Dylan Smith wrote:
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.


In the real world airplanes have flown with pressure sensors
on the wings, confirming lift from the Bernojuli effect in actual
flight.

This does NOT disprove the notion that there is localized downward
flow from some parts of the aircraft. However, there is no NET flow
of air down or up from airplane wings or helicopter blades. Otherwise,

ambient pressure at ground level would steadily increase as more
and more aircraft pushed the air down...

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FF