Directional, Lateral and Speed Stability

Question 1

What’s wing dihedral?

Answer 1

It is the angle between the lateral axis and a line on the wing drawn from root to tip at 25% chord

Question 2

What’s Dutch Roll?

Answer 2

It’s a continuous rolling and yawing oscillatory motion induced when lateral stability is high and directional stability is weak. This imbalance will tend to be greatest when cruising at high altitude

Question 3

What is a Yaw Damper?

Answer 3

It is a system to solve the problem of Dutch Roll. Without moving the rudder pedals, this autostabiliser system applies small rudder movements at the appropriate times which add to the moments created by the fin and restore directional stability to the required level.

Question 4

What’s Spiral Instability?

Answer 4

Opposite to Dutch Roll, it happens when an aircraft has weak lateral stability and strong directoinal stability

Question 5

What’s an Aperiodic motion?

Answer 5

Motion is not periodic, happens when an aircraft never enters an oscillation, therefore it would have no dynamic stability whatsoever.