Question

The lift coefficient for the airfoil section on a wing ______

(a) Depends on local lift slope for airfoil

(b) Is same for the entire wing

(c) Is equal to the aerodynamic twist

(d) Is constant always

This question was addressed to me in a national level competition.

I would like to ask this question from Prandtl’s Classical Lifting-Line Theory topic in chapter Flow over Airfoils over Finite Wing of Aerodynamics

Answer 1

Right option is (a) Depends on local lift slope for airfoil

Easy explanation: In wings, the lift coefficient for local airfoil section is equal to the local airfoil lift curve slope (2π for thin airfoils) into effective angle of attack minus zero lift angle of attack. Thus, it may or may not be same for the entire wing and is not equal to the aerodynamic twist.