Lift em and Thrust
Alright smart people, including at least one aeronautical engineer that stops by every now and then:
A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).
Will the plane be able to take off?
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5 comments
5 Comments:
Yes.
How did you know I was an aeronautical engineer?
I know all.
(Actually, I was talking about John.)
So... how will it be able to take off?
I think "no" is the answer.
I think that planes fly because of the difference in pressure exerted by air flowing at different speeds past the top and bottom of the wing. The faster fluid above the wing exerts little pressure and the slower fluid below exerts more, pushing the plane up.
In the scenario you present, there won't be any air flow past the aircraft, no pressure difference will be created, and it will not take off.
I'm curious to hear what John has to say before I post what I think is the answer.
OK, I think Johnny H's expertise is not forthcoming.
I'm not sure of the answer. I googled this after someone asked it to me, saw that there's tons people giving their opinion, but I didn't read them. I wanted to think about it myself.
Here's what I say:
The conveyor belt is a red herring. It makes no difference. The wheels on a plane are not driven by the engine. They just freely roll when the plane moves. The engines (or prop) is what moves the plane and this is done by pushing against the air and has nothing to do with the ground (or conveyor belt).
Now, a plane does require lift to take off. Lift comes from having the wind blow over (and under) the wings. This can't happen if the plane is standing still. However, since the engines are still working against the air, the plane will move forward no matter how fast the belt is moving. (The wheels will spin faster than normal given the backwards-running belt, but it will still go forward.) Therefore, the plane will move, get lift, and take off.
Am I right? I don't know. But it makes sense to me.
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