Which component of an aircraft primarily acts to maintain stability in the longitudinal axis?

The elevator is the component of an aircraft that primarily maintains stability in the longitudinal axis, which refers to the plane's pitch stability. The elevator is located on the horizontal stabilizer at the tail of the aircraft, and it controls the up and down movement of the aircraft's nose. When the pilot adjusts the elevator's position, it changes the angle of attack of the tail section, resulting in a nose-up or nose-down attitude. This action allows the aircraft to ascend or descend, directly influencing its pitch stability.

Ailerons and rudders serve different functions. Ailerons are located on the wings and primarily control roll around the longitudinal axis, while the rudder is located on the vertical stabilizer and manages yaw, or movement around the vertical axis. Flaps, located on the wings, are used primarily to increase lift during takeoff and landing and do not directly contribute to maintaining pitch stability. Thus, it is the elevator that is specifically responsible for maintaining stability along the longitudinal axis, making it the correct answer.