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Originally Posted by Lightwolf
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That's a different question than the one posed here, which stated:
"A plane is standing on runway that can move (some sort of band conveyer). This conveyer has a control system that tracks the
tire speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."
This means that as the tires try to rotate forward, the conveyor will also rotate forward the same amount to stop the tires from rotating at all. Thus, the conveyor belt and the plane will be moving in the same direction at the same speed. Result: takeoff when airspeed is high enough. It's a piggyback takeoff.
If it's read to indicate that the conveyor is trying to prevent the wheels from moving forward, this only works with powered wheeled vehicles, that derive all their forward motion through the wheels. This means the conveyor is moving in the opposite direction the vehicle is trying to move. This is actually used in testing new cars, and you can find footage of this in action so it's a verifiable fact - the vehicle will remain stationary. Treadmills are another example. Now, put on a rocket or other engine that provides thrust that's not channeled through the wheels and there's nothing the conveyor can do to counter that.
The version of the question you linked to is different and is basically stating the same as my second example above.:
"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?"
But this is a trick question. A plane does not have powered wheels. It does not use them to accelerate down a runway. It uses thrust, pushing a mass of air out the back to send its own mass forward. Even without wheels, it could generate enough thrust to move forward, but generally with disasterous consequences.
In these latter cases, it only works with a vehicle that derives its motion through force applied to the surface it's resting on, or a plane that is not powered up at all. You could use a cart to push or pull the plane, and the conveyor will be able to cancel out that motion without any trouble because the conveyor belt is the sole determining factor against the wheels of the vehicles. This only works until the plane's engine kicks in. Then you have another factor that's outside the conveyor's influence.
He Who Has A Cool Proof That The Universe Is Closed.
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