The empennage, commonly called the tail assembly (see figure 1-7), is the rear section of the body of the airplane. Its main purpose is to give stability to the aircraft. The fixed parts are the horizontal stabilizer and the vertical stabilizer or fin.

 The front, fixed section is called the horizontal stabilizer and is used to prevent the airplane from pitching up or down.

The rear section is called the elevator and is usually hinged to the horizontal stabilizer. The elevator is a movable airfoil that controls the up-and-down motion of the aircraft's nose.

fig 1 - 7 empennage structure

The vertical tail structure is divided into the vertical stabilizer and the rudder. The front section is called the vertical stabilizer and is used to prevent the aircraft from yawing back and forth. The principle behind its operation is much like the principle of a deep keel on a sailboat. In light, single-engine aircraft, it also serves to offset the tendency of the aircraft to roll in the opposite direction in which the propeller is rotating.

The rear section of the vertical structure is the rudder. It is a movable airfoil that is used to turn the aircraft.

Sometimes the fixed stabilizer and separate movable elevators are replaced by a single moving horizontal tail known as a Stabilator. The Piper Pa28 is an example.


Another variation is to combine the vertical fin and the stabilizer into one pair of controls (two instead of three) which form a Vee shape, known as a V-Tail. The theoretical advantage of this design is the reduced interference drag associated with two surfaces instead of three. On the V-tail the combined rudders and elevators are known as Ruddervators. The engineering is more complicated in this system. The early Beechcraft Bonanzas are an example.

Tailless Aircraft
Although the conventional aircraft described above represent 95% of all the worlds aircraft some of the most important designs are Tailless. Concorde, the AVRO Arrow, and the Space Shuttle are three notable examples. As you may have noticed they are all Supersonic aircraft. In the future, when supersonic flight becomes more common we will probably see more tailless aircraft.

On the tailless aircraft the pitch controls and roll controls must both be on the wing. There can be separate elevators and ailerons or they can be combined into one set of controls known as Elevons.
The tailless aircraft still usually has a vertical Fin with a rudder.

Canard Aircraft
A Canard aircraft is one in which the horizontal stabilizer and elevators are ahead of the main wing. Such aircraft still have the same controls as the conventional aircraft they are just in different places. The aircraft below (Cozy) has two vertical fins and two rudders on the tips of the wings. (An interesting side note about this design is that the left rudder pedal operates the left rudder and vice versa. The rudders only extend outboard. Both rudders can be deflected at once by pushing the rudder pedals together, thus acting like drag brakes.)