FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsHard
An airplane is trimmed for straight-and-level flight. A gust of turbulence pitches the nose up, and without any control input from the pilot, the airplane's nose tends to move back down toward the original trimmed attitude. This tendency describes
- Aneutral static stability
- Bdynamic instability
- Cnegative static stability
- Dpositive static stability
Show answer & explanationAnswer & explanation
Correct answer: D. positive static stability
Positive static stability is the initial tendency of an aircraft to return toward its original attitude after being disturbed, without pilot input. This is a desirable design characteristic that makes an airplane easier and safer to fly, and it is typically produced by proper CG location and horizontal stabilizer design.
Why the other options are wrong
- A. Neutral static stability would mean the airplane stays in the new, disturbed attitude rather than returning.
- B. Dynamic stability/instability describes the behavior over time (oscillations), not the initial tendency, which is a static stability concept.
- C. Negative static stability would cause the disturbance to increase rather than the aircraft returning toward the original attitude.
Static Stability
The initial tendency of an aircraft, when disturbed from equilibrium, to either return toward, remain at, or move further away from its original attitude.
- Positive static stability: tends to return toward original attitude
- Neutral static stability: remains in new attitude without returning or diverging
- Negative static stability: continues to move further from original attitude
- Distinct from dynamic stability, which describes behavior over multiple oscillations
Memory trick: Positive stability = the airplane 'wants' to come home to level flight