Backwash Causes Lift?

Le Chaud Lapin writes:

Obviously, any air above the wing can only result in a force downward
on top of the wing. The only force causing the plane to want to move
upward comes from beneath the wing. The effect of any air above the
wing is to cause rarefication above the wing, resulting in lower
pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
"reaction" coming from downward movement of air seems just plain silly
to me.

Lift is a reaction to the force required to push air downward behind the wing
(downwash). How the air gets pushed downward is not very important. The wing
twists air into a downwash as it passes through it, leaving a swath of air
moving gently downward behind it. The force required to do this engenders an
equal and opposite force that is lift. Lift accelerates the wing upward,
counteracting gravity. The wing accelerates a large mass of air downward.

I am also inclined to take issue with the explanations of Bernouilli's
Principle which I see often in the literature, but that's a different
subject. [Note, I don't doubt Bernouilli's Principle, I just think
there is more to it than the way it is being described in context of
flying.]

There are a lot of different ways to examine and describe the aerodynamics of
lift. It boils down to accelerating one mass (a mass of air) downward, which
engenders another acceleration of another mass (the wing, and anything to
which it is attached) upward. Any flat surface moving relative to the air
with a positive angle of attack below the stall angle will generate lift.

Mxsmanic wrote in
:

Le Chaud Lapin writes:

Obviously, any air above the wing can only result in a force downward
on top of the wing. The only force causing the plane to want to move
upward comes from beneath the wing. The effect of any air above the
wing is to cause rarefication above the wing, resulting in lower
pressure, thereby giving the 14.7lbs/in^2 (plus) to do its work. That
"reaction" coming from downward movement of air seems just plain
silly to me.

Lift is a reaction to the force required to push air downward behind
the wing (downwash). How the air gets pushed downward is not very
important. The wing twists air into a downwash as it passes through
it, leaving a swath of air moving gently downward behind it. The
force required to do this engenders an equal and opposite force that
is lift. Lift accelerates the wing upward, counteracting gravity.
The wing accelerates a large mass of air downward.

I am also inclined to take issue with the explanations of
Bernouilli's Principle which I see often in the literature, but
that's a different subject. [Note, I don't doubt Bernouilli's
Principle, I just think there is more to it than the way it is being
described in context of flying.]

There are a lot of different ways to examine and describe the
aerodynamics of lift. It boils down to accelerating one mass (a mass
of air) downward, which engenders another acceleration of another mass
(the wing, and anything to which it is attached) upward. Any flat
surface moving relative to the air with a positive angle of attack
below the stall angle will generate lift.


Nope.


Bertie

It is clearly time to revisit airplanes taking off on tredmills.

Tina wrote in news:1191401433.827965.190080
@o80g2000hse.googlegroups.com:

It is clearly time to revisit airplanes taking off on tredmills.




Do tell. Must have been before my time here.

Bertie

It is clearly time to revisit airplanes taking off on tredmills.

I have to agree. ANYTHING would be better than hearing the resident idiot
troll's blithering.

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?
--
Jim in NC

"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, 6:33 pm, "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.

Tricky question. I will take a stab at it.

You said "sense the airplanes speed". Relative to what?

Assuming no friction between wheels and treadmill, the prop of the
plane will cause the airplane to move in the wind. The speed
"sensing" of the airplane by the treadmill does not really make sense
and less you mean that the treadmill senses relative to the wind.

If the treadmill senses that the plane has a relative wind speed of
Vpw, and starts moving in the opposite direction, and the relative
speed of wind against treadwill were nil before all this started, then
the treadmill will only cause the wheels to turn twice as fast as they
would have if the treadmill had not been moving. In this case, the
speed of the plane relative to the treadmill will simply be twice the
speed of the plane relative to the win, in opposite direction, of
course. The plane will take off.

If you mean to imply that there is some way for the treadmill to sense
the speed of the plane relative to the treadmill, then adjust the
speed of treadmill accordingly, of course, that won't work, as it is a
circuitous proposition.

-Le Chaud Lapin-

Morgans wrote:
"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.

Oh god,. imagine having been hios spiritual teacher when he was
young.

Do dogs get into heaven, et al...







Bertie