# How does airfoil affect the coefficient of lift vs. AOA slope?

I'm trying to understand whether the airfoil shape can affect the slope of Cl vs. AOA (coefficient of lift vs. angle of attack) in the "linear" portion, e.g., from a few degrees negative to about 10 degrees. As an example, I picked 9 different airfoils from the NACA 4 and 6 series on airfoiltool.com and they all have pretty much the same slope in their linear regions (Rn 1'000'000):

The question I have is, if I would like a steeper slope (more effect on lift with less change in AOA) are there specific airfoils I should look at? Or any specific airfoil characteristics? Or is this slope basically given by physics for "reasonable overall well-performing" airfoils?

• This very good YouTube lecture by Andrew Ning at BYU has a thorough explanation of thin airfoil theory and why the lift slope dCL/dalfa of any airfoil is roughly 2*pi per radian (or about 0.1CL/deg) of angle of attack. This result is derived and finally appears about 49-50 minutes in Andrew's lecture. youtube.com/watch?v=VD0SP0RAPd0. Commented May 31 at 7:32

But there is one trick to artificially increase the lift curve slope for a given planform and flight speed: Add a camber flap and move it in sync with angle of attack. This will shift the zero-lift angle inversely to the change in angle of attack. A purely mechanical solution would use a flap with a large control horn, so that $$c_{r\alpha}$$ becomes positive while $$c_{r\eta}$$ stays negative. However, this is prone to flutter at higher speeds, so depending on the planned speed range a hydraulic or electric actuator, driven by a control unit which is hooked up to an AoA sensor, might be the better solution.