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Backwash Causes Lift?



 
 
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  #11  
Old October 3rd 07, 05:54 AM posted to rec.aviation.piloting
Mxsmanic
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Posts: 9,169
Default 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.
  #12  
Old October 3rd 07, 05:54 AM posted to rec.aviation.piloting
Mxsmanic
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Posts: 9,169
Default Backwash Causes Lift?

Dan Luke writes:

Then why does the wing stall and cease lifting when flow separates from the
upper surface?


Because it is no longer accelerating air efficiently downward.
  #13  
Old October 3rd 07, 05:56 AM posted to rec.aviation.piloting
Mxsmanic
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Posts: 9,169
Default Backwash Causes Lift?

Le Chaud Lapin writes:

However, that mess will be less than
static pressure, and there will still be compression beneath the wing.
So if thrust is great enough, airplane should be able to do whatever
it wants.


Pressure beneath the wing is not what lifts the aircraft. It's the twisting
acceleration of air above the wing downward that results in lift.
  #14  
Old October 3rd 07, 05:58 AM posted to rec.aviation.piloting
Mxsmanic
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Posts: 9,169
Default Backwash Causes Lift?

Le Chaud Lapin writes:

What is the definition of a stall anyway?


An abrupt loss of lift.

I'm saying that, if you take a plane with certain critical angle,
throw away engine, put on an engine that can generate 10x the thrust,
the plane should still fly, even if you exceed critical angle.


No, the thrust of the engine doesn't matter, unless the engine itself is
supporting the weight of the aircraft with thrust (possible in a few fighter
aircraft). A wing above the critical angle will stall at any speed.

These books imply that the critical angle is angle at with bad things
happen above the wing, and because of that, the plane will fall.


Yes, true.

I'm saying that, you can have all the bad things happen above the wing and
still be able to keep the plane aloft due to compression that occurs
beneath the wing.


The wing is not supported by compression. It is supported by the displacement
of a mass (of air) downward. If this displacement ceases to take place, lift
disappears. A stalled wing does not divert air downward, so it doesn't
generate lift.
  #15  
Old October 3rd 07, 07:36 AM posted to rec.aviation.piloting
Bertie the Bunyip[_19_]
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Default Backwash Causes Lift?

Mxsmanic wrote in
:

Le Chaud Lapin writes:

What is the definition of a stall anyway?


An abrupt loss of lift.

I'm saying that, if you take a plane with certain critical angle,
throw away engine, put on an engine that can generate 10x the thrust,
the plane should still fly, even if you exceed critical angle.


No, the thrust of the engine doesn't matter, unless the engine itself
is supporting the weight of the aircraft with thrust (possible in a
few fighter aircraft). A wing above the critical angle will stall at
any speed.

These books imply that the critical angle is angle at with bad things
happen above the wing, and because of that, the plane will fall.


Yes, true.

I'm saying that, you can have all the bad things happen above the
wing and still be able to keep the plane aloft due to compression
that occurs beneath the wing.


The wing is not supported by compression. It is supported by the
displacement of a mass (of air) downward. If this displacement ceases
to take place, lift


This should be entertaining.


Bertie
  #16  
Old October 3rd 07, 07:37 AM posted to rec.aviation.piloting
Bertie the Bunyip[_19_]
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Posts: 3,851
Default Backwash Causes Lift?

Mxsmanic wrote in
:

Le Chaud Lapin writes:

However, that mess will be less than
static pressure, and there will still be compression beneath the
wing. So if thrust is great enough, airplane should be able to do
whatever it wants.


Pressure beneath the wing is not what lifts the aircraft. It's the
twisting acceleration of air above the wing downward that results in
lift.


No, it isn't, fjukkktard.

Unless the rules of physics have changed.


Bertie
  #17  
Old October 3rd 07, 07:38 AM posted to rec.aviation.piloting
Bertie the Bunyip[_19_]
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Posts: 3,851
Default Backwash Causes 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

  #18  
Old October 3rd 07, 09:50 AM posted to rec.aviation.piloting
Tina
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Posts: 500
Default Backwash Causes Lift?

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



  #19  
Old October 3rd 07, 09:59 AM posted to rec.aviation.piloting
Bertie the Bunyip[_19_]
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Posts: 3,851
Default Backwash Causes Lift?

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
  #20  
Old October 3rd 07, 11:32 AM posted to rec.aviation.piloting
Matt Whiting
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Posts: 2,232
Default Backwash Causes Lift?

Dan Luke wrote:
"Le Chaud Lapin" wrote:

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.



Then why does the wing stall and cease lifting when flow separates from the
upper surface?



It doesn't cease lifting. It doesn't lift as hard, and not hard enough
to support the airplane, but the force doesn't magically go away.

Matt
 




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