Backwash Causes Lift?

"Morgans" wrote in news:XaYMi.122$uc1.57
@newsfe12.lga:


"Bertie the Bunyip" wrote

It´s the main reason I´m here.

Remind me again. What is the main reason you're here?

I think I just told you.

Why do you feel the need to answer his posts?

Sport

Bertie

Dudley Henriques wrote in
:

TheSmokingGnu wrote:
Dudley Henriques wrote:
Crash Lander wrote:
I'd like to see what his thoughts are on String Theory.
LOL.

I'm sure he'd most likely say that twine was better :-))


What, and discount the obvious implications that Duct Tape has on
modern thinking?

TheSmokingGnu

Ah, duct tape!! Where would aviation be without it ?


Absolutely. Or speed tape if you go a bit faster.



Bertie

On Oct 3, 10:48 pm, wrote:
On Oct 3, 9:26 pm, TheSmokingGnu

wrote:
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.

And the other is the displacement of air downward.

By the bottom part of the wing, right?

Remember, when Newton was talking about the whole action/reaction
thing, he did not say you could arbitrarily define the sources of
forces. He was talking specifically about two objects, A and B, A
generating a force on B, and B generating a reciprocal force on A.

If you have compression under a wing do to extended flaps and laminar
friction of airflow, for example, then the lower surface of the wing
forces air downward, and the air beneath the lower surface forces wing
upward.

If you have have downwash above the wing, the downwash has to be due
to a force acting to move the air downward. I've argued that it is
effectively normal atmospheric pressure, acting against what
effectively becomes a partial vacuum generated by the forward
displacement of the wing, above the wing. Newton did not say that you
could arbitarily say, "Oh, there is some air moving downward, I'll
just pick a convenient reason arbitrarily."

Another way to look at this is to imagine a "level" wing with heavy
flap extension. Have an "air gorilla" move the entire wing forward, in
an abrupt motion, not given air anytime to redistributed. If this is
done, there will be compression beneath the wing, strong at the
boundary of compression, or in the flap pocket. Behind the win (above
it, but behind flaps), there will be ....

a huge void!

Now, if air is suddenly allowed to flow, yes indeed, there would be
downwash above the wing into the void, but the wing itself will not be
causing this downwash. It will be the pressure surrounding the void
causing the downwash. Since the source of movement of this air is not
the wing but the air above it, Newton's law cannot be used will-nilly
to say thay that there was some kind of action, so this must be the
reaction. You have to attribute the forces to their sources.

In this case, someone said Newtons law had to be use under penalty of
death, it would be simple:

Take a thin layer or air right at the boundary between the void and
ambient air. If another thin layer of ambient air pushes against this
thin layer, the thin layer will will push back against the ambient
thin layer. This is reciprocity of forces. The reason that the first
thin layer "loses" the pushing battle is because there nothing to
oppose the first thin layer as it moves into the void. The molecules
of the second thin layer has its friends to contend with. After the
first thin layer has moved into the void, those molecules can no
longer participate in pushing at the ambient air (because they have
assumed new position in space - neither air nor people are
telekinetic) and thus we get air flow.

Of course, there are not layers, but a distribution of momentum of the
particles, but this is close enough.

So in summary, downwash cause by high ambient pressure confronting a
void must not be used to contribute to lifting force of the wing. One
_can_ say that the pressure under the wing see no opposing force in
the relative void above the wing does result in net upward force.

-Le Chaud Lapin-

Bertie the Bunyip wrote:
Dudley Henriques wrote in
:

TheSmokingGnu wrote:
Dudley Henriques wrote:
Crash Lander wrote:
I'd like to see what his thoughts are on String Theory.
LOL.

I'm sure he'd most likely say that twine was better :-))

What, and discount the obvious implications that Duct Tape has on
modern thinking?

TheSmokingGnu
Ah, duct tape!! Where would aviation be without it ?


Absolutely. Or speed tape if you go a bit faster.



Bertie


NASCAR!!!! Great folks!
D

--
Dudley Henriques

TheSmokingGnu wrote:


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).

Think "Relative Wind". Then rethink negative AOA.

Still waiting for the conservation of momentum derivation. My husband,
also trained as an engineer, casually remarked he didn't think you
could get from Newton's First Law to the that confirms my memory,
but we are both willing to have that belief rebutted.

He also pointed out that how a CFI might explain how a VOR works would
not satisfy an engineer. For that matter, the physics of flight as
explained to a student pilot would not satisfy someone who might be
interested in designing, as opposed to flying, an airplane, but I
don't think the manuals you are looking at are in error. I would point
out that each field has its own language, and you denying the
conventions used in aviation -- drag, lift and so on -- demonstrates
an unbecoming trait for a student, and even a worse one for an
employee. You may want to rething that attitude if you use it in real
life.






On Oct 3, 11:14 pm, Le Chaud Lapin wrote:
On Oct 3, 8:38 pm, Tina wrote:

"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.

Hmm...I was afraid you would say that.

A non-hand-waving explanation would too close to the quantum, and
so...it's a bit much to discuss, at least right now. I've posted more
messages in this thread in small period of time than I have ever for
any other topic, in the history of using USENET, or...as one might
say, dN/dt 0, where N is number of messages.

-Le Chaud Lapin-

Crash Lander writes:

I'd like to see what his thoughts are on String Theory.

String theory is a theory based on math rather than physical reality.

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 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.

TheSmokingGnu writes:

Then why do wings generate lift at negative AOA?

They don't. That's a very common misconception, even among pilots.

The effective AOA is always positive when the wing is generating lift.