Which is the minimum requirement for pure directional stability?

Negative lift curve slope

Positive zero lift pitching moment coefficient

Slope of yawing moment curve positive

Negative pitching moment coefficient curve slope

Correct Answer : Slope of yawing moment curve positive

Explanation : An aircraft is said to be in directional stability if the yawing moment curve slope is positive. Negative pitching moment coefficient curve slope is minimum criteria for longitudinal static stability. Positive value of zero lift pitching moment coefficient will be used to design an aircraft to trim at positive AOA.

Recently Updated in Aircraft Design Questions

Which of the following is not the type of aircraft dynamic mode?

Phugoid

Flap

Dutch roll

Lateral mode

Correct Answer : Option (B) : Flap

Explanation : Flap is a high lift device. Flap is used to increase lift produced by the wing. Flaps are used to increase camber and overall surface area of the wing. This results in increased lift. Dutch roll, phugoid, lateral mode etc. are typical aircraft dynamic modes.

Which of the following is an example of longitudinal mode?

Dutch

Lateral

Phugoid

Aileron

Correct Answer : Option (C) : Phugoid

Explanation : Phugoid mode is an example of longitudinal mode. Dutch and lateral mode are not example of longitudinal mode. Aileron is known as primary control surface. Aileron is used to control the aircraft rolling moment.

Find critical damping coefficient if damping ratio is 0.5 and damping coefficient is 1.1.

2.2

4.1

4.9

5.2

Correct Answer : Option (A) : 2.2

Explanation : Critical damping coefficient damping coefficient/ damping ratio 1.1/0.5 = 2.2.