# For a given airfoil, with known Cl and Cd curves, how can I calculate the autorotation AoA range?

I'm trying to tabulate the differences of (vertical) autorotating behavior for rotors of equal chord and span, but with different airfoils. Of course, they can be studied case by case, but there may be a simpler, less laborious way... Hence my question...

Basically, determine $v_i$ = the induced velocity in the hover, then vertical autorotation speed is around:
• 2 * $v_i$ for a rotor with 12 degree blade twist.
• 1.8 * $v_i$ for an untwisted rotor.