"Dan Luke" wrote in
:


"Le Chaud Lapin" wrote:

Obviously, any air above the wing can only result in a force downward
on top of the wing. The only force causing the plane to want to move
upward comes from beneath the wing. The effect of any air above the
wing is to cause rarefication above the wing, resulting in lower
pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
"reaction" coming from downward movement of air seems just plain
silly to me.


Then why does the wing stall and cease lifting when flow separates
from the upper surface?



Actually, that's not the definition of the stall, seperation occurs just
after the stall with most airfoil/planform combinations and in most
flight situations, ordinarily. Some wings will have seperation at the
stall, but I've never flown one.
The defintion is an abrupt loss of lift when the critical angle is
reached. Seperation usually occurs immidiatly after (*but not always,
for instance, deltas will continue to have smooth flow way below he
point they will actually keep flying) This is not to be confused with
the back siide of the drag curve, BTW.
Having said all hat, there are some reputable design texts that define
stall as the point at which the bubble breaks down and buffet occurs and
as far as I know, this doesn't disturb engineers (of which I am not one,
BTW, so take this all with a large grain of salt) any more than a "po-
tay-to, po-tah-to" argument would.
Bottom line is you're interested in keeping your airplane from going
down and the point at which the wing ceases to do what you would like it
to do is the point at which you're most interested.

Make sense? If it does I must not have explained it well.



Bertie