What defines longitudinal stability in an aircraft?

The correct answer identifies that longitudinal stability in an aircraft is determined by the position of the center of pressure relative to the center of gravity. When the center of pressure, which is the point at which aerodynamic forces act, is located aft of the center of gravity, it creates a restoring moment that helps return the aircraft to its original flight attitude after an upward or downward disturbance. This inherent design leads to stable flight characteristics along the longitudinal axis, which is primarily concerned with pitch control and stability.

If the center of pressure is positioned forward of the center of gravity, the aircraft could become unstable, leading to a tendency to dive or pitch erratically. Thus, the relationship between the center of pressure and the center of gravity is critical for achieving effective longitudinal stability during flight. This understanding is essential for pilots and engineers when considering aircraft design or evaluating performance characteristics.