Backwash Causes Lift?

On 3 Oct, 13:27, "BDS" wrote:
"Mxsmanic" wrote

Le Chaud Lapin writes:

What is the definition of a stall anyway?

An abrupt loss of lift.

Son, for someone who continually chastises the pilots here for their lack of
knowledge, you sure can come up with some doozies yourself!


Actually, it's correct, but only because he read it off wickepedia or
something.

It's not like he'd actually ever DO a stall.


Bertie

On 3 Oct, 05:54, Mxsmanic wrote:
Dan Luke writes:
Then why does the wing stall and cease lifting when flow separates from the
upper surface?

Because it is no longer accelerating air efficiently downward.

Wrong again, fjukktard.


Bertei

On 3 Oct, 22:33, Mxsmanic wrote:
Le Chaud Lapin writes:
Also, if you don't mind, I would like to understand what you mean
here.

You can only push the wing upward if something else is pushed downward. Thus,
the wing generates lift only to the extent that it diverts a substantial mass
(of air) downward. No downwash, no lift.



Nope.

Wrong again, fjukkwit.

Of course, it doesn't matter sionc eyou will never fly and your
sockpuppet there won't either.


Bertie

jimp wrote

I think the main issue is that it doesn't require a Phd in physics to
fly an airplane and the explanations of lift, stall, drag, etc.
for pilots tend to be highly simplified, and rightfully so.

A full explanation that would satisfy a physisicist would likely
cause exterme eye glaze in the average pilot.

If one want's that level of insight, I would suggest they go read
a good aerodynamics text and not expect to find it in a couple of
paragraphs in a USENET posting.

Exactly.

To learn to fly, it is important to understand aerodynamics to the point of
knowing what you can do to mess them up, and what you can do to fix things.
Only the most basic understanding of the subject is needed to achieve these
goals.
--
Jim in NC

On 3 Oct, 22:26, John Godwin wrote:
Bertie the Bunyip wrote roups.com:

Ah, a cluelessness vaguely remiscent of someone else I may have seen
around here.

Bertie

I wonder if Mx is really Bobo in sheep's clothing.



Nah. just as k00ky, different style.

Anthony needs something a little different from Bobo and Bertie will
provide..

BTW, if you feel the urge to harass bobo, you can still find him in
alt.security .alar,s, where he still causes just as much trouble as he
ever did. I pop in and pull his chain every once in a while.


Bertie


Bertie

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.

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.

-Le Chaud Lapin-

Le Chaud Lapin wrote:

Both you and Mxmanic are wrong.

-Le Chaud Lapin-

ooooo.....wait for it.....here it comes....

--
Message posted via http://www.aviationkb.com

On Oct 3, 4:04 pm, Le Chaud Lapin wrote:

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.


So, if it has nothing to do with Bernoulli, what has it to do
with lift? With tables and straws and the like we're talking static,
not dynamic pressures. The airplane uses dynamic AND static
pressures.
In cruise flight (low AOA), I would expect a reduced pressure
on the bottom of the wing, though not as low as on the top. The
velocity of air across the bottom will drop its pressure, there, too.
Air has mass. Anytime you try to push it out of the way,
there will be some reaction. Newton says so. We know this as drag.
But we also know it as lift reaction. A flat plate flying
through the air at some tiny angle of attack doesn't have much faster
air over the top than the bottom, if any difference at all, yet it
will generate plenty of lift. Try this on, if you want to think
outside the box: The airfoil we know is just that: a foil (device to
deceive) to trick the air into flowing over it without breaking up at
much higher angles of attack than a flat plate would let us. So the
leading edge has to have some radius so the air can get around the
corner from the natural stagnation point under the LE at high AOA, and
that curve must gradually taper off toward the rear or the now-
disturbed air would want to separate and turbulate, and if it did that
it would then slow down dramatically, pressure would rise and lift
would decrease. But, happily, Newton is still at work underneath so
the airplane falls, but not as if the wings fell off. We're still
moving forward and the wing is still shoving air out of the way
downward, so lift is still generated.

Dan

"Morgans" wrote

It goes something like this.

An airplane is about to takeoff on a runway, that is really a treadmill; a
very expensive treadmill.

The treadmill senses the airplane's speed, and matches the aircraft's
speed, with speed increases of its own.

Can the airplane takeoff? Why or why not?

I forgot one important qualifier of the treadmill's operation.

It goes in the opposite direction of the intended direction of travel for
the airplane.
--
Jim in NC

On Oct 3, 5:56 pm, wrote:
So, if it has nothing to do with Bernoulli, what has it to do
with lift?

You can have lift of an object with no Bernoulli. It's simple vector
addition.

With tables and straws and the like we're talking static,
not dynamic pressures. The airplane uses dynamic AND static
pressures.

Right.

In cruise flight (low AOA), I would expect a reduced pressure
on the bottom of the wing, though not as low as on the top. The
velocity of air across the bottom will drop its pressure, there, too.

Right. The AOA matters here. Angle the wing up any significant amount,
and over-pressure will build under the wing.

Air has mass. Anytime you try to push it out of the way,
there will be some reaction. Newton says so. We know this as drag.

Hmm...ok, sure. I wouldn't call that drag necessarily. That's like
saying that a hydraulic piston assembly has drag. I more prefer to
think of drag as laminar fricitional forces of the fluid. Pushing out
of way implies that plane doing the pushing is perpendicular to the
direction in which pushing is being done (which is true at leading
edge of wing). But I guess this is acceptable.

But we also know it as lift reaction. A flat plate flying
through the air at some tiny angle of attack doesn't have much faster
air over the top than the bottom, if any difference at all, yet it
will generate plenty of lift. Try this on, if you want to think
outside the box:

Thinking outside the box is what lead me to refuse to accept hand-
waving explanations of aerodynamics from CFI's.

The airfoil we know is just that: a foil (device to
deceive) to trick the air into flowing over it without breaking up at
much higher angles of attack than a flat plate would let us. So the
leading edge has to have some radius so the air can get around the
corner from the natural stagnation point under the LE at high AOA, and
that curve must gradually taper off toward the rear or the now-
disturbed air would want to separate and turbulate, and if it did that
it would then slow down dramatically, pressure would rise and lift
would decrease. But, happily, Newton is still at work underneath so
the airplane falls, but not as if the wings fell off. We're still
moving forward and the wing is still shoving air out of the way
downward, so lift is still generated.

Yes this is true, but the explanation in the Jeppensen book is wrong.
it defines downwash:

downwash: - "the downward deflection of the airstream as it passes
over the wing and past the trailing edge"

It goes on to say:

"According to Bernoulli's principle, the increase in speed of air on
top of an airfoil profdues a drop in pressure and this lowered
pressure is a component of lift."

Ok, we really know that the lift results from what's under the wing no
longer being balanced out, but I won't nit-pick this explanation.

Next paragraph it says:

"In addtion to the lowered pressure, a downwar-backward flow of air is
also generated from the top surface of the wing. The reaction to this
downwash results in an upward force on the wing which demnstrates
Newton's third law of motion."

This is plane false. That is *NOT* what Newton said. Newton did not
say you could take any action and willy-nilly find what you think is
the reaction, and say, "Hey, this looks good, let's use this."

Newtons law, in fact, is better stated as reciprocity of force, IMO.
This says that, if you take two objects, one apply force to the other,
the other, by reciprocity, must appy an opposite force against the
first.

Newton's law, conbine with F=ma, also yields the notion of
conservation of momentum.

But getting back to Jeppensen, the downwash, if they mean what's
happening on the top surface of the wing, is *not* contributing to
lift. Note that they say "results in", but don't explain how. This
seems to be typical of books of flight dynamics.

I'd like to point something else out regarding Bernouilli's principle.

I haven't tried, but I suspect that I could build a contraption that
consists of surface where the velocity of air above the surface is
much higher than that below, but the pressure above the surface is
higher.

-Le Chaud Lapin-