Backwash Causes Lift?

Matt Whiting wrote in news:5VxOi.240$2n4.17124
@news1.epix.net:

Bertie the Bunyip wrote:
Mxsmanic wrote in
:

writes:

There is nothing after leaving the rotor disk to change the direction
of air flow.

The airplane, helicopter, gyrocopter, and gyroplane all fly straight
and level for the same reason and it isn't air being deflected
downward.
No heavier-than-air aircraft flies without deflecting air downward,


Yes, they can, and do.

Dynamic lift is usually at play but is by no means required.

Examples where it isn't required???


When t's enough.

Bertie

Le Chaud Lapin wrote in
ps.com:

On Oct 8, 4:14 pm, Phil wrote:
On Oct 8, 3:46 pm, Le Chaud Lapin wrote:

On Oct 8, 2:45 pm, Phil wrote:

Then how do you explain what happens when a wing stalls? When a
wing reaches a high enough angle of attack to stall, the bottom
surface is still deflecting air downward. Yet when the airflow
over the top of the wing detaches and becomes turbulent, most of
the lift of the wing is destroyed. If the attached airflow over
the top of the wing is not generating lift, then why does the
lift disappear when that airflow detaches?

Because the turbulent air on top of a wing during a stall pushes
down on the wing harder than does when the airflow non-turbulent.

-Le Chaud Lapin-

Do you know of any research that supports that theory?

Well, no, it's only speculation.

You might be asking how one could speculate on something so complex,
and the only answer i can give is that everything that I have
speculated about does not seem complex at all. I have only used high
school physics so far. It could be that I am wrong of course, but I
do understand Newton's theory of reciprocity of force.

There is another way to look at the air-over-the-wing-does-not-pull-up
on the wing point of view:

Take a wing, and one single diatomic molecule, say nitrogen, N2.

Put your N2 on top of the wing. Someone will offer to pay you
$1,000,000US, if you can use that N2 molecule to impart a force on the
wing to get the wing to move upward. You can throw the molecule at
the wing as hard as you want. You can drag it side ways. The only
requirement is that you have to keep the molecule in the region above
the wing. You will probably not get the prize.

But, if someone ask you to cause the net lift on the wing to increase
by manipulating the molecule, you might ask:

You: "Must I still impart a force upon the top surface of the wing?"
Challenger: "No, that stipulation has been removed."
You: "Is there already air pressure beneath the wing?"
Challenger: "Yes"
You: "Well, this is easily. I take my N2 molecule and put it in my
pocket. Done."

The net change in lift would be so small, it would be immeasurable by
any equipment we have, but the net lift would increase.

This is the process that is happening with a wing in flight. The air
molecules above the wing, by virtue virtue of a process that is
heavily influence by both the aerodynamics of the leading eade and the
camber of the wing going backwards, has a reduced rate-of-impartation
of their momentum against the top of the wing.

Naturally, the impartations are completely removed, then, assuming
quasi-static conditions under the wing, standard atomosphere would
generate 14.7lbs/in ^ 2. The net lift on the wing would be found by:

(14.7 lbs/in^2 * area-under-the-wing) - (average-pressure-above-wing *
area-above-wing)

In still air, the average-pressure above the wing is the same as the
average-pressure below the wing. That's why a wing that is in still
air, perhaps supspended off the ground by thin steel wires for
dramatic effect, will be neither inclined to move upward nor downward,
because the force on both top and bottom are equal.

In steady-state, pure-stream flow, the pressure above the wing will be
reduced. Ane experimentalist might have unrealistic expectations that
they are going to eliminate the entire 14.7 lbs/in on top of the wing,
so that they get a glorious net pressure of 14.7lbs from the bottom of
the wing, when this is obviously not the case. You can see this by
doing some simple cacluations with a Cessna Centurion 210.

http://www.airliners.net/info/stats.main?id=148

From the link above, this aircraft has a wing area of 175.5 square
feet. We know that at STP, the pressure is 14.7 lbs/in^2. Since
there are 144 square inches in a square foot, the pressure on 175.5 sq
ft sheet of whatever is...

175.5 sq-ft * 144 sq-inches/sq-ft * 14.7lbs/sq-inch = 371,498 lbs.

But the max takeoff weight of this aircraft is only 3800 lbs.

With so much potential for lift, why such a measly 3800lbs (assuming
structural capacity not breached)?


It's that, during flight, at no time will all the pressure on top of
the wing be removed. One can only hope, in the best of situations, to
remove some of it. The pressure goes from two extremes:

1. One the ground, no pressure is removed, wing has no reason to go up
or down, because it is same on top and bottom.
2. Optimum lift situation, maximum pressure is removed. [You can
almost calculate this pressure, in ounces / in^2, based on weight in
flight]

In between 1 and 2 is the situation of turbulence. This situation is
not "as bad" as no-movement-on-the-ground (no pressure removed), and
it is not as good as optimum-flight-maximum-depletion-above-wing-in-
effect. It is somewhere in between.

-Le Chaud Lapin-




Well, thank god you'll never fly.


Ever


Bertie

writes:

If the vertical postion of an aircraft is constant, i.e. straight and
level flight, the first derivative of the vertical position is zero and
hence the second derivative is also zero.

Gravity is constantly trying to accelerate an aircraft downwards; something
else has to compensate for this, or it will descend.

An aircraft in straight and level flight is not accelerated.

Because a force is being applied to it that exactly counters gravity. Whence
comes this force?

On Oct 8, 5:08 pm, Le Chaud Lapin wrote:
On Oct 8, 4:14 pm, Phil wrote:





On Oct 8, 3:46 pm, Le Chaud Lapin wrote:

On Oct 8, 2:45 pm, Phil wrote:

Then how do you explain what happens when a wing stalls? When a wing
reaches a high enough angle of attack to stall, the bottom surface is
still deflecting air downward. Yet when the airflow over the top of
the wing detaches and becomes turbulent, most of the lift of the wing
is destroyed. If the attached airflow over the top of the wing is not
generating lift, then why does the lift disappear when that airflow
detaches?

Because the turbulent air on top of a wing during a stall pushes down
on the wing harder than does when the airflow non-turbulent.

-Le Chaud Lapin-

Do you know of any research that supports that theory?

Well, no, it's only speculation.

You might be asking how one could speculate on something so complex,
and the only answer i can give is that everything that I have
speculated about does not seem complex at all. I have only used high
school physics so far. It could be that I am wrong of course, but I
do understand Newton's theory of reciprocity of force.

There is another way to look at the air-over-the-wing-does-not-pull-up
on the wing point of view:

Take a wing, and one single diatomic molecule, say nitrogen, N2.

Put your N2 on top of the wing. Someone will offer to pay you
$1,000,000US, if you can use that N2 molecule to impart a force on the
wing to get the wing to move upward. You can throw the molecule at
the wing as hard as you want. You can drag it side ways. The only
requirement is that you have to keep the molecule in the region above
the wing. You will probably not get the prize.

But, if someone ask you to cause the net lift on the wing to increase
by manipulating the molecule, you might ask:

You: "Must I still impart a force upon the top surface of the wing?"
Challenger: "No, that stipulation has been removed."
You: "Is there already air pressure beneath the wing?"
Challenger: "Yes"
You: "Well, this is easily. I take my N2 molecule and put it in my
pocket. Done."

The net change in lift would be so small, it would be immeasurable by
any equipment we have, but the net lift would increase.

This is the process that is happening with a wing in flight. The air
molecules above the wing, by virtue virtue of a process that is
heavily influence by both the aerodynamics of the leading eade and the
camber of the wing going backwards, has a reduced rate-of-impartation
of their momentum against the top of the wing.

Naturally, the impartations are completely removed, then, assuming
quasi-static conditions under the wing, standard atomosphere would
generate 14.7lbs/in ^ 2. The net lift on the wing would be found by:

(14.7 lbs/in^2 * area-under-the-wing) - (average-pressure-above-wing *
area-above-wing)

In still air, the average-pressure above the wing is the same as the
average-pressure below the wing. That's why a wing that is in still
air, perhaps supspended off the ground by thin steel wires for
dramatic effect, will be neither inclined to move upward nor downward,
because the force on both top and bottom are equal.

In steady-state, pure-stream flow, the pressure above the wing will be
reduced. Ane experimentalist might have unrealistic expectations that
they are going to eliminate the entire 14.7 lbs/in on top of the wing,
so that they get a glorious net pressure of 14.7lbs from the bottom of
the wing, when this is obviously not the case. You can see this by
doing some simple cacluations with a Cessna Centurion 210.

http://www.airliners.net/info/stats.main?id=148

From the link above, this aircraft has a wing area of 175.5 square

feet. We know that at STP, the pressure is 14.7 lbs/in^2. Since
there are 144 square inches in a square foot, the pressure on 175.5 sq
ft sheet of whatever is...

175.5 sq-ft * 144 sq-inches/sq-ft * 14.7lbs/sq-inch = 371,498 lbs.

But the max takeoff weight of this aircraft is only 3800 lbs.

With so much potential for lift, why such a measly 3800lbs (assuming
structural capacity not breached)?

It's that, during flight, at no time will all the pressure on top of
the wing be removed. One can only hope, in the best of situations, to
remove some of it. The pressure goes from two extremes:

1. One the ground, no pressure is removed, wing has no reason to go up
or down, because it is same on top and bottom.
2. Optimum lift situation, maximum pressure is removed. [You can
almost calculate this pressure, in ounces / in^2, based on weight in
flight]

In between 1 and 2 is the situation of turbulence. This situation is
not "as bad" as no-movement-on-the-ground (no pressure removed), and
it is not as good as optimum-flight-maximum-depletion-above-wing-in-
effect. It is somewhere in between.

-Le Chaud Lapin-- Hide quoted text -

- Show quoted text -

I think you are really describing Bernoulli. If you agree that the
pressure on the top of the wing is lowered by the wing's progress
through the air, then that is just what Bernoulli suggests. If you
don't like the concept that the top of the wing is being sucked upward
by that lower pressure, then think of it this way. Imagine a cross-
section of the wing. The top surface of the wing forms a line. The
air just above this line has lower pressure. The air below this line
(inside the wing) has normal pressure. So the air below the line is
pressing upward against it with more force than the air above is
pressing down. This is lift, and since the upper surface of the wing
is attached to the ribs and spars, this lift is imparted to the
airplane.

Phil

Mxsmanic wrote in
:

writes:

If the vertical postion of an aircraft is constant, i.e. straight and
level flight, the first derivative of the vertical position is zero
and hence the second derivative is also zero.

Gravity is constantly trying to accelerate an aircraft downwards;
something else has to compensate for this, or it will descend.

An aircraft in straight and level flight is not accelerated.

Because a force is being applied to it that exactly counters gravity.
Whence comes this force?




From somewhere that's waaaaay beyond you , obviously.


Bertie

Matt Whiting writes:

Examples where it isn't required???

On the ground? Or immediately following any flight into terrain?

Mxsmanic wrote:
writes:

If the vertical postion of an aircraft is constant, i.e. straight and
level flight, the first derivative of the vertical position is zero and
hence the second derivative is also zero.

Gravity is constantly trying to accelerate an aircraft downwards; something
else has to compensate for this, or it will descend.

Your original statement:

"How do you accelerate an aircraft without accelerating anything downward?"

Go get a high school physics text and look up the difference between force
and acceleration.

An aircraft in straight and level flight is not accelerated.

Because a force is being applied to it that exactly counters gravity. Whence
comes this force?

Lift, obviously.

--
Jim Pennino

Remove .spam.sux to reply.

Mxsmanic wrote in
:

Matt Whiting writes:

Examples where it isn't required???

On the ground? Or immediately following any flight into terrain?


Way beyond you but if you send me $400 I'll tell you how.

You won't understand it of course.


Bertie

"Bertie the Bunyip" wrote

Well, thank god you'll never fly.

Can you make him go fast, yet? Please, pretty please? I want you to put
the pedal to the metal, now. I really want to see him going fast! g
--
Jim in NC

On Oct 8, 5:18 pm, Phil wrote:
I think you are really describing Bernoulli. If you agree that the
pressure on the top of the wing is lowered by the wing's progress
through the air, then that is just what Bernoulli suggests.

This is true...but even if you do, there seems to be a lot of people
who do not realize the implications of what you just wrote. Yes it's
Bernoulli, but the Bernoulli that is taking place has nothing to do
with the Bernoulli that is being described in flight education texts.
And no it is not a matter of style, or equivalent models that are
interchangeable, or anything like that. There is a fundamental
difference in perception going on.

If you
don't like the concept that the top of the wing is being sucked upward
by that lower pressure

It is not a matter of whether I like it or not. It is something that
simply does not happen. There is no sucking force.

then think of it this way. Imagine a cross-
section of the wing. The top surface of the wing forms a line. The
air just above this line has lower pressure. The air below this line
(inside the wing) has normal pressure.

So the air below the line is
pressing upward against it with more force than the air above is
pressing down.

Right...I have been saying this all along. Then the net force on the
wing is upward.

This is lift, and since the upper surface of the wing
is attached to the ribs and spars, this lift is imparted to the
airplane.

Yes, and the all the upward force that is being imparted comes from
the bottom surface of the wing.

The upper surface of the wing can only help by *not* imparting a
downward force.

The upper surface of the wing does not impart and upward force on the
wing.

-Le Chaud Lapin-