what the heck is lift?

buttman wrote:
I have always been under the impression that lift is the product of
airspeed and angle of attack, and that lift is the measure of upward
force acting on the plane at a given time. For instance, if you are
doing slow flight, your wings are producing the same amount of life
that you would be if you were cruising, GIVEN that you did not lose or
gain any altitude during the maneuver.

My instructor, which is a very knowledgable guy tried telling me that
lift has nothing to do with airspeed. He said that lift is directly and
soley related to AOA and AOA only. So if you are doing slow flight, you
are producing more life than you are when you're cruising. I overheard
a ATP guy who flies King Air's say that this huge 20 ton military plane
he used to fly would fly approaches at 110 knots, and I heard him say
"It is able to do this because it producing so much lift", which I took
as him defining lift as my instructor does.

So whats the deal here? Are we just thinking of two diffrent concepts?



Good question,

In its most basic form, the amount of lift is determined by how many air
molecules are being deflected by the lifting surfaces, what angle they
are being deflected at, and how fast they are being deflected. We can
mostly ignore the low pressure over the wing stuff, since that is, a.
relatively minor, and b. is also a product of how many molecules are
flowing over the wing and how fast they are flowing.

Obviously, the faster the wing, or rotor, is moving through the air, the
more molecules it will be encountering and accelerating downward in a
given period of time. It is also obvious that the greater the AOA, the
steeper the angle of deflection and the greater the number of molecules
being deflected.

Therefore lift is a product of the airspeed of the lifting surface and
it's angle of attack.

Drag is another issue altogether.