Backwash Causes Lift?

flightoffancy wrote in news:MPG.2172cb3db6410d90989680
@news-server.hot.rr.com:

In article . com,
says...
Now, in Chapter 3, section about airfoils, it actually says:

"In addition to the lowered pressure, a downward-backward flow of air
also is generated from the top surface of the wing. The reaction to
this downwash results in an upward force on the wing which
demnstrates
Newtons' third law of motion. This action/reaction principle also is
apparent as the airstream strikes the lwoer surface of the wing when
inclinded at a small angle (the angle of attack) to its direction of
motion. The air is forced downward and therefore causes an upward
reaction resulting in positive lift."

IMHO, the latter part of this paragraph is correct, but the former
part is wrong.

JC, you're confusing yourself.

Instead of focusing on "fixed" wing, think for a moment about
helicopter
blades and propellers. These are airfoils not fundamentally different
than one attached to the side of an aircraft.

Anyone who has ever seen video of a helicopter hovering or has been
near
a helicopter hovering knows that air is being pushed down by the
blades
with massive force and that is the equal and opposite force exerted by
the mass of air on the bottom of the blades that keeps the helicopter
from falling out of the sky.

A fixed wing aircraft is only different in that it pushes air under it
by moving forward, rather than in a circle.

The bottom line is simple: an airplane can only stay aloft by pushing
air down.

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

Nit-picking Jeppensen's watered down description, which was not
authored
for aeronautical engineers (which I note you are NOT), will not
advance
your piloting skills in any significant way.





Nope, wrong.


Bertie

flightoffancy writes:

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

No, the curved surface simply reduces drag and/or increases the stall angle.

John Doe wrote:
wrote:

If you really want to know the "truth", USNET is not the place to
find it.

USENET is the wisdom and folly of the world.

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.


--
Jim Pennino

Remove .spam.sux to reply.

flightoffancy wrote:
In article . com,
says...
Now, in Chapter 3, section about airfoils, it actually says:

"In addition to the lowered pressure, a downward-backward flow of air
also is generated from the top surface of the wing. The reaction to
this downwash results in an upward force on the wing which demnstrates
Newtons' third law of motion. This action/reaction principle also is
apparent as the airstream strikes the lwoer surface of the wing when
inclinded at a small angle (the angle of attack) to its direction of
motion. The air is forced downward and therefore causes an upward
reaction resulting in positive lift."

IMHO, the latter part of this paragraph is correct, but the former
part is wrong.

JC, you're confusing yourself.

Instead of focusing on "fixed" wing, think for a moment about helicopter
blades and propellers. These are airfoils not fundamentally different
than one attached to the side of an aircraft.

Anyone who has ever seen video of a helicopter hovering or has been near
a helicopter hovering knows that air is being pushed down by the blades
with massive force and that is the equal and opposite force exerted by
the mass of air on the bottom of the blades that keeps the helicopter
from falling out of the sky.

A fixed wing aircraft is only different in that it pushes air under it
by moving forward, rather than in a circle.

The bottom line is simple: an airplane can only stay aloft by pushing
air down.

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

Nit-picking Jeppensen's watered down description, which was not authored
for aeronautical engineers (which I note you are NOT), will not advance
your piloting skills in any significant way.

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

--
Jim Pennino

Remove .spam.sux to reply.

Mxsmanic wrote in
:

flightoffancy writes:

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

No, the curved surface simply reduces drag and/or increases the stall
angle.


Nope.


Bertie

On Oct 7, 11:54 am, flightoffancy wrote:
JC, you're confusing yourself.

Instead of focusing on "fixed" wing, think for a moment about helicopter
blades and propellers. These are airfoils not fundamentally different
than one attached to the side of an aircraft.

Agree.

Anyone who has ever seen video of a helicopter hovering or has been near
a helicopter hovering knows that air is being pushed down by the blades
with massive force and that is the equal and opposite force exerted by
the mass of air on the bottom of the blades that keeps the helicopter
from falling out of the sky.

More agreement.

A fixed wing aircraft is only different in that it pushes air under it
by moving forward, rather than in a circle.

Even more agreement.

The bottom line is simple: an airplane can only stay aloft by pushing
air down.

Still even more.

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

Still even more.

Nit-picking Jeppensen's watered down description, which was not authored
for aeronautical engineers (which I note you are NOT), will not advance
your piloting skills in any significant way.

There is one small problem with your exposition:

You are referring to the bottom of the wing.

Jeppesen is talking about the top of the wing.

-Le Chaud Lapin-

On Oct 7, 11:54 am, flightoffancy wrote:
In article . com,
says...

Now, in Chapter 3, section about airfoils, it actually says:

"In addition to the lowered pressure, a downward-backward flow of air
also is generated from the top surface of the wing. The reaction to
this downwash results in an upward force on the wing which demnstrates
Newtons' third law of motion. This action/reaction principle also is
apparent as the airstream strikes the lwoer surface of the wing when
inclinded at a small angle (the angle of attack) to its direction of
motion. The air is forced downward and therefore causes an upward
reaction resulting in positive lift."

IMHO, the latter part of this paragraph is correct, but the former
part is wrong.

JC, you're confusing yourself.

[Note, I just re-read your post and realized that you too are implying
that a the top wing surface can accelerate air molecules downward.,
hence my double response.]

Instead of focusing on "fixed" wing, think for a moment about helicopter
blades and propellers. These are airfoils not fundamentally different
than one attached to the side of an aircraft.

Agreed.

Anyone who has ever seen video of a helicopter hovering or has been near
a helicopter hovering knows that air is being pushed down by the blades
with massive force and that is the equal and opposite force exerted by
the mass of air on the bottom of the blades that keeps the helicopter
from falling out of the sky.

Well that is certainly true.

A fixed wing aircraft is only different in that it pushes air under it
by moving forward, rather than in a circle.

True.

The bottom line is simple: an airplane can only stay aloft by pushing
air down.

This true and not true. A wing does not necessarily have to push air
downward to cause 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.
The air below the wing remains more or less steady at ambient
atmosphere. The air above the wing is rarefied and therefore causes
less force above the wing. The net result of the difference between
the full force below the wing and the reduced force above the wing,
minus the weight of the paper due to gravity, results in an upward net
force on the paper, causing it to rise. As soon as you stop blowing,
the ambient atmosphere works to replenish the rarefied air above the
paper to its natural state, which causes a net force on the paper due
to pressures above the paper and below the paper to equalize [taking
normal vectors into account, yada..], and gravity becomes the
determining force, causing the paper to flop back down.

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.

Yes, the angle of attack gives the greater impulse to knock the air
downward. But a curved upper surface gives even more downard force to
the air.

How? How can a the top surface of a wing cause a downward force on air
molecules that are on top of the wing?

The uppper surface of the wing can only exert a force on the air
molecules above the wing either in the upward direction, or in the
lateral direction due to friction. Ionized particles and charged
surfaces notwithstanding, it is not possible for a (theoretically
smooth) upper surface to exert a downward force on air molecules that
are sitting on top of it.

-Le Chaud Lapin-

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.

On Oct 7, 12:15 pm, Le Chaud Lapin wrote:

An airplane can stay aloft if rarefication is somehow created above
the wing. This is what's happening with the blow-over-paper trick.
The air below the wing remains more or less steady at ambient
atmosphere. The air above the wing is rarefied and therefore causes
less force above the wing. The net result of the difference between
the full force below the wing and the reduced force above the wing,
minus the weight of the paper due to gravity, results in an upward net
force on the paper, causing it to rise. As soon as you stop blowing,
the ambient atmosphere works to replenish the rarefied air above the
paper to its natural state, which causes a net force on the paper due
to pressures above the paper and below the paper to equalize [taking
normal vectors into account, yada..], and gravity becomes the
determining force, causing the paper to flop back down.

"Rarefaction" again. I don't see that term used by
aerodynamicists, unless they're dealing with supersonic or hypersonic
flight, and I think that's where you are haywire. (Google "aerodynamic
rarefaction" to see what comes up.) Bernoulli said that as velocity
increases, static pressure decreases. We can measure this phenomenon
inside a pipe that has no change in cross-section. As velocity
increases, the dynamic pressure increases and therefore subtracts from
the static pressure to keep the total pressure the same. On an
airfoil, the lowest pressures are found where the velocity is highest,
just atop the leading edge, where we'd expect COMPRESSION to be
happening, not rarefaction. LIFT IS GENERATED BY LOWERED STATIC
PRESSURE, NOT LOWERED DENSITY. Until you get that through your head,
you will waste years trying to prove everyone else wrong. You are, as
the NASA site says, mistakenly applying the physics of solids to the
problem, not the physics of gases.
The air moves to fill any void over a wing in subsonic
flight. It moves far more quickly that you could generate any
significant rarefaction above a wing.

From that site:

"For example, from the conservation of mass, a change in the
velocity of a gas in one direction results in a change in the velocity
of the gas in a direction perpendicular to the original change. This
is very different from the motion of solids, on which we base most of
our experiences in physics.

Dan

On Oct 7, 2:14 pm, flightoffancy wrote:
In article . com,
says...

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

What you are saying is: if less pressure exists above the wing than
below, then airpressure will force the wing higher, just like a round
weight sealed in a round tube will be forced higher if the pressure
under the weight exceeds the pressure above the weight.

Right, that's what I'm saying.

No one questions that.

But I don't think the blowing on paper "experiment" demonstrates the
principle.


There are too many uncontrolled variables for you to draw such a
conclusion. For instance, it could simply be the case that some airflow
gets under the sheet of paper and pushes it up -- just like air

Certainly you don't believe that the air is actually running around
the paper so it can get under the wing?

impacting any plane at an angle will impart some vector force in an
"up" direction. Also the paper does not remain stiff -- it undulates.
That introduces a tremendous amount of complexity which casts your
interpretation in doubt.

Also: the airspeed of your paper is not 0 -- it's groundspeed is zero.

The leading edge of the airfoil, the paper in this case, will have an
airspeed of 0. You can do this by making sure that, when you blow
over the paper, your mouth is a good 3 or 4 centimeters beyond the
leading edge, on top of the paper in fact.

-Le Chaud Lapin-