Question

The relation between lift coefficient and moment coefficient about the leading edge is_______

(a) cm,le=-(\(\frac {c_l}{2}+\frac {\pi }{4}\)(A1-A2))

(b) cm,le=-(\(\frac {c_l}{4}+\frac {\pi }{4}\)(A1-A2))

(c) cm,le=-(\(\frac {c_l}{4}\)+(A1-A2))

(d) cm,le=(\(\frac {c_l}{2}+\frac {\pi }{4}\)(A1-A2))

The question was asked in semester exam.

My enquiry is from The Cambered Airfoil in chapter Incompressible Flow over Airfoils of Aerodynamics

Answer 1

Correct choice is (b) cm,le=-(\(\frac {c_l}{4}+\frac {\pi }{4}\)(A1-A2))

To explain I would say: The lift coefficient is cl=π(2A0+A1). When we put this in the formula for moment coefficient about the leading edge, cm,le=-0.5π(A0+A1-0.5A2) we get the desired relation.