[tomsto]

This is not how it works, no falling or positive angle of attack is required for an asymmetrical aerofoil. Imagine swinging a bucket of water over your head - the force your arm feels is similar to what the top surface of the wing feels.

[bbojan]

Is that so? I thought that for asymmetric airfoil, zero angle of attack is by definition the angle where it creates no lift. So, tautologically, if it's creating lift a (positive) angle of attack is required.

[tomsto]

For a symmetric aerofoil, 0 angle of attack is 0 lift. For an asymmetric - there is (some) lift, which comes entirely from the suction side.

https://www.wolframalpha.com/input/?i=NACA+6409+airfoil&assu...