieve lift. I too saw the episode and it appeared the plane was in fact moving forward, that's why there was enough lift for the plane to take off.
Posted 19 Jul 2010 at 9:25pm #
for those of you who want more info: check out this link: http://www.airplaneonatreadmill.com/
Posted 20 Jul 2010 at 7:55am #
[quote comment="62392"]…it seems to me if the plane were on a treadmill, and thus not moving forward…[/quote]
"Thus" is used to precede a logical conclusion.
That the plane is not moving forward is not a logical conclusion. The plane moves forward because the engine (props, jets, whatever) pulls itself against the air, not the ground like a car or bike.
Posted 20 Jul 2010 at 10:44am #
Steve,
You have reached a correct conclusion to an incorrect premIse.
"IF" the plane were rendered "stationary" by the treadmill, it would indeed not take off. However,(now this is very important) the plane CANNOT remain stationary, no matter how fast the treadmill is traveling backward, because the treadmill does not effect the forward motion of the plane, brought about by it's propellers PULL THROUGH THE AIR! The wheels are not dependent on a surface to create forward motion, like a car, bicycle or feet. It just needs the air.
The challenge makes no mention of the plane being stationary. Most "no fly" proponents just assume this. That is the whole reason for the controversy. The situation, to some, is counter-intuitive, and that is what makes it appear to be a trick question.
Posted 20 Jul 2010 at 7:22pm #
This quote seems to be the best way to describe the reasons people "don't get it".
"You see, the confusion all arises from misses - misconceptions, misinterpretations, and misunderstandings. Consider three rewordings of the question:
1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?
2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?
3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?
Posted 20 Jul 2010 at 8:19pm #
[quote comment="62404"]On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground.[/quote]
The problem with that is that a treadmill cannot keep a plane stationary.
Posted 21 Jul 2010 at 11:12am #
That's why a conspiracy to keep the plane stationary is necessary. the pilot would throttle the plane to only the amount necessary to counter the friction of the wheel bearings.
Posted 20 Jul 2010 at 9:44pm #
If he starts the treadmill before you throttle up, you will move backwards. As soon as you throttle up you will move forward relative to the ground and the treadmill. There is no way to keep the plane stationary no matter how fast the treadmill is moving. Only if the treadmill is NOT moving, and the engine is off.
Posted 21 Jul 2010 at 9:19am #
Since this string is in response to MythBusters' attempts to either prove or bust this myth, the only wording that should be considered is theirs. This is how the myth reads, taken from their websight:
""An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.""
No "stationary to the ground", no "pilot speeds up while treadmill speeds up", no "spirit of the challenge". It's a matter of physics, and fairly simple physics, at that!
Since the guys on MythBusters demonstrated in several ways, to the best of their abilities, that the plane will move forward and take off, they succeeded in busting the myth. fini
Posted 21 Jul 2010 at 11:14am #
The question is simpler than that. Most people simply are concerned with the question as to whether or not a treadmill can prevent a plane from taking off.
The answer is no, at any speed.
Posted 21 Jul 2010 at 12:52pm #
"(EDIT: Really, you should substitute the word "air" for ground in the above facts. I use "ground" throughout this post because of a consistent mistake made by "no-flys" in their assumption that the plane remains stationary. It doesn't remain stationary, relative to the ground or the air. The important point is that it moves relative to the air, not the ground, but I'm assuming throughout this post that there is no significant tailwind or headwind. I discuss the implications of this briefly in the section about windtunnels.)"
I agree with using "ground" as opposed to "air" (because air is not stationary, by nature) or "treadmill" (because the treadmill is moving, but is presumably on top of or parallel to the ground).
Posted 02 Oct 2010 at 3:25am #
Imagine an aircraft carrier going 50 mph. A plane requires a speed of 50 mph to achieve liftoff. The carrier is going west and the plane is going east. If the "no-flys" were correct, then the plane would need to go 100 mph to achieve liftoff. This is not the case as proven everyday in the navy. The plane simply goes 50 mph and is airborne because it does not rely on friction with ground to move as cars do (try driving on ice, you dont go so fast even with power output.) Instead, it propels through air except for the friction from the wheels which is negligible. The aircraft carrier is no different than the conveyor belt in this case.
Posted 03 Oct 2010 at 3:57pm #
[quote comment="62916"]The aircraft carrier is no different than the conveyor belt in this case.[/quote]
I agree with your end result but you're wrong: an aircraft carrier can affect airspeed, which is why they try to launch planes in the same direction as the carrier is traveling.
Posted 03 Oct 2010 at 11:13pm #
yea but you could say the same thing about the wind movement generated by the conveyor belt...obviously it is at a much lesser scale but there is still some wind movement which technically could affect the plane in very minute ways. The aircraft carrier definitely exasperates the wind change, but the concepts are still equivalent. I do agree though that the AC will definitely affect the plane because of the air displacement caused.
Posted 03 Oct 2010 at 11:47pm #
[quote comment="62922"]yea but you could say the same thing about the wind movement generated by the conveyor belt...[/quote]
In a word, Greg, no.
Posted 04 Oct 2010 at 12:00am #
haha, fair enough
Posted 04 Oct 2010 at 2:44pm #
[quote comment="62916"]Imagine an aircraft carrier going 50 mph. A plane requires a speed of 50 mph to achieve liftoff. The carrier is going west and the plane is going east. If the "no-flys" were correct, then the plane would need to go 100 mph to achieve liftoff. This is not the case as proven everyday in the navy. The plane simply goes 50 mph and is airborne because it does not rely on friction with ground to move as cars do (try driving on ice, you dont go so fast even with power output.) Instead, it propels through air except for the friction from the wheels which is negligible. The aircraft carrier is no different than the conveyor belt in this case.[/quote]
The first part is right. If an airspeed of 50mph is needed, and the ship is going through dead air at 50mph (generating a deck-level airspeed of 50mph), the plane WILL take off temporarily (if it's not tied down, which I assume it is, as the large gusts of wind common at sea will move planes about the deck). If the same conditions exist and the plane goes in the opposite direction, it will require 100mph in relation to the deck (50mph airspeed). The only way a plane could take off in the opposite direction at 50 mph deck speed is if there is a 50mph tail-wind.
Why you got off track is beyond me.
Posted 04 Oct 2010 at 3:03pm #
No, you're wrong, my concept was right the only problem is that in reality the aircraft carrier displaces the air while it moves so it changes a bit. But the concept is still correct.
Posted 04 Oct 2010 at 3:15pm #
Changes a BIT is the key phrase here. Planes take off into the wind for a reason, and THAT is the reason.
Posted 04 Oct 2010 at 3:43pm #
They take off into the wind because the lowers the ground speed necessary to achieve liftoff. The wind caused by the AC moving 50 mph the opposite direction is not equal to 50 mph wind going the opposite direction.
Posted 04 Oct 2010 at 3:59pm #
Right...but if the "ground" is moving in the opposite direction at the speed the plane needs to take off, then the plane needs to be moving twice as fast relative to the "ground" to take off.
Posted 09 Oct 2010 at 2:41am #
JCBoston that is incorrect, the plane needs to be moving at take off speeds in relation to the AIR around it...
A plane needs force pushing it forward in order to take off. The point of the conveyor belt is to theoretically provide enough force in the opposite direction to prevent the plane from moving forward.
However, the lateral force of the treadmill (We'll call this "Backwards" from now on) is transfered to the wheels as rotational force (IE the wheel's spin). A very small portion of this force is transfered to the airplane through the friction in the bearings of the wheels. With 0 thrust from the plane this force would cause the plane to begin moving backwards. This force transfered through the bearings is the ONLY thing pushing the plane backwards. It is a miniscule fraction of the force provided by the conveyor belt.
When the plane begins providing forward thrust, this provides a "forwards" force which is opposite and competes with the "Backwards" force generated by the belt.
The bearings cannot, and will not, transfer enough "Backwards" force into the plane to overcome the forward thrust. Even if you had bearings that defied the laws of physics and could transfer that much force without falling apart, the wheels themselves could create enough friction to stop the plane.
Without breaking the laws of physics the conveyor belt could NOT stop the plane, at any speed, because the force of the conveyor belt cannot be transfered to the plane.
Take a wheel on a stick, and hold the wheel down on a moving tread mill. Now push the stick forward to cause the wheel to roll up the treadmill. See how little force it takes? Take your hand and slide it up the moving treadmill (Don't actually, you could hurt yourself). It's quite difficult. This is because with the wheel, nearly all of the force from the treadmill is transfered into rotating the wheel. Your hand however, has lots and lots of friction compared to the bearings, and does not rotate, so lots of the treadmill's force is transmitted into moving your hand backwards.
Put in a single sentence, "The bearings prevent the conveyor belt from transferring enough force into the plane, to overcome the thrust and prevent the plane from moving forward."
Posted 09 Oct 2010 at 9:27pm #
"JCBoston that is incorrect, the plane needs to be moving at take off speeds in relation to the AIR around it..."
That's exactly what I said. My suggestion is that you work on reading comprehension.
Posted 10 Oct 2010 at 1:21am #
"plane needs to be moving twice as fast relative to the "ground" to take off."
I suggest you work on writing.
Posted 15 Oct 2010 at 11:39am #
My writing is fine, and if you've read all my posts instead of just the last one (if it seems at all ambiguous, you should have maybe told me that rather than ASSuming anything), you would know EXACTLY where I stand on the issue.
Anyway, nice comeback. It's pretty consistent with your overall quality.
Posted 15 Oct 2010 at 12:22pm #
So JCBoston, you said, "My suggestion is that you work on reading comprehension." However, he read it correctly and it was you who wrote it incorrectly. Yet you think he is the ass for defending himself against your undeserved insult? I read your other comments and knew you either didn't understand the true reasoning or mistakenly wrote it and i didnt care to respond but the correction by LazyLemmings was completely justified because you did get it wrong.
Posted 15 Oct 2010 at 1:16pm #
I may have not been clear in ONE post. However, ALL of my posts from over the years are still here, and if Lazy (apropos name if there ever was one) bothered to read it, he wouldn't have wasted his time.
And I didn't write it wrong. I said it has to be the plane relative to the air. My reference to the moving ship might have confused you, but it wasn't wrong.
If the ship is moving through dead air at 50mph, the plane needs to be moving in the other direction at 100mph relative to the ship (which, if your powers of inference were up to snuff, you would easily see means an AIRspeed of 50mph). It's NOT rocket science people.
Posted 16 Nov 2010 at 4:28pm #
Similar question I've seen about.
Imagine a plane is sitting on the beginning of a massive conveyor belt type arrangement, as wide and as long as a runway, and intends to take off. If the conveyer belt exactly matches the speed of the wheels at any given time, but in the opposite direction of rotation, can the plane take off? There is no wind.
Opposite answer though.
Posted 16 Nov 2010 at 11:29pm #
[quote comment="63347"]Opposite answer though.[/quote]
That's a lousy variation of the question though, because if the wheels precisely match the speed of the belt at any given time then the plane is idling, tied down, or otherwise not even trying to take off.
Posted 07 Dec 2010 at 7:26pm #
Except for one thing... they never established that the tarp could be moved with the plane remaining stationary, as would be the case with an actual conveyor belt. Considering that the tarp ripped when Adam ran across it, it's pretty obvious that it lacked the strength required to act as a conveyor with an airplane upon it, which is an integral element of the myth. The tarp simply had no effect, as the truck and airplane move simultaneously at the same speed and so the tarp simply passes under the wheel of the airplane. IT NEVER ACTS AS A CONVEYOR.
I think their conclusion is correct, but it should be evident to anyone watching that this experiment was very flawed in its execution and does nothing to prove that a plane would take off in the conditions described in the myth.
Posted 07 Dec 2010 at 8:49pm #
[quote comment="63439"]Except for one thing... they never established that the tarp could be moved with the plane remaining stationary, as would be the case with an actual conveyor belt.[/quote]
That's wrong; the plane does not remain stationary.
Posted 07 Dec 2010 at 9:31pm #
Stationary as in not moving under it's own power, but solely under the truck/tarp's. Like I said, the tarp never acts as a conveyor.
Posted 07 Dec 2010 at 9:43pm #
[quote comment="63441"]Stationary as in not moving under it's own power, but solely under the truck/tarp's. Like I said, the tarp never acts as a conveyor.[/quote]
I'm not sure why it matters that the tarp can move while the plane is stationary. That's not in the problem - the tarp matches the ground speed of the plane. If the plane is stationary, so is the tarp.
Posted 07 Dec 2010 at 10:09pm #
[quote comment="63442"][quote comment="63441"]Stationary as in not moving under it's own power, but solely under the truck/tarp's. Like I said, the tarp never acts as a conveyor.[/quote]
I'm not sure why it matters that the tarp can move while the plane is stationary. That's not in the problem - the tarp matches the ground speed of the plane. If the plane is stationary, so is the tarp.[/quote]
I think you're misunderstanding my point (or I'm not expressing it clear enough); my point of contention isn't that the tarp can move, but rather that it doesn't seem to drag the plane and create conditions where the actual ground speed is where it is supposed to be... it does not act as a conveyor belt would. At no point do they test the strength of the tarp to ensure that it can pull the plane with the assistance of the truck. If the tarp can't pull the plane (which would seem to be the case, since it rips when Adam runs across it, Adam being of considerably less mass than an airplane) it isn't acting like a conveyor belt... the tarp should be able to support the mass of the airplane (and move it when attached to the truck) without requiring the airplane to move on its own power... otherwise the force required to overcome it is negligible. This is indeed an integral part of the problem, one which having a tarp merely pass under the wheels of the plane does not account for; they're basically just pulling tarp under the wheels of the plane and creating very little resistance in the opposite direction in terms of ground speed.
Think of it this way; the experiment worked with the model plane because the material could hold the lightweight model in such a way that it would drag it when external force is applied; the ground speed in effect matches the takeoff velocity as it is supposed to. Had they used something of insufficient strength, and instead had the model airplane and the other vehicle move at the same time, the ground speed would remain close to normal because it would have little to no effect on the on the motion of the plane while at rest. The methodology of their final experiment is flawed.
Posted 07 Dec 2010 at 11:03pm #
once the plane starts moving there is so little friction between the wheels and the tarp that i hardly see that as mattering...correct me if im mistaken but it seems like you are saying they should have taken into account something they know wouldnt effect the experiment.
Posted 08 Dec 2010 at 9:44am #
[quote comment="62342"]Sweet jesus... the explanations justifying Adam and Jaime's conclusions are laughable.
The whole point of the myth is that the velocity and acceleration of the plane are matched by the belt, such that the plane is stationary relative to the ground. Real simple concept.
The fact that the plane - while still on the ground - was moving forward relative to the ground automatically implies that it had greater velocity forward than the belt did backward, thus nullifying the experiment. It doesn't matter whether that forward velocity was generated by the propellers of the tires or the pilot farting last night's chili, or that the plane is a barrel on an incline on ice dangling by a rope in the sky, and whatever other nonsense you goofballs have come up with.
In the Mythbusters experiment, THE CORE PREMISE WAS NOT MET. PERIOD.
Myth not busted. End of discussion.[/quote]
This is exactly what I meant. (And I appreciate you posting this) That the velocity and acceleration were clearly NOT matched by the belt, or the plane would have shown no movement, and it clearly did. With the plane showing movement forward, rather than staying stationary while the engines propelled it, you're now testing what little amount of distance a plane must travel forward to take off. I know very little about physics, but it sure doesn't take someone who KNOWS about them, to realize that experiment was flawed. The premise of the experiment was to match the conveyor belt speed to that of the moving plane with the engines on, propelling it. There is no excuse for the belt not matching the speed that the engines were propelling it, other than sloppy experimenting.
The belt cannot have a constant speed of being pulled in the opposite direction, because the plane's engines do not have a constant speed of propulsion. Assuming that cars and jet engines propel at the same speed is ludicrous, which was an accepted value when they pulled the tarp by means of a vehicle (If I'm not mistaken).
I want to think it's more complicated than that, but I can't. I read and try to understand everyone's explanations, but I just believe it's more simple. I'm not saying a plane is unable to take off on a conveyor belt. I'm saying the experiment was wrong for trying to prove it can or it can't. I don't know why anyone would deny that.
If you care about science, you shouldn't go in rooting for the experiment to go either way. Sure, you have an assumption about what will happen, thus the purpose of a hypothesis. But they didn't approach this myth unbiased. Instead, they went in with the desire to prove something would happen, and flawed the dynamics of the experiment in the process, to accommodate their theory. You're a scientific referee, not a bookie.
Posted 08 Dec 2010 at 1:53pm #
OK, just because you cant understand the explanations does not mean that it has to be more simple than that. The fact is, the experiment was a success. The thing you overlook is that the plane's wheels barely experience any friction with the conveyor belt so the conveyor belt can be going the same velocity as the plane but the plane will still take off because it is propelled by friction with the air. They did not flaw the dynamics of the experiment, the plane took off exactly as it should given the myth's conditions. Even if they were flawed somehow in their experiment, which they were not, but even if they were, there is nothing they could have done that would have made it act diferently while still following the guidelines. But if you couldnt understand that after reading Erik's comments then i cannot imagine i can convince you because a 3rd grader could understand his straightforward logic which perfectly explains why Mythbusters were right.
Posted 08 Dec 2010 at 2:19pm #
[quote comment="63446"]With the plane showing movement forward, rather than staying stationary while the engines propelled it, you're now testing what little amount of distance a plane must travel forward to take off.[/quote]
Colleen, you're wrong. The plane does not stay stationary for the same reasons that a roller skate on a treadmill being pulled by one of its laces can go forward even if the treadmill is moving 100 MPH in the opposite direction.
Posted 08 Dec 2010 at 3:35pm #
Why would the roller skate move forward, unless the velocity of the treadmill moving at 100mph decreased? I don't think a roller skate being pulled on a level treadmill at 100mph would exceed the speed of 100mph and travel even faster on it's own to move forward? I don't think I understand your analogy. In theory, the roller skate would ALWAYS be traveling forward, however, if it's rate of speed is matched by the treadmill, I wouldn't think it should move at all. Where would you get the added inertia to coax the skate either forward unless the treadmill couldn't match speed? Energy can't be created or destroyed, so where would it come from to push the skate over 100mph to actually move forward? Not to mention, we're talking about a skate...not a jet-engine powered skate.
And once AGAIN, I'm claiming the experiment could go either way with an acceptable percentage of error. And yet the experiment had too much error to be conclusive. I'm eager to track down this myth and watch it again to pull quotes from the Mythbusters themselves. I remember the plane being stationary (which in the footage, it clearly is not), being a large part of the myth's mystery.
Posted 08 Dec 2010 at 9:53pm #
Colleen,
You have based your conclusions about this myth on an incorrect premise. Nowhere is it stated on the show that the treadmill has rendered the airplane stationary. That is YOUR presumption, as well as many others who believe that the tests run on Mythbusters were flawed. The myth in question is as follows:
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
This is taken directly from the episode, which can be viewed at the following website:
mythbustersresults.com/episode97
It is, in fact, a physical impossibility to keep a free-wheeling plane stationary, relative to its' surroundings, no matter what surface it's on. Once those props are turning it's going to go forward unless it has something holding it in place, like breaks, on a stationary surface. In this case, however, it would just move backwards with the treadmill.
It is understandable that some people have a hard time grasping the point that a plane functions differently than a car, a bicycle or anything else that is dependent on surface friction for its' locomotion. A plane uses the air.The ground just supports it until it reaches sufficient speed to go UP. The treadmill WILL NOT CAUSE IT TO APPEAR STATIONARY!!! This was never intimated anywhere!
No "velocity and acceleration of the plane are matched by the belt, such that the plane is stationary relative to the ground", no "pilot speeds up while treadmill speeds up", no "spirit of the challenge". It's a matter of physics, and fairly simple physics, at that!
Someday a light may dawn in your brain as to what this challenge is all about, as I have personally witnessed happen to many, many naysayers once I kicked the "stationary" notion out of the way.
Since the guys on MythBusters demonstrated in several ways, to the best of their abilities, that the plane will move forward and take off, they succeeded in busting the myth. fini
Posted 17 Dec 2010 at 7:20am #
Can I just say that anyone who even remotely thinks that a conveyor belt will stop a plane from taking off has obviously no idea of how lift is produced in an aircraft or how an aircraft works and doesn't even deserve the energy required to try convince them otherwise. Your all idiots! Especially that Tom guy!!
Posted 19 Dec 2010 at 9:50am #
Anyone who is still not sure what's going on, please watch this video:
http://www.youtube.com/watch?v=bEyfHwDdXSg
Thank you!
Posted 20 Dec 2010 at 6:08pm #
Had an Air Force captain, a pilot, in my place of business recently. He thought the plane would not take off. SCARY!!! He finally admitted he was wrong after I queried him about it. As with most, his snap judgement and presumption did him in.
Posted 28 Dec 2010 at 12:20am #
The only thing a conveyor or treadmill going back wards at x mph is make the tires of the plane spin x mph faster as they are the only things that are affected by it. Planes don't need ground to operate, moving or not.
Posted 29 Dec 2010 at 11:57am #
[quote comment="65884"]Your all idiots! [/quote]
Irony?
Posted 04 Jan 2011 at 10:38am #
[quote comment="66006"][quote comment="65884"]Your all idiots! [/quote]
Irony?[/quote]
Not irony...delusion!!
Posted 17 Jan 2011 at 4:07pm #
Read number 3. It explains that they didn't do the experiment correctly and re-did it even though they didn't air it. A PLANE WILL NOT FLY WITHOUT AIR OVER ITS WINGS!
http://dsc.discovery.com/fansites/mythbusters/top-ten/mythbusters/myths-about.html
Posted 17 Jan 2011 at 4:22pm #
[quote comment="66145"]Read number 3. It explains that they didn't do the experiment correctly and re-did it even though they didn't air it. A PLANE WILL NOT FLY WITHOUT AIR OVER ITS WINGS!
http://dsc.discovery.com/fansites/mythbusters/top-ten/mythbusters/myths-about.html%5B/quote%5D
Uhm, brain fart alert. I really hope it's just a brain fart, because the point of that page is to share the "top 10 myths about Mythbusters."
If you click through to page two you can read this:
[quote]3. Planes on a Conveyer Belt Myth
Busted. We won't ever revisit this story because we were right![/quote]
The myth about Mythbusters - the one you accepted as "explained" - was busted. They stand by what they proved.
Of course a plane won't fly without air over its wings, but that ends up being irrelvant to the discussion. The plane moves forward because the jet engine, propeller, etc. pulls the plane through the air… as has been explained a few thousand times already.
You've not only got the original answer wrong, but you've misread a post that's further proving that original (correct) answer as if it supports your incorrect conclusion!
Classic!
Posted 17 Jan 2011 at 6:38pm #
[quote comment="66145"]Read number 3. It explains that they didn't do the experiment correctly and re-did it even though they didn't air it. A PLANE WILL NOT FLY WITHOUT AIR OVER ITS WINGS![/quote]
Actually, Erik, I liked your reply so much I thought it needed repeating. Maybe Mike will eventually "get it"!
Anyway, Mike, you've got it all wrong, but I refuse to keep repeating what is so obvious to most thinking humans.
Which brings me to #1 on the same list you pointed us to, where they state the Jamie Hyneman is a robot! Should we take THAT as gospel?
Posted 18 Jan 2011 at 12:37am #
Ok watched it again tonight, and have been following several forums on the topic. Originally, when it aired, I scratched my head thinking how could they possibly call that "Busted" because the plane is clearly moving forward. But now I understand the fallacy of my presumption that the plane cannot move forward.
The whole setup of the myth leads many to believe what they are going to "attempt" to do is keep the plane stationary by matching the tarp speed to the planes take off speed, and the plane will magically hover for a few seconds from a stationary position, and clearly that cannot and will never happen.
When it comes down to it , its a good trick question posed by Mythbusters. The "no flys" , including myself , were fooled in assuming what they meant was flying from a stationary position at take off throttle - this obviously cannot be done.
The "no flys" (again including myself at one point) cant get past the fact that the underlying myth is not about keeping the plane stationary, its about PREVENTING the plane from moving forward, which I now understand you cannot do by pulling the tarp underneath it.
If the myth were restated such that : "If you had a treadmill with unlimted speed potential and moving in the reverse direction of the plane, can you prevent a plane from moving forward? Or a rocket powered car, or a jet fighter ?" The answer is NO you cannot prevent it from moving forward regardless of how fast the treadmill is going as long as the potential energy of the plane , rocket car or jet has enough power to overcome only the little friction that the wheels present. And as long as the plane can move forward it will eventually move fast enough to fly, because thats what planes do.
So in the end the trick that fooled me was believing that you could actually prevent a plane from moving forward in the first place under those conditions !
Posted 28 Jan 2011 at 7:18am #
Glad you have seen the light, Kris. I would not exactly call this a "trick" question, however, as in "If a rooster lays an egg on top of a barn, which side will it roll down?", or "How many animals did Moses load into the ark?", because when you tell people the answer they understand immediately that the question was misleading.
Many people, as we have seen, will argue the results to Mythbusters expeiments, and try to change the wording of the myth itself to prove their beliefs as to what the answer SHOULD be.
Since this sight was created to discuss the results of the experiments conducted on the show, we should stick to their wording of the myth. The wording does not mislead in any way. People just reach the wrong conclusion because they, as you said, presume the plane is stationary, or they just don't understand how an aircraft flies.
Understandable, really, unless that individual is a pilot, and I have met several. Very disturbing!!!
Posted 28 May 2011 at 12:18pm #
Rerun just aired, so I figured I'd resurrect this discussion (even though I'm sure people have probably already said pretty much the same thing above.)
To quote the pilot at the end of the show when asked to predict if the treadmill will prevent him from taking off:
"Yes, if I match my speed exactly the same speed forward as it's going backwards and there's no air over the wings, I should just sit there like a brick."
So, while the myth should be (is) about whether or not the plane moves forward (which it clearly does) and anyone that gives enough thought about it would come to that conclusion, it is also entirely ridiculous to state that the show presents the myth in absolutely consistent terms. IF he WERE to match his speed exactly (even though this obviously doesn't happen when providing normal power to the propeller), then, as everyone consistently states, he of course wouldn't be moving relative to air and would of course not experience any lift. So his statement wasn't wrong (even though the show acts like it was), it just wasn't on point.
This is just one example where the Mythbusters presentation blurs the line between two interpretations of the myth. And such blurring is the source of 99.9% of the confusion on all of these forums. (And yes, that statistic is made up.)
Posted 24 Feb 2016 at 10:26pm #
This reminds me of the "Monty Hall Problem" or the "Birthday Problem (Google if you're not familiar)." Though those are probability problems, they are all similar in that they seem counter intuitive to our assumptions and experience. Most of us walk on treadmills, and don't skate on them. We make the mistake of running with this bad information.
Posted 30 May 2011 at 8:55am #
[quote comment="67258"]This is just one example where the Mythbusters presentation blurs the line between two interpretations of the myth. And such blurring is the source of 99.9% of the confusion on all of these forums. (And yes, that statistic is made up.)[/quote]
The problem with your entire rant is that there are not two interpretations of the myth. There aren't. You could move the conveyor belt at a 1000 MPH - the plane will still roll forward because its forward motion is not governed by the wheels.
The "matching the same speed" is the mental hurdle in understanding the true physics of the question. It's the "stumper" part. Once you realize that a plane's locomotion has nothing to do with the wheels (the only thing touching the conveyor belt), then you "get it" and you can get the right answer.
There are not "two versions." And if there are, it's "people who understand the question and people who don't understand the question."
Posted 30 May 2011 at 11:57am #
Fair enough Erik...I'm not purporting that there are two equally interesting (or even valid) "myths". I'm just suggesting that some of the phrasings used in the show are what has led to (much of) the confusion you've been helping people overcome. Thanks for the reply!
Posted 30 May 2011 at 12:05pm #
[quote comment="67258"]To quote the pilot at the end of the show when asked to predict if the treadmill will prevent him from taking off:
"Yes, if I match my speed exactly the same speed forward as it's going backwards and there's no air over the wings, I should just sit there like a brick."[/quote]
All this proves is that the "pilot" didn't understand the physics involved in the operation of his own plane, and that's the scary part!
Posted 31 May 2011 at 10:13am #
Hmmm...I don't know that my example "proves" anything, but I do think it supported my overall hypothesis that there are (what I called) inconsistencies in the presentation of the episode that may have led to some of the confusion seen on this forum.
The facts are clear: The pilot made a true statement and after the experiment, the show indicates that he had made a false statement. I don't care why he made the statement, what question he thought he was answering, what he really meant, whether his statement addresses any point that we care about, etc. All I care about is that carefully parsing his words reveals a true statement. IF he WERE to match his "speed exactly the same speed forward [relative to the treadmill] as it's going backwards [relative to ground] and there's no air over the wings, [he] should just sit there like a brick." Later treating this statement as false is an error.
That's the only point I'm making with this example. Again, I don't care if his statement was nonsense from the perspective of what really happens when the propeller is operated. He made a true statement and Mythbusters indicated it was false.
This example is given only to support my opinion that inconsistencies such as this one are the source of much of the confusion here and that most people aren't arguing physics but rather semantics.
Posted 31 May 2011 at 11:37am #
[quote comment="67316"]The facts are clear: The pilot made a true statement and after the experiment, the show indicates that he had made a false statement.[/quote]
The problem is that the pilot did not make a true statement. I've bolded the incorrect parts:
"Yes, if I match my speed exactly the same speed forward as it's going backwards and there's no air over the wings, I should just sit there like a brick."
That part about the plane sitting still (no air over the wings) is false in the context of the question. He misunderstood (frighteningly so) how the physics of a plane's takeoff work. He made the same dumb mistake others have made.
The show did not misrepresent the pilot or his answer. The pilot simply got the answer wrong (like many other people) because his reasoning was wrong. He didn't give a true statement.
Posted 31 May 2011 at 2:39pm #
Erik, I'm not concerned with the "context of the question."
This is simple mathematical logic. The pilot made a statement, "if A then B". For this statement to be true, all that is required is that B is true whenever A is true. I don't care that A isn't true in the "context of the question." That is irrelevant to the logical truth of the statement.
Posted 31 May 2011 at 3:02pm #
[quote comment="67321"]Erik, I'm not concerned with the "context of the question."[/quote]
It's fine if you want to do that. To each his own, regardless of how dumb or pointless…
The entire show was about the context. It was about answering the question, determining the veracity of the myth. He was asked if the plane would take off and he could have just as easily answered "no, because my aunt's name is Jemima." He'd be "right" in stating that his aunt's name is Jemima but he'd still get the question wrong.
You can't say context is irrelevant, then claim that some of the context - the part in which they say "the pilot was wrong" - matters.
Edit: Previous math-based reasoning replaced with one that makes more sense.
Posted 18 Dec 2011 at 2:13am #
He's right. I happen to be a mathematician, and technically, the pilot said: 'a lack of the plane's motion' IMPLIES 'the plane will not move and therefore won't take off.' The statement is true. I get what you're saying: the plane DID move, and therefore DID take off, but the statement is still technically true.
Posted 23 Jun 2011 at 12:08am #
The plane will obviously move forwards and eventually take off. Let me explain. If the engine of the plane is off, yet the conveyor belt is running, we can all agree that the plane will move backwards because there is no propulsion thrusting it forwards. The same will happen in this scenario if you replace the plane with a car, right? If the car is traveling at the same speed as the conveyor belt is in the opposite direction, the car will remain perfectly stationary because the car's source of propulsion is in contact with the conveyor belt. A car relies on moving the road backwards (relative to itself), yet the "road" is already moving backwards. However; if the plane is traveling at the same speed as the conveyor belt is in the opposite direction, the plane will move forwards regardless the fact that the tires move backwards because the plane's source of propulsion is NOT in contact with the conveyor belt, making it irrelevant. A plane relies on moving the air backwards (relative to itself), NOT the ground. Turn a bicycle upside-down so that the tire is not touching the ground. Imagine that the air's relation to the tire is the plane's relation to the tire. Did the bike move?
Posted 04 Jul 2011 at 11:24am #
It appears to me that the people who are posting on this site and others fall into three categories.
1) Those who "get it," and understand that there is a major blind spot causing some individuals to arrive at an incorrect conclusion.
2) Those who donât "get it," and stick to the premise that the plane behaves like an automobile or jogger. That is, will somehow remain in place when the speed of the plane and the treadmill are matched.
3) Those who initially began as category 2s, but later realize they are wrong. These people are most interesting because rather than outwardly "jumping ship" they stick to their original declaration, and try to convince others that there is an underlying "spirit" to the myth that substantiates their claim.
I could argue that there is a 4th group of individuals who belligerently declare that it is a stupid myth and we shouldn't even be discussing it. Evidently, the hundreds of postings we have seen disprove that position. If nothing else, it is an intriguing insight as to how people perceive and go about solving a brain teaser.
Posted 13 Jul 2011 at 9:44pm #
really, a two old year argument? I don't believe people who advocate the "plane on a conveyor belt will not fly" side would be convinced otherwise unless someone built, at the cost of millions of dollars, an actual runway sized conveyor belt and ran the experiment.
Since that would be a senseless waste of money to prove something most people already "get", this will have to remain a thought experiment that drives many people to humorous distraction.
Posted 29 Jul 2011 at 11:28am #
Alright. All analogies aside, it looks like this discussion has gotten away from the original myth.
The Mythbusters' idea for conducting this experiment was to take a propeller driven plane and put it on a treadmill. If the plane took off, myth busted. If the plane stayed still, myth plausible.
During the design of the experiment, there was an animation showing how busting this myth was supposed to work. The treadmill would start, the plane would turn on it's propeller, and the plane would either lift off of the ground right where it was, or not. Again, that was in the animated presentation before the actual experiment.
When the Mythbusters actually conducted their experiment in full-scale, the plane did not stay in the same place on the treadmill. It moved forward, lift was generated, and the plane took off.
Now, since the myth claimed it was impossible to take off on a treadmill, myth busted. The plane was on a treadmill, then it took off. The fact that it moved forward and had adequate lift is irrelevant.
Posted 26 Sep 2011 at 4:24am #
I just watched the episode and still didn't understand. I didn't really doubt the conclusion, I just couldn't understand it.
I think things would have been better to understand if the Busters had mentioned that the wheels on the plane are, in fact, going 50 miles an hour, because the treadmill only adds to the forward moment that the engine generates due to the nature of wheels on a plane being free.
That's what confused me, I thought that the wheel's speed was matching the conveyor belt.
Posted 08 Dec 2011 at 4:21am #
The whole point of debate is to challenge each other's assumptions and help each other learn.
Calling people "stupid" and other vitriolic things might make you feel better about yourself, but anti-social remarks like are not in the spirit of discussion, even if you do hold the opinion that certain people are stupid and idiots.
Posted 08 Dec 2011 at 4:54am #
And yes, I understand clearly why the plane takes off, but some of you guys' attitudes are appalling. You're right. Get over it.
Posted 18 Dec 2011 at 1:58am #
I enjoy looking at an argument and then arguing both sides. This is a kind of problem where there should be only one right answer, and the right answer as it appears in the natural world is that the plane will take off--the conveyor belt will cause no impedance to the forward velocity of the plane (but more on that later). However, the no-fly camp is correct in a way.
The no-fly camp assumes that the plane is held from moving forwards by the conveyor belt. This is essentially false: the conveyor belt provides no impedance to the forward velocity of the plane. However, they believe that the spirit of the problem is that by some means the plane is prevented from moving forward and yet is still allowed to take off if it receives the necessary lift. If the problem is interpreted this way, then it is true that the plane will not take off, as no wind is moving over the wings (and the wind created by the propeller is negligible), and therefore there is no lift, and the plane sits there like a rock.
The take-off camp doesn't take that the plane is held still as a given. In fact, that is their essential argument: the conveyor belt has no affect upon the speed of the plane whatsoever. This means that the plane will still move forward in spite of the conveyor belt and, because there IS air moving over the wings in this case, the plane takes off. The reasoning behind this is deceptively simple, but first, we will contrast the plane with a car. With a car, the motor sends power from the engine into the drive train into the drive wheels. These wheels then exert their rotational energy on the surface below them, and this makes the car move forward. If a conveyor belt is placed below the car, it will be held stationary because the tires' velocity in relative to the ground determines the actual velocity of the car (meaning that the velocity of the car is determined by both the velocity of the tires and the velocity of the conveyor belt). This means that the velocity of the tires will cancel with the velocity of the conveyor belt and the net velocity of the car is zero. The plane is different. The plane's engine sends its power to the PROPELLER, not the tires, and the propeller spins, pushing the wind back, and therefore pushing the plane forward. The velocity of the plane then determines the velocity of the tires. So, where the car's velocity is the speed of the tires in relative to the speed of the conveyor, the speed of the plane's TIRES is the velocity of the PLANE in relative to the velocity of the conveyor belt. The speed of the plane's tires in relative to the speed of the conveyor belt is meaningless, as the tires are design for no other purpose than to reduce the friction between the plane and the ground. Since the friction of the wheel bearings is negligible, the speed of the conveyor belt has no noticeable affect upon the plane's velocity. All the conveyor belt does is cause the wheels to spin twice as fast as they would without the conveyor belt. Assuming the wheel's can withstand this additional speed, the plane will move forward regardless of the conveyor belt. The conveyor belt could move 100 times as fast as the plane and the plane would move forward as if the conveyor belt weren't there at all. And, since the plane is moving forward and wind is getting across the wings, it will take off, whether or not the conveyor belt is there.
Posted 21 Dec 2011 at 2:46pm #
I just saw the episode and as the myth was presented on the show, it wasn't done propery.. lets just leave it at that.
Ok if the tarp can not hold the plane stationary relative to the ground, that's a fact. But why don't they even mention this in the first place?
For me who's not a physics expert, and I guess 95% of all their viewers, the plane was supposed to be stationary and then fly off, that's how they showed the myth at first. And I thought that would be impossible on so many levels.. And when Jamie said that the myth was rediculous (or whatever he said) I couldn't agree more.
Then the plane clearly moves forward and takes off.
Conclusion: Mythbusters BUSTED!!!
Posted 21 Dec 2011 at 2:55pm #
Oh Erik, you're obviously a really cool guy who can sit behind a computer and call people names. That is so awesome and you're my hero.
Anyway, the first thing you wrote here was:
"It's not clearly evident." (that the aircraft is accelerating faster than the treadmill is being pulled.)
WHAT????
If you can't even tell if a plane on the tv is moving forward or not, you shouldn't go around calling other people stupid...
Posted 21 Dec 2011 at 3:31pm #
[quote comment="68841"]Oh Erik, you're obviously a really cool guy who can sit behind a computer and call people names. That is so awesome and you're my hero.
If you can't even tell if a plane on the tv is moving forward or not, you shouldn't go around calling other people stupid...[/quote]
Moron (I may have misspelled your name): you are being stupid. Your own pre-conceived notions are preventing you from truly understanding the problem and, thus, from intelligently commenting on it.
Of course the plane moves forward. DUH. There's nothing which says it cannot. The only people who think that's proving something are the idiots who "read into" the problem something that isn't there.
The plane's wheels are free to rotate. The plane has a velocity related to the ground. The belt moves the same speed in the opposite direction. The wheels spin.
Nothing prevents the plane from moving forward.
Posted 21 Dec 2011 at 3:32pm #
This has got to be the BEST comment thread EVAR! So much entertainment.
And I don't even know why.
The wheels of the plane are not powered. They could be frickin' blocks of ice and the plane could still take off (barring weight issues), conveyor belt be damned.
The only way a conveyor belt could stop the plane is if the wheel bearings were so crappy that the wheels didn't move and -- and this is key -- the engine/propellor was incapable of providing sufficient thrust to overcome the friction.
Dead simple.
Posted 23 Dec 2011 at 4:13pm #
[quote comment="68843"]The only way a conveyor belt could stop the plane is if the wheel bearings were so crappy that the wheels didn't move and -- and this is key -- the engine/propellor was incapable of providing sufficient thrust to overcome the friction.[/quote]
Oh Bill. What if the Roadrunner bought Super Duper Glue from Acme and glued the plane to the conveyor belt? Surely that would be another way. đ
Posted 24 Dec 2011 at 7:11am #
[quote comment="68839"]I just saw the episode and as the myth was presented on the show, it wasn't done propery.. lets just leave it at that.
Ok if the tarp can not hold the plane stationary relative to the ground, that's a fact. But why don't they even mention this in the first place?
Perhaps, during the filming of this episode the producers and others involved could not have imagined that so many people would make such ridiculous assumptions after hearing what, to my mind, is a fairly simple brain-teaser. Especially after the answer has been explained over, and over, and over, and over....[/quote]
Just read the statement, as given on the Mythbusters show and website:
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
Later, they tried to make their results of their tests clearer to those less gifted among us with the following video:
http://www.youtube.com/watch?v=bEyfHwDdXSg
There are not two answers.
Posted 19 Jan 2012 at 7:53pm #
Wow, this argument got extremely heated for no reason. I'll agree that MythBusters did a poor job explaining the myth ahead of time. They simply said "will an airplane be able to take off when it is on a conveyor belt moving backward the same speed that the plane is moving forward?" I at first thought that meant that the plane would be moving at the same speed relative to the belt, meaning that it wouldn't be moving at all relative to the ground. Obviously, if this were the case, the plane would have no chance of taking off. If it's not moving, it doesn't matter at all how much its wheels spin on a conveyor belt; it will absolutely never get the lift as no wind will go over the wings. Then in the Mythbusters video, the plane is shown moving forward relative to the ground. I then realized that this meant the plane would move at the same speed as the conveyor belt but relative to the ground. Then, it is ridiculously obvious that the plane will take off. It will still be moving forward relative to the environment at its normal takeoff speed and get all the lift it needs. Sitting on the conveyor belt does nothing because spinning wheels don't make a plane take off. My only interest in the show was that their poor explanation made me think they were going to try to make a practically stationary plane take off, leaving me angry at the end when I realized what they actually meant.
Posted 19 Jan 2012 at 10:18pm #
[quote comment="69059"]" I at first thought that meant that the plane would be moving at the same speed relative to the belt, meaning that it wouldn't be moving at all relative to the ground. [/quote]
Perhaps Mythbusters felt that since what you describe above is a physical impossibility, it wasn't necessary to explain it further. They evidently over-estimated the average persons' knowledge of aerodynamics. Come to think of it, I've met pilots who, when I described the myth, thought the plane would not take off. Scary!!!
Posted 19 Jan 2012 at 10:25pm #
[quote comment="68843"]The only way a conveyor belt could stop the plane is if the wheel bearings were so crappy that the wheels didn't move and -- and this is key -- the engine/propellor was incapable of providing sufficient thrust to overcome the friction. [/quote]
Actually, this wouldn't "stop" the plane. The plane would be moving backwards on the belt.
Posted 16 Feb 2012 at 5:16pm #
[quote comment="69061"][quote comment="69059"]" I at first thought that meant that the plane would be moving at the same speed relative to the belt, meaning that it wouldn't be moving at all relative to the ground. [/quote]
Perhaps Mythbusters felt that since what you describe above is a physical impossibility, it wasn't necessary to explain it further. They evidently over-estimated the average persons' knowledge of aerodynamics. Come to think of it, I've met pilots who, when I described the myth, thought the plane would not take off. Scary!!![/quote]
Perhaps you don't understand the question in the myth.
1. It is a THEORETICAL question, where it assumes there exists the conveyor belt that can generate counter speed (however large necessary).
Which is NOT how the test was done in Mythbuster show. They simply measure the take off speed (relative to stationary ground/runway) & tested with conveyor belt/sort of moving at opposite direction at that FIXED speed.
And the result was lift off, simply because plane can exert more force to overcome the moving belt (in the mythbuster show, I believe was 45 mph, I forgot the exact speed) and still able to move at necessary forward movement. In another word, assuming 45 mph was the required take off speed, the plane in the show took off because the plane generated force resulting in 90 mph forward moving speed.
[quote]They evidently over-estimated the average persons' knowledge of aerodynamics [/quote]
2. Don't talk down on other peoples as if you are smarter.
From theoretical perspective, if there exist a conveyor belt that can counter spin the force generated by the plane then, the plane will be stationary on the ground/run way regardless of how fast the wheels spin, it won't have forward movement and the result would be NO lift off (unless you are using helicopter or using vertical lift off capable airplane).
Posted 16 Feb 2012 at 11:38pm #
[quote comment="69206"]And the result was lift off, simply because plane can exert more force to overcome the moving belt (in the mythbuster show, I believe was 45 mph, I forgot the exact speed) and still able to move at necessary forward movement. In another word, assuming 45 mph was the required take off speed, the plane in the show took off because the plane generated force resulting in 90 mph forward moving speed.[/quote]
You're wrong. The plane did not generate extra force. You're 100% wrong.
[quote comment="69206"]2. Don't talk down on other peoples as if you are smarter.[/quote]
What if he is? Cuz, he's smarter than you.
[quote comment="69206"]From theoretical perspective, if there exist a conveyor belt that can counter spin the force generated by the plane then, the plane will be stationary on the ground/run way regardless of how fast the wheels spin, it won't have forward movement and the result would be NO lift off.[/quote]
You're an idiot.
The conveyor belt acts on the wheels.
The plane takes off because the force it applies is to the AIR. Whether they're jet engines or propellers, they pull or push the plane through the AIR.
Duh.
Posted 17 Feb 2012 at 3:57am #
[quote]The plane takes off because the force it applies is to the AIR. Whether they're jet engines or propellers, they pull or push the plane through the AIR.[/quote]
I bet that is the reason EVERY SINGLE airplane is capable of vertical lift off!!! You should be an aeronautical engineer.
The plane can lift off on the (SINGLE) force it is applying through air; hence, helicopter, vertical lift off capable fighter jets, etc... However, that is NOT what this myth is about.
[quote]You're wrong. The plane did not generate extra force. You're 100% wrong.[/quote]
Let me give you a new perspective on problem/myth for you idiot. Use the SAME plane that was used on the mythbuster show. Now measure the maximum horizontal speed it can generate on its wheels (yes I know the engine isn't connected to the wheels by drive shaft like in a car). In case you don't know how to measure that ..... adjust the wing angle so that plane won't lift off (and won't generate additional downward force to increase the friction between its wheels and runway), but keep moving on the runway & max the throttle and THEN calculate the speed (of its wheels).
Now build a conveyor belt to match that maximum speed & do the test to see if it lift off.
By the way, using tarp as conveyor belt is not the best thing.
In another word, the real myth to test is, "Will the conveyor belt be able to cancel out the forward momentum of wheels which is generated by the thrust of the engine pushing/pulling through air."
Another way to view this myth, assume that you can pull a 100Lbs object on a set of wheels at the maximum speed of 20 mph via a rope tied through your waist. Now put that object on a conveyor belt that can spin 20mph on opposite direction. And the question is, can you move that object at all in the opposite direction of conveyor belt is moving?
If your answer is YES, then you should really test it out.
If your answer is NO then stop saying that stationary plane can generate lift off. Ofc, we are not talking about helicopter or any other kind of vertical take off capable planes.
If your answer is NO and yet still claiming that plane can life off while it has no forward momentum, then I get nothing to say.
Posted 17 Feb 2012 at 9:50am #
[quote comment="69211"]I bet that is the reason EVERY SINGLE airplane is capable of vertical lift off!!![/quote]
That doesn't make any sense. Sorry.
[quote comment="69211"]The plane can lift off on the (SINGLE) force it is applying through air; hence, helicopter, vertical lift off capable fighter jets, etc... However, that is NOT what this myth is about.[/quote]
The plane lifts off because it moves through the air, the air across the wings provides the forces necessary to lift off. This is not complex, but the fact remains that the force applied to move the plane in the first place is against the air surrounding the plane. Whether it's propellers or jet engines, they act against the air.
[quote comment="69211"]Let me give you a new perspective on problem/myth for you idiot.[/quote]
To be clear, I get to call you an idiot because I'm right and you're wrong. You don't get to call me one. đ
[quote comment="69211"]Use the SAME plane that was used on the mythbuster show. Now measure the maximum horizontal speed it can generate on its wheels (yes I know the engine isn't connected to the wheels by drive shaft like in a car). In case you don't know how to measure that ..... adjust the wing angle so that plane won't lift off (and won't generate additional downward force to increase the friction between its wheels and runway), but keep moving on the runway & max the throttle and THEN calculate the speed (of its wheels).
Now build a conveyor belt to match that maximum speed & do the test to see if it lift off.[/quote]
The plane will still take off.
In fact, the plane would take off if you had it sitting there on a belt moving backwards at maximum speed before you started the engine. It'd take a lot longer, but it's a simple physics problem at that point.
[quote comment="69211"]In another word, the real myth to test is, "Will the conveyor belt be able to cancel out the forward momentum of wheels which is generated by the thrust of the engine pushing/pulling through air."[/quote]
That's not the myth. There's no "forward momentum of the wheels." The wheels are a goose for dolts such as yourself to chase.
Planes take off from sheets of ice. They take off from rivers, streams, and lakes.
[quote comment="69211"]Another way to view this myth, assume that you can pull a 100Lbs object on a set of wheels at the maximum speed of 20 mph via a rope tied through your waist. Now put that object on a conveyor belt that can spin 20mph on opposite direction. And the question is, can you move that object at all in the opposite direction of conveyor belt is moving?[/quote]
You bet your ass I could… if I had a jet pack on my back.
Classic. The wheels on an airplane exist simply so the plane rolls smoothly. The wheels on a simple plane have no real capacity to make themselves turn. They're simply wheels on an axle. They spin freely.
[quote comment="69211"]If your answer is YES, then you should really test it out.
If your answer is NO then stop saying that stationary plane can generate lift off. Ofc, we are not talking about helicopter or any other kind of vertical take off capable planes.[/quote]
Uhm, as has been stated a few thousand times across the Internet: IT'S NOT A STATIONARY PLANE.
The plane's engines (propellers, jets) move the plane through the air.
Posted 17 Feb 2012 at 1:10am #
[quote comment="69061"][quote comment="69059"]" I at first thought that meant that the plane would be moving at the same speed relative to the belt, meaning that it wouldn't be moving at all relative to the ground. [/quote]
Perhaps Mythbusters felt that since what you describe above is a physical impossibility, it wasn't necessary to explain it further. They evidently over-estimated the average persons' knowledge of aerodynamics. Come to think of it, I've met pilots who, when I described the myth, thought the plane would not take off. Scary!!![/quote]
Clearly you don't understand what I meant if you think what I said is a physical impossibility. The conveyor belt is moving backward at one set speed. Let's say that speed is v. Now Mythbusters said that the plane would move at the same speed (v) forward. If we take the speed of the plane to be relative to the conveyor belt, the plane's speed would be v minus v, meaning zero. If we take this speed to be relative to the ground, the plane would move forward at its typical speed (v). If it is the first case, it is blatantly obvious that the plane won't take off, as the plane doesn't move through the air at all to produce any lift. If it is the second case, it is blatantly obvious that the plane will takeoff as it moves forward at its typical takeoff speed and the air will produce lift. What I'm saying is the myth is blatantly obvious no matter which way they spin it, but they described it in a vague way that made me think they would try to make it takeoff from an essentially stationary position. For that reason, I was interested in the myth, then very disappointed when they "tested" it. No reason to insult my intelligence now.
Posted 17 Feb 2012 at 9:39am #
"In another word, the real myth to test is, "Will the conveyor belt be able to cancel out the forward momentum of wheels which is generated by the thrust of the engine pushing/pulling through air.""
No, it will not. Since there is only an extremely small amount of friction on the wheels (otherwise a plane would not be able to take off, moving belt or not), the plane will still need pretty close to the same amount of thrust to move forward at the same speed relative to the air or, to make it clearer, the stationary floor on which the moving belt is sitting. It does not matter if you have the wings set at an angle to generate lift or not.
Posted 17 Feb 2012 at 2:09pm #
[quote]The plane lifts off because it moves through the air, the air across the wings provides the forces necessary to lift off. This is not complex, but the fact remains that the force applied to move the plane in the first place is against the air surrounding the plane. Whether it's propellers or jet engines, they act against the air. [/quote]
Get your head checked, the plane does NOT move through the air "as if it is already floating" BEFORE it lift off. THE PLANE GENERATE FORCE THROUGH AIR TO OVERCOME THE FRICTION (however small/large it maybe). Once it overcomes that friction it moves forward THEN generate lift because of wing angle & air flow around its wings.
The engine generate force through air which in turn move on whatever the ground the plane is on as in your stupid example below.
[quote]That's not the myth. There's no "forward momentum of the wheels." The wheels are a goose for dolts such as yourself to chase.
Planes take off from sheets of ice. They take off from rivers, streams, and lakes.[/quote]
[quote]You bet your ass I could⌠if I had a jet pack on my back.[/quote]
First thing first, Learn the meaning of the word "assume". And then go learn, how to work the problems logic ways. (aka you cannot just make stuffs up outside the parameter just to get to the result you wanted). If you even know whatever that means.
[quote]Uhm, as has been stated a few thousand times across the Internet: IT'S NOT A STATIONARY PLANE.[/quote]
That is what really need to be proven. Have you given out the proof yet OR You just ASSUMING it is.
Say: If A+B=C then X^Y=Z
Here is your faulty logic.
You are saying "since someone proves that X^Y=/=Z therefore (YOU ASSUME) A+B=C statement is incorrect" instead of checking if A+B=C is correct or not.
I do need to make a correction on what I posted.
[quote]Another way to view this myth, assume that you can pull a 100Lbs object on a set of wheels at the maximum speed of 20 mph via a rope tied through your waist. Now put that object on a conveyor belt that can spin 20mph on opposite direction. And the question is, can you move that object at all in the opposite direction of conveyor belt is moving? [/quote]
Just to take out the human factor out of this example (so idiot like you won't accidentally blow yourself up by trying to use jet pack).
ASSUME that x psi of air pressure can push 100 LBs (or whatever amount of mass you prefer) object on a set of wheels at maximum speed of 5 mph.
Now put the same objects on conveyor belt and spin the conveyor belt until that object moves at 5mph (not conveyor belt spinning at 5mph)and note the speed of conveyor belt & say Z mph.
Now try to push that same object on conveyor belt (spinning at Z mph) with x psi of air pressure in the opposite direction of conveyor belt. And observe if it moves.
By the way, you can replace the set of wheels with whatever you like (for those idiots giving example on water planes & such). In case, if you do replace, use something that can create the LEAST amount of friction, so the odd will be on your side.
No one is arguing if the plane will take off while it moves forward (at least I am not arguing that fact).
The people who said NO lift off, are assuming the plane WON'T move forward at all therefore no lift is generated ....... say group A
The people who said CAN lift off are assuming the plane DOES move forward therefore it will generate lift as it speeds up ...... say group B
Well both groups are correct "IF EACH OF THEIR ASSUMPTION IS CORRECT".
Back to my first original post: I am merely saying I am in the group B
My simpler problem above is to test whether or not if their assumptions are correct.
If you are stupid enough to keep saying you are right regardless, testing/proof then you know what you are.
what we really should test is whether the plane will move or won't .... it is NOT even about lift off (unless you are the idiot that thinks stationary plane can generate instantaneous lift off without rocket attached to it & generating enough force to overcome gravity).
[quote comment="69212"]"In another word, the real myth to test is, "Will the conveyor belt be able to cancel out the forward momentum of wheels which is generated by the thrust of the engine pushing/pulling through air.""
No, it will not. Since there is only an extremely small amount of friction on the wheels (otherwise a plane would not be able to take off, moving belt or not), the plane will still need pretty close to the same amount of thrust to move forward at the same speed relative to the air or, to make it clearer, the stationary floor on which the moving belt is sitting. It does not matter if you have the wings set at an angle to generate lift or not.[/quote]
Well, why/how can you say flat out "No, it will not." All I am saying is that we should test it.
Posted 17 Feb 2012 at 2:13pm #
[quote]Back to my first original post: I am merely saying I am in the group B [/quote]
Correction: I am in group A
Posted 17 Feb 2012 at 2:15pm #
Irony -- you could replace the wheels with bricks and, as long as the propeller/engine were strong enough to overcome the friction, the plane would take off, conveyer belt or no.
Posted 17 Feb 2012 at 3:33pm #
[quote comment="69217"]Irony -- you could replace the wheels with bricks and, as long as the propeller/engine were strong enough to overcome the friction, the plane would take off, conveyer belt or no.[/quote]
Bingo.
Posted 17 Feb 2012 at 3:45pm #
[quote comment="69215"]Get your head checked, the plane does NOT move through the air "as if it is already floating" BEFORE it lift off.[/quote]
You added the "as if it is already floating" comment. I didn't say that. A plane taxiing on the runway is moving through the air, too. Air is being moved over the wings.
[quote comment="69215"]THE PLANE GENERATE FORCE THROUGH AIR TO OVERCOME THE FRICTION (however small/large it maybe).[/quote]
That's the entire point of WHEELS - to make the friction really, really small.
[quote comment="69215"]Once it overcomes that friction it moves forward THEN generate lift because of wing angle & air flow around its wings.[/quote]
You seem to vastly over-estimate the friction of wheels.
[quote comment="69215"]The engine generate force through air which in turn move on whatever the ground the plane is on as in your stupid example below.[/quote]
You don't get it. How much force is required to stand on a treadmill going 30 MPH in roller skates? Not much. If you were holding onto a rope and someone in front of the treadmill pulled you forward, the force required to pull you forward would be almost the same as the force required to pull you across flat, unmoving ground.
[quote comment="69215"]First thing first, Learn the meaning of the word "assume". And then go learn, how to work the problems logic ways. (aka you cannot just make stuffs up outside the parameter just to get to the result you wanted). If you even know whatever that means.[/quote]
I don't need to look it up as I'm doing no such thing. You might want to learn some grammar though.
[quote comment="69215"]You are saying "since someone proves that X^Y=/=Z therefore (YOU ASSUME) A+B=C statement is incorrect" instead of checking if A+B=C is correct or not.[/quote]
No I'm not. It's basic physics.
[quote comment="69215"]ASSUME that x psi of air pressure can push 100 LBs (or whatever amount of mass you prefer) object on a set of wheels at maximum speed of 5 mph.
Now put the same objects on conveyor belt and spin the conveyor belt until that object moves at 5mph (not conveyor belt spinning at 5mph)and note the speed of conveyor belt & say Z mph.
Now try to push that same object on conveyor belt (spinning at Z mph) with x psi of air pressure in the opposite direction of conveyor belt. And observe if it moves.[/quote]
It will. If it was already moving backwards at the time you started because you started the conveyor belt first, it'll first slow down moving backwards, then will move forwards. If the wheels are good it'll reach a top speed of 4.9 MPH.
But the problem with your simplified logic is that continued application of air pressure will continue to accelerate the wheeled "object" until such time as wind resistance balances out the actual speed of the compressed air.
[quote comment="69215"]No one is arguing if the plane will take off while it moves forward (at least I am not arguing that fact).
The people who said NO lift off, are assuming the plane WON'T move forward at all therefore no lift is generated[/quote]
Those people are wrong. They assume improperly that the plane won't move forward. It WILL MOVE FORWARD.
[quote comment="69215"]If you are stupid enough to keep saying you are right regardless, testing/proof then you know what you are.[/quote]
Stupid is not a synonym for "intelligent." đ
[quote comment="69215"]Well, why/how can you say flat out "No, it will not." All I am saying is that we should test it.[/quote]
No need. It's a simple physics question. And, despite what you think, Mythbusters did a fine job of testing the simple physics empirically.
Posted 17 Feb 2012 at 7:24pm #
[quote]It will. If it was already moving backwards at the time you started because you started the conveyor belt first, it'll first slow down moving backwards, then will move forwards. If the wheels are good it'll reach a top speed of 4.9 MPH.[/quote]
Where is your test/proof besides idiotically claiming that it is!!!
You can start conveyor belt & engine same time as it is irreverent.
Engine will need time to gradually build up pressure unless you are using rocket even then it is not instantaneous.
[quote]
But the problem with your simplified logic is that continued application of air pressure will continue to accelerate the wheeled "object" until such time as wind resistance balances out the actual speed of the compressed air.
[/quote]
First off, it is NOT simplified logic, it is simplified version of problem. Logic of the problem remain the same. I simplified the problem, so that less logical person like yourself can understand it a little better.
There is a logical KEYWORD on your reply for the first time "continued application of air pressure will continue to accelerate". Yes, the keyword is continuously increasing pressure is required to overcome the friction on wheels. Hence, bigger/heavier plane requires more powerful engine. Regardless of the engine's power/size/rev, it will flat line its output energy at some point. That is what I am using in the simplified problem. Maybe learn the meaning of "maximum". You cannot go on saying, "I can just get more powerful engine" so that the result will tip toward you.
That is another reason I simplified/scaled down the problem to the point where physically testable scale size.
[quote]
You seem to vastly over-estimate the friction of wheels.
[/quote]
There is a reason why Boeing doesn't use your lawn mower engine on its 747.
Another way to look at this.
If the friction of wheels are extremely small then if you put 1000Lbs wheeled object (yes, free spinning wheels, NOT a car) onto a conveyor belt that is rotating (say 100 mph), that object will be stationary, according to your physics. Since its friction is extremely small & negligible. Will it?
According to your physics, negligible friction will simply cancel out 100 mph spin from conveyor belt. It won't translate into movement in the direction of conveyor belt spinning.
Here is the real physics, however small the friction, it won't simply cancel out the 100 mph spin from conveyor belt. It (the small friction) will create slow movement in the direction of conveyor belt spinning.
But it require very little force to overcome the small movement generated by friction+conveyor spin. (This is the fact you chose to ignore, just like you discard the friction factor because it is too small).
[quote]
Mythbusters did a fine job of testing the simple physics empirically.
[/quote]
They proved what I have stated above, it only required extremely small force to overcome that tarp going in opposite direction at 20 mph on their show. And the plane took virtually the same way.
[quote]
Those people are wrong. They assume improperly that the plane won't move forward. It WILL MOVE FORWARD.
[/quote]
Because you disagree with other people assumption, it doesn't make it right or wrong. Maybe go learn the meaning of the word "assumption"? ....
what I am saying to test/prove that assumption is right/wrong.
That is NOT even my point.
[quote][quote]
You are saying "since someone proves that X^Y=/=Z therefore (YOU ASSUME) A+B=C statement is incorrect" instead of checking if A+B=C is correct or not.
[/quote]
No I'm not. It's basic physics.
[/quote]
What I said in there is NOTHING about physics. It is PURE general Logical statement.
Here is the simplified version of it.
If A happens then B will happens ..... that is general Logical statement. (where A & B are arbitrary events)
You countered by by saying, since B doesn't happen it implies that A doesn't happen ...... which is logically WRONG statement.
back to my simplified problem, to make it even simpler.
x psi = the assumed maximum force generated
M LBs object on a set of wheels (or whatever medium you wish)...
M = arbitrary weight/mass in my other post it was 100 LBs object
Y mph = the speed at which the object with M LBs on a set of wheels moves when applied by x psi pressure on the ground/whatever stationary surface you wish.
Z mph = conveyor speed which will generate (through however small/large friction of wheels) movement of the object with M LBs on a set of wheels at Y mph
Here is what you have been idiotically saying.
you are saying x psi is "continued application of air pressure" that is NOT what I have said.
You can have increasing pressure 1 psi, 2 psi, 3 psi up to x psi where x psi is where it flat line its energy output. You are assuming X psi will NEVER stop increasing its pressure.
That is why you are logically wrong, you want to keep increasing x psi to x+100 psi, x+1000 psi ect, while all other variables remain constant ...... until it moves at Y mph (till your result kick in).
Likewise, I can illogically claim that I am correct (without testing) by increasing M to M+100 LBs, M+10000 LBs etc, while all other variables remain constant .... to increase friction, and tip the result toward myself. (which I am not).
What I want is to have a test on scaled down (simplified as you wish to say) version of the problem.
You are appeared to be correct on the real world test, NOT because of physics or Logically correct. But because it is extremely (or even impossible at today technology) hard to get Z mph conveyor belt for real plane (because of friction is really small).
That is NOT to say that we cannot test at scaled down version.
Here is what is really come down to ...... the relationship (or whatever you wish to call) between X psi & Z mph is extremely large mainly because of very small friction on the wheels.
All I am saying is that we should scale down the test to where we can achieve Z mph then adjust X psi or increase the M LBs accordingly.
Don't come giving me physics lecture on psi & mph are not even the same unit. I know they are not, but they are connected by the friction on wheels.
Perfect analogy would be "at current human technological level, it is extremely hard for human to create Star/Sun, we should not even attempt to test/create small scale (controlled) thermonuclear fusion reactor!!!"
If all human beings are like you, we will still be living in caves.
Posted 17 Feb 2012 at 7:30pm #
Irony: you are way way over thinking this.
Once again: You could replace the wheels with bricks and the plane will take off *as long as the prop/engine are able to overcome friction*. Doesn't matter what speed the conveyer belt is going. Doesn't actually matter if the conveyer belt is even there.
It is really that simple.
Posted 17 Feb 2012 at 8:07pm #
[quote comment="69220"]Where is your test/proof besides idiotically claiming that it is!!![/quote]
Basic physics.
A plane moving backwards on a conveyor belt will still be able to take off.
[quote comment="69220"]First off, it is NOT simplified logic, it is simplified version of problem.[/quote]
Not really. It's a different problem altogether. PSI of air pressure? A continued force will accelerate the object until the forces are equal and opposite (i.e. wind resistance + a tiny bit from the wheels).
[quote comment="69220"]There is a logical KEYWORD on your reply for the first time "continued application of air pressure will continue to accelerate". Yes, the keyword is continuously increasing pressure is required to overcome the friction on wheels.[/quote]
No, not increasing pressure. The same pressure will accelerate the object until the forces are equal and opposite.
The force applied by the wheels is negligible. That's kind of the purpose of wheels.
[quote comment="69220"]Hence, bigger/heavier plane requires more powerful engine. Regardless of the engine's power/size/rev, it will flat line its output energy at some point. That is what I am using in the simplified problem. Maybe learn the meaning of "maximum". You cannot go on saying, "I can just get more powerful engine" so that the result will tip toward you.[/quote]
As bbum said, the engine must simply overcome the friction of the wheels - which it does normally when it takes off from a standard runway - the conveyor belt adds virtually no extra friction or force. You don't need a larger engine at all. The same one will work just fine.
[quote comment="69220"]There is a reason why Boeing doesn't use your lawn mower engine on its 747.[/quote]
Huh? The fact remains that a 747 on a conveyor belt will take off almost exactly the same as a 747 on a runway.
[quote comment="69220"]But it require very little force to overcome the small movement generated by friction+conveyor spin. (This is the fact you chose to ignore, just like you discard the friction factor because it is too small).[/quote]
We've said the same thing. The conveyor belt spinning the wheels will add a teeny, tiny amount of friction. An amount easily overcome by the same engines on the plane. The wheels will simply be spinning, at takeoff, at twice the speed they'd be spinning at on a runway. That's the only added "force" applied to the system - a force, once again, easily overcome by the plane's engines. Wheels - again - are made to spin with little friction.
[quote comment="69220"]They proved what I have stated above, it only required extremely small force to overcome that tarp going in opposite direction at 20 mph on their show. And the plane took virtually the same way.[/quote]
Uhm. That's the point. You're the one saying the plane will be stationary for some reason.
[quote comment="69220"]What I said in there is NOTHING about physics. It is PURE general Logical statement.
Here is the simplified version of it.
If A happens then B will happens ..... that is general Logical statement. (where A & B are arbitrary events)[/quote]
If the conveyor belt moves at all, the plane will still be able to take off. There's your simple logical statement.
This is a physics problem. It's not a logical problem. Especially when you screw up the basic logic.
[quote comment="69220"]x psi = the assumed maximum force generated[/quote]
PSI is not a force.
[quote comment="69220"]M LBs object on a set of wheels (or whatever medium you wish)...
M = arbitrary weight/mass in my other post it was 100 LBs object
Y mph = the speed at which the object with M LBs on a set of wheels moves when applied by x psi pressure on the ground/whatever stationary surface you wish.[/quote]
Another bit that's wrong. The item will accelerate when you blow your air against it. It will not instantly hit some speed and then stop when you turn off the air. It will accelerate until the force generated by your air is equal and opposite to the wind resistance and the resistance the wheels provide.
[quote comment="69220"]Here is what you have been idiotically saying. you are saying x psi is "continued application of air pressure" that is NOT what I have said.
You can have increasing pressure 1 psi, 2 psi, 3 psi up to x psi where x psi is where it flat line its energy output. You are assuming X psi will NEVER stop increasing its pressure.[/quote]
No, you're not understanding basic English. If you apply a stead PSI - say 50 PSI - against an object on wheels the object will accelerate. It will not instantly reach a steady speed and maintain it, then instantly stop when the air is turned off.
I've never said a thing about increasing the PSI.
[quote comment="69220"]Don't come giving me physics lecture on psi & mph are not even the same unit. I know they are not, but they are connected by the friction on wheels.[/quote]
You're an idiot.
Thanks for playing. đ
BTW, apologies, Bill. This is one of the few places I allow myself some cathartic release, picking on the dolts who continue to treat this problem as if it's somehow still not been proven properly or something. đ
Posted 18 Feb 2012 at 4:13am #
[quote]
The wheels will simply be spinning, at takeoff, at twice the speed they'd be spinning at on a runway
[/quote]
Sad understanding of basic physics ........ the wheels will spin at EXACT speed .... either on the conveyor belt or on the runway.
[quote]
PSI is not a force.
[/quote]
The definitive proof of how stupid you really are.
You are an idiot.
Posted 18 Feb 2012 at 7:40am #
You're blocking people who disagree with you?
Hahaha, that's the spirit!
Why do you have a place where people can comment on your blog for in the first place? Just write what you think is correct and then state that as a fact, that would allow you to "get more work done"...
Posted 18 Feb 2012 at 1:41pm #
Erik is quite reasonably blocking people who repeat nonsense without adding anything to the discussion. Very different than outright blocking the nonsense in the first place.
I've had to do much the same on FaceBook (but that is because I discuss politics on FB only).
Erik -- thanks for keeping this thread alive as it has provided a consistent spot of entertainment every few months.
Posted 18 Feb 2012 at 8:40am #
[quote comment="69227"]Sad understanding of basic physics ........ the wheels will spin at EXACT speed .... either on the conveyor belt or on the runway.[/quote]
Wrong. If the plane's moving 25 MPH in one direction and the ground - the conveyor belt - is moving 25 MPH in the opposite direction, the wheels will be spinning, at the moment of takeoff, at twice their normal RPM on a normal liftoff from a standard runway.
[quote comment="69227"]The definitive proof of how stupid you really are. You are an idiot.[/quote]
Wrong. The "P" is a force, but pound-force per square inch is not a measure of force. It's a measure of force over an area. Big difference.
[quote comment="69228"]You're blocking people who disagree with you?[/quote]
Yep. After awhile, arguing with idiots who think 1+1=3 gets old.
Posted 18 Feb 2012 at 2:53pm #
Concerning all the claims that the mythbusters experiment got it wring because they did not manage to keep the airplane stationary:
The purpose of the experiment was not to keep the airplane stationary on the treadmilll and then see if it takes off. The purpose of the experiment was to determine if the moving treadmill would be able to keep the airplane from taking off. At no time did Mythbusters ever mention any intention to determine if a stationary airplane can takeoff. Anyone who objects to the Mythbusters experiment on these grounds is just making stuff up. This is called a Straw Man argument.
Clearly a stationary airplane (relative to the surrounding air) cannot takeoff. Mythbusters proved that the moving treadmill was incapable of keeping the airplane from moving relative to the surrounding air. This was its only intention.
Posted 18 Feb 2012 at 7:45pm #
Interesting topic.
After seeing the episode myself i too was confused,especially about the plane's liftoff.
But the Mythbusters could have explained this test a little better themselves because from seeing this test one could not believe a plane (a small one no less) could have a liftoff with what appears to be such little speed.Apparently it was all just very normal.
It looked like all forces of nature were applied from the conveyor belt onto the airplane untill the airplane took off.
Atleast that was what i was thinking or wanted to believe.
Think of a runway where a Piper, F-16 or jumbo jet would throttle after a few meters smoothly on a speeding treadmill before take-off;
Maybe for some blue smoke coming from accelerating tires everything would look the same for each individual airplane.
Posted 18 Feb 2012 at 8:15pm #
[quote comment="69235"]… one could not believe a plane (a small one no less) could have a liftoff with what appears to be such little speed.[/quote]
I believe take-off velocity was only 25 MPH. I too was unaware that planes could take off at such low speeds, but like you said, it was all perfectly normal. Except that it made me want to buy and learn to fly a small little kit plane that can take off at 25 MPH! đ
On second thought, remote-controlled planes take off at reasonable speeds. There's no reason, I guess, to suspect that a scaled model (same lift to weight ratio) wouldn't take off at the same speed.
Posted 05 Mar 2012 at 12:45pm #
*sigh* people still debating this? One theory more complex than the next. "physics" of different degrees. PhD without BASIC knowledge of the simplest equations? Here's the final solution, and it can be verified by any high school level physics book.
Forces involved:
-thrust from the propeller, Tp
-friction between the wheels and the conv.belt, Fw
-gravitational force (plane's mass times gravity constant) G
-ground force pushing on the plane, N
-lift generated by the wings, Lw
Vertical speed = (N + Lw) - G
Horizontal speed:
Tp - Fw
Fw would be neglible since wheels are made to roll as easy as possible; that means with as little friction as possible.
Here's the key: if the speed of the conv.belt is the same as the plane's speed through the air, the friction will be ca. Doubled. That's the ONLY impact a conv.belt would have. And since the friction is neglible in the beginning, if it is doubled it's still neglible. The plane will use a slightly longer distance before takeoff, but it can't be accurately measured due to variables such as wind, weight, temperature, uncertainty in the measurements and so on.
Do not over-complicate this. It is physics, not math. Physics tells you that it is impossible to cut a donut so that 360 people get an equal piece each. Math says it is okay - one degree of donut per person. đ
All powered planes depends on thrust from a propeller or a fan (ignore rocketpowered ones, they are not "normal" aircrafts) to move forward, be it through the air or over the ground (two sides of the same coin, really). Thus, if an airplane was placed on a super-long conveyor, the brakes full on and the belt speeded up to, say 200 mph - the plane would go bacwards with 200 mph. As soon as the brakes are released, the plane would SLOW DOWN because of drag. Sooner or later, the plane would travel backwards at a constant speed. Then start the engine and hit full power. The plane would slow down, stop, then move forward and eventually take off.
The only significant occurrence will be that the wheels and the bearings would be warmer than normal since the wheels would turn twice as fast as normal.
The thrust from the propeller determines the plane's forward movement. The resistance from the wheels is insignificant and can never stop the plane from moving forward. As a matter of fact, on a lightly loaded Boeing 737 you need to give a small boost with the engines to start rolling, after that you need to brake every now and then in order to taxi at a safe speed.
A plane cannot take off vertically unless it tries to take off in a hurricane. Theoretically, you could do it even with a 747, but it would not be a good idea...
It needs air to move past the wings at a certain speed, and that can only happen if the plane moves forward.
About the catapults on carriers: the use them because the carriers aren't long enough to house the necessary length of runway. The use wires as brakes too, or the planes cannot land.
The original question was: if a plane is placed on a conveyor belt that has the same speed as the plane - but in opposite direction - will the plane take off?
The answer will allways be: yes.
At least if we keep the experiment within possible limits. Light speed on a conveyor belt is impossible, therefore a moo point. (reference to Friends)
And thisnis the physics of this conundrum. Nobody can conspire against physics and win.
Still, a "PhD in theoretical physics" argued against this. He or she should ask for his/her student loans back.....
And I do not have a degree in physics, nor am I a pilot. But i know a lot about planes, and I got an A on my physics exam when I studied engineering (dropped out because i lost interest in the field I studied). Therefore I was puzzled when I saw the show the first time. Still am puzzled by all the conspiracy theories out there. People are ignorant, and in a LOT of cases: stone cold stupid. Cudos to the blogger for not being PC about it. A PC world is insane; let us just say it in stead of polishing a turd in case someone is offended. If you are offended, I say my observation was actually spot on!
Ps: to you PhD's out there overcomplicating this: this is NOT theoretical physics. It is PRACTICAL physics. The frame of reference can only be between the plane and the earth. No matter what you cram in between. What's in between will only determine a small factor in a bigger picture.
Waiting for the flame war to commence... đ
Posted 05 Mar 2012 at 12:55pm #
As a side comment to what I wrote above: at a certain speed on the conv.belt the non-believers will be right. Because if the conv.belt approaches the speed of light, so will the wheels. And at the spped of light the mass is infinite. Somewhere between normal takeoff speed and the speed of light, the mass of the wheels will become more than what the maximum lift the wings can generate, resulting in the plane not being able to take off. Would be a scary scenario though... đ
Posted 06 Apr 2012 at 5:08pm #
Has anyone thought about placing the propellers outside the wings? In that case the propellers will only work as keeping the wheels of the airplane rotating as fast as the CB, reaching the ground speed (GS) necessary to take off. What will happen then? There will be no airflow on the wings, then the airplane will not get off the ground.
Go to any flight sim and put a wind aligned with the airplane, the same speed as the take off speed and see what happens. You can do this without the engine working and brakes ON. Will it fly? Why is it flying? ground speed? engine? wheels? Nope, only airflow through the wings.
Change the propeller for a jet engine in which you also, don't have any airflow through the wings (place the engines outside the wings). If the engines allows you to reach a ground speed at which the airplane should take off, I bet the airplane will not move... not even an inch above the ground.
What happens on the video is that the propeller is pushing air though the small portion of the wings and tail surface control parts that allows the plane to take off with the lowest speed it can have (on the air) to take off.
I'm no pilot, I like planes and I'm an experimental physicist. No equations just facts. I would like to see it happening with the other engine configuration.
Best regards,
Gzo
Posted 15 Apr 2012 at 11:44am #
[quote comment="69846"]There will be no airflow on the wings, then the airplane will not get off the ground.[/quote]
There would be airflow over the wings.
You seem to lack a fundamental understanding of the purpose of the propellers. It's not to throw air over the wings. It's to pull the plane forward through the air (which is how the air gets "over" the wings).
Posted 15 Apr 2012 at 1:31pm #
Experimental physicists, huh? Yeah. You better get your student loans back. Physics is ALL ABOUT equations, at least if you want to GET the facts. Do not throw a fancy title around without actually having a degree, dude!
Where are the engines fastened? To the airplane! The propellers push the air, the air pushes back. The propeller wants to go forward, ergo there is a force acting on the propeller. Equal and opposite reaction. That force is transferred through the engine to the plane, thus there is a force acting on the plane. Moving it forward. The friction between the wheels and the ground act the opposite way, but since that force is tiiiiiiiny - the plane moves forward.
The "wind" over the wings at the back of the propellers does not create enough lift to make the plane take off. There needs to be a certain degree of wind over most of the wing surface for that to happen.
Flight simulators is great fun, but you cannot use them to test physics. Of course, a headwind of about 140 knots (+/- 20 knots), a 737 could be lifted off the ground while standing still (depending on weight and model). EVEN if it is placed on a conveyor belt moving the same direction as the wind at the same speed, and the plane was kept from moving backwards without stopping movement in any other directions).
I really, really, really, really cannot for the LIFE of me understand how this concept eludes people - even those who claim to be physicists! Newtons laws, folks! Equal and opposite forces, the sum of all forces and so on.
It does not matter where you put the engine(s) - as long as they are connected to the plane, they WILL move the plane regardless of how fast the wheels are turning!
And I am not a physicist, nor a pilot. However, I got an A on my physics exam when I studied engineering. And I know a lot about aircrafts (especially the boeing 737 series).
This one made me laugh:
"Change the propeller for a jet engine in which you also, don't have any airflow through the wings (place the engines outside the wings). If the engines allows you to reach a ground speed at which the airplane should take off, I bet the airplane will not move... not even an inch above the ground."
Dude, a propeller or a jet engine does the same thing - they create a force acting on the plane!
Besides, that quote is completely stupid. ALL jet powered planes has the engines "outside the wings". And still, hundreds of thousands of passengers get to their destination every single day! It's a conspiracy!
And when the air moves over an airplane's wings at the takeoff speed for that aircraft, the aircraft WILL take off.
There is, nor will ever be, a situation where a plane won't take off from a conveyor belt. Ever. Get a treadmill and try it yourself! Model aircrafts works on the exact same principles as their big siblings.
Posted 04 Jul 2012 at 3:57pm #
So let me get this straight. If I stand in roller skates on a treadmill then I will feel a breeze as the treadmill runs, even though I am standing in place? If I put a rocket in my butt to propel me forward, but the magic treadmill anticipates my acceleration and speeds up to counter that impulse so that my body remains stationary relative to the moving treadmill belt, I will still feel a breeze?
Posted 04 Jul 2012 at 6:24pm #
No, you won't feel a breeze, because you would not move (well, at first - soon you'll start to move backwards, but SLOWLY).
If you light the rocket, you'll feel a breeze because you would move forward. Fast! What the threadmill does has NO effect on you - you'll still move forward.
Let me repeat this: NO MATTER WHAT YOU DO, THE CONVEYOR BELT WILL NOT STOP YOU FROM MOVING FORWARD OR TAKING OFF!
And stop changing the premises! We're talking about an airplane on a conveyor belt, not a moron on rollerskates with a rocket in his butt. đ
BTW: Where did that theoretical physicist go? đ
Posted 09 Jul 2012 at 1:23pm #
Quote from vidarf: Let me repeat this: NO MATTER WHAT YOU DO, THE CONVEYOR BELT WILL NOT STOP YOU FROM MOVING FORWARD OR TAKING OFF!
The whole premise of the experiment on the show was that the plane would be moving the SAME SPEED as the conveyor belt but in the opposite direction. They certainly implied that the speed of the plane would be relative to the moving conveyor belt, not the ground. And if they didn't imply that then they certainly left it vague.
Color me stupid but that's clearly not what happened - The plane was moving faster than the conveyor belt - obviously if you have a plane travelling at 100mph (exaggerating) on a 25mph conveyor then the plan will take off.
Posted 09 Jul 2012 at 9:19pm #
[quote comment="70639"]Color me stupid but that's clearly not what happened - The plane was moving faster than the conveyor belt - obviously if you have a plane travelling at 100mph (exaggerating) on a 25mph conveyor then the plan will take off.[/quote]
What color is stupid? Whatever it is, you're that color. The plane takes off even if the conveyor belt is moving 10x as fast as the plane (so long as the bearings in the wheels don't fall apart).
Posted 10 Jul 2012 at 4:01am #
Hold on - Ben makes a (somewhat) valid point here. The way Mythbusters might have told the story could be the reason he's confused.
Ben, if a plane can take off at 40 mph (a small cessna private aircraft can do that), it will take off at that speed.
What I think Mythbusters tried to do, was to match the speed of the conveyor belt to the takeoff speed of the plane. I actually do not remember why (think they spoke about it in the show).
Of course the plane will travel faster - it can do that. It will do that. It will accelerate until it cannot stay on ground anymore
But again - the speed of the conveyor belt is irrelevant. A plane takes off because the lift generated by the wing passing through the air (!!! Note how I phrased that!!!) generating high pressure under the wing, low pressure over the wing - and the plane takes off.
As long as the plane is capable of moving forward and reaching its minimum takeoff speed, it will take off and fly. And with absolutely ALL conceivable, REALISTIC conveyor belt that could carry an airplane, that's what going to happen. Every time. No matter the speed of the belt (although at some point, the wheels on the aircraft will melt or explode due to heat buildup in the rubber).
So to repeat Ben's example, but with realistic speeds:
If the conveyor belt moves backwards at 40 mph, the plane will take off when the plane reaches 40 mph. Same deal if the conv.belt stands still or moves at 300 mph.
The difference would be the speed of the wheels - and of course, the temperature of the wheels.
Posted 16 Jul 2012 at 4:39pm #
Takeoff speed is relative to the air around the wing.
The conveyor belt is the key to this. The reverse speed of the conveyor belt negates the forward progress of the plane, and thereby reduces the lift to zero as the wing is not passing through the air. The air is independent of the conveyor belt. The air is independent of the plane. Unless the wing if making forward progress through the air, there is no lift.
Do you feel a breeze from running in place? No? Running on a treadmill? No?
Posted 16 Jul 2012 at 7:00pm #
[quote comment="70661"]The conveyor belt is the key to this. The reverse speed of the conveyor belt negates the forward progress of the plane, and thereby reduces the lift to zero as the wing is not passing through the air. The air is independent of the conveyor belt. The air is independent of the plane. Unless the wing if making forward progress through the air, there is no lift.[/quote]
Flat out wrong.
Unlike running on a treadmill, the plane pulls itself through the air. The wheels are free-spinning.
Posted 10 Jul 2012 at 4:27am #
Ok seriously people. If you haven't understood that the plane will take off by now there's no hope for you. Who cares how the mythbusters presented it. It was pretty simple to understand, and if you understood it any other way than they run a conveyor belt backwards matching the minimum take off speed of the plane, will the plane produce enough lift to take off if it matches that speed in the opposite direction, then I'm surprised you actually have the skills to turn your computer on and post to this thread.
The planes thrust will always overcome the wheels spinning at any speed, be it 40mph or 400mph.
Just stop posting to this thread and watch the friggin Mythbusters episode.
Bottom line is the Mythbusters presented the myth the way they felt necessary and came to a conclusion and proved the bloody plane will take off.
WATCH THE EPISODE and stop trying to pick apart the way they presented it cause you don't understand it.
You seriously are all EFFIN STUPID. Oh and just incase you didn't know. The plane will take off, PERIOD!
Posted 10 Jul 2012 at 9:55pm #
In ground school you must learn the four laws of physics involved in flight. before you begin actual in the air flight training
1) Weight, (Gravity never changes but weight does)
2) Lift
3) Drag
4) PROPULSION
The law of physics in question hers is propulsion, if what the non believer say is true the propulsion from an airplane was governed by wheel speed, then how does an airplane continue to propel itself once airborne, it would have to land regain Ground-speed to lift again.
The keyword is airspeed, not ground speed if this plane were to take off against a 25 mph head wind it would require no ground-speed only airspeed and could take off and never move forward.
Against a 30 mph head wind theoretically the plane could take off and fly while moving backwards at 5 mph (not advisable due to safety concerns)
If ground speed were an issue then it would not explain head winds slowing you down, or tail winds speeding you up!
(A quote from my favorite pilot and all around great guy)
"Anybody could be as good or better bush pilot as me, if they have as many hours of flying as I do" ~Paul Claus "undisputed King of the bush pilots."
Posted 16 Jul 2012 at 4:29pm #
No, you won't feel a breeze, because you would not move (well, at first - soon you'll start to move backwards, but SLOWLY).
But the principle is the same. For a wing to generate lift there must be air moving across it. If an aeroplane on a treadmill is not moving forward on the treadmill then there is no velocity of the air surrounding the wings. No velocity....no breeze....no lift.
To put it another way, would an airplane lift if the nose were against a solid wall? No matter how far you ran up the thrust, if the wall holds then there is no air flowing across the wings, and no lift.
Posted 16 Jul 2012 at 5:02pm #
The treadmill does not negate forward speed of the plane. It negates a runner's speed because the runner is pushing against the treadmill. A plane pushes against the air, not the ground, meaning there is no effect from ground movement.
Posted 17 Jul 2012 at 11:06am #
Phil: stop altering the question! No, a plane parked against a wall won't move. But that is NOT the question!
When YOU are running on the treadmill / a conveyor belt, your feet pushes against the belt, pushing you forward. If the speed of the belt matches up with you, you won't move. And of course - you won't feel any breeze on your face.
A plane, however, does NOT push against the ground, conveyor belt or whatever it is standing on. The propeller / jet engine pushes against the air.
Sit on a office chair with wheels. Strap pizza boxes on your arms and start waving, keeping the cardboard horizontal when you move your arms forward and vertical when you move them backwards.
You will move forward, although very slow. It's the same thing.
You need to get your facts straight. Where does the force pushing/pulling the plane forward come from? The propeller. Which force pushes/pulls the plane backwards? The friction between the wheels and the belt. How big are those forces compared to each other? The friction force is extremely small, so it does not matter.
The proof of that last statement is this: does an aircraft move forward when you start the engine and throttle up a bit? Yes, very easy (in fact, a 747 jumbo jet will move forward at idle thrust if it has very little cargo and few passengers - you need to apply brakes to hold it in place!).
If you add a conveyor belt under the wheels, the only thing you will do is spinning the wheels faster. The friction force will increase, but very, very little.
In fact, forget all the fancy words. Focus on the FACT that the propeller / jet engine pushes against the AIR. The wheels do NOTHING to move the aircraft anywhere.
Read my posts. They explain this over and over again. I do not have any degrees, I am not an airplane pilot. I _am_, however, an aircraft enthusiast and therefore know a lot about how planes work. I also took several physics classes in high school and at the university.
The fact that you don't understand this does not make you an idiot, it just proves that you don't know how airplanes works - and you have very little understanding of physics. That's okay! But listen to us who know what we're talking about.
We even have a TV episode that proves it. There is no conspiracy there. If you conspire against physics, it's going to bite your behind pretty hard pretty fast! đ
To quote Adam:
"Gravity - it's not just a good idea. It's the LAW!"
Posted 17 Jul 2012 at 11:22am #
[quote comment="70661"]Takeoff speed is relative to the air around the wing.
[/quote]
Correct.
[quote comment="70661"]
The conveyor belt is the key to this.
[/quote]
Incorrect. The fact that the plane's forward momentum is generated by a propeller or jet engine pushing against the AIR, however, is.
[quote comment="70661"]
The reverse speed of the conveyor belt negates the forward progress of the plane,
and thereby reduces the lift to zero as the wing is not passing through the air.
[/quote]
That is impossible. No conveyor belt can do that. Ever.
[quote comment="70661"]The air is independent of the conveyor belt.[/quote]
Correct, and you should remember that!!! Because the plane pushes against - exactly right! - THE AIR! Not the conveyor belt.
[quote comment="70661"]The air is independent of the plane. [/quote]
Absolutely correct.
[quote comment="70661"]Unless the wing if making forward progress through the air, there is no lift.
[/quote]
Kind of correct, but the fact is that the lift is generated by air passing over the wing creating a low pressure OVER the wing and a high pressure UNDER it. If the wind is blowing strong enough, a plane sitting still on the ground can get enough lift to take off. In fact, pilots from the propeller airliner area can tell you about times they passed the same spot in the terrain several times without changing the course! If the wind blows hard enough, an aircraft can "fly backwards"; the wind blows faster than what the engine can cope with. This can happen with modern jet aircrafts as well, but that won't happen too often nowadays since you need to keep the passengers happy. "Shaken, not stirred" should not be applied to an aircraft passenger!
[quote comment="70661"]
Do you feel a breeze from running in place? No? Running on a treadmill? No?[/quote]
Correct, but you are pushing against the treadmill, not the air. Not the same scenario.
A car on a conveyor belt will not move, and THAT would be a comparable scenario. Unless you fart a hurricane, you cannot push against the air hard enough to move yourself forward. Now, THAT would've been a comparable scenario! đ
Posted 25 Jul 2012 at 9:16am #
I just saw this episode on Netflix. I'm a 68 year old woman with a Master's in Education and a Bachelor's in Social Work and the mere thought of Physics gives me the vapors.
That said, I'd like to thank the "will fly" folks for giving such clear explanations that I now think I understand this, completely. With my (non) background, if I can understand that the propeller pulls the plain forward and the wheels, and what's under them, don't matter, why do so many people have a problem with it?
Thanks, guys. I'm sitting here grinning like a fool and thinking, "Wow! I actually understand something Physics!"
How cool is that?
Posted 25 Jul 2012 at 9:17am #
Oops! "Plane".
Why do my fingers insist on doing what my brain knows is just, "plain" wrong?
Posted 26 Jul 2012 at 1:59pm #
That is actually pretty cool! đ If you're interested, I would recommend you to head over to Youtube and search for "physics for future presidents". It's a lecture series with an easy approach to physics, without a lot of math and without digging into the topic too much - gives you the grand overview. To learn even more, I HIGHLY recommend the lectures given by mr. Walter Levin. At youtube, search for "physics 8.01"
At least, watch this one:
http://www.youtube.com/watch?v=SRh75B5iotI
Physics is FUN! đ
Posted 26 Jul 2012 at 11:35pm #
[quote comment="70695"]That is actually pretty cool! đ If you're interested, I would recommend you to head over to Youtube and search for "physics for future presidents". It's a lecture series with an easy approach to physics, without a lot of math and without digging into the topic too much - gives you the grand overview. To learn even more, I HIGHLY recommend the lectures given by mr. Walter Levin. At youtube, search for "physics 8.01"
At least, watch this one:
http://www.youtube.com/watch?v=SRh75B5iotI
Physics is FUN! :)[/quote]
Oh, how very nice of you! Truly!
I will check out your links. Maybe I'll actually learn something else.
Had it not been for this blog and this topic, I'd have seen myself as a Physics clod...forever...and I do thank you all. I hope to keep learning until I've been dead for 3 days, at least. Y'all have opened a window on a new world for me.
Posted 27 Jul 2012 at 9:21am #
@vidarf
I watched the Lewin lecture and I was enthralled! I started it very late and I kept telling myself that "I'll go to bed right after he finishes this..." and found myself at the end of the Q&A before I knew it.
I loved the whole thing. I understand the "rule" about the pendulum, even if I don't yet understand why, and Lewin certainly gave a riveting demonstration! I'm going to see if I can find any (easy) lectures of his on the Inet and I'm going to buy that book!
THANK you...and thank all of you who helped me to see that you can teach an old dog new...ahem...disciplines.
Tredz
Posted 30 Jul 2012 at 11:30am #
I don't refute the myth that was tested. A plane on a conveyor belt will take off. Now ask the question that was not addressed on the show.
If you limit the wheel speed to the conveyor belt speed will the plane take off? Only with VTOL or a wind storm.
As stated the only thing that matters to the plane is air speed which requires the plane to move forward. Wheels can move at 5,000 mph for all I care air speed must reach the point where circulation occurs. I could go to great detail on that but no reason.
Assuming the plane canât move backwards and because the wheels move independently of the aircraft wheel speed can have one of two values. Wheel speed equals conveyor belt speed or wheel speed equals belt speed plus a forward value.
Now the plane only cares about the relative speed of the plane with the air. Assuming no wind or wind is insignificantly different to prevent takeoff without thrust we can say it is relative to the ground. The wheel will move relative to the belt and the belt will move relative to the wheel. Once the two are equal compare them to the ground.
If the belt moves back at 100 mph it will appear that the wheel are turning at 100 mph and the belt is not moving. If forward thrust is applied it will appear that the wheels are moving at 100 mph + x. If the thrust is reduced back to 0 than the wheels will appear to move at 100 mph. The same is true if you swap wheels for belt. Showing that if thrust is applied relative speed will increase. As per the question relative speed must be equal to keep them equal.
So we start the belt and under the assumption that the plane canât move backwards the wheels equal belt speed. If it is easier to understand say there is a wall behind the plane where the belt can move under but keeps the plane in place. By no means is this wall preventing the plane from moving forward. At this point the relative air speed or ground speed per our assuming that they are equal is zero. If we throttle the plane it will move forward and take off. Problem occurs because the added thrust increased the relative speed of the wheels to the belt. The plane took off only because it broke the constraint that the values are equal.
Using terms like stupid only prove your own ignorance. I studied aerospace engineering for 4 years at Saint Louis University the 4th best college in the nation for the degree. All students and teachers all have the same answer to this simple question. When I continued my career in the Air Force Research Lab the same answer was among all of the experts there. The smartest minds in the world know that it wonât take off due to the way that it is asked. Reword the question and it can takeoff. The biggest arguments come from those that like to issue the question worded one way and answer it by changing the question to fit their answer. Pick the question and stick with it.
Posted 31 Jul 2012 at 12:23am #
Joe,
Here's a summary of your post:
"I did not understand what was going on."
The speed of the wheels was not part of the question. They picked one and stuck with it. When the airplane is moving at 10 MPH or 100 MPH, the conveyor belt is moving in the opposite direction at 10 MPH or 100 MPH.
What the wheels are doing is irrelevant (though they'll always be spinning at 2x the speed of either the plane or the conveyor belt, both relative to a stationary spot on the ground).
That's it. It's very simple.
Posted 31 Jul 2012 at 11:00am #
Joe, if the wheels has the same speed as the conveyor belt and they aren't skidding, the plane will not take off since it will be stationary. Correct.
HOWEVER: That is NOT the myth! You can nitpick all you want about which words are being used, but the "problem" in the myth is easy:
If an airplane is placed on a conveyor belt and the speed of the conveyor belt is matched to the speed of the airplane, but in the opposite direction - will the plane take off?
The answer is yes. And Adam even pointed out why people are getting confused over this. He placed a R/C car on the belt and matched the speed of the car and the conveyor belt - and the car did not move. Because a car gets the forward momentum by the wheels pushing on the ground, where an airplane gets its momentum from the propeller or jet engine.
As long as an airplane - of any size - have the necessary speed relative to the air around the wings, it will take off. Nothing else matters. Zip. Nil. Nada.
And I absolutely think that people are being stupid if they continue to doubt this even after they have SEEN it be done.
But then again - some people believe that the moon landings was fake, that Elvis isn't dead... Still stupid.
Or do you prefer moronic? Ignorant? Braindead? Pick your word, I picked "stupid" and I'm stickin' with it.
Posted 01 Aug 2012 at 6:07am #
I have a question and I'd be grateful for a words-of-one-syllable answer...
I know that it takes a certain speed for planes to get enough lift to fly. After all, one sees them taxiing all over the airport all the time. And, the original question posited doesn't specify a particular speed. So, if a plane were to taxi at, say, 10 mph and that belt were set at 10 mph (backwards), what would happen?
Since the propeller is the thing actually pulling the plane and the wheels are just going along for the ride, so to speak, would the pull of the 10 mph propeller just make the conveyor belt as irrelevant as it would be at liftoff speed? Would the wheels be going forward because of propeller pull or would the wheels be going backward because of the belt? (I do realize that they'd have no effect on anything but which thing, propeller or belt, would govern how they turn?)
And, before you do the facepalm thingy, do remember that it is a noble thing to bring light to a mind darkened by ignorance and mine is a coalbin at midnight.
Posted 01 Aug 2012 at 6:09am #
Addendum because editing isn't possible...
I do know that the original myth did specify that the plane needed to "take off", thus a speed to make this possible is inferred. I'm just curious about those wheels.
Posted 01 Aug 2012 at 6:46am #
The wheels would spin at the same speed as if the plane was moving 20 mph. Speed of plane + speed of conveyor belt = "speed" of wheels.
The plane would move forward at only 10 mph though - nothing changes there.
Again, if the conveyor belt speed is matched to the plane's speed - but in opposite direction - the "speed" of the wheels will be doubled.
I say "speed" because the actual speed of the wheels are the same as the plane's speed (if they stay attached, that is... đ ). It would be more correct to say that they SPIN. đ And we measure that in RPM - revolutions per minute.
If the wheels spins 200 RPM when the plane moves at 10 mph, they would spin with 400 RPM if the conveyor belt moves "backwards" at 10 mph, as in your example.
You are correct that the wheels does not affect the plane in any way it would be possible to measure accurate. Some planes have skis in order to land on snow and ice, some have pontoons in order to land on water. Nothing spins there, and yet the planes take of like there's no tomorrow! đ
Posted 01 Aug 2012 at 2:26pm #
@vidarf---
I guess what I was asking was which direction would the wheels spin? Sorry if I expressed myself badly. I'm just curious...since the wheels affect nothing, would they move as if they were on stationary ground or would the conveyor belt "spin" them in the opposite direction?
I'm just trying to picture it in my mind.
Posted 01 Aug 2012 at 3:10pm #
They will spin in the same direction as they would on ground, only faster (plane speed + conv.belt speed).
Do you have a rolling pin lying around the house? Test this: Roll it on your arm slowly. Halfway, drag your arm in the opposite direction at the same speed (or as close you can). đ
To spin the wheels in the opposite direction, the conv. belt would have to move WITH the plane, faster than the plane moves.
I really like your curiosity! That's the key if you want to learn and understand physics. Physics is extremely easy - you have it around you every day without thinking about it!
The key to learning and understanding physics is to remove clutter. Remove all elements that does not play a significant role in the topic you're working on. If one element that SEEMS significant really isn't, ignore it. The friction in the wheels, for instance - that force is so small it won't affect the plane in any way you could measure with any degree of accuracy. There would be too many other variables that would play a MUCH bigger role for the end result.
I'm yet again pointing to Mr. Lewin. As he so often states in his lectures: any result without knowing the uncertainty is _meaningless_!
What he means by this, is that if you don't know the inaccuracy in the measurements, you cannot say anything about what's going to happen with any kind of reliability. How accurate can you measure the lenght? How accurate is your clock? What is your reaction time? All those uncertainties will play a big role when you measure speed. If your length is off by just a fraction of a millimeter, your reaction time will play a MUCH bigger role for the end result - therefore, you ignore the uncertainty in your length.
And this plays right into our plane conundrum. The friction force is so small that it doesn't matter.
But I've moved off course here. đ
Good luck with your physics! Have fun with it!
Did you know that you can slow down the speed of light? Just shine a torch through your window. The light will move slower through the glass than the air. The mind-blowing thing is that the light accellerates back up when it leaves the glass!
Posted 04 Sep 2012 at 5:14pm #
Simple explanation:
The myth was simply saying that if a plane tries to take off on a tread mill/conveyer belt, it will not be able to. There are four main parts to this: 1, the ground (including the belt and cones). 2, the plane (meaning the propellers, wheels, and wings). And 3, the air. In still conditions, the plane takes about 85 feet and 25 miles per hour to achieve takeoff. This means that the ground and the air are both not moving and the engine running for a normal takeoff.
Now, if the ground was still, the air was moving 25 mph backwards, and the plane had the engine power to move it 25 mph forwards, then the net speed of the plane will be 0 mph. HOWEVER, the plane will still takeoff! Why? Because the air around the wings will be moving at takeoff speed, even if the plane is moving at the same speed as the ground (0 mph).
Finally, if the ground (meaning the belt) was moving at 25 mph backwards, the air was moving 0 mph, and the plane was being powered so it would move 25 mph forwards, then the net speed of the plane would be 0 mph, and there would be no air moving around the wings. That means the plane DOES NOT take off.
Myth busted.
BUT THERE'S MORE. Since the wheels do not spin relative to the propellers, this changes things. Imagine there was no friction between the wheels and the "axial" of the plane. In still conditions, when the belt moves 25 mph backwards, the plane will not move, and the wheels will spin at 25 mph backwards. Now if the engine is turned on to move the plane 25 mph forwards, then three things will happen: 1, the ground will move 25 mph back. 2, the wheels will be spinning 50 mph back. And 3, the plane will move 25 miles per hour forward. Since this is takeoff speed, the plane will take flight.
In real life, the wheels will have friction. This means that the plane will move backwards relative to the friction (I do not have the exact numbers). Now that the plane is moving backwards at (an estimated) 10 miles per hour, with the engine giving enough power to move the plane forward at 25 miles per hour. In order to make the plane move at a net speed of 0 mph, the plane is required to use more power. Therefore, in application, the plane will not take off until enough power is applied to move the plane forward at 25 mph. In the myth, the plane was moving forward not only relative to the belt, AND THE GROUND, and also the air. With shifting wind conditions, it is possible that the plane had enough speed for takeoff.
Most people think that this busts the myth, but the myth was only about a treadmill moving at the plane's takeoff speed, and not keeping the plane still. I don't like the results of this experiment and I think it should be revised and retested, but the data is valid.
Posted 06 Sep 2012 at 1:13pm #
[quote comment="70831"]In real life, the wheels will have friction. This means that the plane will move backwards relative to the friction (I do not have the exact numbers). Now that the plane is moving backwards at (an estimated) 10 miles per hour, with the engine giving enough power to move the plane forward at 25 miles per hour. In order to make the plane move at a net speed of 0 mph, the plane is required to use more power. Therefore, in application, the plane will not take off until enough power is applied to move the plane forward at 25 mph. In the myth, the plane was moving forward not only relative to the belt, AND THE GROUND, and also the air. With shifting wind conditions, it is possible that the plane had enough speed for takeoff.
Most people think that this busts the myth, but the myth was only about a treadmill moving at the plane's takeoff speed, and not keeping the plane still. I don't like the results of this experiment and I think it should be revised and retested, but the data is valid.[/quote]
WRONG! And the reason is this: the friction is NEGLIGIBLE! The reason why it is very hard to push a car is NOT the friction of the wheels, but it is hard to change momentum in a big mass. A wheelbarrow is easy to push when it's empty, but hard(er) to move when loaded. That is SOLELY because a big mass is hard to "get going" (give momentum), not because the friction from the wheel increases (which it does, but it has no significant impact).
The way MB tested this was good enough. There is NO WAY a conveyor belt can hold back an airplane unless you apply the brakes. THE FRICTION DOES NOT MATTER!!!!
And the myth has its roots in the fact that (most) people does not know / understand how an airplane works; they assume it works like a car. Which easily could be held stationary on a conveyor belt (as proven on MB).
Trust me on this. I know I come across as an a****le that laughs at people and provide demeaning comments. But I know what I am talking about.
The fact that people cannot accept FACTS when they see it on TV, and that they think the physics involved somehow changes because one use different words or phrases - I think such people are stupid when they CONTINUE to argue even after their misunderstandings has been explained to them. And I have no intentions about being Politically Correct. If the truth is hard to hear, too bad for you.
FORGET THE WHEELS AND THE FRICTION ONCE AND FOR ALL!
No conveyor belt will EVER stop a plane from taking off, no matter how fast you run it. The plane will of course use a fraction more time and distance before taking off, but it will take off. The difference in time and distance will be very, very small. And the uncertainty within the accuracy of your measurements will have a bigger impact on your results anyway.
Posted 04 Sep 2012 at 5:17pm #
And by the way, that comment about putting a jet pack on a person on a treadmill was honestly pretty dumb.... Just saying
Posted 06 Sep 2012 at 12:48pm #
Why? Because you didn't understand the sarcasm? đ Or perhaps because it would actually work (but MAN it would be dangerous!)?
Just saying.
Posted 06 Sep 2012 at 3:50pm #
[quote comment="70832"]And by the way, that comment about putting a jet pack on a person on a treadmill was honestly pretty dumb.... Just saying[/quote]
Yeah, it's a legit comment. Some airplanes have "jet packs" on them (basically).
Posted 05 Sep 2012 at 5:55pm #
JEBADIA451, Plane wheels don't slow a plane's take-off speed by 40%. The number is a fraction of a percent. The plane will take off at 25 MPH but it may take 85.4 feet to do it.
Posted 05 Sep 2012 at 6:16pm #
It was an estimate using general numbers to prove a point. That's all. I'm not giving exact data, and I never claimed to be. It was large simple numbers. That's all.
Posted 06 Sep 2012 at 4:00pm #
Did this plane have a "jet pack"? No. End of story. Invalid comment. Goodbye.
Posted 06 Sep 2012 at 5:25pm #
"jet pack" or propeller - it's the same thing. Both moves air, although at different levels of efficiency.
It was a LEGIT comment, and the fact that you does not understand that just proves the point. Let me try to explain it to you:
If you strap a jet pack, jet engine, propeller, rocket engine - anything that pushes against or moves AIR, to a "thing", and the output force is large enough, a "thing" WILL move forward regardless of any realistic and opposite speed the conveyor belt moves at - if you put the "thing" on wheels with normal friction. Given that most wheels are constructed with the least amount of friction in the bearings possible, the resistance to roll is so small that it won't impact the result in any significant way.
And that has nothing to do with which words you use, how you phrase the question / myth or which planet or moon you are on. Physics is the same in the whole known universe, and so far it is impossible to go against it.
If you STILL think this is wrong, please come up with an explanation! I have provided LOTS of explanations, and so far I've yet to see any PROOF or explanations that show different results. Even by people claiming to be educated physicists... And I am just a layman with just a little more than basic understanding of physics and airplanes.
PROVE me wrong, don't throw an argument! If you cannot back it up, shut the ************** up!
Well????
Posted 05 Sep 2012 at 6:08pm #
Jebadia451 you are a deadset f'ing idiot if you think that there is that much friction in the bearings of an aeroplane. As if engineers are going to design plane wheels that have friction in them that slow the plane that much.
The wheels have no effect on the forward airspeed unless the brakes are on moron. It baffles me as to the stupidity of the comments on this website. You're all idiots if you don't get this myth. Mythbusters proved it so clearly. Why don't you get it you idiot!
Posted 06 Sep 2012 at 3:56pm #
Jesus Christ.. People: STOP TAKING MY NUMBERS LITERALLY. I said that those numbers were NOT accurate. In an explanation I will not use numbers exact to the ten thousandth decimal place. GET OVER THE NUMBERS. It was an EXAMPLE. I know for a FACT wheels on an airplane do NOT have that much friction! I'm using large numbers for an EXAMPLE. A fucking EXAMPLE. Get off my ass. Good day.
Posted 05 Sep 2012 at 6:30pm #
Erik, thanks for letting your preconceived answer prevent you from reading my post. The myth tested on the show was not the original wording of the question. Leaving out the wheel speed makes for an easier test but completely changes the results. What the show failed to dowas to test the strict condition or acknowledge that there was a more strict one. The show didn't bust a myth as the group agreeing the original wording prevents flight would have said ignoring wheel speed allows for flight.
Posted 06 Sep 2012 at 1:27pm #
Joe, I am going to be respectful this time:
The wheel speed does not matter at all, since an airplane gets its forward momentum from the propeller - NOT the wheels.
If you jack up the aircraft, you can spin the wheels without any difficulty. Just like the wheels on a bike.
You could easily hold the aircraft stationary on that conveyor belt with a couple of fingers!
The ONLY impact that conveyor belt would have, is to increase the spinning speed of the wheels - and that does not matter in respect to the aircraft. No more that if you place the front wheel of a bicycle on a treadmill. The bike will not move backwards even if you spin that sucker at 100 MPH (do NOT try it at home!!! đ ).
True, there is some friction in the mix - but the friction force is so small it won't do anything.
Put it this way: when an airplane lands, the wheels are stationary until they impact the runway. If they acted like the myth states, the airplane would flip over (do a "nose over") upon landing.
The wording does not matter. Any way you put it, no conveyor belt could EVER stop an airplane from taking off. The physics does not allow it. Slam on the airplane's brakes, and the whole story changes. But that is not the myth.
Mythbusters busted the myth and all variations of it.
If you STILL doesn't believe this, follow Adam's advice: get a model airplane and a treadmill and test it for yourself. If you get any different results, post a video on Youtube and become famous! I am not holding my breath, though...
Posted 06 Sep 2012 at 3:49pm #
[quote comment="70839"]Erik, thanks for letting your preconceived answer prevent you from reading my post. The myth tested on the show was not the original wording of the question.[/quote]
I didn't, and it was tested properly.
[quote comment="70839"]Leaving out the wheel speed makes for an easier test but completely changes the results.[/quote]
The original question said nothing about wheel speed.
The wheel speed CANNOT match the forward speed of the plane because the conveyor belt will be going backwards. The only time they'd "match" is when they're both 0 MPH. At 1 MPH, the "wheel speed" would be 2 MPH (it'd be in RPM, really, but you could extrapolate that out to the linear speed around the circumference of the wheel).
[quote comment="70839"]What the show failed to dowas to test the strict condition or acknowledge that there was a more strict one. The show didn't bust a myth as the group agreeing the original wording prevents flight would have said ignoring wheel speed allows for flight.[/quote]
Wrong. But have a nice day. đ
Posted 08 Sep 2012 at 12:14am #
Go back to the original question. *Note it is not mentioned in the show.* If you go purely on the question in the show there are no issues the problem is this is not the actual question. If you go back to the blogs that made this such a requested myth you will see the original question and that it does mention wheel speed matching belt speed. That is why people dispute the episode. Its like asking the question x + y = 4 neither x or y = 2 give a value of x. Than on the show they ask the question x + y = 4 give a value of x. In flight the wheel speed doesn't matter what so ever I mentioned this in my first post and you agree. However, in the original question it imposes a limit to the wheel speed. This is not a physical limit but a numerical limit that can only be achieved by adjusting the controls or adding a physical control. If you limit the wheel speed to equal the belt speed as stated in the original question (once again never mentioned on the show) the plane is not allowed to take off because of this imposed limitation.
The reason that this myth is so disputed is because of this imposed limit. It does not physically prevent flight but if applied it does but there is no physical way to apply it unless you tie the plane down. By simply dropping or adding that the wheel and belt speed is equal changes the answer.
A great way to make this question easier to understand is to reword it. Lets say takeoff airspeed relative to ground speed is 50 mph. If the plane is on a belt and the belt is moving at 50 mph can the plane takeoff? Yes. If the plane is on a belt and the belt is moving at 50 mph will the wheels be moving at a speed greater than 50 mph at takeoff? Yes. That simple rewording is the whole question and few would dispute both those answers but worded the other way they do. In this example the wheel speed is at 50 mph when the airspeed is 0. So if you limit wheel speed to 50 mph the plane would never take off because airspeed equals 0. Even if belt speed is only 1 mph you would never make the airspeed requirement before the wheels start turning at 50 mph you would takeoff when relative to the ground is 50 mph and the wheels are 51 mph.
Once again the question the show asked and answered is correct. However, it mocked those that wanted the other question addressed by saying they don't understand the question when in fact the producers didn't understand that there were 2 questions.
Posted 26 Sep 2012 at 11:49am #
You're all fucking stupid it's so simple.
The test is conducted wrong because the plane is moving. The myth asks if the treadmill matches the planes speed would it take off. It would not because it is stationary, if it took off then it would be a helicopter not a plane because it is taking of vertically. It is not a rocket. There is no wind to lift the plane, that would eliminate the use of wings.
Posted 26 Sep 2012 at 10:25pm #
We are the stupid ones? That's so ironic that you should say that. Have you looked in the mirror lately?
Posted 27 Sep 2012 at 10:00am #
"You're all fucking stupid it's so simple.
The test is conducted wrong because the plane is moving. The myth asks if the treadmill matches the planes speed would it take off. It would not because it is stationary, if it took off then it would be a helicopter not a plane because it is taking of vertically. It is not a rocket. There is no wind to lift the plane, that would eliminate the use of wings."
Stupid me, trying to fly on calm days with no wind. I'm so fucking stupid. Oh, wait...the plane always takes off anyway.
Posted 26 Sep 2012 at 5:19pm #
[quote comment="70921"]You're all fucking stupid it's so simple.[/quote]
Yet you manage to get it completely wrong.
[quote comment="70921"]The test is conducted wrong because the plane is moving. The myth asks if the treadmill matches the planes speed would it take off.[/quote]
The test is conducted properly. You're wrong. Try again.
Posted 26 Sep 2012 at 8:21pm #
[quote comment="70921"]"The myth asks if the treadmill matches the planes speed would it take off. It would not because it is stationary"[/quote]
Wrong, wrong, wrong!!! Take a physics class or read a book before calling other people stupid!
Posted 26 Sep 2012 at 10:21pm #
I am just utterly amazed at the sheer ignorance of people who claim that the experiment was conducted improperly because the plane moved. The experiment's goal was to determine if the treadmill would be capable of preventing the plane from moving. The experiment proved that the treadmill was incapable of preventing the plane from moving. End of story!
Obviously a plane that did not move relative to the surrounding air would not be able to take off. That wasn't what the experiment was investigating.
Posted 27 Sep 2012 at 8:41am #
[quote comment="70921"]You're all fucking stupid it's so simple.
The test is conducted wrong because the plane is moving. The myth asks if the treadmill matches the planes speed would it take off. It would not because it is stationary, if it took off then it would be a helicopter not a plane because it is taking of vertically. It is not a rocket. There is no wind to lift the plane, that would eliminate the use of wings.[/quote]
Someday, if you're lucky, you will realize your error. However, you will probably try to redeem yourself by saying "They worded it wrong" or "The question is theoretical".
Just man-up everyone!! Mythbusters got it right!
Posted 28 Sep 2012 at 4:15am #
I've never been so enraged over internet arguments before, but the amount of people with zero knowledge about aviation or aerodynamics throwing around their theories as if they're 100% accurate is insulting. And all of the name calling is just childish.
First off, the plane moved forward, which totally did not achieve what the myth stated.
Secondlly the propeller pulls the airplane forward, which increases airflow over the wing, which generates lift. The propeller does not generate lift, and it does not generate enough airflow over the wings to take off.
I'll give you an example. The wheels mean nothing for raw lift. This was stated in the myth, even though the experiment was a bust. If you sit on the runway with the brakes on (again, only stopping the wheels from moving), and jam that throttle all the way in, you're not going to take off. You'll just sit there, going nowhere. The speed of the wheels means nothing for lift, so being completely stopped is the SAME THING as being on a treadmill matching your speed in the opposite direction. Think about it.
I can't watch Mythbusters anymore because of how wrong they were. Also, you guys need to stop this name calling crap.
Source: I fly airplanes for a living, and have extensive knowledge in aerodynamics.
Posted 29 Sep 2012 at 6:33pm #
[quote comment="70939"]Source: I fly airplanes for a living, and have extensive knowledge in aerodynamics.[/quote]
Fortunately for both you and your passengers, flying a plane clearly does not require a basic knowledge of physics.
The treadmill cannot stop the plane from moving forward.
The props (or jet engines) does not pull air over the wings. It pulls the wings through the air.
Aeronaut: stupid person.
Posted 29 Sep 2012 at 8:23am #
Actually...... "Me" _is_ correct. The treadmill won't take off if its speed matches the plane's speed.
Who knew? đ
Posted 29 Sep 2012 at 6:09pm #
With great amusement I read the various theories presented in this blogs posts. The fact is that the plane would definitely take flight under the proposed scenario. Kindly consider that air has a fluid property, and that directly above the belt surface of a treadmill, as in this case, there would be a laminar flow or current for a height determined by the square of the area of the treadmill. A moving treadmill belt of sufficient area to contain an airplane would have a current of a sufficient height to provide an airflow about the wings to generate lift whether the airplane was making forward progress or not. In fact, even a glider suspended above the belt would demonstrate sufficient lift, rendering the issue of engines or wheels moot.
Posted 29 Sep 2012 at 6:36pm #
[quote comment="70951"]With great amusement I read the various theories presented in this blogs posts. The fact is that the plane would definitely take flight under the proposed scenario. Kindly consider that air has a fluid property, and that directly above the belt surface of a treadmill, as in this case, there would be a laminar flow or current for a height determined by the square of the area of the treadmill. A moving treadmill belt of sufficient area to contain an airplane would have a current of a sufficient height to provide an airflow about the wings to generate lift whether the airplane was making forward progress or not. In fact, even a glider suspended above the belt would demonstrate sufficient lift, rendering the issue of engines or wheels moot.[/quote]
That's not right either. But nice try.
Posted 29 Sep 2012 at 7:47pm #
Sorry, that is not correct. The layer you're referring to is not big enough to have any effect at all. It would be - at best - a few cm. high. Probably a LOT less, but I don't remember the specific physics on this topic. The wind generated from the propeller will have a bigger effect on the plane, and that is negligible too.
Lift is ONLY created because air moves at a given speed (or greater) over a wing-shaped object. The form of the wing makes the air go faster over the wing than under it, resulting in higher pressure under the wing and lower pressure over it.
http://en.wikipedia.org/wiki/Lift_(force)
------------------
Here's another link to Wikipedia, not related to the topic in this post but I thought it is important:
http://en.wikipedia.org/wiki/MythBusters_(2008_season)#Airplane_on_a_Conveyor_Belt
Posted 29 Sep 2012 at 7:03pm #
[quote comment="70953"][quote comment="70939"]Source: I fly airplanes for a living, and have extensive knowledge in aerodynamics.[/quote]
Fortunately for both you and your passengers, flying a plane clearly does not require a basic knowledge of physics.
The treadmill cannot stop the plane from moving forward.
The props (or jet engines) does not pull air over the wings. It pulls the wings through the air.
Aeronaut: stupid person.[/quote]
You need to go to your local community college and take a course in Logic and learn about fallacious arguments.
Also, what are your qualifications in this field?
Posted 30 Sep 2012 at 12:48am #
[quote comment="70955"]Also, what are your qualifications in this field?[/quote]
I'm not a moron. Which beats your qualifications.
Again, I'm glad for both you and your passengers that a basic understanding of simple physics is not required to actually fly a plane.
Cheers.
Posted 29 Sep 2012 at 7:40pm #
Aeronaut, Mythbusters DID test the myth!!! AND proved that it is just a myth.
The myth probably has its origin in the fact that a car on said treadmill won't move forward since the movement of the belt cancel out the movement of the wheels. And people without any knowledge of how airplanes actually work would - understandable enough - conclude that an aircraft won't take off.
You are perfectly correct in your statement about slamming the brakes. The plane won't move (well, that depends a little on how powerful the engine is, but that's a detail). But that is NOT the same situation as stated in the myth!
If you hit the brakes on the airplane on that treadmill, it WILL take off - but backwards and not literally. đ
Since you are a pilot (as per your statement), you know that a free spinning aircraft wheel provides very little resistance when you try to spin it (i.e. low friction).
You might have good knowledge in aerodynamics, but the physics part lacks a bit - or you have very little experience with physics from an educational standpoint. And that does not make you stupid at all! Very many pilots did (and do) make the same mistake as you do.
Proof of the fact that lift ONLY relies on air being moved over a wing:
http://www.youtube.com/watch?v=cHhZwvdRR5c
In this clip, the wind is blowing pretty hard. The aircraft is WAY lighter than normal (the engines are removed and the plane is mostly stripped inside) and the flaps are fully extended (as they are for landing, not for takeoff). The huge thingamabob is actually very close to taking off. Standing still. Due to air moving fast enough over the wings.
As for that darn treadmill: I have provided explanations, both politely and sarcastically. Read them. They are correct.
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
WHERE in the myth does it state ANYTHING about the wheels?????
Posted 29 Sep 2012 at 7:55pm #
If the treadmill matches the speed of the airplane completely, then the airplane is basically a stationary object, with spinning wheels. If it's not moving, there won't be any airflow over the wings (assuming winds are calm), and therefore will not produce any lift. The only airflow being produced will be by the propeller, and that has a negligible effect on lift.
If the airplane makes enough forward progress against the treadmill then yeah, it'll take off but the myth states that it will take off if speed is completely matched. This doesn't happen in the myth, invalidating the experiment.
Posted 29 Sep 2012 at 9:05pm #
[quote comment="70958"]If the treadmill matches the speed of the airplane completely, then the airplane is basically a stationary object, with spinning wheels. If it's not moving, there won't be any airflow over the wings (assuming winds are calm), and therefore will not produce any lift. The only airflow being produced will be by the propeller, and that has a negligible effect on lift.
If the airplane makes enough forward progress against the treadmill then yeah, it'll take off but the myth states that it will take off if speed is completely matched. This doesn't happen in the myth, invalidating the experiment.[/quote]
I was just going to ignore your comments, Aeronaut, because I've read and heard the same erroneous flap-jawing from so many others, including pilots. However, when you continued to repeat your mistakes even after Vidarf quoted the myth to you, taken word for word from the tv show and the Mythbuster website, I just had to weigh in.
The myth states that the speed of the treadmill moving backwards is "equal to the normal ground speed during takeoff". It just means that if the aircraft will liftoff at a speed of 50 mph then the treadmill is moving backwards at 50 mph. It does not say that the plane is rendered stationary. That was YOUR assumption.THE PLANE CANNOT BE RENDERED STATIONARY. It will move forward and take off. Mythbusters showed this was true several ways on the show, and you just continue to foolishly stick to you guns.
Sit down in a quiet space, read the myth again, and roll it over in your mind. You are coming to a correct conclusion for an incorrect premise. If you finally "get it" that's great. Although you're going to feel quite stupid for awhile, especially after claiming to be a pilot. Don't worry, though, the great thing about the Internet is anonymity. Just don't let your friends and relatives know how you screwed this one up.
Posted 30 Sep 2012 at 2:48am #
[quote comment="70958"]If the treadmill matches the speed of the airplane completely, then the airplane is basically a stationary object, with spinning wheels. If it's not moving, there won't be any airflow over the wings (assuming winds are calm), and therefore will not produce any lift. The only airflow being produced will be by the propeller, and that has a negligible effect on lift.
If the airplane makes enough forward progress against the treadmill then yeah, it'll take off but the myth states that it will take off if speed is completely matched. This doesn't happen in the myth, invalidating the experiment.[/quote]
Chuck, is that you?
http://www.chickenwingscomics.com/?p=1328
Posted 08 Oct 2012 at 3:25am #
As long as the thrust of the propeller is equaled by an opposing force, the airplane will just set on the treadmill and not take off. Many posters mention the friction of the wheels to the treadmill (which can be ignored, it is assumed that the wheels do not skid or slip) or the friction in the bearings (so small as to also be ignored).
What is overlooked is the ineria of rotating bodies, and how much energy get tied up in accellerating the wheels to ever higher velocities. This creates the force that prevents the airplane from moving, since it is made equal to the force from the propeller.
Of course in the real world, the tires would explode at some point and the treadmill would not be able to accelerate fast enough to maintain a balance of forces very long. But since it is only a thought experiment it has more to do with people's thought processes and limited understanding of the physics than most everyday problems.
Posted 08 Oct 2012 at 6:43pm #
[quote comment="70978"]As long as the thrust of the propeller is equaled by an opposing force, the airplane will just set on the treadmill and not take off.[/quote]
Yes, but the opposing force would need to be a steel chain or something holding the plane in place. The wheels are not an "equal and opposing force."
They'd be the worst damn wheels in the history of wheels if they could prevent a plane from taking off. Gimme a break.
[quote comment="70978"]What is overlooked is the ineria of rotating bodies, and how much energy get tied up in accellerating the wheels to ever higher velocities. This creates the force that prevents the airplane from moving, since it is made equal to the force from the propeller.[/quote]
Wrong. See above about "worst damn wheels in the history of wheels."
The energy spent to get the wheels rotating twice as fast as normal (wheels rotate during normal takeoffs, dude) is a drop in the ocean compared to the forces generated by the jet engines (or propellers).
Posted 09 Oct 2012 at 1:42pm #
[quote comment="70978"]What is overlooked is the ineria of rotating bodies, and how much energy get tied up in accellerating the wheels to ever higher velocities. This creates the force that prevents the airplane from moving, since it is made equal to the force from the propeller.[/quote]
And what do you suppose that the moment of intertia for the wheels are? How much work do you need to apply to the wheels to make them spin at normal takeoff speed? How much force do you think the propeller can apply to the plane?
Remember - on a NORMAL takeoff, the wheels - as Erik states - spin. They spin at normal takeoff speed (which I have no interest in calculating now). The propeller makes that happen all by itself. AND - the propeller has to drag the whole plane plus pilot, pax and cargo too! This happens thousands of times each and every day. Even on a 747 (jumbo jet), and that bird has a LOT more wheels which are a LOT heavier than on a puny Cessna!
And you still think that just because the wheels spins in the wrong direction, the plane won't take off? THAT. CANNOT. HAPPEN. EVER.
But nice try though. Remember to use moment of inertia for a ring, not a disc wit uniform distribution of the mass. Most of the mass on an airplane wheel is located at the outer edge. Won't make a big difference, but hey - let's try to be scientific? đ
Posted 09 Oct 2012 at 9:31pm #
All I can say is "wow".
Posted 08 Oct 2012 at 3:36pm #
So the myth is back. Well folks When I was in 7th grade the big question was if one was on a train traveling 60MPH and fired a .45 cal (subsonic speed) backward would the round just fall to the ground. Older now and having access to a CRC I must just laugh
Posted 09 Oct 2012 at 1:27pm #
Well - would it? đ Depends on your frame of reference. Does the bullet fall to the ground or is it shot some distance backwards from the train? That simple 7th grade question becomes much more difficult over time. đ
Posted 09 Nov 2012 at 7:27pm #
Hello,
I just watched the "experiment", and as some have pointed out , it was WRONGLY conducted. The plane was NOT stationary. Just look at the video.
Physics don't lie, my friend.
But, if you simply don't know anything about physics and WANT to believe the experiment was a "success", then by all means, believe that, and as long as you are on it, believe also in Big Foot, the Lochness monster and fairies.
There really is nothing to discuss, any non-blind person can see the plane WAS moving.
And what is this about "just as it would if it were on ice"? LOL!
Yes, the motion is generated by the propeler, but is doesn't matter how fasy the propeller may be going if there is no lift. It is NOT the propeller who creates the lift, it is the wings.
Period, nothing to dicuss.
Have fun!
Posted 09 Nov 2012 at 7:51pm #
[quote comment="71209"]I just watched the "experiment", and as some have pointed out , it was WRONGLY conducted. The plane was NOT stationary. Just look at the video.[/quote]
Stupid person: the experiment does not state that the plane remain stationary. A conveyor belt can't keep a plane stationary, and if the plane wasn't moving, the conveyor belt wouldn't be moving either since its speed matches the plane's speed (0 MPH = 0 MPH). Please read the many posts above which point this out.
Thank you.
P.S. David, I'm talking to you. Just in case you weren't able to figure that out.
Posted 09 Nov 2012 at 8:16pm #
Hey David,
Snap-judgement's a bitch! Best to think something out before posting your opinions for all to see! Considering the hundreds of entries above (none of which you've read, evidently) there's a little more to the matter than you have surmised.
Simply put, there is no mention of the plane being rendered "stationary". In fact, there is no way, under these conditions, that the plane CAN be rendered stationary. You just assumed that this was what the myth inferred.
The plane moves forward and takes off when it reaches the necessary speed.
Don't feel too bad. Many, many, many others have erred in the same way.
There's ALWAYS more to discuss!
Have fun!
Posted 10 Nov 2012 at 9:24am #
[quote comment="71209"]Hello,
I just watched the "experiment", and as some have pointed out , it was WRONGLY conducted. The plane was NOT stationary. Just look at the video.
[/quote]
Yeah, at FIRST it was stationary. Then it magically started to MOVE! WOW!
[quote]
Physics don't lie, my friend.
[/quote]
Indeed not, but to UNDERSTAND physics on the other hand - THAT is evidently an issue here...
[quote]
But, if you simply don't know anything about physics and WANT to believe the experiment was a "success", then by all means, believe that, and as long as you are on it, believe also in Big Foot, the Lochness monster and fairies.
[/quote]
HEY! Don't flame Nessie! And what has Bigfoot done to you??? đ
[quote]
There really is nothing to discuss, any non-blind person can see the plane WAS moving.
[/quote]
A blind person would actually HEAR the plane move. Courtesy of the doppler effect amongst a few others...
[quote]
And what is this about "just as it would if it were on ice"? LOL!
[/quote]
A concept lost on the ignorant/stupid/morons. What ever word offends you most, that's YOU. đ
[quote]
Yes, the motion is generated by the propeler, but is doesn't matter how fasy the propeller may be going if there is no lift. It is NOT the propeller who creates the lift, it is the wings.
Period, nothing to dicuss.
Have fun![/quote]
Sprakling correct on that last piece. Unless of course the propeller is pointed straight up, but I bet that was not your point either. Nor is it relevant here.
Sorry if I'm coming down on you like a ton of bricks, but I just had to. Despite a LOT of comments from me, Erik and several other people - you still argue against Mythbusters and their CORRECTLY EXECUTED TEST!
Myth: any two or more people can teach a moron physics.
I believe that myth is busted. At best, plausible.
(and yeah, I really think people are both stupid and moronic if they continue to argue against several independent explanations. Flat out retarded if they go against educated people with a degree in the field!
And if that offends you - you're probably in that group.)
Off to the cropcircleheads and chemtrailers! đ
Posted 19 Nov 2012 at 2:07am #
[quote comment="71210"][quote comment="71209"]I just watched the "experiment", and as some have pointed out , it was WRONGLY conducted. The plane was NOT stationary. Just look at the video.[/quote]
Stupid person: the experiment does not state that the plane remain stationary. A conveyor belt can't keep a plane stationary, and if the plane wasn't moving, the conveyor belt wouldn't be moving either since its speed matches the plane's speed (0 MPH = 0 MPH). Please read the many posts above which point this out.[/quote]
Wait a minute. The whole point of the scenario is that the airplane is kept in place by the movement of the treadmill. "The whole basis for the myth was that the airplane could take off from a treadmill traveling at the same speed as the aircraft." If the plane could accelerate faster than the treadmill belt then there would be no point to having a treadmill at all. The scenario is that the plane is stationary because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed. No forward motion, no air over the wings, no lift.
Posted 21 Nov 2012 at 9:23am #
[quote comment="71310"]Wait a minute. The whole point of the scenario is that the airplane is kept in place by the movement of the treadmill.[/quote]
Wrong. That's not even one of the minor points let alone "the whole point."
[quote comment="71310"]"The whole basis for the myth was that the airplane could take off from a treadmill traveling at the same speed as the aircraft." If the plane could accelerate faster than the treadmill belt then there would be no point to having a treadmill at all.[/quote]
You're an idiot. The plane has WHEELS. Let's make this so simple hopefully even you can understand it.
The plane is traveling north, on conveyor belt, at 100 MPH.
The treadmill is traveling south at 100 MPH.
As the plane accelerates to 200 MPH, the conveyor belt accelerates to 200 MPH.
The plane takes off.
[quote comment="71310"]The scenario is that the plane is stationary[/quote]
Wrong.
[quote comment="71310"]because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed.[/quote]
You're an idiot. You're wrong.
Posted 21 Nov 2012 at 11:08am #
Phil,
Here is the myth as given on the show:
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
No "stationary". That was your assumption.
The plane takes off. Myth busted!
Posted 21 Nov 2012 at 3:11pm #
[quote comment="71310"]Wait a minute. The whole point of the scenario is that the airplane is kept in place by the movement of the treadmill. "The whole basis for the myth was that the airplane could take off from a treadmill traveling at the same speed as the aircraft." If the plane could accelerate faster than the treadmill belt then there would be no point to having a treadmill at all. The scenario is that the plane is stationary because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed. No forward motion, no air over the wings, no lift.[/quote]
No no NO NO!!!!!!! This is the SAME BULLSHIT posted over and over and over again!!!
The treadmill can do what the $"#$%$%& it will, the plane will still move forward!!!! THE ONLY THING AFFECTED BY THE BELT IS THE SPEED OF THE WHEELS!!!!!!!
Dude, this is an AIRPLANE! Not a car!!! Is it really that impossible to get you to understand that??? What you are stating above is perfectly true for any vehicle that gets its movement from the wheels. A car. A bicycle. Anything that utilizes the friction force between something (tires, belts, legs...) and the ground in order to push itself in some direction.
But if the vehicle pushes against the AIR, it will move regardless of what the ground is doing.
This is the simple fact, governed by physics. Basic physics. Since you do not understand any physics at all (based on your posts), PLEASE stop posting against Erik and me. WE KNOW PHYSICS!
As for the "points" you're trying to make about the myth: you are reading way too much between the lines here! You are making a new myth based on basically nothing from the original myth.
The scenario is: WILL the plane be held stationary by the treadmill if the treadmill matches the speed of the airplane? (this is a re-phrasing of the myth that is accurate).
The answer is, and will always be: NO!
If you still doesn't agree, make a youtube video where you test your theory based on your own premises. Or shut the #$%#$% up!
Do - or do not. There is no try. Capiche?
Posted 21 Nov 2012 at 10:14am #
[quote comment="71310"] The scenario is that the plane is stationary because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed. No forward motion, no air over the wings, no lift.[/quote]
Yes, that was the myth. It was busted because a treadmill cannot negate the forward speed of a plane that is pushing against the air, not the ground.
Posted 21 Nov 2012 at 2:51pm #
[quote comment="71393"][quote comment="71310"]because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed.[/quote]
You're an idiot. You're wrong.[/quote]
Nonsense.
Your mom is a whore.
Posted 21 Nov 2012 at 2:56pm #
[quote comment="71406"]Nonsense.
Your mom is a whore.[/quote]
Unfortunately, you have no evidence to support EITHER of your statements. You cannot prove that my mom's a whore any more than you can prove the plane will remain stationary and thus not take off.
Wanna know why?
Cuz both are false. Duh.
Posted 21 Nov 2012 at 3:41pm #
[quote comment="71406"][quote comment="71393"][quote comment="71310"]because as the plane engines develop thrust to propel it forward, the treadmill belt instantly speeds up to negate that forward speed.[/quote]
You're an idiot. You're wrong.[/quote]
Nonsense.
Your mom is a whore.[/quote]
Well, I was being polite, but after that post, I don't see the need. You ARE an idiot.
Maybe you can explain how a treadmill would negate a plane's forward motion. Are you equating it to a runner on a treadmill? If you're pushing back against the treadmill at the same speed the treadmill is moving, of COURSE you're not going to move. Runners run through a park because they're pushing back on the ground. Problem is, planes don't push back on the ground. If they did they could only fly for seconds at a time. Every time the plane left the ground, it would lose its propulsion and land again. They push back on the air, which makes the ground irrelevant. The wheels are designed to have as little friction as possible allowing the plane to move freely and without resistance from the ground, so a treadmill would have infinitesimal effect on a plane's forward movement.
So maybe you should rethink your position, idiot.
Posted 27 Dec 2012 at 6:47pm #
> Maybe you can explain how a treadmill would negate a plane's forward motion.
I can answer that. For the plane to take off, the wheels have to spin. For the wheels to spin, a torque has to be applied to them to overcome their rotational inertia. This torque is developed between the force of the plane pushing the wheel axles forward and the force of the ground pushing the tires backwards. The component of horizontal force (not torque -- we agree the bearings are frictionless) the plane applies to the axles is in addition to the force needed to linearly accelerate the wheels' centers of mass.
The problem states that the treadmill speed matches the wheel speed. In the case where the airplane is traveling, say, at 100 MPH forwards and the treadmill is moving at 100 MPH backwards, the wheel speed is 200 MPH, and the condition stated in the problem is not met. The only way the condition can be met is if the airplane is not moving. Then the treadmill speed matches the wheel speed.
For this to occur, the airplane must not accelerate, meaning the net force of the treadmill on the tires is exactly equal and opposite to the engine thrust. When that is the case, the wheels will undergo constant angular acceleration. Their rotational speed will increase linearly without bound and the power consumed by friction with the ground will cause them to heat up to infinite temperature.
If the wheels had zero inertia, the acceleration would be infinite.
Clearly, this is a contrived situation. And I am sympathetic to your position, because I initially agreed with it. But the fact is, as the problem is stated, the airplane cannot take off. All due to the peculiar feedback between wheel speed and treadmill speed that imposes the constraint that the plane does not move.
This is an authoritative explanation. Now, who's the idiot?
Posted 29 Dec 2012 at 11:21am #
[quote comment="72207"]For the plane to take off, the wheels have to spin.[/quote]
False.
[quote comment="72207"]The problem states that the treadmill speed matches the wheel speed.[/quote]
No it doesn't. The problem is stated as such:
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?
I've bolded the relevant part.
I will point out that if by "wheel speed" you mean the speed of the precise middle of the wheel (the point which experiences no rotation), then that's one and the same as the plane's speed. If you're talking about the linear speed of the outer edge of the wheels, then that's always going to be 2x the speed of the conveyor belt: when the plane is going 100 MPH forward, the conveyor belt is going 100 MPH backwards, and the wheels are spinning at the equivalent of 200 MPH.
[quote comment="72207"]In the case where the airplane is traveling, say, at 100 MPH forwards and the treadmill is moving at 100 MPH backwards, the wheel speed is 200 MPH, and the condition stated in the problem is not met.[/quote]
Again, the problem does not state that the speed of the WHEELS is matched. It's the speed of the PLANE.
[quote comment="72207"]Now, who's the idiot?[/quote]
You, for failing to note that the problem never says the speed of the WHEELS is matched by the treadmill.
In fact, I addressed this in the POST at the top of the page (not the comments, but the post itself):
Posted 29 Dec 2012 at 12:01pm #
Hey, thanks for the reply. When I posted my comment the other night, I had been reading airplane-treadmill discussions for hours, so I hope you'll forgive me if I've missed some of the details on your blog.
The version of the problem I'm working from was posted here:
http://boards.straightdope.com/sdmb/showthread.php?t=348452
It states:
> Imagine a plane is sitting on a massive conveyor belt, as wide and as
> long as a runway, and intends to take off. The conveyer belt is
> designed to exactly match the speed of the wheels at any given time,
> moving in the opposite direction of rotation.
I hope you'll agree this version of the problem is ambiguous as to the definition of "wheel speed." It's unclear to me what the "authentic" version of the problem is.
I think the only thing that makes the problem interesting is if we define "wheel speed" as "the speed a speedometer connected to the wheels would read." Otherwise the answer is obvious, and anyone who disagrees is obviously an... idiot.
Let me ask you this. If you change the definition of wheel speed to be the one I propose here, can the airplane take off? I suspect most people who debate this problem don't see that this difference is crucial.
Do you?
Regards,
-Henry
Posted 29 Dec 2012 at 12:22pm #
[quote comment="72360"]The version of the problem I'm working from was posted here:
http://boards.straightdope.com/sdmb/showthread.php?t=348452%5B/quote%5D
Simple answer: you chose a poorly worded version of the question, unless by "wheels" you mean the axle of the wheels, or you measure a point on the wheel like "the middle of the wheel" or "the top of the wheel" and don't consider the rotation of the wheel, but considering the wheels at all is folly.
[quote comment="72360"]I think the only thing that makes the problem interesting is if we define "wheel speed" as "the speed a speedometer connected to the wheels would read."[/quote]
It would make absolutely no sense to do so and completely changes the problem to that of a car trying to move while sitting on a conveyor belt, not a plane.
[quote comment="72360"]Otherwise the answer is obvious, and anyone who disagrees is obviously an... idiot.[/quote]
The answer is not obvious, which is why people get it wrong. The answer to your proposed question is much easier: it's a car on a treadmill.
Posted 29 Dec 2012 at 12:29pm #
Not that it's definitive by any means, but Wikipedia states:
Myth: A plane cannot take off while sitting on a conveyor belt moving in the opposite direction.
Notes: Busted.
Discussion: The MythBusters first performed a small scale test with a model airplane and a small conveyor belt and were not able to get the model plane to take off from the belt, it merely fell off the front of the conveyor belt. They then tested a model remote-controlled plane on a moving length of paper. The plane moved forward from its starting position and took off. Finally they upgraded to full scale using an actual manned plane and a runway-sized tarp as a makeshift conveyor belt. Like the small scale test, the plane moved forward from its starting position and was able to take off from the conveyor belt. The MythBusters explained that this was possible because unlike cars, an airplane's means of propulsion is through its propeller or jet engine, not its wheels; a car's engine mechanically moves its wheels, which use their contact with the road and the traction it provides to generate forward movement, while the plane's wheels are free-moving and independent of the propeller, which uses air displacement for forward thrust. Therefore, the conveyor belt has no bearing on the forward momentum of the plane.
Posted 29 Dec 2012 at 12:49pm #
Besides, whether that infamous belt matches the rotational speed of the wheels, the speed of the axle or any other scenario, the end result will always be the same: the plane will take off.
Within normal circumstances, there is nothing you can do to prevent an airplane to move forward when the engine provides sufficient thrust - unless you attach the plane somehow to a non-moveable object (wire to a secure point in the ground). And that means that the aircraft is free to accelerate to its takeoff speed (which will vary slightly depending on several factors; air temperature, pressure, weight of the aircraft and so on). Once the takeoff speed is reached, the plane will take off.
To state that the myth is not busted based on how one phrases the myth is just stupid. The plane will take off no matter which words you use. How you match the speed of whatever part of the plane does not matter. You could let the belt have a speed of 10 times the speed of the wheels/axles/aircraft, and the plane would still take off. Provided the tires could take it.
If anybody STILL want to debate this, why don't they provide EVIDENCE based on SCIENCE and FACTS?
Because Physics
Posted 29 Dec 2012 at 12:53pm #
> Simple answer: you chose a poorly worded phrasing of the question,
> unless by "wheels" you mean the axle of the wheels, or you measure
> a point on the wheel like "the middle of the wheel" or "the top of the
> wheel" and don't consider its rotation.
A little history. When I first saw this question, I was incensed, like you, that people could be so stupid as not to understand that the jet engines react against the stationary frame of reference, not the moving one. Therefore, it was obvious to me that the plane would take off.
I started reading a lot of forum discussions and gradually became aware of this question of the definition of wheel speed. It was then that I realized, as I said above, that the problem becomes much more interesting if you define "wheel speed" as "speedometer speed." Unfortunately, we don't know who originally posed the problem or what he/she intended. But we certainly can feel free to change the parameters of the problem for the sake of discussion, provided we're clear on our assumptions.
> It would make absolutely no sense to do so and completely changes
> the problem to that of a car trying to move while sitting on a
> conveyor belt, not a plane... The answer to your proposed question
> is much easier: it's a car on a treadmill.
Aha. Now we're getting somewhere. My proposed problem is NOT just a car sitting on a treadmill. There is still no torque transmitted through the wheel bearings. All I've done is set up a little servo mechanism that measures the rotational speed of the plane's wheels, converts that to the linear velocity that the plane would be traveling if it were on stationary ground with the wheels spinning that fast, and then programs the treadmill to move backwards at that speed. A seemingly subtle, but very important distinction.
The jet engines still push against the stationary frame of reference, the wheels are assumed to have no bearing torque or frictional losses, the treadmill is still assumed to have no effect on aerodynamics.
Now, I want to pose my question to you again. Given these assumptions can the airplane take off? I say no. I wonder if you understand my reasoning here. If not, I would be very happy to discuss it with you, because it's an interesting and satisfying variation of the problem to understand.
Regarding the Wikipedia article, I didn't watch the whole MythBusters episode, but I do agree that an airplane can easily take off from a treadmill runway that it moving backwards at a constant speed equal to the takeoff speed of the plane.
> The answer is not obvious, which is why people get it wrong.
Hah! To me it is obvious. Maybe that's why I'm drawn to the alternate version of the problem, because there's actually some challenge to it, even if you know basic physics.
-Henry
Posted 29 Dec 2012 at 1:06pm #
[quote comment="72366"]It was then that I realized, as I said above, that the problem becomes much more interesting if you define "wheel speed" as "speedometer speed."[/quote]
The problem becomes incredibly stupid if you define it as "speedometer speed." It becomes the question of a car on a conveyor belt, because at any point during which a PLANE is moving, its wheels are spinning at 2x the speed of the conveyor belt.
So again, it's either a question of a car on a conveyor belt or its an impossibility, please take your pick, and stop posting about how it would be more interesting.
[quote comment="72366"]Unfortunately, we don't know who originally posed the problem or what he/she intended. But we certainly can feel free to change the parameters of the problem for the sake of discussion, provided we're clear on our assumptions.[/quote]
No, we aren't free. It's my blog, and I see no point in discussing "speedometer speed" for the two reasons I've re-stated a few times now: changing the words turns it into either a car or an impossibility.
[quote comment="72366"]All I've done is set up a little servo mechanism that measures the rotational speed of the plane's wheels, converts that to the linear velocity that the plane would be traveling if it were on stationary ground with the wheels spinning that fast, and then programs the treadmill to move backwards at that speed. A seemingly subtle, but very important distinction.[/quote]
A plane that's moving forward will always have a wheel speed that's 2x the speed of the conveyor belt. It's entirely un-interesting, and no further comments about this from you will be published.
Posted 29 Dec 2012 at 5:32pm #
The problem is NOT the wording of the myth, but the logic behind the words. Which is impossible.
There is NO WAY you can match the speed of the wheels and the speed of the conveyor belt (in opposite direction of course) when the plane starts moving. The rotational speed of the wheels depends on the speed of the belt plus the speed of the plane. Take a coin and a sheet of paper and try it yourself. When you drag the paper and at the same time move the coin in the opposite direction at the same speed as you drag the paper, the coin will spin at twice the speed. QED.
In stead of arguing over semantics, I think it is PRETTY clear what the myth is all about. Where it has its roots.
And in the real world, the physics works. Try to stick to it. Mathematically I am sure there are some solution to your conundrum, but math and reality does not always agree. Try to cut a doughnut in 360 equal pieces. Mathematically, that's one degree per slice. Try to do it, though...
Posted 29 Dec 2012 at 5:42pm #
[quote comment="72388"]The problem is NOT the wording of the myth, but the logic behind the words. Which is impossible.[/quote]
Yes, I've tried to tell him the same thing. The only time at which the "speedometer" and the conveyor belt can have the same reading is when the readings are 0 MPH. Anything else in even a loose version of this problem is an impossibility.
Posted 11 Mar 2013 at 11:08pm #
I just heard of this myth, March 2013. I think it depends on the wording. If it is being described in terms of the terms of the plane moving being cancelled out from the treadmill, yeah it makes no sense. You are basically talking about vertically lift off. The plane not moving forward and then just lifting off.
But when the wording is really that you are talking about the treadmill having no effect at all then it is a different issue and that is what I think the Mythbusters did. And maybe that was the Myth the whole time. The plane is at a point in relation to the ground or in tree in background for visual purposes. The treadmill could be running at 10,000 MPH for all we care and we are saying the plane stays at the same position in relation to that tree. The as you give power to to the engine the plane will move forward and speed up because the wheels would just roll to 10,060MPH. But the plane in relation to the Original Tree in the back ground is starting to move away at 60MPH.
So the plane still takes off as normal we are just saying that because the plane has wheels that have no axel they will just spin free. Because the wheel don't drive it the propeller does then it will still move forward from a stop. No surprise.
But the plane still needs to move forward at 60+ miles an hour from Point A to create lift.
This is different from it Starting at Point A, Staying at Point A, and Lifting from Point A, which I think is sort of what the original myth sort of sounded like and some people may have argued you could due. ie. Magical Vertical take off. The reality is MUCH less exciting. The wheels spin free. Big deal. The plane still spins as normal. The plane still travels forward to take off. If take a video on a normal run way then on the Trap Take off from far away, then just put you hand over the ground, I think they would look the same, ie the plane travels "forward" from point A to B. So nothing to see here really.
Posted 12 Mar 2013 at 8:24am #
[quote comment="76281"]I just heard of this myth, March 2013. I think it depends on the wording. If it is being described in terms of the terms of the plane moving being cancelled out from the treadmill, yeah it makes no sense. You are basically talking about vertically lift off. The plane not moving forward and then just lifting off.[/quote]
The problem with that is that NO VERSION of the myth states that. It's the trap people fall into because they ASSUME that's what it says.
So I disagree with you that it "depends on the wording." It depends entirely upon how likely the person is to assume the wording is saying this, when the reality is that the conveyor belt can do NOTHING to keep the place in one place against the force of the jets or propellers.
Posted 20 Mar 2013 at 4:39am #
Ok, just saw the episode. Here are a couple of thoughts.
1 When you run on a treadmill at 8 MPH do you feel wind passing over your body...No. When you run out side on a calm day do you feel wind passing over your body,,,Yes. The wind you feel or do not feel would be able to create lift in a airplane.
2. Say you are in a plane (which requires 25 MPH of wind for lift) and you take off with the wind in a 25 MPH wind (not into the wind as required) You would need to achieve 50 MPH for the lift to happen.
Both examples prove Mythbusters wrong.
Posted 21 Mar 2013 at 7:32pm #
[quote comment="76523"]Both examples prove Mythbusters wrong.[/quote]
You're an idiot.
Posted 22 Mar 2013 at 12:35pm #
Ok Chuck, you are definitely one of the aforementioned stupid people.
So you can run on a treadmill and not feel wind.. Great. You can't see the curvature of the earth either so I guess you assume it's flat.
Try this, instead of running shoes, put wheels on your feet. Then strap on a powerful propeller to your chest. Tell me if things might be a little different for you on that treadmill.
Posted 21 Mar 2013 at 7:57pm #
[quote comment="76523"]Ok, just saw the episode. Here are a couple of thoughts.[/quote]
Before you can have "a couple of thoughts" you must first be able to THINK !
You are completely wrong.
At least read SOME of the previous posts.
Posted 21 Mar 2013 at 10:15pm #
No, I am right! You guys are completely wrong.
Posted 21 Mar 2013 at 10:18pm #
Nice trolling, dude, but your arguments are as unoriginal as they are obviously stupid.
Next!
Posted 21 Mar 2013 at 11:35pm #
Ok, Chuck. I've got nothing going on tonight. I'll quickly go over it again just for you. Now pay attention because this is some "highfalutin thinking" going on!
You walking on a treadmill is not the same as a plane on a treadmill
An automobile on a treadmill is not the same as a plane on a treadmill
A bicycle on a treadmill is not the same as a plane on a treadmill
A duck billed platypus on a treadmill is not the same as a plane on a treadmill
All of the above examples require traction to move forward on said treadmill. When the treadmill moves backward at the same speed as their forward motion they will, indeed, be stationary relative to their surroundings.
The plane, however, does not rely on traction. It moves through the air by means of the props. It will move forward no matter what it's sitting on. Grass, dirt, water, ice, boat, whipped cream, and even a treadmill. There is no way to keep it stationary. Once it reaches take-off speed, it will. ( take off, that is)
I doubt if this will help you, but at least I tried. What sucks is that if I did get through to you we will never know because no one writes back to say how stupid they were. They just write back to say something even more stupid.
Posted 22 Mar 2013 at 1:40pm #
From the forum
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."
The part of "speed of the conveyer to be exactly the same" means it can't fly.
The show left out that wording so it is possible. Add that last part and it can't by having to add a control system that will put the two in a steady state where the plane is not moving foward.
Also Aeronaut is correct. Props pull the plane not force air over the wings.
Posted 22 Mar 2013 at 5:51pm #
[quote comment="76575"]The part of "speed of the conveyer to be exactly the same" means it can't fly.[/quote]
No it does not.
Posted 22 Mar 2013 at 4:21pm #
I've already explained it on this site last year and I thought my explanation was clear enough but apparently not. I'll try again.
The purpose of the MythBusters experiment was not to determine if a stationary airplane can take off. Clearly it cannot. The purpose of their experiment was to determine if given a treadmill that moves backwards at the airplane's takeoff speed would that cause the airplane to never achieve takeoff speed. in other words, would the moving treadmill keep the airplane stationary relative to the ground.
The resounding answer was that the plane was able to achieve takeoff speed relative to the ground. The backwards moving treadmill was not able to keep the airplane stationary. This is because the airplane does not depend on traction with the treadmill and hence moves independently of the moving treadmill.
Now, if you still insist on contributing nothing to this discussion by claiming that MythBusters failed in their objective because the plane moved then I don't know how else to explain this so you can understand.
Posted 22 Mar 2013 at 6:20pm #
Sorry, John, but you are wrong. The extra wording does not change the outcome. The conveyor belt could be moving at the same speed, slower speed, or even faster speed than the plane. It will still move forward and eventually take off.
Posted 23 Mar 2013 at 4:04am #
Triffid I appreciate your "highfalutin thinking" but, I still fail to grasp your thinking. The propeller does not place wind over and around the wings, which is required for lift. What the propeller does is propel the aircraft forward which in turn provides the required lift. If the aircraft was not moving forward then there is no lift.
Posted 23 Mar 2013 at 7:31am #
[quote comment="76558"] What sucks is that if I did get through to you we will never know because no one writes back to say how stupid they were. They just write back to say something even more stupid.[/quote]
[quote comment="76593"]If the aircraft was not moving forward then there is no lift.[/quote]
See, Chuck, THAT is your problem. You're stuck on the idea that the plane is not moving forward. The myth never states that the plane is stationary. THAT is your presumption, and the presumption of anyone who believes that Mythbusters got it wrong. IT IS NOT POSSIBLE TO RENDER THE AIRCRAFT STATIONARY UNDER THESE CONDITIONS!!
It HAS to move forward, creating airflow, creating lift!
Am I being punked?
Posted 23 Mar 2013 at 7:52am #
I see what you are saying now. But in reality that is what could be said about any myth to either confirm or deny it. IE skew the numbers to show either way. I just watched the show and they were trying to keep the aircraft stationary during the test and mentioned it several times, so you can see where I presumed that.
Posted 23 Mar 2013 at 8:15am #
[quote comment="76599"]I see what you are saying now. But in reality that is what could be said about any myth to either confirm or deny it. IE skew the numbers to show either way. I just watched the show and they were trying to keep the aircraft stationary during the test and mentioned it several times, so you can see where I presumed that.[/quote]
No they weren't. The treadmill (conveyor belt) cannot keep the plane stationary.
Posted 23 Mar 2013 at 9:38am #
[quote comment="76599"]I see what you are saying now. But in reality that is what could be said about any myth to either confirm or deny it. IE skew the numbers to show either way. I just watched the show and they were trying to keep the aircraft stationary during the test and mentioned it several times, so you can see where I presumed that.[/quote]
Glad you are beginning to see the light, Chuck, but the Mythbuster group were just attempting to create the conditions, to the best of their abilities, put forth by the myth, which I will now show you, as stated on the show and their website:
An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.
The fact that so many people jump to the conclusion that the plane will operate like a car or a bicycle under these conditions and remain stationary is what created the myth, that it won't take off, in the first place. Whereas logic, and a passing understanding of the physics involved, tells us that it MUST move forward and fly.
Posted 23 Mar 2013 at 8:37pm #
Are my posts invisible? Chuck, right after I explained how mythbusters were not claiming that a stationary plane can takeoff you post the same things again. Am I not writing in English?
Posted 23 Mar 2013 at 10:25pm #
I never said that the plane can't take off on a moving belt. If you add a control limit that forces the belt and the wheels to be moving at equal speeds than the plane can't take off due to the control limit. Mythbusters did not test the original wording of the thought question. This is a question that can easily be solved on paper.
Ultimate simplified answer. Belt speed and wheel speed are equal. Belt speed equals 0 at all times. Can a plane take off with out the wheels rotating? Answer, no.
That is because the moment you apply thrust and the plane moves forward an additional force is applied to the wheels causing rotation. If you don't understand this solution it is only because you either refuse to except the wording of the original question (Mythbusters altered the wording for the show and refuse to except it) or you don't understand basic physics.
Posted 24 Mar 2013 at 12:19am #
[quote comment="76575"]
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."[/quote]
[quote comment="76618"]If you add a control limit that forces the belt and the wheels to be moving at equal speeds than the plane can't take off due to the control limit. [/quote]
John,
Since this string was created to discuss Mythbuster's attempt to either prove or disprove a particular myth, we should only be concerned with the version represented by them. Not with a version you may have heard elsewhere, or pulled out of your butt. However, these are my thoughts about what you have (as far as I can determine) tried to say.
Your version is quoted above. Mythbuster's version (as stated on the show and website) is as follows:
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
Neither version mentions "wheel rotation". Only "plane speed" or "takeoff speed".
[quote comment="76618"]
Ultimate simplified answer. Belt speed and wheel speed are equal. Belt speed equals 0 at all times. Can a plane take off with out the wheels rotating? Answer, no.[/quote]
Again you mention wheel speed. The only scenarios in which the wheels aren't rotating is if the belt isn't moving, or the plane has it's engine off. Yet, in both versions it is clearly stated that the plane and belt move.
The myth itself is not meant to be some complex mathematical problem, but an example of how people can arrive at a correct answer to an incorrect premise. That is, using the conditions given, "a stationary aircraft on a moving conveyor belt cannot take off, but you can't have a stationary aircraft on a moving conveyor belt"!
That's akin to the riddle, "If a rooster, that is sitting on the roof of a barn, lays an egg...which side will the egg roll down?" Some people are so intent on trying to figure which side, they ignore the fact that roosters don't lay eggs. Old one, I know, but I believe the analogy fits. Someone might question "What if it was a genetically altered rooster?"
That is what I, Misters Levy, Barzeski, Boston ... And others have been dealing with. It's a frustrating task, but someone has to do it!
Posted 24 Mar 2013 at 11:33pm #
Triffid, you say that it has nothing to do with the myth as posted on the forums? So does the show just pull random myths that they make up? They get many of the myths from the forum so it does have everything to do with the show and how the myth was tested. Lets take your example.
Mythbusters buys 10 hens and watches what direction the eggs rolls and say that they all roll south. Myth busted. Happy now? Or would you complain that they didn't get roosters that can't lay eggs?
Posted 24 Mar 2013 at 11:46am #
Yup. I am persona non grata on this discussion forum.
Posted 24 Mar 2013 at 12:03pm #
[quote comment="76638"]Yup. I am persona non grata on this discussion forum.[/quote]
Hey, Nissim...I gave you props at the end of my last post.
Hang in there, dude!
Posted 24 Mar 2013 at 12:34pm #
Thanks Triffid. I missed that.
Posted 25 Mar 2013 at 12:39am #
[quote comment="76650"]Triffid, you say that it has nothing to do with the myth as posted on the forums? So does the show just pull random myths that they make up? They get many of the myths from the forum so it does have everything to do with the show and how the myth was tested.[/quote]
John, I could care less where either version of this particular myth came from. Just what was presented to me in the show, since that is what we are discussing. In this case, however, it makes no difference as to the outcome.
What does concern me is the inability of so many people to "get it", or read more into it than necessary.
My personal belief is that they jump to the quick, inaccurate answer (that the plane won't take off), and when proven wrong try to cover up their mistake by blaming Mythbuster's presentation, or by saying there is a "theoretical spirit" to the myth that "forced" them to think the plane won't fly!
I like a good debate as much as the next guy, but COME ON people, you're beating a dead rooster on this one!
Posted 25 Mar 2013 at 10:02pm #
You summed up everything nicely now, thank you. So it doesn't matter if everyone else is right or wrong as long as they agree with you. There is a reason why they revisit myths. Sometimes they reverse the original decision other times they don't but they remain open to the idea.
As I said based on what the show tested nothing was wrong. People are upset because they left out an important part of the question and than told everyone who understands it they are wrong. It has been shown many times that the Mythbusters team is unskilled in the aero field. Concrete glider is an example if you understand flight you will have noticed things that were said were incorrect.
My question to you is this. If you go by the wording posted on the forum that led to the myth being tested that wheel speed and belt speed are always equal, do you think the plane can take off?
Posted 26 Mar 2013 at 12:24am #
[quote comment="76672"] My question to you is this. If you go by the wording posted on the forum that led to the myth being tested that wheel speed and belt speed are always equal, do you think the plane can take off?[/quote]
As I have stated, this question has nothing to do with what is being discussed in this platform. However, I will refer you to someone that I believe has given this matter a good deal of thought, and expressed himself quite well:
[quote comment="72388"] There is NO WAY you can match the speed of the wheels and the speed of the conveyor belt (in opposite direction of course) when the plane starts moving. The rotational speed of the wheels depends on the speed of the belt plus the speed of the plane. Take a coin and a sheet of paper and try it yourself. When you drag the paper and at the same time move the coin in the opposite direction at the same speed as you drag the paper, the coin will spin at twice the speed. QED.[/quote]
Therefore, in my opinion, it is a non-question. I suppose if someone can believe that a conveyor belt will magically cause a plane to remain stationary, they will believe that the speed of the conveyor belt and the speed of the wheels of a moving plane can be equal.
The only time wheel speed and conveyor belt speed match is when they are at 0 mph! There would be no forward progress of the plane, so it would not take off.
Now that I've answered your question, here's mine...how much force will it take to get you off of your high horse?
Posted 26 Mar 2013 at 12:48am #
[quote comment="76575"]From the forum
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."[/quote]
Once again, John, let me point out that the version of the myth you have provided mentions nothing about wheel speed, but does say both the plane and conveyor belt are in motion. Under those conditions the plane will take off!
Posted 26 Mar 2013 at 1:35pm #
It doesn't matter if the conveyor speed is increased to match the forward speed of the plane. Actually, the conveyor belt's speed can be set to be ten times the airplane's speed, or one hundred times, or one thousand times. It's completely irrelevant because the airplane does not depend on traction with the conveyor. The airplane is independent of the conveyor. Once people understand this they will no longer concoct these silly thought experiments about adjusting conveyor speed.
Posted 26 Mar 2013 at 9:26am #
[...] I could monetize planes and conveyor belts I'd be [...]
Posted 26 Mar 2013 at 2:04pm #
[quote comment="76684"]It doesn't matter if the conveyor speed is increased to match the forward speed of the plane. [/quote]
Exactly, Nissin, but I believe John and his ilk are confusing the speed of the plane with the rotation speed of the wheels.
Dumb, I know, but what can you do?
Posted 26 Mar 2013 at 2:28pm #
Triffid, it is nice to see that you agree that if wheel speed is equal to the belt speed that the plane will not take off. Like you many people see this is a "non-question".
These same people also see that if you remove the limit that belt speed and wheel are equal it is a "non-question" that it will take off.
No one is saying that the belt can magically keep the plane from moving. I use the term control limit in the engineering sense that either by design or human interaction the limit is kept.
I've followed this on the mythbusters forum long before the show aired. I first heard the question 12 years ago at Parks College where wheel and belt speed was always part of the question. Everyone there understood the control limit being the "trick" to the question. When I first saw the question posted on the forum the "fly" group always remove the control limit from the question to make them right.
The arguement today is that Mythbusters had 2 questions to pick from. During the show they decided on the "non-question" who cares what the belt vs. wheel speed is. So obviously it can fly. What made it worse is they during the show said that people don't understand why a plane can fly as if there was only 1 version of the question. Mythbusters could easily have during the show shown that if you limited the wheel speed to match belt speed it couldn't fly and than continued to show that with out that limit it could fly. Many shows are done this way when half way through they have an out come they change the variables. This show they didn't.
It will continue on with the "fly group" refusing the original question that is over 20 years old and the "no fly group" saying stop changing the wording. The question was originally written by the aero field to "trick" aero experts into saying it could fly and then reminding them about the control limit.
Posted 26 Mar 2013 at 2:47pm #
John, what are you talking about? Triffid said that the only time the wheel speed will be equal to the belt speed is when both the belt and the wheels are not moving. Of course when the airplane is stationary it will not fly. Otherwise, as soon as the airplane's engines provide enough thrust for the airplane to take of then the airplane will take off. This is regardless of what the belt is doing.
When either or both the airplane and the conveyor belt are moving then the wheel speed will equal the conveyor speed plus the airplane speed so that the wheel speed will never equal the belt speed when the belt and/or the plane are moving.
Posted 26 Mar 2013 at 3:21pm #
[quote comment="76675"]
The only time wheel speed and conveyor belt speed match is when they are at 0 mph![/quote]
[quote comment="76687"]Triffid, it is nice to see that you agree that if wheel speed is equal to the belt speed that the plane will not take off.[/quote]
John, you are a pistol and definitely deserve to be ranked in the upper eschelon of those to whom this site is dedicated.
In case you missed it, like you have with most of what I have been writing, THAT was a major dig!
Not worth any more of my time.
Posted 27 Mar 2013 at 6:41pm #
Said Dr. McCoy to Mr. Spock. I'm sorry that the question is above your level of experience and knowledge base. After all the last line of defense in any arguement is to defame. Good luck in your future endeavors and please leave physics to the experts.
Posted 27 Mar 2013 at 6:53pm #
[quote comment="76719"]Said Dr. McCoy to Mr. Spock. I'm sorry that the question is above your level of experience and knowledge base. After all the last line of defense in any arguement is to defame. Good luck in your future endeavors and please leave physics to the experts.[/quote]
John, you're wrong.
That's not defaming. It's just a simple fact. đ
Posted 27 Mar 2013 at 7:00pm #
John, why can't you admit that you are wrong and move on? Triffid's Physics understanding on this issue is just fine. Why do you have to keep beating a dead horse? You are WRONG on this topic. The way MythBusters conducted the experiment was fine. There was nothing wrong with it. I understood right away the intent and outcome of their experiment and saw that it was correct.
Posted 27 Mar 2013 at 7:55pm #
[quote comment="76719"]Said Dr. McCoy to Mr. Spock. I'm sorry that the question is above your level of experience and knowledge base. After all the last line of defense in any arguement is to defame. Good luck in your future endeavors and please leave physics to the experts.[/quote]
You're quoting Star Trek? NOW I understand!
Wow! What a waste of my time.
Posted 28 Mar 2013 at 1:03pm #
Given your need to insult to win your argument I'm sure you will never understand this but last chance for you to get it explained to you in terms you can understand. Back to the original question where a plane is on a conveyor belt. The conveyor belt is moving in the opposite direction of the plane and matching the wheel speed. Can the plane take off?
Put the plane on the belt and turn it on. At this point the plane will begin to move backwards due to the inability to overcome friction. Add forward thrust until the plane is no longer moving backwards. Now measure the speed of the belt and the wheels and they will be equal. Now add forward thrust to the plane until air speed is enough to take off but maintain a 0 angle of attack. In other words able to takeoff but still on the conveyor belt. Now compare the belt and wheel speed and you will see that the belt speed is unable to match the wheel speed. No matter how much you increase the belt speed it will never match the tires as this will increase the force on the tires causing them to spin faster. So although you can increase the AOA to take off you cannot match the two speeds. So the plane cannot take off if the belt and wheels are moving at the same speed because you have to kill the thrust and move to a standstill point relative to the ground.
Posted 28 Mar 2013 at 2:00pm #
So...you guys still haven't figured out whose dick is bigger yet?
" The conveyor belt is moving in the opposite direction of the plane and matching the wheel speed. Can the plane take off?"
John...that's not the question. The question is matching the speed of THE PLANE. If you match the WHEEL speed, the plane isn't moving and therefore cannot take off, period. If the plane is moving at all, then the WHEEL speed MUST be the treadmill speed PLUS the plane speed, and therefore the match is broken.
Posted 28 Mar 2013 at 2:43pm #
I miss Chuck!
Posted 28 Mar 2013 at 4:58pm #
[quote comment="76743"]The question is matching the speed of THE PLANE. If you match the WHEEL speed, the plane isn't moving and therefore cannot take off, period. If the plane is moving at all, then the WHEEL speed MUST be the treadmill speed PLUS the plane speed, and therefore the match is broken.[/quote]
No the original question was wheel speed not plane speed. The question as presented over 20 years ago amonst the aero field. The problem is that the question became so popular over the years that people kept rewording it incorrectly.
This is what Mythbusters should have done during the episode and the war would have ended.
Ignore speed = fly
Match wheel speed = won't fly
The continued arguement today is because Mythbusters failed to mention during the show that multiple tellings of the question exist today. They played it off that there is only 1 version of the question and told everyone else that they were wrong. When in fact right or wrong depends on what version of the question you think is the original. Myself who first heard the question about 13 years ago from aero engineers who were in the field for 40 years all heard only the one version, wheel speed. It wasn't until about 5 years ago people started rewording it, I believe by accident because they didn't understand the importance of the wording.
But for anyone to use the arguement that using the wheel speed question isn't worth asking because it can't take off don't realize that they other versions are just as equally easy to answer and therefore not worth asking.
I feel that when they tested this myth they jumped the gun, as they do occasionally, and didn't focus on the whole thing. First part of the show should have been about focusing only on the wording of the question and explaining why they picked it and noting that additional wordings are out there. The point of this blog is to say people are "stupid" for not understanding the question where I am saying that this episode was flawed from the start and you can't call these people "stupid" because by the wording they heard they are just as correct as you are with the wording you stand by.
Posted 28 Mar 2013 at 5:14pm #
"No the original question was wheel speed not plane speed."
Then this "myth" is a non-starter, because not only is the plane not going to take off, it won't even move. The plane sitting stationary on a stationary treadmill matches the speeds at 0. The plane sitting stationary on a treadmill moving at takeoff speed of, say 70 mph, matches the wheel speed and treadmill speed at 70 mph. The plane isn't moving and therefore generates 0 lift. The second that plane moves forward at 1mph, the wheel speed is now 71 mph, and the match is broken.
It is a physical impossibility to match the wheel speed of a moving plane to the speed of a treadmill.
So that "version" of the myth is invalid...so can we get past it now?
Posted 28 Mar 2013 at 5:19pm #
And to add to that...
If the takeoff speed is 70mph and that's the speed of the treadmill, the plane WILL be able to move forward at 70mph and take off, but the wheel speed will be 140mph.
THIS is the question I think most people are thinking about with this myth...can a plane reach its take off speed if the treadmill is moving the other direction at that speed. The answer is, and always has been, YES, because the plane is pushing back on the air, not on the treadmill, and no matter how fast the treadmill is moving backward, the air is still stationary.
Posted 28 Mar 2013 at 6:43pm #
Who cares how the question is worded. The simple fact is that nothing the moving conveyer belt can do will prevent the plane from taking off. That's the bottom line. End of argument.
Posted 28 Mar 2013 at 7:11pm #
[quote comment="76748"]No the original question was wheel speed not plane speed. The question as presented over 20 years ago amonst the aero field. The problem is that the question became so popular over the years that people kept rewording it incorrectly.[/quote]
I'm going to block you from responding further, Joe, because you're too dense to realize that for the wheel speed (you're measuring it as rotation) to match the conveyor belt speed, the only time that condition can be true is when both are 0 MPH.
Because if the plane and thus the wheels firmly attached to it moves 100 MPH, the belt will be moving 100 MPH, and the wheels will be spinning at the equivalent of 200 MPH.
And guess what? Even if you ramped the belt up to 200 MPH (which means the wheels would be spinning 300 MPH if the plane is still only going 100 MPH), it won't matter anyway. Wheels are made to spin.
The speed of the wheels is measured not at how fast they're spinning but how fast they're moving linearly down the runway.
Otherwise you'd be talking about RPMs or revolutions per minute or second or something. Your numbers don't even match up: how many MPH does the belt have to move to match the wheel "speed" of 3000 RPM?
Stop posting stupid stuff, Joe, or be banished from posting more.
Posted 28 Mar 2013 at 7:08pm #
He's not done yet. Watch!
Posted 28 Mar 2013 at 7:36pm #
Erik,
May I humbly request that you not block John, just yet? It's the high point of my day.
I've never really thanked you for starting this thread, so I'll do so now. I find myself reading the posts over and over, amazed at the heights and depths of the minds out there.
I consider myself of average intelligence, but these writing have made me want to improve myself, and look at the world with clearer eyes.
Thanks again!
Posted 28 Mar 2013 at 7:42pm #
I just had a very startling thought. Is it possible that Triffid and John are the same person? Wow my mind is blown.
Posted 28 Mar 2013 at 7:53pm #
HAH! Maybe those experiments with drugs in my college years are kicking in!
Good one, Nissim. See, I do read your posts.
Posted 28 Mar 2013 at 7:59pm #
Last year I was corresponding with a computer/science nerd over the internet for a couple of months. I eventually discovered that he wasn't a computer nerd like he claimed at all. it was some 21 year old bikini model pretending to be a computer nerd.
Posted 28 Mar 2013 at 9:01pm #
Ban me if you want it won't change the facts. The point of your blog has been shown that you want to call people "stuipd" just because they don't agree with you.
First off, belt speed and wheel speed can match at any velocity not just 0 mph. (And you say I'm being stupid) The only time that they would not be equal is with forward movement of the plane relative to a person not on the belt. So if the belt is moving at 100 mph and the plane isn't moving forward the wheels are moving at 100 mph. Given that no one measures their car speed in RPM, although you could, I assumed that was understood. So please don't try to side track.
Under normal wind conditions there is no point in time that where wheel speed and belt speed can be equal that allows the plane to takeoff.
As you are too obstinate to understand that people are not stuipd just because they disagree with you and the show failed to present both wordings of the question I leave you to your blissful world of ignorance.
Posted 28 Mar 2013 at 9:18pm #
John, for f--uck-'s sake. I'm getting annoyed now. Can't you get it through your thick head? If the plane on a treadmill is moving forwards using propellers or jet engines and the treadmill underneath is moving backwards then the freely spinning wheels of the plane will be moving faster than if just the plane was moving and the treadmill was stationary. Come on man, give your head a shake.
Posted 28 Mar 2013 at 9:19pm #
I've changed my mind. BLOCK THIS PSYCHO!!!
Posted 28 Mar 2013 at 9:20pm #
I still think John is Triffid. I think we're all being punked. That's my only explanation as to why John keeps saying these rediculous things.
Posted 28 Mar 2013 at 9:23pm #
[quote comment="76762"]John, for f--uck-'s sake.[/quote]
Uh, Nissim, what are the dashes for?
Posted 28 Mar 2013 at 9:25pm #
I thought I'd get censored otherwise. No?
Posted 28 Mar 2013 at 9:32pm #
The dashes are suppose to replace some of the letters. All of the letters are there, unless you meant to type "floucky's" or something. Anyway, I digress. I" m NOT John!
Posted 28 Mar 2013 at 9:39pm #
In order to get around censoring software you can just put various characters between all the letters. I've tried this on the CNN forum and it worked. So no, the dashes do not need to replace letters, they can just come between the letters.
Posted 28 Mar 2013 at 9:36pm #
Funny thing, though. The wheels *could* be locked to the same speed as the treadmill and the plane would still take off.
The wheels would just be skidding over the treadmill surface.
Kinda like the planes that take off and land on water with pontoons instead of wheels.
Posted 28 Mar 2013 at 9:46pm #
[quote comment="76772"]In order to get around censoring software you can just put various characters between all the letters. I've tried this on the CNN forum and it worked. So no, the dashes do not need to replace letters, they can just come between the letters.[/quote]
I stand corrected.
See, John, I can admit when I am in error. You should give it a try.
Posted 28 Mar 2013 at 9:48pm #
Are you talking to yourself again Triffid? đ
Posted 28 Mar 2013 at 10:05pm #
[quote comment="76774"]Are you talking to yourself again Triffid? :-)[/quote]
Feels that way sometimes.
Wait a minute, maybe YOU are John!
I've got a foolproof way of finding out...how much is 2 + 2?
Posted 29 Mar 2013 at 12:21am #
[quote comment="76769"]Funny thing, though. The wheels *could* be locked to the same speed as the treadmill and the plane would still take off.
The wheels would just be skidding over the treadmill surface.
Kinda like the planes that take off and land on water with pontoons instead of wheels.[/quote]
As I understand it, what you are proposing is to modify the plane so that it is no longer a "free-wheeling" aircraft, but instead has some sort of motor that controls their rotation.
The "wheel-motor" will not allow them to spin any faster than the backward speed of the conveyor belt. Thus, when the belt is moving at say 25 mph the "wheel-motor" will turn them at that speed. With the planes' engine OFF, the aircraft will be stationary, like a car or bicycle, since the wheels are motorized. If you raise the belts' speed to 50 mph the "wheel-motor" also increases their speed to 50 and the plane is stationary.
The question here is...what happens when you then engage the engine and apply thrust? If the plane requires 100 mph airspeed to take off, how much extra thrust would it need to overcome the drag caused by wheels only "allowed" to spin at 50 mph? Achieving takeoff would depend on the power of the engine.
All speculation, of course, and nothing to do with the myth as stated (either version), but I would really like to get your thoughts.
Posted 29 Mar 2013 at 1:21am #
Too much think; far simpler.
My only point was that the wheel speed is irrelevant as long as the plane's engine is powerful enough to overcome friction between wheel and treadmill.
Hell, the plane could have bricks for wheels and it'd fly just fine once the coefficient of friction is overcome.
Posted 29 Mar 2013 at 7:07am #
[quote comment="76780"]Too much think; far simpler.
My only point was that the wheel speed is irrelevant as long as the plane's engine is powerful enough to overcome friction between wheel and treadmill.[/quote]
Blum,
Agreed. I was just trying to figure out where these "wheel speed to belt speed" people might be coming from in their thinking.
By expanding on your idea the wheel speed would at least be variable, instead of "locked" at one speed.
It throws the myth out the window, but I thought it might be worth exploring.
Posted 29 Mar 2013 at 11:00am #
That's just it, though. The wheels could be variable speed such that the wheels are rotating such that the outer bit is going the exact same speed as the conveyor belt (which, as Erik points out above, is quite a silly way to measure wheel speed).
As long as the plane's engine is powerful enough that the plane hits take off speed, the plane'll take off.
It also underscores how preposterous of a position John has attempted to claim is at the core of the myth.
Posted 29 Mar 2013 at 12:22pm #
[quote comment="76792"
As long as the plane's engine is powerful enough that the plane hits take off speed, the plane'll take off.[/quote]
Exactly! John contradicts himself on several points, and the example he gives as to the how the myth was originally suppose to read does not even mention wheel speed:
[quote comment="76575"]From the forum
"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."[/quote]
So we should just disregard his comments for the most part. However, he claims there is a forum, which I have not seen, that discusses this premise at great length and I was just wondering how they could possibly justify such a claim.
That is why I expanded on your idea of locking the wheels to a variable speed mechanism in order to explore a more palatable concept of where these people might be coming from.
Posted 29 Mar 2013 at 12:49pm #
" The wheels could be variable speed such that the wheels are rotating such that the outer bit is going the exact same speed as the conveyor belt (which, as Erik points out above, is quite a silly way to measure wheel speed). "
Did you really just say that? The wheel speed is measured by the outer part of the wheel (tread in contact with the ground/treadmill). It doesn't matter what the diameter is, if your belt is moving and your wheels are matching the speed, THE PLANE IS NOT MOVING. The wheels need to be moving at the speed of the belt PLUS the takeoff speed of the plane for the plane to take off.
Posted 29 Mar 2013 at 12:51pm #
You missed the part where the wheels are also skidding across the surface. The wheels could be rotating at a 100mph backwards and the plane would still take off if the engine is powerful enough to drag the plane through the air fast enough to achieve lift.
Posted 29 Mar 2013 at 1:58pm #
"You missed the part where the wheels are also skidding across the surface. "
Maybe because that part was just stupid. If there's that much friction the plane will probably do a face plant.
How about we stick to the original myth and stop making dumba$$ $hit up?
Posted 29 Mar 2013 at 2:03pm #
If you focused more on the argument at hand and less on rudeness, you might have noted in previous iterations of this particular never ending argument that amphibious planes make the point that wheel speed doesn't matter at all quite effectively.
And, maybe, if you put a couple of your brain cells towards thinking as opposed to chest thumping, you might have imagined the awesome innovation that would wheels not made of rubber. Oooh... imagine that! Wheels that slide, thus further proving that wheel speed just doesn't matter.
Posted 29 Mar 2013 at 2:23pm #
[quote comment="76797"]How about we stick to the original myth and stop making dumba$$ $hit up?[/quote]
I agree we should stick to the original myth, as presented on Mythbusters, but many of the "no fly" people make up "dumba$$ $hit" in their arguments. By discussing outrageous ideas now we may be better prepared in our noble cause to set them straight.
Posted 10 Jun 2013 at 6:12pm #
I have had endless fun reading these arguments and thought I might as well put my 5 (rooster) eggs in.
We've already established that once the plane moves, the speed of the conveyor belt is irrelevant and so the plane will take off.
The Mythbusters did it right from the wording of the problem as they had it.
IF, you are trying to use the other wording that says wheel speed as opposed to plane speed, then:
A) we are talking the speed f the wheels and not the rotational speed so that is the same as plane speed anyway. The plane will take off.
B) We are talking rotational speed.
In this case, if the plane moves, the belt CANNOT match speed with the wheels.
John has said that the pilot will throttle down to make the speed 0 so as to fulfill the conditions. This is clearly rubbish. As the original problem says the belt is set to match wheel speed, NOT "the pilot is instructed to ensure that these conditions are met", the pilot is clearly trying to take off. so the plane will move and therefore take off.
We have established that the belt cannot match the wheel speed as the wheel speed is belt speed + plane speed. Therefore the belt will TRY to match it but never succeed. This is all irrelevant cos the plane is still moving. The plane will take off.
As the belt is continually accelerating, you will then get to the point where the wheels are at light speed. People will try and argue some stupid case with this but time dilation says time will not pass for the wheels ROTATING at light speed and time will be moving VERY SLOWLY for the belt (at light speed - plane speed) which is still accelerating.
The plane however, is not going at light speed, it is accelerating to take off speed and time is passing as it would for the same plane on a runway. The plane will take off.
So the only way the plane will NOT take off whatever the wording is if the pilot deliberately doesn't try to move. Which would be the same for a plane in any scenario.
what new dumbass shit will the "no-flys" come up with now?
Posted 16 Aug 2013 at 11:04pm #
the myth implies that the belts purpose is to move at a speed to match the potential speed of the object through space!
i am not arguing that the craft could not move forward under these conditions. the myth implies that, if the belt prevents this, will it fly, and it will not.
if the plane does not move through space, it will never fly.
no lift no flight
saying that the craft can move forward has nothing to do with yje premise of the thought experiment.
Posted 05 Aug 2013 at 4:12am #
Interesting. I just watched this episode for the first time.
The experiment they did is definitely not the experiment I was expecting. It seems that people tend to fall into two camps here.
1. People who think that the thought experiment is about whether a plane can take off when it is moving relative to the surface it is on, but not moving relative to the rest of the surroundings (no air movement over the wings).
2. People who think that the thought experiment is about whether a plane on a surface that is moving in a direction opposite to the plane's forward motion can effectively ignore that surface movement and still accelerate relative to its surroundings, causing air to move over its wings and generate lift.
To me these are two entirely different thought experiments.
I was expecting the first experiment, but what they did was the second. I'm pretty sure that most of the "vitriolic" argument is due to the people in the two camps not understanding that there ARE two thoughts about what this "myth" represents and how it should be tested.
I think, ultimately, adjectives like "stupid" should be reserved for people who aren't able to see that there are two very different ideas regarding what this "myth" is about.
Posted 26 Aug 2013 at 5:01pm #
[quote comment="79938"]The experiment they did is definitely not the experiment I was expecting.[/quote]
Then you were expecting the wrong thing.
[quote comment="79938"]1. People who think that the thought experiment is about whether a plane can take off when it is moving relative to the surface it is on, but not moving relative to the rest of the surroundings (no air movement over the wings).[/quote]
Those people have it wrong.
[quote comment="79938"]I was expecting the first experiment, but what they did was the second. I'm pretty sure that most of the "vitriolic" argument is due to the people in the two camps not understanding that there ARE two thoughts about what this "myth" represents and how it should be tested.[/quote]
There are not two different camps. The people who "believe" the first experiment is the accurate one don't understand basic physics (or logic).
[quote comment="79938"]I think, ultimately, adjectives like "stupid" should be reserved for people who aren't able to see that there are two very different ideas regarding what this "myth" is about.[/quote]
Nah. đ
Posted 06 Aug 2013 at 11:39pm #
Before I say anything I want to note that I did not read every post here before I typed this reply,but I read a lot of them. I'll try to address this in the simplest manner. Sorry to say but the mythbusters got it wrong. If there is no airflow moving over the aircraft's wing(airfoil),there will be no lift produced and the aircraft will not get airborne. Lift can only be produced by air flowing over and under the wing(low pressure travels over the wing,high pressure travels under the wing. The high pressure tries to balance with the low pressure and generates lift). Without lift an airplane cannot fly. If an airplane is matching the speed of a conveyor belt,lets say 25 knots (the conveyor is moving aft at 25 knots and the airplane is moving forward at 25knots),the aircraft has no forward motion,therefore there is no generated air flowing over the wings,thus no lift is being produced and the airplane will remain grounded. It doesn't get any simpler than that. Instead of using a conveyor belt,they could've performed the same test by chaining an aircraft to a runway and going full throttle. The wheels do nothing but provide a smooth,rotating surface to accelerated upon. The wheels have nothing to do with the propulsion of the aircraft. Have any comments? Please feel free to email me at jlock6116@gmail.com
Thanks for reading,
JLock
CFI,MEI,CFII
Posted 26 Aug 2013 at 4:55pm #
[quote comment="79977"]Before I say anything I want to note that I did not read every post here before I typed this reply,but I read a lot of them. I'll try to address this in the simplest manner. Sorry to say but the mythbusters got it wrong. If there is no airflow moving over the aircraft's wing(airfoil),there will be no lift produced and the aircraft will not get airborne.[/quote]
[quote comment="79977"]Before I say anything I want to note that I did not read every post here before I typed this reply,but I read a lot of them. I'll try to address this in the simplest manner. Sorry to say but the mythbusters got it wrong. If there is no airflow moving over the aircraft's wing(airfoil),there will be no lift produced and the aircraft will not get airborne.[/quote]
I agree about lift.
Where you go wrong is that you think there should not have been air flow over the wings to cause lift.
So, you are, in fact, the one who is wrong.
A conveyor belt cannot keep a plane in place. It takes off normally. It pulls itself through the air with the jets or propellers, it doesn't push itself along the ground.
It's very simple.
Posted 16 Aug 2013 at 10:48pm #
jamie hyneman is an idiot.
the only thing that the belt did is to create a low coefficient of static friction. a light aircraft will get lift at a fairly low speed.
aircraft get lift br moving through space that contains an atmosphere, not over a moving carpet. without forward momentum through space you will never get lift. this is not an opinion its a physical property of our universe.
The belt allowed low friction and a stabilised foil, thus allowing for a shorter window for lift.
IF the belt had actually matched speed with the ultralight, it would have gotten zero lift
Posted 26 Aug 2013 at 4:53pm #
Fred, read the many, many posts above. You're wrong, both about what actually happens and what is implied.
Just because YOU misunderstood things, and added an implication that wasn't there, doesn't mean it actually exists.
The plane takes off, and it doesn't have much of anything to do with the "low coefficient of static friction."
Posted 26 Aug 2013 at 7:57pm #
the myth it self is the biggest troll ever.
it implies that the belt somehow be able to keep the plane stationary.
the fact that it cant is irrelevant.
Posted 26 Aug 2013 at 8:30pm #
[quote comment="80476"]it implies that the belt somehow be able to keep the plane stationary.
the fact that it cant is irrelevant.[/quote]
The "myth" does not imply any such thing.
Just because someone who doesn't understand the physics behind it thinks that it's a condition of the myth doesn't make it so.
It's a trick question, but that doesn't mean anything that violates the laws of physics is "implied."
I can show you a math equation that shows that 1=2, but the trick is that somewhere in there you divide by zero. If you were shown that equation, you'd probably say that proof "implied" that our number system was all screwed up, when really it's just your lack of understanding.
Posted 26 Aug 2013 at 8:17pm #
[quote comment="80476"]
it implies that the belt somehow be able to keep the plane stationary.
the fact that it cant is irrelevant.[/quote]
There is no implication on the part of Mythbusters, there IS an assumption on your part.
Posted 26 Aug 2013 at 8:44pm #
[quote comment="80479"][quote comment="80476"]it implies that the belt somehow be able to keep the plane stationary.
the fact that it cant is irrelevant.[/quote]
The "myth" does not imply any such thing.
Just because someone who doesn't understand the physics behind it thinks that it's a condition of the myth doesn't make it so.
It's a trick question, but that doesn't mean anything that violates the laws of physics is "implied."
I can show you a math equation that shows that 1=2, but the trick is that somewhere in there you divide by zero. If you were shown that equation, you'd probably say that proof "implied" that our number system was all screwed up, when really it's just your lack of understanding.[/quote]
If the myth does not imply the belts ability to counteract the effects of thrust than, the whole premise is pointless. of coarse it will not move forward.... why even pose the fucking question.
At best its a trick question, NOT a thought experiment at all..
don't assume that i would say anything.
its pointless, to argue about semantics.
Posted 27 Aug 2013 at 7:40am #
[quote comment="80481"]of coarse it will not move forward.... why even pose the fucking question.[/quote]
To expose idiots like you? It does kind of act as a rudimentary IQ test. đ
P.S. It's "Of course". And you're missing a "?" at the end of your sentence. And "than" should be "then" (without the extra comma). "It's" should have an apostrophe since it's a contraction of "it" and "is."
Posted 26 Aug 2013 at 11:21pm #
[quote comment="80481"]If the myth does not imply the belts ability to counteract the effects of thrust than, the whole premise is pointless. of coarse it will not move forward.... why even pose the fucking question.[/quote]
All of the previous postings should give you some indication as to why Mythbusters aired this episode. Many people approach the myth as they would the "Rooster laying an egg on top of a barn" riddle.
People HEAR the word âroosterâ but ignore itsâ implication when they hear the words âlays an eggâ. They then set their mind to solving the problem of which side the egg rolls down.
In the question at hand, some people have it fixed in their mind that the âtreadmill-airplaneâ scenario has resulted in an aircraft that is âstationaryâ in relationship to itsâ surroundings. Even though the original myth makes no such determination. It only states that:
âAn airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.â
They ignore the fact that it doesnât matter whether the surface under the planesâ wheels is moving backwards, forwards or standing stillâŚTHE PROPELLERS ON THE PLANE ARE PULLING IT FORWARD AND THE AIRCRAFT WILL TAKE OFF WHEN IT REACHES THE PROPER AIR-SPEED. It doesnât matter if itâs a toy plane, an ultra-light, a Beechcraft, or Howard Hughesâ Spruce Goose, the result will be the same.
As I was saying, having now overlooked this, they set their minds to the other fact of fixed-wing flight. âWithout airflow there can be no liftâ. Since they now believe that this plane is âstationaryâ how can there be airflow? They have reached a correct conclusion, but to an incorrect premise.
Posted 27 Aug 2013 at 10:33am #
[quote comment="80494"][quote comment="80481"]of coarse it will not move forward.... why even pose the fucking question.[/quote]
To expose idiots like you? It does kind of act as a rudimentary IQ test. đ
P.S. It's "Of course". And you're missing a "?" at the end of your sentence. And "than" should be "then" (without the extra comma). "It's" should have an apostrophe since it's a contraction of "it" and "is."[/quote]
yeah laying in bed with a ruptured disk, typing with one finger, and making lots of typos is fun.
This myth is not a myth. its a trick of words, and nothing else. It is worded in a way to leave open different interpretations.
If taken at face value, than of obviously the craft will achieve flight.
Thought experiments rarely involve real world physics.
I find it amusing that you will not even acknowledge that this is more of a play on words than anything else. The results of the literal interpretation are to simplistic to even consider and experiment.
You must have a real small dick
Posted 28 Aug 2013 at 10:33am #
[quote comment="80496"]You must have a real small dick[/quote]
At this point, I just think it's funny that you're lying in bed thinking about my sexual organs. đ Enjoy.
Posted 27 Aug 2013 at 3:49pm #
[quote comment="80496"]yeah laying in bed with a ruptured disk, typing with one finger, and making lots of typos is fun.
This myth is not a myth. its a trick of words, and nothing else. It is worded in a way to leave open different interpretations.
You must have a real small dick[/quote]
Many people seriously believe that the aircraft, under these conditions, will not lift off, even when it has been repeatedly explained to them. They are incorrect! Therefore, I believe that it fits the the definition of a myth:
"an unproved or false collective belief"
Sorry about your dick...uh, disk!
Some males have big dicks, some have big brains, some even have both!
Mr. Barzeski is, at least, one up on you!
Posted 28 Aug 2013 at 4:07pm #
[quote comment="80512"][quote comment="80496"]You must have a real small dick[/quote]
At this point, I just think it's funny that you're lying in bed thinking about my sexual organs. đ Enjoy.[/quote]
He might not have a spine for the facts... đ
Fred: Allow me to provide you with a useful link at this point:
http://www.ameriburn.org/
đ đ
(Not making fun of those who really need that info!!!)
Posted 11 Oct 2013 at 7:53pm #
I just came across this plane/treadmill question a couple of days ago. I am in the camp of the plane can't fly. I think I can identify exactly where I depart from the explanations I am reading.
Those who say the plane will fly, assert that the wheels are 'free-wheeling' which I take to mean they rotate independently of the body of the aircraft.
With free-wheeling wheels, when the treadmill rolls it is asserted those wheels will start to rotate and the plane will not be moved backward through the air. Therefore when normal take-off thrust is applied by the engines, the plane is totally unaffected by the treadmill beneath, and at even a purely nominal engine speed, the plane will roll forward into the wind and will ultimately achieve take off at its usual (not-on-a-treadmill) take off speed.
I find it very difficult to comprehend this concept of free-wheeling wheels. This whole idea and scenario above are counter-intuitive to me.
My belief instead, is that as the treadmill starts to turn, the wheels of an unpowered plane will not rotate, (other than a little bit at first if the acceleration causes the plane to 'jerk'). Instead the plane (note: the wheels are not rotating) is carried backwards along the treadmill. Now when the treadmill achieves a speed equivalent to take off speed, the plane engines are engaged and finally the wheels start to roll forward. Eventually the plane reaches its 'normal' take off speed, matching the backward speed of the treadmill. At this point the wheels are spinning at the normal rate for take off (they are rotating at the speed of the treadmill). But the plane is now at 0 mph in terms of airspeed and is not taking off. Only when the engines thrust to twice the take-off speed do the wheels spin at double their normal rate, and the plane can finally take off. But of course in this scenario the treadmill is matching the plane's taxi speed and the plane is always balanced at 0 mph airspeed.
Note I am not asserting in any way that the wheels of the plane are 'powered'. Their movement is solely as a consequence of their contact with a treadmill as the powered plane above it moves forward relative to that treadmill.
So if I am in error, my mistake is not believing that a plane's wheels will just spin and spin on a treadmill and that the unpowered plane will not be dragged backwards. My hang-up is the 'free-wheeling' concept.
Posted 14 Oct 2013 at 12:48pm #
Quoting Triffid Aug 26th:
(restating the Myth) âAn airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.â
They ignore the fact that it doesnât matter whether the surface under the planesâ wheels is moving backwards, forwards or standing stillâŚTHE PROPELLERS ON THE PLANE ARE PULLING IT FORWARD AND THE AIRCRAFT WILL TAKE OFF WHEN IT REACHES THE PROPER AIR-SPEED.
(end quote)
I think you are mistaken about the 'no-flyers' ignoring this fact. You are missing a step here and it is the intervening step which the 'no-flyers' have a problem with.
The missing step is the one you get to before asserting that the aircraft requires the proper air speed. I ( a "no flyer") would like to know how the aircraft can possibly reach the proper airspeed when it is only applying enough engine power to surmount the backward drag from the treadmill?
If your answer is that there is no backward drag from the treadmill, due to a property of aircraft wheels that transfers the treadmill's drag into a force which will rotate the wheels and will prevent that backward drag being transferred to the body of the aircraft, then that is where you part ways with the "no flyers".
Convince me of that and I will have the required epiphany.
Posted 14 Oct 2013 at 3:02pm #
[quote comment="81202"]The missing step is the one you get to before asserting that the aircraft requires the proper air speed. I ( a "no flyer") would like to know how the aircraft can possibly reach the proper airspeed when it is only applying enough engine power to surmount the backward drag from the treadmill?[/quote]
The question says nothing about "applying only enough engine power" to overcome anything.
Posted 14 Oct 2013 at 4:04pm #
The engine doesn't have to overcome drag from the treadmill. It may need to overcome wind (as the engine pushes against the AIR, not the GROUND), but that's why planes take off in different directions from airports given the present wind conditions.
If the engine is capable of propelling a plane at several hundred miles per hour through the air as well as ascend at a 30 degree angle, then it can more than compensate for any friction created in the wheel bearings, which were specifically engineered to have as little friction as possible.
Overall, pretty stupid comment on your part.
Posted 14 Oct 2013 at 3:55pm #
[quote comment="81165"]But of course in this scenario the treadmill is matching the plane's taxi speed and the plane is always balanced at 0 mph airspeed.[/quote]
Get the idea of a "stationary" aircraft out of your mind and you will achieve nirvana!
As soon as the engine starts up the plane will pull itself forward. It will continue to move forward until it takes off or, if the pilot just taxis, it will run off the end of the treadmill. It will NEVER reach a point where it will become stationary.
Posted 14 Oct 2013 at 4:17pm #
[quote comment="81165"]
My belief instead, is that as the treadmill starts to turn, the wheels of an unpowered plane will not rotate, (other than a little bit at first if the acceleration causes the plane to 'jerk'). Instead the plane (note: the wheels are not rotating) is carried backwards along the treadmill. Now when the treadmill achieves a speed equivalent to take off speed, the plane engines are engaged and finally the wheels start to roll forward. Eventually the plane reaches its 'normal' take off speed, matching the backward speed of the treadmill. At this point the wheels are spinning at the normal rate for take off (they are rotating at the speed of the treadmill). But the plane is now at 0 mph in terms of airspeed and is not taking off. Only when the engines thrust to twice the take-off speed do the wheels spin at double their normal rate, and the plane can finally take off. But of course in this scenario the treadmill is matching the plane's taxi speed and the plane is always balanced at 0 mph airspeed.
.[/quote]
Your belief is wrong. If you start the treadmill without the engines on, there will only be a "jerk" if the brakes are on. If they are off, the wheels will spin while, at the same time, the very small amount of friction in the wheel bearings will break inertia and start the plane moving backward very slowly.
If the plane's engines are on, then it will start pushing backward against the air, independent of the treadmill and irrespective of treadmill speed, and will start moving forward. It will reach its takeoff air speed, the treadmill will reach takeoff speed in the opposite direction, and the wheels will be spinning at twice the normal spin rate for takeoff.
If this is counter-intuitive for you, then you aren't very intuitive.
If I'm on a skateboard and you're pulling the board back with as much force as I'm pushing it forward, it will not move. But if I'm grabbing a rope and pulling myself up into the air, it doesn't matter at all with what force you are pulling my skateboard. I'm taking off.
Posted 14 Oct 2013 at 5:25pm #
Listen.....
Again this is not even a physics thought experiment, it is more of a play on words than anything.
Without the notion that the treadmill "could" hold the plane in place there is no puzzle even. It a trick, a ruse, nothing more.
Without applying a hypothetical universe that would allow a conveyor belt to hold a wheeled plane in one position the thought experiment is useless and pointless to think about, or argue about.
otherwise of coarse the craft will take off
Posted 23 Oct 2013 at 6:18pm #
I came across this some time ago, and like most, i thought the plane would not take off. The experiment on Mythbusters seemed odd, because the plane did move forward, so I thought: hey, they're not moving the belt fast enough.
It wasn't until someone mentioned momentum in this tread that I saw the light, so to speak.
That said, the arguments back and forth are always the same, so I'd like to make a contribution.
Planes, either with propellors or jet engines, move air in order to gain speed, and don't push off against the ground like cars, bikes or other vehicles.
So compare the forward motion of a plane to swimming, where you're moving the water in order to gain speed. It won't matter if the swimming pool floor is moving or not, or whether you're your feet are paddling on a treadmill, you'd still be able to swim forward.
Fun debate though...
Posted 03 Feb 2014 at 5:16pm #
Still unconvinced.
The swimming pool analogy doesn't work as the swimmer is not in contact with the pool floor.
An aircraft is pushed down by gravity directly onto the conveyor belt. Which is why a conveyor belt is perfectly capable of dragging an aircraft backward and thus negating the engine thrust.
If we were talking about a hovercraft then the conveyer belt has no effect on its ability to get airborne - the craft just rises up because the push is downwards. But with an aircraft the push is backwards versus the conveyer belt's drag and they will balance out if the same force is applied to each.
Posted 18 Feb 2014 at 11:19am #
[quote comment="89571"]An aircraft is pushed down by gravity directly onto the conveyor belt. Which is why a conveyor belt is perfectly capable of dragging an aircraft backward and thus negating the engine thrust.[/quote]
No it isn't.
Your statement might be (partially) true if the plane didn't have these modern marvels we call "wheels."
Posted 18 Feb 2014 at 11:19am #
"The wheels on the plane go around and around. Around and around. Around and around."
"The wheels on the plane go around and around. Around and around. Around and around."
Seriously -- the wheels turn, thus negating the drag on the plane.
As has been repeated a bazillion times above.
Posted 18 Feb 2014 at 1:48pm #
Again, again , again.
If You take the wording literally, you believe that the experiment states that the "belt" will "MATCH" the forward momentum of the plane which will render the craft stationary with only its prop in motion. In other words it suggests conditions in which that were possible.
That is why this is a trick question and not a thought experiment at all.
It tricks the reader into believing that somehow this belt is meant to keep the craft in one spot and there for unable to achieve lift for obvious reasons.
Presenting this experiment with no inclination towards deception:
A air plane is on a conveyor belt.
If the belt is moved in the opposite direction of travel, accelerating to match any forward movement of the aircraft, will the aircraft take flight.
Answer: Hell no
THAT is what people think that this myth implies.
To deny that is simply being disingenuous.
Posted 18 Feb 2014 at 2:40pm #
[quote comment="90949"]If You take the wording literally, you believe that the experiment states that the "belt" will "MATCH" the forward momentum of the plane which will render the craft stationary with only its prop in motion. In other words it suggests conditions in which that were possible.
That is why this is a trick question and not a thought experiment at all.[/quote]
Again, again, again⌠you are wrong.
Additionally⌠the wording I used is:
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?
No "matches" and DEFINITELY no "matches momentum."
Also, look up "match" in a dictionary please.
Posted 18 Feb 2014 at 5:03pm #
[quote comment="90949"]
If You take the wording literally, you believe that the experiment states that the "belt" will "MATCH" the forward momentum of the plane which will render the craft stationary with only its prop in motion. In other words it suggests conditions in which that were possible.
A air plane is on a conveyor belt.
If the belt is moved in the opposite direction of travel, accelerating to match any forward movement of the aircraft, will the aircraft take flight.[/quote]
This is the actual wording, taken from the show and its' website:
"An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff."
No "accelerating to match any forward movement of the aircraft, "
Get it straight!
Posted 09 Mar 2014 at 12:59pm #
[quote comment="90947"]"The wheels on the plane go around and around. Around and around. Around and around."
"The wheels on the plane go around and around. Around and around. Around and around."
Seriously -- the wheels turn, thus negating the drag on the plane.
As has been repeated a bazillion times above.[/quote]
When Mythbusters shows an unpowered plane on a treadmill which is moving, and the plane does not get dragged back by the treadmill, because of these miraculous wheels, then I will believe you.
Posted 09 Mar 2014 at 1:51pm #
[quote comment="92782"]When Mythbusters shows an unpowered plane on a treadmill which is moving, and the plane does not get dragged back by the treadmill, because of these miraculous wheels, then I will believe you.[/quote]
The wheels on the Mythbuster plane were not powered. They were just wheels. The propellers were powered, of course.
Seriously, Phil, c'mon.
Posted 19 Jun 2014 at 9:04am #
[quote comment="68803"]Tom. You are correct in everything you say until the last paragraph. As soon as the plane's engines overcome the friction between the wheels and the treadmill the two systems (plane and treadmill) become independent. This means that the treadmill's action no longer is communicated to the body of the plane. This means that the treadmill can be accelerating (not constant velocity) and the plane will still take off.[/quote]
This is the answer that helped me understand the " busted" outcome.. Since the aircraft will be standing relatively still to the ground even if the conveyer is traveling 100 mph backwards. The wheels will just be spinning backwards at 100 mph. The prop only has to overcome the wheel bearings friction to keep the plane physically stationary.From then on you just need the normal plan acceleration to take off.
Posted 28 Mar 2015 at 7:37am #
[quote comment="70662"]The treadmill does not negate forward speed of the plane. It negates a runner's speed because the runner is pushing against the treadmill. A plane pushes against the air, not the ground, meaning there is no effect from ground movement.[/quote]
This seems to be the most concise explanation. Thanks John. đ
Posted 25 Feb 2016 at 12:27am #
I just spend the last 90minutes enjoying these comments!
Posted 01 May 2016 at 6:31pm #
Problem is, while on the ground, a plane can only move as fat as its wheels spin. So if the treadmill matches the wheels RPM and converts that to relevant MPH, the plane will have no velocity and therefore won't take off.
Ypou can add as much thrust as you want, a plane on he ground will only move as fast as it wheels turn.
No take off
Posted 06 Nov 2016 at 12:11pm #
[quote comment="345513"]Problem is, while on the ground, a plane can only move as fat as its wheels spin. So if the treadmill matches the wheels RPM and converts that to relevant MPH, the plane will have no velocity and therefore won't take off.[/quote]
That's not true at all. The wheels will spin at twice the speed they'd normally spin. If the plane is going 100 MPH, the wheels will be spinning as if the plane was going 200 MPH.
Really, it's very simple.
The plane takes off.
Posted 07 Nov 2016 at 11:49am #
"Ypou can add as much thrust as you want, a plane on he ground will only move as fast as it wheels turn."
This remark is predicated on one of two things:
1. The thrust is conveyed through the wheels.
2. There is an inherent limit to the speed at which a plane's wheels can turn.
Number one is not true.
Number two is only true in that at a very very fast speed, far faster than twice the takeoff speed, the bearings of the wheel will have a friction thermal failure. Add to that that the plane's wheels are free-spinning.
The thrust is conveyed directly into the air. Picture this...instead of the engine of the plane pushing the air behind it to move the plane forward, you're a giant several times bigger than the plane and capable of running at twice takeoff speed. You tie a rope capable of bearing the load to the front of the plane and proceed to run down the runway towing the plane. How are the wheels of the plane going to stop you?
Posted 27 Nov 2016 at 8:19pm #
You have it backwards, the the wheels will spin as fast as they need to to not slip on the ground. the wheels have no function in pushing the plane
Posted 18 Aug 2016 at 9:41am #
3. The physics are correct. Lift is generated by airspeed. Forward motion is generated because the engine (jet or propeller) acts against the air, not the ground.
---- OMG how stupid are you???!!!
the whole thing is so simply. A normal plane like we know it will ONLY take off if the wind is passing fast enough the wings of the plane to creatie the 'up-force'. That's it! Nothing more.
It doesn't matter what the ground is doing. And the engine is only 'handy' to make the wind going fast on the wings!
The whole misunderstanding is in the following (and therefore it WAS a terrible experiment):
- plane and conveyor belt same speed --> plane doesn't move (towards the road!) and does not go backwards, and will NEVER go up.
- with the engine making more speed (here the different speeds..), going faster towards the road, if will lift off. It needs to be said that with the conveyor belt the engine needs to go faster to lift off, than normally from the road.
Again....conclusions:
Will a plane lift off with a conveyor belt? Ofcourse just make enough power the plane ACTUALLY moves TOWARDS the road (which means towards the wind that needs to 'fly' by the wings đ đ
Posted 06 Nov 2016 at 12:03pm #
Remco, the plane doesn't need to generate much more speed than normal - that's the entire purpose of wheels, to be relatively low friction.
Posted 28 Feb 2017 at 10:00pm #
The truck pulls on the conveyor belt as if someone's pulling table cloth under a set of dishes. The plane has inertia to stay put with just the belt rolling under the wheels.
Posted 24 Jul 2017 at 10:58pm #
I believe that Mythbusters people got it wrong as well. They proved forward and reverse cancel each other out like the vehicle with the air cannon shot a ball on their show when matched by speed the ball fell flat to ground.!
Posted 28 Aug 2017 at 1:58pm #
[quote comment="406052"]I believe that Mythbusters people got it wrong as well. They proved forward and reverse cancel each other out like the vehicle with the air cannon shot a ball on their show when matched by speed the ball fell flat to ground.![/quote]
You're wrong. They proved the simple physics: the plane takes off.