The Impossibility of Flying Heavy Aircraft Without Training

Are there any airfoils that produce lift at an AOA at or below zero?

Depends how AOA is defined (I don't know the precise definition). But
if we define it as the angle between the line from split to rejoin
point, and the direction of travel (or relative wind), then I think not.

But the pressure that supplies the lift is in the air below the wing
whereas it is the air above the wing that washes down. You're
attributing lift to the wrong air.

It doesn't matter. The molecules collide all over the place and
momentum is moved around (but never lost).

If he air above the wing washed sideways, and not down at all
you'd still get lift as the thumbtack, notecard and soda straw
demonstrates. No downwash from the notecard.

Describe the notecard setup better and I will do the experiment, and
then tell you what I think.

Jose
--
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Jose wrote:
Are there any airfoils that produce lift at an AOA at or below zero?

Depends how AOA is defined (I don't know the precise definition). But
if we define it as the angle between the line from split to rejoin
point, and the direction of travel (or relative wind), then I think not.

ISTR that AOA is defined relative to the chord.


But the pressure that supplies the lift is in the air below the wing
whereas it is the air above the wing that washes down. You're
attributing lift to the wrong air.

It doesn't matter. The molecules collide all over the place and
momentum is moved around (but never lost).

Of course it matters. It is the undisturbed molecules (or minimally
disturbed molecules) under the wing that push up on the wing.

The air flowing over the top of the wing cannot push UP on the
wing.


If he air above the wing washed sideways, and not down at all
you'd still get lift as the thumbtack, notecard and soda straw
demonstrates. No downwash from the notecard.

Describe the notecard setup better and I will do the experiment, and
then tell you what I think.


Take 3 x 5 index card or a similar light small card like a playing
card and push a thumbtack through the center.

Leave the thumbtack in and set the card on a table point up.

Put a soda straw, standing on end over the point of the tack.

Blow through the straw and while blowing lift the straw
straight up.

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FF