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
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
Piper Pa28 is an example.
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.
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.
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