empennage

The empennage is the tail assembly of an aircraft, comprising the horizontal stabilizer, the vertical stabilizer, and the control surfaces mounted on them. It typically includes the elevators on the horizontal stabilizer and the rudder on the vertical stabilizer, with trim tabs and sometimes anti-flutter weights or mass balances to reduce dynamic instability. In many designs the tail surfaces are carefully sized and positioned to provide stable recovery from disturbances and to reduce control forces.

The empennage serves two primary functions: it provides stability in pitch and yaw and furnishes the pilot with control authority. The vertical stabilizer offers directional stability and houses the rudder for yaw control; the horizontal stabilizer provides pitch stability and houses the elevator for pitch control. Trim tabs allow aerodynamic trimming without continuous control input. The configuration is influenced by aerodynamics, structural considerations, and interference with the fuselage and wings.

Common configurations include the conventional tail, with separate vertical and horizontal stabilizers located at the rear of the fuselage; the T-tail, where the horizontal stabilizer is mounted atop the vertical stabilizer; the cruciform tail, where stabilizers intersect in a cross shape; and the V-tail, in which two surfaces form a V and are actuated as ruddervators to provide combined pitch and yaw control. Some designs employ twin vertical stabilizers for redundancy or improved directional stability.

Design considerations for the empennage include flutter avoidance, weight balance, structural loads, and aerodynamic efficiency. Tail design also influences control feel, stability across flight regimes, and the aircraft’s behavior during stalls and spins.