Brainteaser Options

[james]

Here's a question for you:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

A couple of links discussing it (and some funny rationalizations for peoples incorrect assumptions):
www.kottke.org/06/02/plane-conveyor-belt
www.straightdope.com/columns/060203.html

[james]

The planes lift is certainly not just being caused by air being forced under it and lifting it up - at least not in the sense that I think you wrote it (Jamie) - but I may have misinterpreted your explanation.

The wing is affectively 2 curved surfaces (the top and the bottom of the wing), the top is longer (it's a convex curve) and the bottom is shorter (a concave shape). The shape and the angle of attack of the wing causes the air to flow faster above the wing than below, and so the pressure above the wing is less than below the wing (Bernoulli's principle, relating to the pressure of air to its local velocity). This pressure difference causes a force, called lift that acts at right angles to the air-flow. Also both the upper and lower surfaces of a wing produces lift by deflecting air downward, which propels the flying body upward with an equal and opposite force (Newton's Third Law).

Going back to another point about flaps (BAHH!) -

Flaps are hinged surfaces on the trailing edge of an airplane wing which, when deployed, increase the lift (and drag) of a wing by changing the camber of the airfoil. They are usually used while landing to allow the aircraft to fly more slowly and to steepen the approach to the landing site.

So flaps only increase the properties of the wing to help give lift at lower speeds for control at take-off and landing, they aren't the sole reason planes take off (again I may have misinterpreted Paul's earlier post about flaps)