[kwertzzz]

I was asking myself the same question. I would love to see a derivation from e.g. the Navier Stokes equation for this. I think, intuitively, when you draw the streamlines under the rectangular wings, the applied force should be related to the curvature of the streamlines (which is larger at the beginning of the wing).

I made some simple 2D Navier-Stokes solver here where you can use the mouse to draw a section of a wing:

https://alexander-barth.github.io/FluidSimDemo-WebAssembly/

The color represents the pressure (I should add a proper color bar!)