Definition

The section of the airplane that consists of the vertical stabilizer, the horizontal stabilizer, and the associated control surfaces.

Pilot’s Handbook of Aeronautical Knowledge

Description

The empennage(also referred to as "tail" or "tail assembly") is located at the rear of an aircraft and provides stability and control. The "regular" tail, which is the most common version of an empennage and is found on e.g. Boeing 737 series, the A320 family, Cessna 172, etc., comprises:

• a vertical stabiliser attached to the rear fuselage
• two horizontal stabilisers attached to the rear fuselage
• a rudder attached to the vertical stabiliser
• elevators attached to the horizontal stabilisers
• trim tabs, attached to the rudder and elevators

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Stability (i.e. the ability to fly in a straight line) is achieved through the horizontal and vertical stabilisers. These are airfoils and are aerodynamically similar to the wings. A random pitch or yaw deviation would cause increased drag at the tail which would automatically create an opposing force that would negate the initial random movement. Being located at the rear end of the aeroplane (and therefore, furthest from the centre of gravity (CG)) allows to achieve the desired effect with smaller surfaces.

The control functions of the empennage are achieved through the rudder and the elevators. These work similarly to flaps and ailerons. For example, when the rudder is deflected to the right, the airflow generates force that pushes the vertical stabiliser to the left, thus causing the aeroplane nose to yaw to the right. Similarly, when the elevator is deflected downwards, the effective angle of attack of the horizontal stabiliser increases, which increases lift and causes a pitch that moves the nose down. Again, being located furthest from the CG allows small surfaces to exert the necessary force.

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While the regular tail is found in most designs (and on most aircraft), alternatives do exist. Examples of these include:

• T-tail. The horizontal stabiliser is located on top of the vertical stabiliser. This design provides better airflow through the horizontal stabiliser as it is not disturbed by the wings. An example of this design is the MD82
• V-tail. Two slanted tail surfaces are used instead of three and these provide both horizontal and vertical stability and control via a ruddervator (a combination of a rudder and an elevator). An example of this design is the CM-175 Zephyr
• H-tail. Two vertical stabilisers are mounted at the ends of the horizontal stabiliser. An example of this design is the Antonov An-22

Stability and control are not always acheieved by the tail assembly. Alternative designs include:

• canard (the horizontal stabiliser is placed in front of the wing). An example of this design is the Saab Viggen
• tail-less design (horizontal stabilisation and control is done via the wing) which often includes a vertical stabiliser. An example of this design is the Dassault Mirage 2000.

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