Private Pilot License (PPL) Aerodynamics Practice Exam

What determines the longitudinal stability of an airplane?

1. The speed of the airplane

2. The location of the center of gravity with respect to the center of lift

3. The design of the wings

4. The weight of the aircraft

The correct answer is: The location of the center of gravity with respect to the center of lift

The longitudinal stability of an airplane is primarily determined by the location of the center of gravity relative to the center of lift. When the center of gravity is positioned ahead of the center of lift, it creates a restoring moment that brings the airplane back to its original attitude after a disturbance. This is crucial for maintaining stable flight, as it helps ensure that the aircraft will naturally return to level flight if it pitches up or down due to external factors, such as turbulence or control input. In contrast, if the center of gravity is located behind the center of lift, the airplane can become significantly less stable, making it difficult to control and potentially leading to uncontrollable flight characteristics. This relationship between the center of gravity and the center of lift is fundamental to aircraft design and flight stability. While speed, wing design, and weight can influence flight characteristics, they do not directly determine longitudinal stability in the same fundamental way that the position of the center of gravity in relation to the center of lift does. Thus, understanding the critical role of the center of gravity location is key to mastering concepts related to aircraft stability.