Which factor does NOT affect UAS stability during flight?

The factor that does not affect UAS stability during flight is the duration of the flight. Stability in unmanned aircraft systems (UAS) is primarily influenced by factors that impact the aircraft's structure, control capabilities, and environmental conditions.

Wind conditions directly affect the UAS's flight by introducing turbulence and altering flight paths, which compel the aircraft's control systems to respond to maintain stability. UAS weight and balance are crucial for maintaining proper center of gravity, influencing how the aircraft behaves in the air; an imbalanced UAS can lead to adverse handling characteristics. Control surface effectiveness is essential for maneuverability and stability since these surfaces (like ailerons, elevators, and rudders) help the operator maintain or regain stability in various flight conditions.

In contrast, while the duration of the flight may influence factors such as battery life or fatigue of components, it does not inherently change the stability properties of the UAS itself. Stability is more concerned with how forces act upon the aircraft in flight, rather than how long it has been flying.