Parte Deux....
But you also put in an interesting point...
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"...how a flat bottom airfoil works (high pressure under the wing and low pressure over the wing),..."
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I've written this part about 4 times now. You're really bending my mind and I'm learning that I have some bad misconceptions.
OK. I'm going to take a stab at this now and hope that I'm not TOO wrong. Looking forward to hearing from Ollie and Ben and the others here.
Drop on by this site for a very interesting app that lets you play with an airfoil in real time.
http://www.grc.nasa.gov/WWW/K-12/aer...let/vj402.html
Start with the symetrical one and add 6 degrees of angle (of attack) using the slider. Use the slider on the right side of the airfoil to zoom back for a wider view. Note that the streamlines have a little bit of deflection downwards at the trailing edge and there's a pressure difference in the chart on the right. Somewhere about a 1/4 psi at 6 degrees if you average it out. Now add .4 on the camber slider. Note the volume between the pressure curve grows. That's lift but it's not a large amount. But look at the way the streamlines have changed. There's now a very healty curve up to the airfoil and a strong downsweep off the trailing edge. That's lift too. You've redirected the air coming up to the foil and squirted it downwards. The acceleration of the air downward in the wing wash is a large part of the lift off a wing.
And here's the kicker.... (FINALLY....
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If I remember one write up accuratley this downwash is the major contributing factor to lift. The pressure differential being a player but a minor one.
So THIS is why symetrical airfoils can generate lift but not as well as cambered airfoils. They both have the ability to redirect the air flow into downwash but the cambered foil has a greater angle of redirection.
PHEW..... Gotta put on my Nomex underwear now and let the experts punch holes in this one.
Having to explain this helped me a lot too but I just hope I'm on the right track.
PS. check over the polars below but they are part of one of the other explanations that I tossed out. I forgot I'd put the graph on this and here it is... Oh well.