Backwash Causes Lift?

Bertie the Bunyip wrote:
wrote in :

Bertie the Bunyip wrote:
"Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in
:

How does a gyrocopter fly because the airflow over it's "wing" is
going up.




They're gliders. The same rules apply.


Bertie

I agree the same rules apply, but they aren't gliders unless the
engine craps out.


Fair enough, but the wing is behaving in exactly the same way.

Bertie

Of course.


--
Jim Pennino

Remove .spam.sux to reply.

Jim Logajan wrote:
wrote:
Mxsmanic wrote:
How do you accelerate an aircraft without accelerating
anything downward?
[ ... ]
An aircraft in straight and level flight is not accelerated.

Cute - classic Usenet response. Simultaneously correct, but not really
addressing the original issue.

The point is that talking about aircraft acceleration in straight and
level flight when discussing lift is irrelevant as the aircraft is
not accelerating.


--
Jim Pennino

Remove .spam.sux to reply.

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-

flightoffancy wrote:
In article ,
says...
Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis
sayonara, Good lucko,

NASA doesn't agree with you.

Not knowing what your qualifications are I'll favor NASA's explanation
of a combination of Newtonian / Bernoulli as described in part by
Euler's equations, the idea being that the airfoil turns the airflow to
generate lift. NASA's done a lot of experiments & measurements and have
a long publication history dating back to the NACA days let alone an
astonishing track record in flying high and low performance aircraft.

I don't think there's any single person out there that can beat the
combined knowledge of NASA's decades of experience.

NASA doesn't say or even imply that Bernoulli and Newton COMBINE to
create lift because they don't combine to create a total. Each is a
complete explanation and can stand alone one without the other, which
BTW is exactly what NASA says.
DH

--
Dudley Henriques

flightoffancy wrote in news:MPG.217387a97cce62d3989691
@news-server.hot.rr.com:

In article ,
says...

Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis
sayonara, Good lucko,

NASA doesn't agree with you.


They do, actually.


Not knowing what your qualifications are I'll favor NASA's explanation
of a combination of Newtonian / Bernoulli as described in part by
Euler's equations, the idea being that the airfoil turns the airflow to
generate lift. NASA's done a lot of experiments & measurements and have
a long publication history dating back to the NACA days let alone an
astonishing track record in flying high and low performance aircraft.

I don't think there's any single person out there that can beat the
combined knowledge of NASA's decades of experience.




I don't think so either.



Bertie

Dudley Henriques wrote in
:

flightoffancy wrote:
In article ,
says...
Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis
sayonara, Good lucko,

NASA doesn't agree with you.

Not knowing what your qualifications are I'll favor NASA's explanation
of a combination of Newtonian / Bernoulli as described in part by
Euler's equations, the idea being that the airfoil turns the airflow to
generate lift. NASA's done a lot of experiments & measurements and have
a long publication history dating back to the NACA days let alone an
astonishing track record in flying high and low performance aircraft.

I don't think there's any single person out there that can beat the
combined knowledge of NASA's decades of experience.

NASA doesn't say or even imply that Bernoulli and Newton COMBINE to
create lift because they don't combine to create a total. Each is a
complete explanation and can stand alone one without the other, which
BTW is exactly what NASA says.


Yep


Bertie

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, 11:38 am, Phil wrote:

First, I would like to point out that your post is interesting because
it implies at first something which I disagree with, but then at the
very end of the post, what you say is exactly true.

Let me try to explain:

If the airflow on top of the wing doesn't contribute to lift, then how
can we explain the phenomenon of the wing stalling? When the wing
stalls, it is the airflow over the top of the wing that detaches from
the curve of the wing and becomes turbulent. This causes a radical
loss of lift. To me, this indicates that the airflow over the top of
the wing plays an essential role in providing lift.

What I am saying is that Newton's law is not at play with downwash,
not in the "uppper surface of wing pull down on molecules" sense. Yes,
there is downwash. Yes, the camber of the wing will influence the net
force exerted on the wing. Yes, there will be stalling, turbulence,
etc. all these things will happen.

The key here is that the air molecules that are above the wing cannot
be pulled down by the wing more can they pull up on the wing. Those
air molecules can only causes the lateral forces of friction (laminar
drag), and a perpendicular downward force on the wing which aircraft
designers obviously want to keep from happening.

I know the Bernoulli effect has been invoked historically to (at least
partially) explain the lift produced by the top surface of a wing. I
think another way to look at it is the Coanda effect (http://en.wikipedia.org/wiki/Coand%C4%83_effect). The airflow tends
to follow the curve of the top of the wing, and is displaced
downward. As long as the air flow follows the curve faithfully, you
have good lift. When the airflow detaches in a stall, you lose most
of your lift. This top surface lift is combined with the downward
displacement of air by the bottom of the wing. The wing is
essentially throwing air downward using both the top and bottom
surfaces. This is why a curved wing is a better lift producer than a
simple flat wing. The top surface curve helps contribute to the lift.

I agree that air is being thrown downward by the bottom surface. I do
not think a top surfaces throws air downward. Even this Coanda effect
says that contact, at least initially, is caused by a pressure
differential. From your link above:

"As a gas flows over an airfoil, the gas is drawn down to adhere to
the airfoil by a combination of the greater pressure above the gas
flow and the lower pressure below the flow caused by an evacuating
effect of the flow itself, which as a result of shear, entrains the
slow-moving fluid trapped between the flow and the down-stream end of
the upper surface of the airfoil. The effect of a spoon apparently
attracting a flow of water is caused by this effect as well, since the
flow of water entrains gases to flow down along the stream, and these
gases are then pulled, along with the flow of water, in towards the
spoon, as a result of the pressure differential. Supersonic flows have
a different response."

"greater pressure above the gas flow and the lower pressure below the
flow caused by an evacuating effect..."

This is what I keep saying. I have been using the words "rarefication
and rarefaction" and instead of "evacuating effect", but this is
essentially what I mean.

Now, how does the wing feel the lift? It feels high pressure on its
bottom surface, and it feels low pressure on its upper surface. It is
pushed up from below, and sucked up from above. That is how the
airplane experiences the effects of the downward displacement of air.

I agree with the downward force. I do not agree that there is a
sucking force above, any more than I agree that there is a sucking
force when a purpose sucks on a straw.

Given that the bottom surfaces of the wing is already 14.7lbs/in^2,
one simply needs to reduce the pressure above the wing to cause lift.
This is what I tried to illustrate with my two-pieces-of-paper-
superposed demonstration.

But in many cases the bottom surface has even more than 14.7lbs/^2.

-Le Chaud Lapin-

On Oct 8, 12:32 pm, Phil wrote:
There isn't any debate about what a wing stall is, and what causes
it. It has been well-explored in wind tunnel testing. The phenomenon
of wing stall is real-world evidence that the top surface of the wing
is a large contributor to lift. The Bernoulli effect and the
associated Coanda effect are well-understood scientific phenomena.
They explain how the curved top surface of the wing displaces air
downward. Unless someone can come up with a better explanation for
the fact that wing stall destroys lift, I think the only debate is by
people who are determined to ignore the scientific evidence.
On Oct 8, 12:32 pm, Phil wrote:
On Oct 8, 11:46 am, Mxsmanic wrote:
There isn't any debate about what a wing stall is, and what causes
it. It has been well-explored in wind tunnel testing. The phenomenon
of wing stall is real-world evidence that the top surface of the wing
is a large contributor to lift. The Bernoulli effect and the
associated Coanda effect are well-understood scientific phenomena.
They explain how the curved top surface of the wing displaces air
downward. Unless someone can come up with a better explanation for
the fact that wing stall destroys lift, I think the only debate is by
people who are determined to ignore the scientific evidence.

What's wrong with the supposition that, all other things being equal,
the configuration of the fluid in a smooth stream results in less
pressure on the upper surface than the configuration of the fluid in
turbulence?

In other words, one could argue that the fluid above the wing, during
streaming (sorry for terminology), no longer exerts its full 14.7lbs/
in^2, but during a stall, even though there is still is some reduction
from the full 14.7lbs/in^2, the reduction is not as complete as it
would have been had there been a nice stream...

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 8, 11:38 am, Phil wrote:

First, I would like to point out that your post is interesting because
it implies at first something which I disagree with, but then at the
very end of the post, what you say is exactly true.

Let me try to explain:

If the airflow on top of the wing doesn't contribute to lift, then
how can we explain the phenomenon of the wing stalling? When the
wing stalls, it is the airflow over the top of the wing that detaches
from the curve of the wing and becomes turbulent. This causes a
radical loss of lift. To me, this indicates that the airflow over
the top of the wing plays an essential role in providing lift.

What I am saying is that Newton's law is not at play with downwash,
not in the "uppper surface of wing pull down on molecules" sense. Yes,
there is downwash. Yes, the camber of the wing will influence the net
force exerted on the wing. Yes, there will be stalling, turbulence,
etc. all these things will happen.

The key here is that the air molecules that are above the wing cannot
be pulled down by the wing more can they pull up on the wing. Those
air molecules can only causes the lateral forces of friction (laminar
drag), and a perpendicular downward force on the wing which aircraft
designers obviously want to keep from happening.

I know the Bernoulli effect has been invoked historically to (at
least partially) explain the lift produced by the top surface of a
wing. I think another way to look at it is the Coanda effect
(http://en.wikipedia.org/wiki/Coand%C4%83_effect). The airflow tends
to follow the curve of the top of the wing, and is displaced
downward. As long as the air flow follows the curve faithfully, you
have good lift. When the airflow detaches in a stall, you lose most
of your lift. This top surface lift is combined with the downward
displacement of air by the bottom of the wing. The wing is
essentially throwing air downward using both the top and bottom
surfaces. This is why a curved wing is a better lift producer than a
simple flat wing. The top surface curve helps contribute to the
lift.

I agree that air is being thrown downward by the bottom surface. I do
not think a top surfaces throws air downward. Even this Coanda effect
says that contact, at least initially, is caused by a pressure
differential. From your link above:

"As a gas flows over an airfoil, the gas is drawn down to adhere to
the airfoil by a combination of the greater pressure above the gas
flow and the lower pressure below the flow caused by an evacuating
effect of the flow itself, which as a result of shear, entrains the
slow-moving fluid trapped between the flow and the down-stream end of
the upper surface of the airfoil. The effect of a spoon apparently
attracting a flow of water is caused by this effect as well, since the
flow of water entrains gases to flow down along the stream, and these
gases are then pulled, along with the flow of water, in towards the
spoon, as a result of the pressure differential. Supersonic flows have
a different response."

"greater pressure above the gas flow and the lower pressure below the
flow caused by an evacuating effect..."

This is what I keep saying. I have been using the words "rarefication
and rarefaction" and instead of "evacuating effect", but this is
essentially what I mean.

Now, how does the wing feel the lift? It feels high pressure on its
bottom surface, and it feels low pressure on its upper surface. It
is pushed up from below, and sucked up from above. That is how the
airplane experiences the effects of the downward displacement of air.

I agree with the downward force. I do not agree that there is a
sucking force above, any more than I agree that there is a sucking
force when a purpose sucks on a straw.

Given that the bottom surfaces of the wing is already 14.7lbs/in^2,
one simply needs to reduce the pressure above the wing to cause lift.
This is what I tried to illustrate with my two-pieces-of-paper-
superposed demonstration.

But in many cases the bottom surface has even more than 14.7lbs/^2.



Meanwhile your airplane is tearing along and you don't have a notion
what to do with it.



Bertie