What primarily determines the longitudinal stability of an airplane?

The longitudinal stability of an airplane is primarily determined by the location of the center of gravity in relation to the center of lift. In terms of stability, the center of gravity is the point where the weight of the aircraft is balanced. The center of lift, on the other hand, is the point where the aerodynamic forces acting on the wings are concentrated.

When the center of gravity is located ahead of the center of lift, the aircraft tends to have a natural tendency to return to its original flight attitude after being disturbed. This means that if the aircraft experiences a pitch change, it will tend to stabilize itself back to that original position. Conversely, if the center of gravity is behind the center of lift, the airplane can become unstable and is less able to self-correct after being disturbed.

Such positioning directly influences how the aircraft responds to control inputs and external forces. Therefore, understanding this relationship is crucial for ensuring safe and stable flight operations.