747 on a treadmill conundrum..

[Jenny A]

Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?


Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:


Yes.
No.
Whoever asked this question is an idiot.

Airplane on a Treadmill January 21, 2008

It comes down to this. Planes take off and remain airborne because of the lift created by airflow over the wings. No airflow, no lift. As long as the plane is stationary relative the air over the wings it won't fly. What's happening to it's wheels is irrelevant.

The best way to think about lift is also the most obvious, at least to a physicist: according to Isaac Newton's third law of motion, if air gives an upward force to a plane, the plane must give an (equal and opposite) downward force to the air. So a plane really generates lift by using its wings to push air downward behind it. That happens because the wings aren't completely flat, as you might suppose, but tilted back very slightly so they hit the air at an angle of attack: As a result, the wings direct the airflow downward, which pushes them upward and produces the lift. To produce extra lift at takeoff and landing (when the plane is moving slower), the planes have flaps on their wings they can extend to push more air down.

How Stuff Works: Airplanes by Chris Woodford. Last updated: May 17, 2014.

So if the plane doesn't move relative to the air, it don't take off. Now say you added a fan in front of the plane in scenario 2. Then we'd get lift-off.