A plane equipped with fixed horizontal engines and wheel landing gear is placed on a huge treadmill runway. The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction. Will the plane take off and fly or not?
I say the plane will take off (see this digg thread or this one or millions of other ones if you search on google.)
Currently we’re 2 for it taking off and 2 against… well 1 and a half as the one isn’t yet 100% sure.
Basically the argument for it taking off goes something like this…
The thrust from the engines pushes against the air and pushes the plane forward, the treadmill as no effect on the plane and cannot cancel the thrust of the engines because it doesn’t have any kind of “grip” on the plane… all that happens is the wheels turn faster and faster as the plane accelerates and the treadmill tries to pull the plane backwards.
For the plane to take off all you need is wind over the wings which you should get because the plane would be moving forward.
Update (8:15pm 06-12-2006):
It’s interesting but most people assume the plane won’t go… and generally the reason given is that it would behave like a car and not move… but everyone forgets that a plane isn’t driven on the ground by the wheels the wheels just make the plane easier to move but don’t have any “drive”.
Well I reckon that it’s probably not going to take off. My reasoning is:
Essentially, the plane is standing still. There is no air resistance that would generate lift on the wings. E.g. when you drive on the highway, and stick hand out the window, you can feel resistance. Put the car on a treadmill, and you wouldn’t feel any air resistance on your hand if you did the same thing.
“The treadmill has a clever design and always matches the speed of the plane.”
So that means that the plane is not moving with respect to the air around it.
Which means that the comment in the second last paragraph is wrong, the plane will not be moving forward.
My vote is that it wont take off because the plane needs the movement of air over it’s wings to take off. If the plane isn’t moving, then there’s no air moving over it’s wings.
Umm ok you guys…
To get a plane to take off it needs to move through the air right? or rather have air moving over the wings?
So take a toy car, with free moving wheels and place it on a piece of paper… now the paper is the treadmill the car is the plane and now your hand is going to be the force from the engines… push the car forward… what happens? it moves forward.. if it moves forward it means that the air is moving over the planes wings and therefor it would take off right?
Now do the exact same thing… except while pushing the car forward pull the piece of paper backward… the paper is now the treadmill… what happens to the car? It moves forward and therefor it takes off. The treadmill will have almost no effect on the plane..
Remember a plane isn’t driven by it’s wheels but rather the thrust from the engines… you see we automatically compare it to things that we know and understand so we think of a car (it has wheels) and people running on a treadmill but both of these things “push” against the treadmill and therefor the treadmill is able to counteract the force we’re exerting on it and the object ends up not moving… a plane is different it’s exerting force against the air and nothing in the air is counteracting the force… therefor it’s going to move forward… different story if the plane is some how fastened to the treadmill..
[…] So yesterday I posted a question about whether a plane on a treadmill runway would take off and most people say No it won’t… which is actually wrong it will take off… […]
Well I guess I’m not quite ready to enter the world of physics just yet. Not all that surprising since I’m a programmer :P. I googled the answer after I posted my comment and it seems straightdope has the same answer as yours.
Don’t worry Richard, I made the same mistake… I think everyone will, your gut reaction is to say No.. little bit of thought or a Google search and you realise that you’re wrong…
Come on you guys. You are all a bunch of computer boffins and are probably in the upper IQ bracket and yet you cannot solve the simple question.
As far as I understand the situation is as follows:
1) We have a treadmill which is mounted to a fixed point with either a revolving belt or rollers
2) We have a plane whose wheels are on the treadmill belt or rollers.
3) No matter how fast the motors try and thrust the plane forwards, the treadmill belt or rollers matches the force in an opposite direction.
Thus my computer boffins, the plane is standing still with no wind passing under or over the wings so no lift. The engines may be causing thrust, the wheels may be turning, but the plane ain’t going nowhere.
The only way to obtain lift is for the wheels to be on a surface which is not revolving in the opposite direction. The plane needs to have forward motion in order to be able to have lift. No forwaed motion, no lift.
Now go ahead and prove me wrong