On Oct 3, 9:26 pm, TheSmokingGnu
wrote:
Le Chaud Lapin wrote:
Yes, I am. It's a combination of many things taking place at once.
Vacuum generation by the forward motion of the wing is one of them.

And the other is the displacement of air downward.


Then why do wings generate lift at negative AOA? Surely the immense
vacuum pressures generated would immediately pull any flying craft
desperately into the Earth the moment the wing crossed that threshold
(say, in a descent).

Must be careful not to mix attitude up with angle of attack. The
path of the wing's chord line through the air determines AOA. If the
airplane is pointed downward a bit so that the chord line is down 2°
with respect to the horizon, and the descent path of the airplane is
3°, the AOA is still 1°. An airplane in a steep climb, with its nose
up 20°, does not have a 20° AOA. Its flight path is upward at maybe
10° so that its AOA is only 10°.

Some wings (thick, heavily cambered wings) will generate lift
at up to -4° AOA. The bottom surface of the wing is not the chord
line; that's the line between the leading and trailing edges. The
bottom surface might be angled downward even more in level flight. the
old Champ was a good example: the bottom surface was angled quite
visibly down in level cruise flight, but the chord line was still at a
positive degree or two.

Admittedly there are instructors who don't understand this
stuff well at all and think they know more than they do. I'm still
learning 34 years after starting to fly. I'm old enough now to realize
how little I knew when I thought I knew it all, and to know that I'll
now never have a good handle on it all. Too little time and too many
other responsibilities. But private pilots need to have the basics,
because that's all they have time for and because they'll kill
themselves without them. I'm appalled when I see a pilot do a low-and-
over and yank back hard for the vertical zoom. They have no idea how
close they come to an accelerated stall doing that. Those that manage
to get the stall don't live to avoid the same mistake again, and the
accident report gives a bland, uninteresting and uninformative "pilot
lost control in the climb after the low pass." They don't give the
real reason: the pilot did not understand AOA, never did, and thought
he was safe because the airplane's speed was well above the stall
speed.


Dan