Quote:
Originally Posted by RobFrost
Planes get lift by sending air downwards, it's simple Newtonian mechanics. There are two ways of looking at this, which are in a way the same thing.
A. Most wings have a convex top which forces the air to move faster round the outside of the circle. Whenever a fluid moves faster it has lower pressure, so the pressure difference from top to bottom of the wing manifests as lift.
And B. Wings usually have an upwards angle of attack to the direction of travel, I.e. the back of the wing is lower than the front.
Both a and b work by sending air downwards as the plane moves forwards. But a curved wing with a level angle of attack would still generate lift.
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^^^This! It's funny, but the answer to this question is more complicated than it seems (like most things). But, the above is correct.
One interesting thing I read once is that this act of "sending the air downwards" creates a pressure (or force) that can be measured on the ground. When a jet flies over your house, there is a pressure footprint below it as it flies. Logically, there must be. Mythbusters did a good episode on this. IIRC, they ended up putting an RC helicopter in the back of an enclosed 18-wheeler trailer. The question being - if the helicopter lifts off the bed of the trailer, does the truck weigh less than with the helicopter sitting on the bed? The answer was, no - the truck weighed the same. The pressure (force) created by the helicopter rotor
sending the air downwards acted on the trailer bed, so the weight didn't change.