Question

Which of the following is correct for hinge moment?

(a) Hinge moment coefficient is function of tail angle of attack

(b) Hinge moment is not dependent on the tail angle

(c) Downwash is used to reduces angle of attack at tail

(d) Lifting property of the airfoil is same as a sphere

The question was posed to me in an interview.

My question is taken from Stick-Free Stability in portion Stability, Control, and Handling Qualities of Aircraft Design

Answer 1

Right answer is (a) Hinge moment coefficient is function of tail angle of attack

Explanation: Hinge moment coefficient is function of number of factors such as tail angle of attack, tail setting angle, etc. Due to downwash the angle of attack at tail will be more. Lifting property of an airfoil and sphere will be different. Airfoil is 2d shape and sphere is 3d shape.