Question

Which of the following is correct to trim an aircraft at positive AOA?

(a) Cm0 > 0

(b) Cm0 < 0

(c) Cm0 will not affect positive trim AOA

(d) Every value of cm0 will trim at positive AOA

The question was posed to me during an interview.

This question is from Longitudinal Static Stability and Control-2 in portion Stability, Control, and Handling Qualities of Aircraft Design

Answer 1

The correct choice is (a) Cm0 > 0

Easy explanation: To trim an aircraft at positive AOA, it is required that aircraft has positive value of zero lift moment coefficient. Hence, to trim aircraft at a positive angle of attack, aircraft should be designed with Cm0 positive i.e., Cm0>0. Negative value of Cm0 will not allow the aircraft to trim at positive AOA.