His theories are used to easily explain Lift to the beginner, but Nature doesn't allow a vacuum, (ever), and the real work is done on the bottom, not the top.
Hi Bearfoil,
That's where I tend to disagree.
If you take a very asymmetrical Wing e.g. a NACA 4312.
The lower side is still slightly convex.
Yet the airfoil has a lift coefficient of 0.3 ! at Alpha = 0°.
I see no other explanation for this than the fact that a low presssure on the upper side creates a 'suction' force on the foil.
And that has nothing to to with Ground effect as Alpha is 0 and thus no compression takes place on the lower side.
When Ground effect takes over you will notice that by a shifting of the center of lift from the quarter chord line towards the mid chord line.
When you have only ground effect the center of lift of a flat plat with AoA will be at 50% chord.
Convex or concave shape of the plate will shift the center of pressure / lift according to the local velocities, i.e. crossection.
Which can btw. also be explained by Bernoulli. I have to confess I'm a believer in Bernoulli as long as no one comes up with a better explanation.