Question

Find the appropriate value of pitching moment coefficient derivative if lift curve slope is 0.032 per degree and Xcg is 0.3. Consider neutral point is located at 60 % of chord from leading edge.

(a) -0.0096 per degree

(b) -7 per degree

(c) 2.56 per degree

(d) 0.1

I had been asked this question by my college director while I was bunking the class.

Question is taken from Longitudinal Static Stability and Control-2 topic in chapter Stability, Control, and Handling Qualities of Aircraft Design

Answer 1

The correct choice is (a) -0.0096 per degree

Explanation: Given, lift curve slope C= 0.032 per degree, Xcg = 0.3

Neutral point is located at 60% of chord i.e. Xnp = 0.6.

Pitching moment derivative = -C*[Xnp-Xcg] = -0.0032*[0.6-0.2] = -0.0096 per degree.