Jimbob wrote:
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
Forced by limiting the space through which the fluid must flow. Think
of your garden hose. If you put your thumb over the end and constrict
the space the water flows faster through the opening. As the speed
increases the pressure decreases, air moves from high pressure to low
pressure and the wing of the airplane is in the way of this movement so
it is lifted up with the high pressure air. This also explains wing tip
vortices and why for a given configuration a higher aspect ratio wing
will produce more lift than a lower aspect ration wing.
Inverted flight and equal camber wings use AOA to create the air
pressure differential.
Margy
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