what the heck is lift?

On Fri, 09 Sep 2005 14:29:18 +0200, Thomas Borchert
wrote:

Wings generally tend to have a curved suface. The upper surface has a
greater arc or curvature than the lower surface. As the air flows across the
surfaces of the wing, the upper surface air is forced to move faster than
the lower surface air thus causing a pressure difference between the two
surfaces.

Forced by what? And how does your "theory" explain inverted flight? I don't
buy it.

BTW, this has been beaten to death in countless aviation newsgroup
discussions. I once thought like you, because I was taught that way. It's
still a bad theory. I suggest googling. Keywords might be: lift, flight,
Bernoulli, Newton.


He is describing the traditional airfoil theory which is correct. It
is the most efficient method as it produces lift with minimal drag.
That's what most people are taught.

There is another mode that is related to the force of the air
impacting on the bottom of the wing at high AOA producing lift as
well. Think of your control surfaces. Your rudder control surface is
symmetric, yet it produces horizontial components of force. IIRC, the
Jeppesen books cover high AOA effects as well.

Inverted flight is accomplished by the second of the two effects.
They have to fly at a higher AOA relative to normal flight to
compensate for the airfoil effect. Some aerobatic planes have
symmetric airfoils for this reason.

As AOA increases, the deflection takes more of a role. At stall, the
deflection is suffcient for the airfoil effect to be interfered with
and ceases. Thus a large component of left is lost. You drop. You
still have some lift, but it is not sufficient to keep you airborne.





Jim

http://www.unconventional-wisdom.org