The Impossibility of Flying Heavy Aircraft Without Training

Jose wrote:
Not until after it passes the high point in the airfoil. Befor it
gets there, it is accelerated upwards.

Does the air split (top/bottom path) at the same level as it rejoins?
If the air splits at a higher altitude, then the air has to have a net
downward motion to get to the rejoin point.

Agreed. Clearly this happens with high AOA.


When the air reaches the trailing edge it is back to where it started.

Is it? I think it's lower than when it started. It certainly is with
any appreciable AOA.

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


No, it is a way of looking at downrushing air that has never
contacted the wing.

It doesn't matter whether it contacts the wing or not. The contact is
by proxy (by contacting the other molecules of air that contact...the
wing.) You call it pressure. I agree. Pressure is ultimately
newtonian; I think we agree there too.

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.

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.




It's a floor wax. It's a dessert topping.

There is more to that. If this collision occurs in outer space, I
guarantee you that the center of mass will =not= quit moving.
But it will not move in a manner that conserves momentum.

Yes it will. What will not be conserved is macroscopic kinetic energy.

Right. My mistake.

...

So, are you saying that in the presence of the Earth there is no
net change in the momentm of the basketballs being thrown by the
dribbler and also no net change in momentum of the air molecules
accelerated by the wing?

Averaged over all basketballs and all air molecules, yes, because the
earth acts as a momentum transfer point.


--


FF

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
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

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.

--

FF