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visualisation of the lift distribution over a wing



 
 
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  #71  
Old December 2nd 09, 06:26 AM posted to rec.aviation.homebuilt
Beryl[_3_]
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Posts: 52
Default visualisation of the lift distribution over a wing

Jim Logajan wrote:
Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in a
perfect vacuum) then there is zero push.


I don't see what a change in air density (such as taking the extreme case
of a vacuum) has to do with lift.


I'm going to build a thick wing, real thick! About 10,000 feet thick.
While the bottom surface of the wing sits at 29.92" sea level
atmospheric pressure, the upper surface will be *way* up there, in a
lower-pressure area. This airplane is gonna to lift off the ground at
zero airspeed with no power.
  #72  
Old December 2nd 09, 06:50 AM posted to rec.aviation.homebuilt
Steve Hix[_2_]
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Posts: 50
Default visualisation of the lift distribution over a wing

In article ,
Scott wrote:

Alan Baker wrote:
In article ,
Scott wrote:

Alan Baker wrote:

Observation can lead you astray: and that is clearly the case here if
you actually think that air can *pull* on a surface.

Why can't air PULL on a surface? Air is made up of molecules.
Molecules have mass. Anything with mass can attract anything else with
mass, can't it?


Gravity?

You're not serious.

Anti-gravity in this case. If air can push something, why can't it pull
something?


It does, but the tiny resulting forces are completely swamped by things
like van der Waals force, static electric charges, magnetic fields, and
any number of things that are usually quite happily ignored by us in
normal life.
  #73  
Old December 2nd 09, 06:51 AM posted to rec.aviation.homebuilt
Steve Hix[_2_]
external usenet poster
 
Posts: 50
Default visualisation of the lift distribution over a wing

In article ,
Beryl wrote:

Jim Logajan wrote:
Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in a
perfect vacuum) then there is zero push.


I don't see what a change in air density (such as taking the extreme case
of a vacuum) has to do with lift.


I'm going to build a thick wing, real thick! About 10,000 feet thick.
While the bottom surface of the wing sits at 29.92" sea level
atmospheric pressure, the upper surface will be *way* up there, in a
lower-pressure area. This airplane is gonna to lift off the ground at
zero airspeed with no power.


Only if you make it from monatomic Unobtanium. Only thing light enough
for the job.
  #74  
Old December 2nd 09, 09:17 AM posted to rec.aviation.homebuilt
Alan Baker
external usenet poster
 
Posts: 244
Default visualisation of the lift distribution over a wing

In article ,
Jim Logajan wrote:

Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in a
perfect vacuum) then there is zero push.


I don't see what a change in air density (such as taking the extreme case
of a vacuum) has to do with lift. Unless you are claiming density change as
a requirement?

I believe lift can be reasonably computed using inviscid _incompressible_
flow theory (e.g. as far back as Kutta's 1902 dissertation,) so I don't see
why any change in _density_ - much less the vacuum edge case - needs to be
invoked.


Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.

I never mentioned density.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg
  #75  
Old December 2nd 09, 01:31 PM posted to rec.aviation.homebuilt
Brian Whatcott
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Posts: 915
Default visualisation of the lift distribution over a wing

Alan Baker wrote:
/snip/
I have never noticed the fabric lifting on my wings, however I have
seen the fuel siphon out of a wing tank due to an improperly applied
fuel cap.
And greater pressure in the tank than outside of it...

Right, but in a sealed metal tank, is all that other fuel PUSHING the
fuel out of the vent since air can't PULL it out?


First of all, the tank is not completely sealed. If it were, the fuel
pumps would soon have difficult pumping the fuel out of the tank.

So, yes, the greater pressure inside the tank is pushing the fuel out.


Hmmm...it probably goes more like this: there's a 100 mph? wind past an
open port, with some venturi effect certainly, but plenty of
turbulence. If you beat up the surface with a gusty blow, it gets
wavelets which can lap the filler and blow out the fuel.

Which reminds me of that trick that suction pumps use for high lift.

As you probably know, if you pump down even to a vacuum above a tall
3water pipe, the water will not rise more than about 30 ft - (if it were
mercury, it would not rise more than 29.92 inches on a standard day,
remember?)

Anyway, the mine engineers who want to pump up water MORE than 30 ft,
say 40 ft without placing a force pump at the foot of the head, blow air
into the water column which has the effect of reducing the density of
the mix. If the relative density goes down from 1.0 to 0.5 they COULD
pump up to nearer 60 ft. How bout that!

Brian W
  #76  
Old December 2nd 09, 01:36 PM posted to rec.aviation.homebuilt
Scott[_7_]
external usenet poster
 
Posts: 256
Default visualisation of the lift distribution over a wing

Steve Hix wrote:

any number of things that are usually quite happily ignored by us in
normal life.



EXACTLY!! I don't have to know if air pushes or sucks (although I'm
quite sure it SUCKS in L.A.) to control the airplane to do what I want
it to do.
  #77  
Old December 2nd 09, 06:08 PM posted to rec.aviation.homebuilt
Jim Logajan
external usenet poster
 
Posts: 1,958
Default visualisation of the lift distribution over a wing

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in
a perfect vacuum) then there is zero push.


I don't see what a change in air density (such as taking the extreme
case of a vacuum) has to do with lift. Unless you are claiming
density change as a requirement?

I believe lift can be reasonably computed using inviscid
_incompressible_ flow theory (e.g. as far back as Kutta's 1902
dissertation,) so I don't see why any change in _density_ - much less
the vacuum edge case - needs to be invoked.


Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.


That assertion is incorrect. You are no dummy so I'm sure you'll correct it
when you realize the errors.

I never mentioned density.


Sorry, but you used the word "vacuum." The notable characteristic of a
vacuum is that its density is zero.
  #78  
Old December 2nd 09, 06:12 PM posted to rec.aviation.homebuilt
Robert Bonomi
external usenet poster
 
Posts: 50
Default visualisation of the lift distribution over a wing

In article ,
Scott wrote:
Alan Baker wrote:
In article ,
Scott wrote:

Alan Baker wrote:

Observation can lead you astray: and that is clearly the case here if
you actually think that air can *pull* on a surface.

Why can't air PULL on a surface? Air is made up of molecules.
Molecules have mass. Anything with mass can attract anything else with
mass, can't it?


Gravity?

You're not serious.

Anti-gravity in this case. If air can push something, why can't it pull
something?


Quote: "There are two things you need to know to be an engineer:
1) F = M x A
2) you can't push on a rope."

Your question involves a violation of rule #2.


  #79  
Old December 2nd 09, 06:50 PM posted to rec.aviation.homebuilt
Brian Whatcott
external usenet poster
 
Posts: 915
Default visualisation of the lift distribution over a wing

Robert Bonomi wrote:


Quote: "There are two things you need to know to be an engineer:
1) F = M x A
2) you can't push on a rope."

Your question involves a violation of rule #2.



Hehe... If you push downwards on a tight rope carefully enough,
you can qualify as a tightrope walker?? :-)

Brian W
  #80  
Old December 2nd 09, 07:58 PM posted to rec.aviation.homebuilt
Alan Baker
external usenet poster
 
Posts: 244
Default visualisation of the lift distribution over a wing

In article ,
Jim Logajan wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in
a perfect vacuum) then there is zero push.

I don't see what a change in air density (such as taking the extreme
case of a vacuum) has to do with lift. Unless you are claiming
density change as a requirement?

I believe lift can be reasonably computed using inviscid
_incompressible_ flow theory (e.g. as far back as Kutta's 1902
dissertation,) so I don't see why any change in _density_ - much less
the vacuum edge case - needs to be invoked.


Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.


That assertion is incorrect. You are no dummy so I'm sure you'll correct it
when you realize the errors.


Sorry, but it's not. Pressure is created by particle collisions.


I never mentioned density.


Sorry, but you used the word "vacuum." The notable characteristic of a
vacuum is that its density is zero.


That is *a* notable characteristic.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg
 




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