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A comment on A Physical Description of Flight, Revisited (2009) [pdf].

Re:A Physical Description of Flight, Revisited (2009) [pdf] by mthiesen on Thursday October 27, 2016 @04:59PM (#12810070)
Wow, Great paper. The most interesting (and counter-intuitive) part for me was that the lift is generated by the top of the wing bending air downwards. In my head I always visualized lift as the bottom of the wing being pushed up, but this paper claims lift is really more like the top of the wing pulling upwards.
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Re:A Physical Description of Flight, Revisited (2009) [pdf] by WalterBright on Friday October 28, 2016 @02:38AM (#12813606)
The lift is the sum of all the pressure vectors around every point on the wing. Since the pressure vectors are all normal to the wing surface, in order to have a net upwards vector, the pressure on the bottom surface has to be higher than that on the top.

I.e. air cannot "pull" anything anywhere.

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Re:A Physical Description of Flight, Revisited (2009) [pdf] by renox on Friday October 28, 2016 @09:19AM (#12815433)
If I remember well: in normal condition the lift come 2/3 from the top of the wing and 1/3 from the bottom of wing.

So the depression above the wing is indeed "pulling up" the wing more than the surpression below the wing is pushing up the wing.

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Re:A Physical Description of Flight, Revisited (2009) [pdf] by WalterBright on Friday October 28, 2016 @07:05PM (#12821527)
No, a vacuum never "pulls". The pressure on the other side of the object pushes it.
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Re:A Physical Description of Flight, Revisited (2009) [pdf] by delinka on Thursday October 27, 2016 @05:15PM (#12810242)
"[T]he shape of the wing affects the efficiency and stall characteristics of the wing but not the lift. That is left to the angle of attack and speed."

So no, the top of the wing is not pulling the wing upwards. The air beneath is "blowing" the wing upwards.

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Re:A Physical Description of Flight, Revisited (2009) [pdf] by nether on Thursday October 27, 2016 @05:30PM (#12810400)
It's really both. Figure 8 in the paper depicts this circulation theory of lift. The top and bottom surfaces interact via this phenomenon, though the top is more critical as the paper explains.

Also terms like "push" and "pull" really confuse the mechanics here. What matters is that a net upward force is being generated, with positive pressure acting on all sides of the airfoil. There is more pressure acting upon the lower surfaces than on the upper surfaces, but at every point the pressure is positive because it is surrounded by fluid (not in a vacuum). If you integrated the pressure acting on a lifting airfoil and computed the average direction, it would be pointed up.

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Re:A Physical Description of Flight, Revisited (2009) [pdf] by mthiesen on Thursday October 27, 2016 @06:08PM (#12810733)
Good point, if the top of the wing diverts air downward via reduced air pressure above the wing, then it would be the higher pressure air underneath (pushing) that creates the lift. Yeah, I can see how terms like "push" and "pull" get pretty confusing.
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