Distinguish static stability and dynamic stability in the longitudinal axis?

• A. Static stability is the initial tendency to return after a disturbance; dynamic stability is how the motion damps over time
• B. Dynamic stability is the initial tendency to return; static stability is how the motion damps over time
• C. Static stability relates to the lateral axis
• D. Dynamic stability is the instantaneous response only

Answer: (B)

In the longitudinal axis, the key distinction is how the aircraft responds initially versus how it behaves over time after a disturbance. Static stability is about the immediate tendency to return to the original trim position after a disturbance in pitch. If the aircraft has positive static stability, a small nose-up or nose-down disturbance will prompt a restoring moment that tends to bring the nose back toward trim right away.

Dynamic stability, on the other hand, describes the motion as time passes after that disturbance—whether the pitch oscillations die out (are damped), grow, or stay constant. So dynamic stability is about the time history of the response, not just the first instant.

Thus the correct understanding is that static stability is the initial tendency to return, while dynamic stability is how the motion evolves and damps over time. The other statements misstate either the order of these concepts, apply them to the wrong axis, or limit dynamic stability to an instantaneous reaction.