Leaving on a jet plane (or, how smart are you again?)

Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, but moving in the opposite direction.

Can the plane take off?

JB

 

no....no airlift....

 

Ok, ground-bound you are.

Myself? I think I'll go flying.

JB

 

Suppose you are in an elevator that is in free-fall. If you quickly step off right before it hits the ground, will you walk away without a scratch??

 

Depends on what you "step off" onto.

JB

 

Ok, I'll bite Cubano -- what makes you think that the plane can't get any "airlift"?

JB

 

It can't move forward if the belt always matches the speed of the wheels. It will always be standing still. Same effect as sailing into a 20 knot current with a 20 knot hull speed, feels like you're booking it but your standing still in relation to the bottom.

 

Unless I've misunderstood the scenario I agree. If the plane isn't moving there would be no relative wind, no lift, no flight.

 

Actually, it will take off. It's not like a car where the engine drives the wheels. The engine of a plane drives the propellors (or jets) which generate the power for lift-off. The wheels of a plane simply spin on its axles or bearings.

 

Technically, if my assumption is correct, the belt doesn't need to be as long as the actual runway (this would defeat the purpose).