Backwash Causes Lift?

flightoffancy writes:

I don't deny those facts; but the greater the curve of the wing the more
the air pushes down behind the wing.

If that were so, then an airfoil with a half-circle for a cross-section would
produce enormous lift. In fact, this isn't the case.

Notice the smoke flow in the photo I link to below:

http://www.aa.washington.edu/uwal/uw.../tech%20guide%
20pics/smokeflowvis.gif

Granted it's at a high AoA. I'm just concluding what I have read about
wing curvature is consistent with what I see the smoke doing in the
picture.

But it would do the same thing with a flat airfoil.

The explanation of why wings with greater curve bend the air down more I
wouldn't want to say without studying aerodynamics more thoroughly.

A greater curve does not increase downwash, unless it also changes the
effective angle of attack. AOA is everything.

flightoffancy wrote:
I don't deny those facts; but the greater the curve of the wing the more
the air pushes down behind the wing.

I am assuming by "the air pushes down", you mean the air above the
wing, toward the back, not the air that is below the wing, toward the
back.

If that is the case, what is pushing the air?

-Le Chaud Lapin-

Le Chaud Lapin writes:

This true and not true. A wing does not necessarily have to push air
downward to cause lift.

Not correct. Air (or some other mass) must be accelerated downward in order
to produce the upward acceleration of lift. There is no way around this. And
so wings must accelerate air downward in order to produce lift.

An airplane can stay aloft if rarefication is somehow created above
the wing. This is what's happening with the blow-over-paper trick.

An airplane can stay aloft by accelerating something downward (typically air).
No rarefaction is required.

Note that, in the paper trick, the airspeed of the paper is 0, and,
for all practical purpurposes, the air beneath the paper has no idea
that you're blowing on top of the wing.

Note also that the paper isn't doing any significant lifting.

On Oct 7, 1:29 pm, Le Chaud Lapin wrote:
flightoffancy wrote:
I don't deny those facts; but the greater the curve of the wing the more
the air pushes down behind the wing.

I am assuming by "the air pushes down", you mean the air above the
wing, toward the back, not the air that is below the wing, toward the
back.

If that is the case, what is pushing the air?

-Le Chaud Lapin-

The wing is, of course. It's a single unit with two sides,
and if it deflects air downward the entire mass around the wing will
move downward. The raised static pressure under the wing and the
lowered static pressure atop it will both move it downward. You aren't
going to leave a void behind the wing. If you have to say that the
atmosphere above pushed it down, so be it --- but the net direction
was downward, the final position of that air was lower than before, so
displacement occurred and there was a reaction. A ship's rudder alters
the liquid flow over both sides of the rudder, and the water flows
into the low-pressure side and fills it, but the weight of water moved
times its velocity is the force applied to turn the ship.
Good picture of downwash:
http://www.physics.unlv.edu/~hilife/...s/downwash.jpg

Something in that picture you haven't mentioned yet at all,
maybe because your instructor hasn't dealt with it: those wingtip
vortices. Another whole are of complex aerodynamics. And a large
contributor to drag. Wing planform determines efficiency to a large
degree, but planform has to be adapted to the requirements of the
airplane.
Most instructors draw airflow over the wing from front to back,
but the increased pressure below and decreased pressure above alters
that. There are significant crossflows outward underneath, and inward
on top, with the angles at a minimum near the roots and max at the
tips, and minimum in cruise and max in slow flight.
I can hardly wait for the next argument after your next
groundschool class. It should take you a good 150 years to get a PPL
if you spend so much time nitpicking instead of studying and flying.

Dan

On Sun, 07 Oct 2007 17:25:03 GMT, wrote:


USENET is an electronic beer and bull**** session.

The starting quality of a USENET post and a B&BS depends on the quality
and number of the attendees.

Both essentially become babbling nonsense if carried on long enough.


That is the best description I've seen. G

flightoffancy wrote:
In article ,
says...

The air through the rotor disk of a gyrocopter flows upward, yet
gyrocopters fly.


I wrote "helicopter" -- not gyrocopter.

They are not aerodynamically the same.

I know what you wrote and I know they are not the same.

The point is that any theory that says an aircraft flys by forcing
air downward fails to explain how gyrocopters and gyroplanes fly.

Airplanes, helicopters, gyrocopters, and gyroplanes all fly in
level flight due to the lift produced by the wings and/or rotor blades.

--
Jim Pennino

Remove .spam.sux to reply.

Mxsmanic wrote:
Le Chaud Lapin writes:

This true and not true. A wing does not necessarily have to push air
downward to cause lift.

Not correct. Air (or some other mass) must be accelerated downward in order
to produce the upward acceleration of lift. There is no way around this. And
so wings must accelerate air downward in order to produce lift.

When in straight and level flight, the air flow through the rotor blades
of a gyrocopter is upward.


--
Jim Pennino

Remove .spam.sux to reply.

wrote:
flightoffancy wrote:
In article ,
says...
The air through the rotor disk of a gyrocopter flows upward, yet
gyrocopters fly.


I wrote "helicopter" -- not gyrocopter.

They are not aerodynamically the same.

I know what you wrote and I know they are not the same.

The point is that any theory that says an aircraft flys by forcing
air downward fails to explain how gyrocopters and gyroplanes fly.

How so? Just because the airflow is up through the gyro disk, doesn't
mean that the air isn't deflected downward by the passage of the rotor
disk. Did you ever notice how much AOA a gyro disk has? Think about
why this is?

Matt

flightoffancy wrote in news:MPG.2172e043702d7a5d989681
@news-server.hot.rr.com:

In article ,
says...

"Nope, wrong" to which claims I made?

I freely admit that my knowledge of aerodynamics is lacking. But I'm
absolutely correct about Lapin's training (or utter lack thereof, in
this case).

It's completely absurd for someone who has not studied aeronautical
engineering to stand up on a soap box and announce that the work of
several generations of aeronautical engineers is WRONG -- and that
he's
leading the charge to finding out what the facts of aerodynamics
really
are.

Lapin does this kind of thing on countless other news groups,
especially
computer science groups. He denounces decades worth of work as
inadequate or completely wrong, claims he has the right answer or
merely
wishes to find the right answer, with the result that nearly everyone
on
the group calls him a crank. Anyone who is really an expert in the
area
he's challenging quickly figures out his meager explorations of the
subject are not worth spending any time participating in.

Lapin believes that he is here to TEACH us.

If you can find hundreds of threads started by LCL on Google groups.
He's an incorrigible usenet troll.




The downwash thing is wrong. Yes, there is some dispacemtn of air that
causes lift, but it' only a minor contribution in the bigger scheme of
things.

Bertie

Mxsmanic wrote in
:

flightoffancy writes:

It's completely absurd for someone who has not studied aeronautical
engineering to stand up on a soap box and announce that the work of
several generations of aeronautical engineers is WRONG -- and that
he's leading the charge to finding out what the facts of aerodynamics
really are.

Most incorrect theories endure for centuries, and not mere
generations. That doesn't make them any less incorrect.


It does when they don't work.


Bertie