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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): Cl vs AOA for 9 NACA airfoils

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?

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The airfoil affects the lift curve slope only very little; theoretically the slope should be a bit steeper for thicker airfoils.

But that pales in comparison to the effects of wing planform. Here the biggest influence is from the wing's aspect ratio and sweep. Another factor is the flight Mach number and the Reynolds number.

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.

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  • $\begingroup$ Do you have a link or short explanation for why the lift curve slope is not (cannot be?) affected by airfoil shape? Thanks for the flap links! $\endgroup$ – TvE Apr 2 at 3:15
  • $\begingroup$ @TvE Potential flow theory. And lots of windtunnel data. Follow the links in the answer or ask more specifically. As it stands, this question is on a level of "why can I not change gravity". You can't. $\endgroup$ – Peter Kämpf Apr 2 at 4:07

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