The ailerons are operated by a lateral (side-to-side)
cantilever design. Monospar and two-spar construction
movement of the control stick or a turning motion of the
are both commonly used. Ribs develop the
wheel on the yoke. The ailerons are interconnected in
cross-sectional shape. A "fairing" is used to round out
the control system and work simultaneously, but in
the angles formed between these surfaces and the
opposite directions to one another. As one aileron
fuselage.
moves downward to increase lift on its side of the
The construction of control surfaces is similar to
fuselage, the aileron on the opposite side of the fuselage
that of the wing and stabilizers. They are usually built
moves upward to decrease lift. This opposing action
around a single spar or torque tube. Ribs are fitted to the
allows more lift to be produced by the wing on one side
spar near the leading edge. At the trailing edge, they are
of the fuselage than on the other side. This results in a
joined together with a suitable metal strip or extrusion.
controlled movement or roll because of unequal forces
For greater strength, especially in thinner airfoil
on the wings. The aileron system can be improved with
sections typical of trailing edges, a composite
the use of either powered controls or alternate control
construction material is used.
systems.
On most modern day fighters like the F/A-18 there
The elevators are operated by a fore-and-aft
is also a stabilator incorporated as part of the flight
movement of the control stick or yoke. Raising the
controls. The stabilator is a control surface located on
elevators causes the aircraft to climb. Lowering the
either side of the tail. In flight, the stabilator deflects
elevators causes it to dive or descend. The pilot raises
symmetrically to produce pitch motion and
the elevators by pulling back on the stick or yoke and
asymmetrically to produce roll motion. The maximum
lowers them by pushing the stick or yoke forward.
surface deflection of each stabilator is 10.5 degrees
The rudder is connected to the rudder pedals and is
trailing edge down to 24 degrees trailing edge up.
used to move the aircraft about the vertical axis. If the
Flight Control Surfaces
pilot moves the rudder to the right, the aircraft turns to
the right; if the rudder is moved to the left, the aircraft
The flight control surfaces are hinged or movable
turns to the left. The pilot moves the rudder to the right
airfoils designed to change the attitude of the aircraft
by pushing the right rudder pedal, and to the left by
during flight. Flight control surfaces are grouped as
pushing the left rudder pedal.
systems and are classified as being either primary or
Power control systems are used on high-speed jet
secondary. Primary controls are those that provide
aircraft. Aircraft traveling at or near supersonic speeds
control over the yaw, pitch, and roll of the aircraft.
have such high air loads imposed upon the primary
Secondary controls include the speed brake and flap
control surfaces that the pilot cannot control the aircraft
systems. All systems consist of the control surfaces,
without power-operated or power-boosted flight
cockpit controls, connecting linkage, and other
control systems. In the power-boost system, a
necessary operating mechanisms.
hydraulically operated booster cylinder is incorporated
The systems discussed in this chapter are
within the control linkage to assist the pilot in moving
representative of those with which you will be working.
the control surface. The power-boost cylinder is still
However, you should bear in mind that changes in these
used in the rudder control system of some
systems are sometimes necessitated as a result of later
high-performance aircraft; however, the other primary
experience and data gathered from fleet use. Therefore,
control surfaces use the full power-operated system. In
prior to performing the maintenance procedures
the full power-operated system, all force necessary for
discussed in this chapter, you should consult the current
operating the control surface is supplied by hydraulic
applicable technical publications for the latest
pressure. Each movable surface is operated by a
information and procedures to be used.
hydraulic actuator (or power control cylinder)
incorporated into the control linkage.
Primary Flight Control Systems
In addition to the current Navy specification
requiring two separate hydraulic systems for operating
The primary flight controls are the ailerons,
the primary flight control surfaces, specifications also
elevators, and rudder. The ailerons and elevators are
call for an independent hydraulic power source for
operated from the cockpit by a control stick on fighter
emergency operation of the primary flight control
aircraft. A wheel and yoke assembly is used on large
surfaces. Some manufacturers provide an emergency
aircraft such as transports and patrol planes. The rudder
system powered by a motor-driven hydraulic pump;
is operated by rudder pedals on all types of aircraft.
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