Question

What is the theoretical value of lift curve slope of a flat airfoil?

(a) 2π per radian

(b) 4aπ per radian

(c) 3π per radian

(d) π per radian

The question was asked in class test.

My question comes from Lift Force topic in chapter Aircraft Force Systems and the Equations of Motion of Aircraft Performance

Answer 1

The correct choice is (a) 2π per radian

Easiest explanation: The theoretical value of lift curve slope of a flat airfoil is 2π per radian i.e. \(\frac{dC_l}{d\alpha}\)=0 here \(\frac{dC_l}{d\alpha}\) is lift curve slope. This factor is depending on thickness of the airfoil and aspect ratio. The lift curve slope is directly proportional to thickness and inversely proportional to aspect ratio.