The horizontal stabilizer is a fixed or adjustable surface located at the tail of an aircraft, specifically at the rear of the fuselage in the conventional configuration. Its fundamental function is to maintain the aircraft in longitudinal balance or trim by exerting a vertical force at a distance, guaranteeing that the summation of pitch moments about the center of gravity is zero. By providing a downward-acting force on the tail to oppose the nose-down pitching moment, this small horizontal tail or tailplane keeps the aircraft flying straight.
Derived from the basic stabilizer - a fixed wing section whose job is to deliver stability - the horizontal stabilizer can be implemented either as a discrete fixed tailplane or as a stabilator, a one-piece horizontal tail surface that pivots up and down about a central hinge point.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is a horizontal stabilizer in an airplane?
The horizontal stabilizer is a fixed or adjustable surface located at the tail of an aircraft. It is part of the tailplane assembly positioned behind the main lifting surfaces of a fixed-wing aircraft. This stabilizer controls the aircraft's pitch motion, balances the longitudinal axis, and maintains stability during flight. The stabilizer provides longitudinal stability and the elevator hinged to it is the movable section that changes the pitching moment.
Where is the horizontal stabilizer located?
The horizontal stabilizer is located at the rear of the fuselage, forming part of the tail behind the main lifting surfaces of the aircraft. In a conventional configuration, the fixed horizontal surface is placed at the tail and integrates the elevator as its control surface.
What is the function of the horizontal stabilizer in an aircraft?
The horizontal stabilizer provides stability for the aircraft and prevents unwanted pitch motions. During normal flight, it creates a constant downward force at the tail. This downward force counteracts the nose-up pitching moment generated by the aircraft's centre of gravity. Because most aircraft are designed to be slightly nose-heavy, the stabilizer provides a downward-acting force on the tail so that the summation of pitch moments about the centre of gravity remains zero.
When the stabilizer is placed in front of the wing, as on a canard aircraft, the canard creates lift and holds the nose up rather than pushing the tail down. On delta-wing aircraft the same surface provides lift at low speed. The basic principle remains unchanged: the aerodynamic forces counteract pitch tendencies and maintain longitudinal stability.
The elevator provides pitch control of the aircraft, while a trim tab is used to relieve pilot input forces. By adjusting the angle of the whole stabilizer, a trimmable stabilizer provides strong trimming power, enabling the pilot to maintain equilibrium without continuous force on the control column. In every configuration, whether the force is upward on a canard or downward on an aft tail, the horizontal stabilizer provides stability for the aircraft and ensures that lift force applied at a distance L from the aircraft’s centre of gravity balances the pitching moments.
I understand that the horizontal stabilizer’s main purpose is to provide longitudinal stability. It does this by creating a downward pressure at the back of the aircraft, which counters the nose-up tendency produced by the wing and the aircraft's center of gravity. Without it, the aircraft would be unsteady along its side-to-side line, making exact command over orientation impossible. The steadying force rectifies small variations.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
How does a horizontal stabilizer work?
Horizontal stabilizers work by balancing aerodynamic forces acting on aircraft. In flight, wings push the fuselage up and generate a nose-down pitching moment because the center of gravity lies forward of the aerodynamic center. To counteract this tendency, the stabilizer provides a downward-acting force on the tail. This downward-acting force opposes and balances the nose-down force, so the vertical force makes the summation of pitch moments about the center of gravity zero and the whole assembly maintains horizontal static equilibrium.
The effective magnitude of this balancing force is varied by the elevators. The elevators work by altering the effective shape of the airfoil of the horizontal stabilizer: altering the angle of deflection at the rear of an airfoil changes the amount of lift generated by the foil. Greater downward deflection of the trailing edge increases lift in the negative (downward) direction, while upward deflection reduces it. Thus, elevator deflection up causes more force to push down on the tail, which lifts the nose up, whereas downward elevator movement decreases the downward tail force and allows the nose to drop. In this way, elevators raise or lower the nose and govern the up-and-down motion of the nose called pitch.
What controls horizontal stabilizer movement?
Horizontal stabilizer movement is governed by a single electric trim motor controlled through stab trim switches on the control wheel or through autopilot trim. The trim motor drives a ball screw actuator assembly that positions the stabilizer Hydraulic pressure from trim modules, regulated by solenoid valves, powers the hydraulic motors that turn the screw. Releasing a stab trim switch directs a trim module to stop the stabilizer, while brakes prevent inadvertent movement when no trim is commanded.
On smaller aircraft, the jackscrew is cable-operated with a manual trim wheel or crank whereas on larger jets it is motor-driven. An alternate pitch trim lever on the center console provides manual control if the electric path fails. Position transducers send continuous stabilizer position indications to the cockpit.
The trimmable stabilizer itself does not respond to control column or control stick deflection. Instead, pitch commands are executed by elevators attached to the stabilizer. These elevators are controlled by forward or aft movement of the control column, altering camber and lift to rotate the aircraft around the lateral axis. When the autopilot is equipped, it commands stabilizer adjustments directly, assuring the airplane remains in the selected pitch attitude without pilot effort.
What are the types of horizontal stabilizer?
The types of horizontal stabilizer are outlined below.
- Trimmable Horizontal Stabilizer: A trimmable stabilizer allows larger center-of-gravity range and provides strong trimming power, while the hinged aft elevator surface supplies primary pitch control.
- Canard Horizontal Stabilizer: A canard configuration provides an upward balancing force rather than the downward force of a conventional tail.
- T-tail Horizontal Stabilizer: The T-tail stabilizer is positioned at the top of the vertical stabilizer, forming a T shape.
What is the design of a horizontal stabilizer?
A horizontal stabilizer is a fixed or adjustable surface whose planform is almost always tapered, a choice that improves lift distribution and reduces drag. The tailplane is designed as an all-moving tail, in which the entire surface rotates for pitch control, or it carries a hinged elevator attached to the back of the stabilizer. In the latter case, the elevator changes the amount of lift generated by the foil by altering the effective shape of its airfoil. Greater downward deflection of the trailing edge increases lift, and upward deflection does the opposite, giving the pilot rapid pitching authority.
Many stabilizers are given a slight negative camber. The fixed incidence angle of around 2° to 3° downwards already makes the horizontal tailplane produce negative lift, and designers strengthen the effect by installing a cambered airfoil upside-down, as seen on the Zenith CH 701 STOL. A reverse-camber section carries negative camber relative to the freestream, reinforcing the nose-down pitching moment needed when the center of gravity sits ahead of the wing's center of lift.
Whether the surface is fixed or trimmable, its leverage depends on the tail arm, the distance between the stabilizer quarter-chord and the aircraft. This determines the stability of the craft and how much pitching moment the tail can generate. Forward-swept horizontal tails are possible but not common in production aircraft, so the dominant layouts remain straight or slightly aft-swept tapered surfaces with either an integral elevator or a trim tab that continues the same contour as the tailplane.
Why don't horizontal stabilizers have winglets?
Horizontal stabilizers do not have winglets because their weight outweighs the very slight aerodynamic benefit when attached to the horizontal stabilizer. Winglets are vertical or angled extensions at the tips of an airplane's wings that inhibit wingtip vortices and reduce induced drag. Stabilizer winglets result in drag without useful lift, and the stabilizer's mission is only to balance pitching moments, not to generate sustained lift. Because the stabilizer spends most flight time at a low angle of attack, wingtip vortices there are weak. Therefore, the devices that reduce wingtip vortex on the main wing offer almost no payoff overhead. Smaller aircraft already achieve adequate trim efficiency, so adding winglets to the tail has the opposite of the desired effect while adding weight exactly where inertia matters most for control response.
Horizontal stabilizers do not carry winglets because their primary duty is to supply pitch steadiness and guidance, not to create the lift that creates strong wing tip vortices. Since the tail is not a main lifting surface, the aerodynamic hindrance at its tips is too slight to justify the added burden, complication, and price of winglets. Inserting such devices would demand a strengthened structure to absorb extra loads, yet the small efficiency gain would fail to warrant the change.
What are the dimensions of a horizontal stabilizer?
Horizontal stabilizer dimensions vary greatly by aircraft but are generally sized as a percentage (around 15-25%) of the main wing's area. For the 747, the horizontal tail area equals 136m (1,464 ft), which is 0.267 of the 511 m (5,500 ft) wing. Horizontal stabilizer semispan is about 40% of main-plane semispan, and its aspect ratio is always less than that of the wing. Preliminary sizing uses non-dimensional volume ratios: the horizontal tail volume coefficient for transport jets is 1.00.
What is the best aerofoil for a horizontal stabilizer?
The best aerofoil for a horizontal stabilizer is a thin, symmetrical airfoil. Sections like the NACA 0009 and NACA 0012 give good pressure recovery and predictable pitching moments. Symmetrical airfoils do not produce lift or lift-induced drag at zero angle of attack, so the pilot trims the aircraft with zero elevator deflection. When the elevator is deflected, the effect is equivalent to adding camber to the section shape, giving the required positive or negative lift for trimmed flight. This keeps induced drag and hinge-moment variations low through the full control range. Because symmetric sections do not generate a pitching moment, they also supply a consistent restoring moment whichever face the wind strikes, an advantage that is helpful on aerobatic and racing aircraft that are otherwise more vulnerable to crosswinds and turbulent air. The airfoil has a low base-drag coefficient so that it remains efficient at the modest Reynolds numbers typical for a tail surface. For these reasons both the horizontal and the vertical stabilizers on almost every airplane, trainer or transport alike, are built with a NACA 0012 profile or a similarly thin symmetric NACA section.
