The horizontal stabilizer is a fixed portion that supplies longitudinal stability and governs up-and-down motion. Hinged to its trailing edge, the elevator is the movable flap that commands pitch. In faster, more agile aircraft, the two surfaces merge into a stabilator - an all-moving tailplane whose entire panel pivots to create and manage pitching motion while simultaneously holding angle-of-attack authority. Thus, where conventional layouts separate stability from control, the stabilator unites them, letting one large, responsive surface change aircraft balance.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the horizontal stabilizer and elevator put together called?
The horizontal stabilizer and elevator put together is called a “stabilator”. A stabilator is a fully movable aircraft horizontal stabilizer, and it combines the functions of both the fixed stabilizer and the movable elevator. On many fighter planes the stabilizer and elevator are combined into one large moving surface called a stabilator.
What is attached to the horizontal stabilizer?
The elevator is attached to the horizontal stabilizer by hinges. On conventional aircraft, the horizontal stabilizer itself is attached to the fuselage near the lower part of the vertical stabilizer, but it is also attached at the midpoint or at the high point in a T-tail design. In that T-tail configuration the horizontal tail surfaces are placed above most of the downwash from the propeller. Some unique aircraft have the horizontal stabilizer attached solid to the vertical stabilizer, and then the entire pair pivots around a point on the empennage.
When the stabilizer is moved as one piece it is called a stabilator. To this stabilator, an anti-servo tab is attached. Whether the elevator is hinged to a fixed stabilizer or forms part of a stabilator, the pilot operates the elevators by moving the control column: forward movement lowers the elevator and depresses the nose, while backward pressure raises the elevator, raising the nose and lowering the tail.
Does the horizontal stabilizer move?
On many aircraft the horizontal stabilizer itself moves, while on others it stays fixed and only the elevator hinges up and down. A fully movable horizontal stabilizer - called an all-moving tailplane - rotates as a single piece to change the pitch moment. Modern aircraft have adjustable stabilizer systems: the entire horizontal tail assembly moves in response to the trim system to stabilize the aircraft in the pitch axis. A trimmable horizontal stabilizer moves when the autopilot commands adjustments, and the same motion is duplicated by the pilot when the plane is flown manually.
The movable horizontal stabilizer is adjusted as speed changes, as fuel is burned, and as the center of gravity moves, so the required nose-up force balances the nose-down force generated by the wings. The leading edge of the stabilizer moves down to give the aircraft a nose-up attitude whereas trailing-edge-up motion produces nose-down pitch. Fully movable horizontal stabilizers on jetliners have the vast majority of their range in the negative angle of attack, and moving the whole stabilizer produces less drag for the same force because camber stays low.
Large commercial airliners have both an all-moving tailplane and elevators, so the flight control system adjusts the stabilizer and its moving parts - usually the elevators - to let the pilot control pitch. Hydraulic motors with differential gears turn the ball screw to which the stabilizer is connected, providing the power for these trim changes. The control stick in the cockpit connects to the aircraft's flight control system, which in turn commands the stabilizer and the elevators. Elevators respond directly to autopilot input. All these surfaces cause a change in pitch: the tail generates a downward force that, when increased or decreased, permits the pilot to move the airplane in curved flight paths.
What is the difference between a horizontal stabilizer and a stabilator?
A horizontal stabilizer is a fixed surface on the tail and its rear edge carries a movable elevator. A stabilator is a flight control surface consisting of a hinged horizontal stabilizer that moves as one piece, so it is alternatively called an all-flying tail. Because the stabilator pivots via a hinge, it combines the functions of the fixed stabilizer and the movable elevator. A conventional stabilizer creates longitudinal stability by keeping the angle-of-attack difference between the main wing and the tail. The small elevator only trims or maneuvers. The stabilator changes the angle of attack of the entire horizontal stabilizer, giving a strong control response and boosted maneuverability. To prevent excessively light stick forces, the stabilator uses an anti-servo tab that provides pilot feedback and appropriate stick force.
What is the difference between a trimmable horizontal stabilizer and an elevator?
A trimmable horizontal stabilizer (THS) differs from a horizontal stabilizer that has only a trimmable elevator. The elevator is the small moving section at the rear of the fixed stabilizer. It is attached by hinges and varies the force generated by the tail surface to generate and control the pitching motion of the aircraft. It changes the effective shape of the airfoil, tilting up or down so the nose goes up or down. Upward deflection produces downward lift at the tail, lowering the nose, while downward deflection creates upward lift, raising the nose. Pilots or the autopilot control the elevator with yoke or stick inputs, and a trim tab on the elevator moves independently to deflect the elevator in the opposite direction, reducing pilot workload and preventing over-controlling.
The entire THS pivots as one rigid surface, forming part of the trimming system and providing trimming power over the full speed and weight range of large transport aircraft and most airliners. Because the stabilizer itself rotates, smaller elevator deflection angles are required for a given pitch change, so the pilot will not notice much difference in handling qualities even though the THS is doing most of the work. The THS is therefore fitted with elevators that still respond to pilot or autopilot pitch commands, but its primary advantage is that it holds the pitch axis in trim as speed changes or fuel is burned, maintaining horizontal static equilibrium with only small additional elevator inputs.
