Question

If moment coefficient about aerodynamic centre of wing is -0.216 and lift coefficient of wing is 1.2. Find moment coefficient about cg. Given cg location as Xcg = 0.3.

(a) -0.156

(b) 0.123

(c) 0.56

(d) -1.56

I got this question in unit test.

My question comes from Longitudinal Static Stability and Control-1 in section Stability, Control, and Handling Qualities of Aircraft Design

Answer 1

Correct choice is (a) -0.156

For explanation I would say: Moment coefficient about CG = Moment coefficient about aerodynamic centre of + (wing lift coefficient*[Xcg-Xac])

= -0.216 + (1.2[0.3-0.25]) = -0.156.