Certified Flight Instructor - Flight Instructor Airplane Practice Exam

If an aircraft has negative dynamic and positive static stability, this will result in?

1. Undamped oscillations.

2. Divergent oscillations.

3. Convergent oscillations.

4. Steady flight.

The correct answer is: Divergent oscillations.

When an aircraft exhibits negative dynamic stability paired with positive static stability, it means that while the aircraft's initial response to a disturbance tends to return to a stable equilibrium position (as indicated by positive static stability), the ongoing response to that disturbance becomes increasingly divergent over time (as indicated by negative dynamic stability). In this scenario, static stability reflects the aircraft's tendency to return to its original position after being disturbed — for example, if you pitch the nose up, the aircraft should eventually settle back down to its original attitude. However, negative dynamic stability implies that the aircraft continues to oscillate away from that position rather than returning to it in a controlled manner. As a result, over time, these oscillations grow larger instead of being dampened down to a calm state. Therefore, the result of this combination of stability characteristics is divergent oscillations, where the aircraft is unable to stabilize itself and instead starts to have increasingly larger deviations from its original flight path. This situation can lead to potentially hazardous flight conditions if not corrected promptly.