vertical stabilizer (or fin) and horizontal stabilizer.
These two airfoils, along with the rudder and elevators,
form the tail section. For inspection and maintenance
purposes, the entire tail section is considered a single
unit called the empennage.
The main purpose of stabilizers is to keep the
aircraft in straight-and-level flight. The vertical
stabilizer maintains the stability of he aircraft about its
vertical axis (fig. 4-9). This is known as directional
stability. The vertical stabilizer usually serves as the
base to which the rudder is attached. The horizontal
stabilizer provides stability of the aircraft about its
lateral axis. This is known as longitudinal stability. The
horizontal stabilizer usually serves as the base to which
the
elevators
are
attached.
On
many
newer,
high-performance aircraft, the entire vertical and/or
horizontal stabilizer is a movable airfoil. Without the
movable airfoil, the flight control surfaces would lose
their effectiveness at extremely high altitudes.
Stabilizer
construction
is
similar
to
wing
construction. For greater strength, especially in the
thinner airfoil sections typical of trailing edges, a
honeycomb-type construction is used. Some larger
carrier-type aircraft have vertical stabilizers that are
folded hydraulically to aid aircraft movement aboard
aircraft carriers.
FLIGHT CONTROL SURFACES
Flight control surfaces are hinged (movable)
airfoils designed to change the attitude of the aircraft
during flight. These surfaces are divided into three
groups—primary, secondary, and auxiliary.
Primary Group
The primary group of flight control surfaces
includes ailerons, elevators, and rudders. The ailerons
attach to the trailing edge of the wings. They control the
rolling (or banking) motion of the aircraft. This action
is known as longitudinal control.
The elevators are attached to the horizontal
stabilizer and control the climb or descent (pitching
motion) of the aircraft. This action is known as lateral
control.
The rudder is attached to the vertical stabilizer. It
determines the horizontal flight (turning or yawing
motion) of the aircraft. This action is known as
directional control.
The ailerons and elevators are operated from the
cockpit by a control stick on single-engine aircraft. A
yoke and wheel assembly operates the ailerons and
elevators on multiengine aircraft, such as transport and
4-9
ANf0409
YAW
PITCH
ROLL
VERTICAL AXIS
LATERAL AXIS
LONGITUDINAL AXIS
Figure 4-9.—Axes and fundamental movements of the aircraft.
