On 2006-02-24, Greg Esres wrote:
There is a *net* downward momentum of air.

I have several aerodynamics books that say differently.

Otherwise there is no lift.

If there is a pressure difference between the top and bottom, you will
have lift. Your airfoil is blisssfully unaware of the air with which
it has no contact.

But air acts as a fluid. The airfoil certainly DOES have an effect on
air that it has no contact.
If you think there is no downward movement of air from an airfoil, stand
underneath a hovering helicopter some day. Or behind the propellor of a
plane - the prop is also an airfoil.

You might be able to get lift out of an airfoil in an enclosed tube with
no downward movement of the air, but that won't happen in the real
world.

--
Dylan Smith, Port St Mary, Isle of Man
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