Private Pilot License (PPL) Aerodynamics Practice Exam

What happens to an aircraft's stability as the center of gravity moves aft?

1. It becomes more stable

2. It becomes less stable

3. It remains unchanged

4. It becomes more controllable

The correct answer is: It becomes less stable

When the center of gravity (CG) of an aircraft moves aft, it affects the stability of the aircraft, typically making it less stable. Stability in aviation refers to an aircraft’s natural tendency to return to a state of equilibrium after experiencing a disturbance. In general, an aircraft with a forward CG tends to have inherent stability because the lift generated by the wings acts in such a way that it helps restore the aircraft to level flight after it pitches up or down. Conversely, when the CG moves aft, the restoring moments during pitch disturbances become reduced, meaning the aircraft may be more prone to excessive pitching movements and become more challenging to control. This reduced stability arises because the aerodynamic forces generated by the wings and tail are affected by the CG location. With an aft CG, the tail has less authority to counteract pitch changes, leading to a condition where the aircraft can exhibit tendencies toward increased sensitivity to control inputs, potentially resulting in a state that feels less stable overall. In summary, as the center of gravity moves aft, the stability of the aircraft decreases, leading to a more challenging flight experience due to reduced control authority and increased susceptibility to pitch changes.