Can the Plane Take-Off?

[EricH]

Originally Posted by Protronie

Yes but... the thrust from the prop pulls the plane forward so air rushes over the wings to produce lift.
Would the prop-wash alone be enough to produce the required air moving over the wings flight surface in order to produce the lift needed?

If the plane is on a belt moving under it at the same speed as the plane then the air above and under the wing would depend on the prop wash.

You aren't getting it. The wheels are NOT repeat NOT connected to the engine and prop. Not in any way, shape, or form (save the mounts to the fuselage).

Think of it this way. You put your car into neutral on a flat surface. It won't move, right? Now, do that on a hill (conveyor belt). It moves, right? The wheels are free-spinning when the car is in neutral and the brakes are off. Same for an airplane, except that there isn't a drive gear.

Prop wash (air pushed by prop) has nothing to do with it. It's whether the plane can move forward on the ground. That is determined by the thrust. The thrust is how strongly the prop pushes on the air. Now, the thrust only has to overcome air resistance (definitely a bit of this) and friction from the wheels (assumed to be negligible) to get the air flowing over the whole wing. If the plane can move forward (thrust > air resistance, or drag), then the lift can come into play against gravity. Because the wheels are free spinning, they can't resist forward motion, even with a conveyor belt. So the plane moves forward, lift comes into play, and the plane takes off. I don't care what speed the conveyor belt is moving. Unless it's moving fast enough to cause a wheel to seize up, the plane will take off.

[Wayne Doenges]

Mythbusters proved that the plane can take off. Nuff said, end the thread

[DonRotolo]

Originally Posted by Wayne Doenges

end the thread

What, and spoil all the fun?

OK, here's a variant: Put wheels on a rocket (say, a Saturn V) and a veryical conveyer belt- will it go up?

Of course it will. So will the airplane. The force of the propulsor (propeller, jet engine, rocket engine) is what moves the plane - wheels are irrelevant to flight (ever hear of a ski plane, or a PBY?)

Don

[Protronie]

Originally Posted by Wayne Doenges

Mythbusters proved that the plane can take off. Nuff said, end the thread

This thread will NEVER die!

What if the plane was jet powered instead of a prop plane?
Say like a MD-80 with the engines mounted on the tail... no air would be pushed over the wings... so no take off.

(that should be good for 100 post at least )

[Graham Donaldson]

But still, the thrust created by the jet engine would move the plane forward, thereby pushing air over the wings. The wheels, same as a prop plane, would just spin faster.

[whytheheckme]

Originally Posted by robotcanuck1676

But still, the thrust created by the jet engine would move the plane forward, thereby pushing air over the wings. The wheels, same as a prop plane, would just spin faster.

Indeed, instead of the groundspeed of the wheels being, say, 100MPH, they would simply be 200MPH, with the motion forward as an observer at 100MPH.

Think about a vertical lift takeoff plane. It has thrusters that hold it in the air before it takes off, and is able to do so. Having supports down with wheels at the end (essentially frictionless, compared to the amount of force we are talking about here), doesn't matter. They will just spin faster as the jet is propelled forward.

-Jacob

[EricH]

Originally Posted by Protronie

This thread will NEVER die!

What if the plane was jet powered instead of a prop plane?
Say like a MD-80 with the engines mounted on the tail... no air would be pushed over the wings... so no take off.

(that should be good for 100 post at least )

As I said earlier, the wheels have nothing to do with it. The plane moves forward and takes off.

Here's something to think about...on my Aero Design team, we coated our axles and wheels with graphite. LOTS of graphite. 4 layers of pencil lead on the axle easily, put some graphite powder inside the wheel, rub the stuff inside the wheel onto the axle. Just before each flight, put a little more powder in.

Would we have done that if the wheels had anything to do with takeoff, other than keeping the prop off the ground and letting the plane move without resistance? No.

[Rick TYler]

Originally Posted by Protronie

Yes but... the thrust from the prop pulls the plane forward so air rushes over the wings to produce lift.
Would the prop-wash alone be enough to produce the required air moving over the wings flight surface in order to produce the lift needed?

No, it doesn't. The prop wash can give a little extra lift, but it's trivial compared to the speed of the aircraft.

Why is this even a three-year question? Assume the airplane is sitting still on a frictionless surface with its wheels spinning at an infinite speed. This is pretty much the situation described in the "conveyor belt" scenario. When thrust is applied, the airplane with infinitely-fast wheels will still take off, right? The rotational speed of the wheels is irrelevant (as others have said -- ski and float planes still work).

By the way, some people have invoked bearing friction to explain why the airplane won't move. If you want to bring real-world physics into this, there is no way to design an runway-sized conveyor belt that would respond instantly to the speed of the aircraft. Inertia and control loop delay would mean that the thought problem isn't possible. If you invoke bearing friction, you have to design an inertia-less conveyor.

[Kit Gerhart]

Originally Posted by KenWittlief

The answer most certainly can be determined by the laws of physics.

All planes move by reacting with the air, either through propellers or jet engines. The speed of the ground under the wheels has almost nothing to do with the speed of the plane down the runway.

In this case, the plane would accelerate down the runway, and the 'runway' would accelerate in the other direction. The plane would still take off more or less normally, the only effect being the wheels will be spinning twice as fast as they normally would when it leaves the ground.

Hey that was easy, we settled the argument on CD in one post! :^)

There is a high probability, though, that the tires would fly apart before the airplane took off, and this could cause very bad consequences.