Will the plane fly

[MARKH]

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

 

[SilentWarrior]

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

Interesting question, so I’ll be the first to bite. I would say no. From my experience from using a treadmill I can not recall feeling the wind rushing by me. I also did not make any forward progress. From that I would surmise that there is no trust to produce air movement over the wings and therefore no lift.

There is trust to produce speed, but without the flow of air over the wing it’s all just an exercise. 😀

 

[BoeingBoy]

Most excellent answer, SilentWarrior. A fixed-wing aircraft needs airspeed to produce lift - groundspeed is irrelevant.

Two examples:

1 - Wind tunnels are used to "fly" scale models routinely. The model doesn't move in relation to the "ground" but "flys" by virtue of the speed of the air over the wings (with the airspeed provided by the fans in the wind tunnel).

It is possible (and not uncommon in sailplanes) to be flying with zero groundspeed. All that's needed is that the wind speed equal the airspeed. I've come close to experiencing this in a DC-3 while flying into the wind while in the downward flowing side of a mountain wave. At climb power and airspeed the groundspeed was only 20 kts - far below stall speed.

2 - Likewise, it is theoretically possible that a 747 would not be able to take off even though the groundspeed was equal to normal takeoff airspeed. Attempting to take off downwind in catagory 5 hurricane winds would produce this situation (don't try this at home). The groundspeed would be normal for the takeoff, but the airspeed would be about zero. This would be the equivalent of the "airplane on a treadmill" in the question.

Jim

 

[SilentWarrior]

Thanks BoeingBoy

My doctor always said that exercising would be good for me. Who knew? 🙂