Airplane Riddle

[garublador]

This one's always fun for message boards:

An airplane is put on a long conveyor belt that matches the plane's speed, but moves in the opposite direction. Can the plane take off?

[RW James]

This one's always fun for message boards:

An airplane is put on a long conveyor belt that matches the plane's speed, but moves in the opposite direction. Can the plane take off?

Yes, because it really has nothing to do with ground speed - it's all about air speed, which gives it lift.

[firebirdV]

Ooh, this sounds fun.

I don't know much about airplanes, but I believe that they get an upward force from the air moving over/beneath their wings. So if the airplane is standing still from the point of view of the air (other than some air blown from the props), then I'd have to say no. There wouldn't be enough air moving to lift it.


Now I'll have to wait for the answer...

[Arkitkt]

No, because the plane's speed relative to ground and air is zero.

[RW James]

No, because the plane's speed relative to ground and air is zero.

got me - I need to read slower before I jump on these. Good one

[firebirdV]

No, because the plane's speed relative to ground and air is zero.

Relative, that's the word I was looking for. I kept on thinking 'reference frame', so similar yet so far apart at the same time. Oh well, my answer's not elegant, but I still got my point out.

[Luís]

I'd think no. The plane would get enough speed to lif off but it wouldn't be able too.

More than likelly if it could lift it would just be thrown back.

Beats me.

[MikeS]

It could if it were a Harrier.

[ErikH]

Turn off the conveyor belt......TAKE OFF!!!

[Budweiser]

No, even if the plane's jets were full throttle, the plane would still be standing still. The purpose of propulsion is to very quickly move the wings through our thick atmosphere thus creating lift to eliminate the gravitational forces keeping the plane on the ground.


Also, if you're ever in a free falling elevator, jumping up off the floor before it's hits ground won't do squat. You'll still be squash.

[garublador]

got me - I need to read slower before I jump on these. Good one

You had it right the first time. The plane would take of just as it normally would.

[GuitarStv]

You had it right the first time. The plane would take of just as it normally would.

No it wouldn't. As posted by Arkitkt, the plane's speed relative to ground and air is zero.

A plane needs air moving over it's wings to generate lift and fly. If a conveyor belt is moving at the same speed and direction as the plane, then the plane is staying at the same place in space. It's wheels are moving, but no air is passing over the wings. This effect also explains why it's easier for pilots to take off when they're facing a strong wind (the wind adds to the speed of the air moving over the wings, generating more lift).

[garublador]

Who says the plane isn't moving forward? The engines push the plane, it moves forward and takes off. The thing people miss is that planes don't propell themselves the same way cars do. A car spins the wheels to push itself forward. A plane pushes itself forward and uses the wheels to reduce friction between itself and the ground.

[MikeS]

Wanna hint? The plane's speed relative to the conveyor belt would be zero.

Think about the propulsion of an airplane works, and you'll quickly realize why the plane will take off.

[RW James]

You had it right the first time. The plane would take of just as it normally would.

You're right (I think). The plane is moving itself through the air - it doesn't matter how fast the ground is moving or in which direction. If the propeller or jet engine is moving the plane through the air at 100 mph, the air is moving over the wings at 100 mph. The wheels on the other hand are moving at 200 mph (because the conveyor is moving the other way at 100 mph.

I feel better now - I think

[ErikH]

Well, if the plane took off, the wheels wouldn't be moving (spinning) at all because they would be tucked away.

[ratherdashing]

Who says the plane isn't moving forward? The engines push the plane, it moves forward and takes off. The thing people miss is that planes don't propell themselves the same way cars do. A car spins the wheels to push itself forward. A plane pushes itself forward and uses the wheels to reduce friction between itself and the ground.

It doesn't matter how it propels itself - it needs enough momentum to overcome the force of the conveyor belt.

Assuming friction and gravity are equal in both cases (conveyor or no conveyor), as long as:

F(conveyor belt) + F(constant factors) > F(airplane engines)

the plane will go backwards.

When:

F(conveyor belt) + F(constant factors) = F(airplane engines)

the plane will be motionless.

The only way for the plane to move is for:

F(conveyor belt) + F(constant factors) < F(airplane engines)

The way F(airplane engines) is produced is irrelevant.

[LesStrat]

I'm taking the train instead.

[ratherdashing]

No it wouldn't. As posted by Arkitkt, the plane's speed relative to ground and air is zero.

A plane needs air moving over it's wings to generate lift and fly. If a conveyor belt is moving at the same speed and direction as the plane, then the plane is staying at the same place in space. It's wheels are moving, but no air is passing over the wings. This effect also explains why it's easier for pilots to take off when they're facing a strong wind (the wind adds to the speed of the air moving over the wings, generating more lift).

Bingo.

[ratherdashing]

Wanna hint? The plane's speed relative to the conveyor belt would be zero.

Think about the propulsion of an airplane works, and you'll quickly realize why the plane will take off.

If this were true, every aircraft carrier would have huge conveyor belts on them so that planes could take off without a long runway.