on the underside of each wing. The jacking points may
also be used as tiedown fittings for securing the aircraft.
Various points on the wing are located by station
number. Wing station 0 (zero) is located at the center
line of the fuselage. All wing stations are measured in
inches outboard from that point, as shown in figure 1-2.
The stabilizing surfaces of an aircraft consist of
vertical and horizontal airfoils. These are known as the
vertical stabilizer (or fin) and the horizontal stabilizer.
These two airfoils, together with the rudder and
elevators, form the tail section, For inspection and
maintenance purposes, the entire tail section is con-
sidered a single unit of the airframe, and is referred to
as the "empennage."
The primary purpose of the stabilizers is to stabilize
the aircraft in flight; that is, to keep the aircraft in straight
and level flight. The vertical stabilizer maintains the
stability of the aircraft about its vertical axis. 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 the lateral axis. This is longitudinal
stability. It usually serves as the base to which the
elevators are attached.
At high speeds, forces acting upon the flight
controls increase, and control of the aircraft becomes
difficult. his problem can be solved through the use of
power-operated or power-boosted flight control
systems. These power systems make it possible for the
pilot to apply more pressure to the control surface
against the air loads. By changing the angle of attack of
the stabilizer, the pilot maintains adequate longitudinal
control by rotating the entire horizontal stabilizer
Construction features of the stabilizers are in many
respects identical to those of the wings. They are usuall y
of an all-metal construction and of the cantilever design.
Monospar and two-spar construction are both com-
monly used. Ribs develop the cross-sectional shape. A
"fairing" is used to round out the angles formed between
these surfaces and the fuselage.
The construction of control surfaces is similar to
that of the wing and stabilizers. They are usually built
around a single spar or torque tube. Ribs are fitted to the
spar near the leading edge. At the trailing edge, they are
joined together with a suitable metal strip or extrusion.
For greater strength, especially in thinner airfoil sections
typical of trailing edges, a composite construction
material is used.
FLIGHT CONTROL SURFACES
The flight control surfaces are hinged or movable
airfoils designed to change the attitude of the aircraft
during flight. Flight control surfaces arc grouped as
systems and are classified as being either primary or
secondary. Primary controls are those that provide
control over the yaw, pitch, and roll of the aircraft.
Secondary controls include the speed brake and flap
systems. All systems consist of the control surfaces,
cockpit controls, connecting linkage, and other
necessary operating mechanisms.
The systems discussed in this chapter are
representative of those with which you will be working.
However, you should bear in mind that changes in these
systems are sometimes necessitated as a result of later
experience and data gathered from fleet use. Therefore,
prior to performing the maintenance procedures
discussed in this chapter, you should consult the current
applicable technical publications for the latest
information and procedures to be used.
Primary Flight Control Systems
The primary flight controls are the ailerons,
elevators, and rudder. The ailerons and elevators are
operated from the cockpit by a control stick on fighter
aircraft. A wheel and yoke assembly is used on large
aircraft such as transports and patrol planes. The rudder
is operated by rudder pedals on all types of aircraft.
The ailerons are operated by a lateral (side-to-side)
movement of the control stick or a turning motion of the
wheel on the yoke. The ailerons are interconnected in
the control system and work simultaneously, but in
opposite directions to one another. As one aileron moves
downward to increase lift on its side of the fuselage, the
aileron on the opposite side of the fuselage moves
upward to decrease lift. This opposing action allows
more lift to be produced by the wing on one side of the
fuselage than on the other side. This results in a
controlled movement or roll because of unequal forces
on the wings. The aileron system can be improved with
the use of either powered controls or alternate control
The elevators are operated by a fore-and-aft
movement of the control stick or yoke. Raising the
elevators causes the aircraft to climb. Lowering the
elevators causes it to dive or descend. The pilot raises