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Stabilizer (aeronautics)

technology Maturity 11-13 Next article →

An aircraft stabilizer is an aerodynamic surface used to provide stability and control.

Tail of a conventional aircraft
Tail of a conventional aircraft

These surfaces manage two main movements: pitch and yaw. Pitch is the up and down movement of the aircraft's nose. Yaw is the side to side movement of the nose. Most aircraft use a tail unit called an empennage. This unit typically includes a vertical stabilizer and a horizontal stabilizer. Together, they allow a pilot or an autopilot to guide the plane through the air.

Horizontal stabilizers are essential for maintaining longitudinal balance, which is often called trim. To achieve trim, the stabilizer exerts a vertical force at a distance from the aircraft's center of gravity. This force ensures that the sum of the pitch moments is zero. The amount of force needed changes constantly during a flight. For example, the force varies based on the aircraft's lift coefficient and the deflection of wing flaps. The center of gravity also shifts as the aircraft consumes fuel or carries different loads.

Adjustable stabilizer
Adjustable stabilizer

Additionally, transonic flight creates unique demands. When air over a wing reaches the speed of sound, the center of pressure moves aft suddenly.

Beyond balancing the plane, horizontal stabilizers provide longitudinal static stability. Static stability is the tendency of an aircraft to return to its trimmed condition if it is disturbed. This allows the aircraft to maintain a constant pitch angle relative to the airstream without constant pilot input. For a conventional wing to be stable, the center of gravity must be ahead of the center of pressure. Because of this, a stabilizer located at the rear of the aircraft must produce a downward force. The elevator is the specific part used to control the pitch axis.

Trimmable horizontal stabiliser
Trimmable horizontal stabiliser

In some designs, the entire tail assembly moves to act as a control surface.

There are several ways to configure a horizontal stabilizer. The most common is the conventional tailplane. This setup uses a fixed surface with a hinged aft section called an elevator. Some light aircraft, such as the Piper PA-28 Cherokee, use a different design called a stabilator. A stabilator is a single, all-moving surface with no separate elevator. This design is also common in supersonic aircraft to reduce drag. Many large airliners use a trimmable tailplane combined with independent elevators. In the Boeing 737, an electrically operated jackscrew powers the stabilizer trim system.

Adjustable stabilizer
Adjustable stabilizer

Some aircraft use more complex arrangements like the three-surface configuration. The Piaggio P.180 Avanti is a notable example of this type.

Piaggio P-180 Avanti Rennes 2010
Piaggio P-180 Avanti Rennes 2010

These planes have a tailplane at the rear and a foreplane, or canard, at the front. The canard provides lift and serves as a balancing surface. This differs from the canard configuration seen on the Beechcraft Starship.

NASA-2000Starship
NASA-2000Starship

In a canard design, the small front wing is often called a stabilizer. While a rear stabilizer usually pushes downward, a front stabilizer lifts upward. In some unstable aircraft, these canards act as part of an electronic stability system.

Other aircraft are designed to be tailless. The Concorde is a famous example of a tailless configuration.

Concorde on Bristol
Concorde on Bristol

These planes do not have a separate horizontal stabilizer. Instead, the main wing itself handles the stabilizing work. This is achieved by designing the wing so its aerodynamic center is behind the center of gravity. Engineers can do this by using reflexed camber airfoils or by varying the wing's angle of incidence through wing washout. This allows the wing to provide both lift and stability without extra parts.

Vertical stabilizers provide directional stability, which manages yaw. This is usually done with a fixed fin and a movable rudder. When a horizontal gust of wind hits the plane, yaw stability causes the aircraft to turn into the wind. Some aircraft lack a vertical stabilizer entirely. They use wing sweep or dihedral to provide directional stability instead. Control is then managed by adding drag to one side using spoilers or split ailerons. Some designs even combine both horizontal and vertical roles into a V-tail.

V-Tailed Beechcraft Bonanza
V-Tailed Beechcraft Bonanza

The Beechcraft Bonanza uses this V-tail arrangement. The moving parts in a V-tail are called ruddervators, which act as both rudders and elevators. While this can reduce the wetted area of the tail, it increases the complexity of the control systems.

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🖼️ Images & Media (7)
File:Tail of a conventional aircraft.svg
Tail of a conventional aircraft.svg
File:Adjustable stabilizer.svg
Adjustable stabilizer.svg
File:Trimmable horizontal stabiliser.JPG
Trimmable horizontal stabiliser.JPG
File:Piaggio P-180 Avanti Rennes 2010.jpg
Piaggio P-180 Avanti Rennes 2010.jpg
File:NASA-2000Starship.jpg
NASA-2000Starship.jpg
File:Concorde on Bristol.jpg
Concorde on Bristol.jpg
File:V-Tailed Beechcraft Bonanza.jpg
V-Tailed Beechcraft Bonanza.jpg
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