Backwash Causes Lift?

On Oct 7, 11:02 pm, flightoffancy wrote:
Did you mess with NASA's online simulations of airfoils?

Yes, 15 minutes ago, in fact after taking a break from my very tedious
work.

Those suggest that the air both "on top" and "on the bottom" of an
airfoil get turned as the airfoil's AoA changes. Those have to be put in
quotes since an aircraft (with the proper engine) can be flown upside
down and in other orientations.

I did notice the turning. The article is claiming that the upper
surface of the wing "turns" the upper flow.

Link: http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

I must admit that I am having problems with this explanation. It is
extremely vague? What is the turning? How, exactly, does the wing
"turn" the flow. The air is made up of molecules. If it is upper
surface of the wing that is turning does air molecules so that they
have a velocity component that is downward, how is this happening?
Since when, could one body, A, of any kind, that does not involve
gravitational or electrostatic fields, induce another body B, to move
in a direction that has a component vector that is aimed directly at
B?

Also NASA does not just explain why the longer length theory, the
Newtonian theory, and Bernoulli theories are incorrect, they also
elaborate what the correct equations to properly calculate observed lift
are, though I didn't see an example calculation. So they do say what is
correct, as well as what is not.- Hide quoted text -

True.

This "turning" theory of NASA makes me suspicious. If anyone else has
any qualtitative explanation of what they mean by the upper surface of
the wing foil turning the air so that it has a downward component in
its velocity, I would like to see it.

Finally, I do agree that the geometry, AoA, etc...interacts with the
atmospher in such a way that the net result of the flow on the top
surface of the wing is back and downward. What I don't see is the how
the wing itself is "turning" that flow.

-Le Chaud Lapin-

On Oct 7, 11:58 pm, Le Chaud Lapin wrote:
On Oct 7, 11:02 pm, flightoffancy wrote:
I did notice the turning. The article is claiming that the upper
surface of the wing "turns" the upper flow.

Link:http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

I must admit that I am having problems with this explanation. It is
extremely vague? What is the turning? How, exactly, does the wing
"turn" the flow. The air is made up of molecules. If it is upper
surface of the wing that is turning does air molecules so that they
have a velocity component that is downward, how is this happening?
Since when, could one body, A, of any kind, that does not involve
gravitational or electrostatic fields, induce another body B, to move
in a direction that has a component vector that is aimed directly at
B?

I just re-read the link above very carefully, and unless I am
mistaken, there is a *huge* amount of hand-waving going on here too.
Sigh.

"Turning" a flow? What would Newton say. It's magic.

Yes, we all know that F=ma, and "a" is the time derivative of
velocity, a = dv/dt, and that v has a magnitude and a direction, and
that if you change either magnitude or direction, you have a
force...that's all fine...

They do not specify how the wing turns the air. They show a picture
of air flowing backward on top of a sligtly-angled wing. Then they
write:

"For a body immersed in a moving fluid, the fluid remains in contact
with the surface of the body. If the body is shaped, moved, or
inclined in such a way as to produce a net deflection or turning of
the flow, the local velocity is changed in magnitude, direction, or
both. Changing the velocity creates a net force on the body. It is
very important to note that the turning of the fluid occurs because
the molecules of the fluid stay in contact with the solid body since
the molecules are free to move."

"the molecules stay in contact with the solid body"...?????????????

Why?

What incentive do the molecules have to stay in contact with the solid
body? Is there a sign on top of the wing that reads:

**** NOTE: ALL MOLECULES, YOU ARE HEREBY ORDERED TO STAY AS CLOSE TO
ME AS POSSIBLE. ****

Are there little molecule-sized pina coladas on top of the wing
waiting for the molecules to drink?

Even if there is a thin layer of air remaining in contact with the
wing for mysterious, magical reasons, what about the layers above it?
What incentive do those layers have "try and stay in contact with the
wing"?

-Le Chaud Lapin-

Le Chaud Lapin wrote:
"the molecules stay in contact with the solid body"...?????????????

Why?

It's what gases do. The particles are constantly bouncing away from each
other. This is pretty simple physics - something that should almost be
intuitive. If you have a cylinder of gas with an air-tight piston and pull
back on the piston and double the size of the volume do you seriously think
the gas will not expand into the other half as fast as it can to try and
stay in contact with the piston?

If you are having this much trouble on a basic concept of gases, then I see
no value in you or anyone else investing time in dealing with your
questions, which you chose to post to an inappropriate newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

"Jim Logajan" wrote

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

No, you need to stay away from discussions with MX, or Le chad, or
flightoffancy, who are all one and the same.

ANY discussion with them is an exercise in futility.

Just say no.
--
Jim in NC

On Oct 8, 1:37 am, Jim Logajan wrote:
Le Chaud Lapin wrote:

It's what gases do. The particles are constantly bouncing away from each
other. This is pretty simple physics - something that should almost be
intuitive. If you have a cylinder of gas with an air-tight piston and pull
back on the piston and double the size of the volume do you seriously think
the gas will not expand into the other half as fast as it can to try and
stay in contact with the piston?

The gas will stay in contact with the piston. But the gas will not
stay in contact because of the piston head. It will stay in contact
because of the fixed cylinder wall and the molecules of the gas
itself.

To take your example further, let us suppose that you pop the top of
the cylinder so that the fixed head is no longer present. Let
pressure on inside equalize to pressure on outside. Now pull the
piston head again to increase the volume. The gas will follow the
piston head, but not because of the piston head. It will follow
because of the pressure of the molecules in the air bombarding each
other, causes some of the molecules to race toward the moving piston
head.

In other words, the piston head is not capable of exerting a force on
the air molecules that is in the direction that you just moved the
piston head. In order for it to be able to do that, there would have
to be an attractive force between the piston head and the molecules
that follow it. But there is no attractive force. The gas expands
because of intermolecular bombardment, and because of richochet from
the cylinder walls.

So one can say that, if you increased the volume in the chamber by
moving the piston head downward, the piston head does not exert a
downward force on any molecule that hits it.

If you are having this much trouble on a basic concept of gases, then I see
no value in you or anyone else investing time in dealing with your
questions, which you chose to post to an inappropriate newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

No trouble at all.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 8, 1:37 am, Jim Logajan wrote:
Le Chaud Lapin wrote:

It's what gases do. The particles are constantly bouncing away from
each other. This is pretty simple physics - something that should
almost be intuitive. If you have a cylinder of gas with an air-tight
piston and pull back on the piston and double the size of the volume
do you seriously think the gas will not expand into the other half as
fast as it can to try and stay in contact with the piston?

The gas will stay in contact with the piston. But the gas will not
stay in contact because of the piston head. It will stay in contact
because of the fixed cylinder wall and the molecules of the gas
itself.

To take your example further, let us suppose that you pop the top of
the cylinder so that the fixed head is no longer present. Let
pressure on inside equalize to pressure on outside. Now pull the
piston head again to increase the volume. The gas will follow the
piston head, but not because of the piston head. It will follow
because of the pressure of the molecules in the air bombarding each
other, causes some of the molecules to race toward the moving piston
head.

In other words, the piston head is not capable of exerting a force on
the air molecules that is in the direction that you just moved the
piston head. In order for it to be able to do that, there would have
to be an attractive force between the piston head and the molecules
that follow it. But there is no attractive force. The gas expands
because of intermolecular bombardment, and because of richochet from
the cylinder walls.

So one can say that, if you increased the volume in the chamber by
moving the piston head downward, the piston head does not exert a
downward force on any molecule that hits it.

If you are having this much trouble on a basic concept of gases, then
I see no value in you or anyone else investing time in dealing with
your questions, which you chose to post to an inappropriate newsgroup
anyway.

Grumble. Now I recall why I had established a personal policy to stay
away from discussions of aerodynamics on this newsgroup: futility
avoidance.

No trouble at all.


"My point is that you should strive to keep your instructions simple and
to the point. The people that come to an instructor for training are not
in the least bit interested in leaning th emathemaical equation that
keeps the airplane in an inverted turn. there only concern should be in
how to use the controls to get it there"


Bertie

On Oct 8, 12:37 am, Jim Logajan wrote:
Le Chaud Lapin wrote:

"the molecules stay in contact with the solid body"...?????????????

Why?

It's what gases do. The particles are constantly bouncing away from each
other. This is pretty simple physics - something that should almost be
intuitive. If you have a cylinder of gas with an air-tight piston and pull
back on the piston and double the size of the volume do you seriously think
the gas will not expand into the other half as fast as it can to try and
stay in contact with the piston?

If you are having this much trouble on a basic concept of gases, then I see
no value in you or anyone else investing time in dealing with your
questions, which you chose to post to an inappropriate newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

I applaud. Very well put.

Dan

On Oct 8, 8:17 pm, wrote:
On Oct 8, 12:37 am, Jim Logajan wrote:





Le Chaud Lapin wrote:

"the molecules stay in contact with the solid body"...?????????????

Why?

It's what gases do. The particles are constantly bouncing away from each
other. This is pretty simple physics - something that should almost be
intuitive. If you have a cylinder of gas with an air-tight piston and pull
back on the piston and double the size of the volume do you seriously think
the gas will not expand into the other half as fast as it can to try and
stay in contact with the piston?

If you are having this much trouble on a basic concept of gases, then I see
no value in you or anyone else investing time in dealing with your
questions, which you chose to post to an inappropriate newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to stay away
from discussions of aerodynamics on this newsgroup: futility avoidance.

I applaud. Very well put.

Not well put.

What Jim is describing here and what I was refuting are two different
things.

Jim is describing why a fluid would have propensity to follow the
piston wall of an expanding cylinder chamber. I have never doubted
that reason the fluid follows the wall is because of intermolecular
bombardment, and with walls...etc.

That was not what I was refuting.

If you read carefully my post, you will see that I was refuting what
the article claims, which is that the fluid follows the piston because
the piston actually pulls on the molecules in the chamber, which, of
course, is ridiculous.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 8, 8:17 pm, wrote:
On Oct 8, 12:37 am, Jim Logajan wrote:





Le Chaud Lapin wrote:

"the molecules stay in contact with the solid
body"...?????????????

Why?

It's what gases do. The particles are constantly bouncing away from
each other. This is pretty simple physics - something that should
almost be intuitive. If you have a cylinder of gas with an
air-tight piston and pull back on the piston and double the size of
the volume do you seriously think the gas will not expand into the
other half as fast as it can to try and stay in contact with the
piston?

If you are having this much trouble on a basic concept of gases,
then I see no value in you or anyone else investing time in dealing
with your questions, which you chose to post to an inappropriate
newsgroup anyway.

Grumble. Now I recall why I had established a personal policy to
stay away from discussions of aerodynamics on this newsgroup:
futility avoidance.

I applaud. Very well put.

Not well put.

What Jim is describing here and what I was refuting are two different
things.

Yeh, he's telling you how it works and you're describing th einside of
your Skull, which apparently has just been set up for staging a tour of
"Fjukkwits on ice"


Bertie

Le Chaud Lapin writes:

"the molecules stay in contact with the solid body"...?????????????

Why?

Supposedly this is the Coanda effect at work, but there remains considerable
debate about this.