Backwash Causes Lift?

On Oct 3, 7:29 pm, Tina wrote:
In fact, if there is a downward component of the air's velocity that
had come from its passage over the upper surface of the airfoil, then
there had been an acceleration provided to that air -- acceleration in
this case being conventionally defined as the second time derivative
of position.

The acceleration is indeed downward. If God declared that all air
molecules in the universe must remain still for the sake of USENET
explication, and the wing move forward, and you took a snapshot of
that picture, there would be a vacuum created above the wing. It would
be quite large (not laminar). The floor of this vacuum would be the
wing itself. The ceiling would be the underside of an air mass above
the entire wing, ready to move downward to fill the void. Now if God
said, "Let molecules move!", the air mass above would, indeed, push
downward. But they would not be allow to go completely downward.
Molecules accelerated from the leading edge of the wing would fly
backward, colliding with those coming from above, and the net-effect
would be a stream.

Now, if the air is accelerated downward, and it has mass, it means
there had been a force applied. The local prime mover is of course the
wing, so it must experience an upward force. Maybe you have a
different idea as to on what that equal and opposite force is
operating on -- I'd be interested in hearing about that.

The force is coming from the air mass above the wing, the air mass
that would be right above the vacuum created if no molecules were
allowed to move. That airmass pushes downward, toward the void. This
has nothing to do with the wing, except that the wing created the
void, and also created high-pressure area at tip of wing causing
acceleration of air backwards.

There are a number of basic principles in operation here, be careful
not to paint yourself into too tight a corner unless you are quite
expert.

I am not claiming skill in this area -- physics was a minor a long
time ago -- but I remember some of the basics.

I am not an expert either, but I know enough to know that the
explanations I am reading in books are, at best, misleading. Some of
them are plain wrong. Note: going to start a new thread so we can get
to the bottom of this.

And yes, I am certain.

-Le Chaud Lapin-

"We" are not in need of getting to the bottom of this. Most of us have
been there and done that.This particular writer, if she chooses to
analyse physics problems, tends to use the Newtonion approximations as
first principles. The good news is my profession doesn't demand those
skills often. I would, however, be interested, as I mentioned earlier,
how you derive conservation of mV from Newton's force/acceleration
relationship. I think you made that claim earlier in this thread.

Le Chaud Lapin writes:

I am not an expert either, but I know enough to know that the
explanations I am reading in books are, at best, misleading.

That's an open secret in aviation. The mechanism of lift has been widely
explained incorrectly for years.

Le Chaud Lapin wrote:
You can have lift of an object with no Bernoulli. It's simple vector
addition.

1. You are talking about nature's abhorrence of a vacuum.
2. Vacuum abhorrence is not lift.
3. Airplanes do not generate lift as a result of vacuum abhorrence.
----------
Conclusion: you are not talking about how aircraft generate lift.

QED.

TheSmokingGnu

On Oct 3, 9:26 pm, TheSmokingGnu
wrote:
Le Chaud Lapin wrote:
You can have lift of an object with no Bernoulli. It's simple vector
addition.

1. You are talking about nature's abhorrence of a vacuum.
2. Vacuum abhorrence is not lift.
3. Airplanes do not generate lift as a result of vacuum abhorrence.
----------
Conclusion: you are not talking about how aircraft generate lift.

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.

QED.

-LCL-

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.

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).

My goodness, it's a good thing you got on here to tell us all this;
imagine all those airliners going overhead that have been doing it wrong
all this time, actually descending to a destination. They ought very
well to know that they could never do such a thing because the vacuum
pressures won't allow it!

TheSmokingGnu

Le Chaud Lapin writes:

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.

Gravity does that, not the forward motion of the wing. Without gravity, the
wing would simply move upwards until the effective angle of attack were no
longer positive.

Le Chaud Lapin wrote:
On Oct 3, 9:26 pm, TheSmokingGnu
wrote:
Le Chaud Lapin wrote:
You can have lift of an object with no Bernoulli. It's simple vector
addition.

1. You are talking about nature's abhorrence of a vacuum.
2. Vacuum abhorrence is not lift.
3. Airplanes do not generate lift as a result of vacuum abhorrence.
----------
Conclusion: you are not talking about how aircraft generate lift.

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.


Enjoying yourself there Anthony_

i know I am!

Bwaahwahwhahwhahwhahwhahwhahwhahwhha!


Bertie

Le Chaud Lapin wrote:
On Oct 3, 4:14 pm, Bertie the Bunyip
wrote:
Whoowh!
Zero point energy!


Surely, you must be joking. The exposition I wrote above is nothing
more than high school physics.

Where do you see me implying zero point energy?

I know my physics. Do you? There is no "zero point" energy.

Actually, there is. Not theory anymore, proven in a lab..

You´re proving to be quite the plaything.


Plain and simple:

If a person sucks on a straw, the reason the fluid rises has *NOTHING*
to do with Bernoull's principle. It has to do with the balance in
force being eliminated. In particular, the air in the straw is
removed, so the 14.4lbs/square in will lift the fluid in the straw.

This should be familiar to you, since you are a pilot. Where do you
think 29.92 Hg comes from? It comes from the height that a column of
mercury will rise in a complete rarefied tube in STP, which just
happens to be 29.92.

Both you and Mxmanic are wrong.


Maybe, but I can fly.



Bertie