CHAPTER 16
FIXED-WING FLIGHT CONTROL SYSTEMS
INTRODUCTION
push-pull rods, cables, bell cranks, sectors, and idlers.
Figure 16-1 schematically illustrates the elevator
A flight control system is either a primary or
portion of a mechanical (unboosted) flight control
secondary system. Primary flight controls provide
system. The control stick is mounted in such a way that
longitudinal (pitch), directional (yaw), and lateral
it can pivot backwards and forwards on its mounting
(roll) control of the aircraft. Secondary flight controls
pin. The control stick is connected to a push-pull rod
provide additional lift during takeoff and landing, and
attached to its lower end. As the stick is moved fore and
decrease aircraft speed during flight, as well as
a f t , i t c a u s e s t h e e l eva t o r s t o b e d e f l e c t e d
assisting primary flight controls in the movement of
proportionately.
the aircraft about its axis. Some manufacturers call
The push-pull tube (rod) that connects to the
secondary flight controls auxiliary flight controls. All
lowest point of the control stick extends aft to the
systems consist of the flight control surfaces, the
pulley. Notice that the function of the pulley is to
respective cockpit controls, connecting linkage, and
change the direction of the push-pull action from fore
necessary operating mechanisms.
and aft to up and down. The second push-pull tube
The systems discussed in this course are
(rod) connects the forward cable sector and the pulley,
representative systems. Values such as tolerances,
and causes the sector to rotate according to the stick
pressures, and temperatures provide better
movements.
understanding of the text material. You should bear in
From the forward sector, the cables extend back
mind that these values are for representative units and
through the aircraft to the aft cable sector. They have
are not accurate for all systems. When actually
been reduced in length so that the remaining essential
performing the maintenance procedures discussed,
components of the elevator control system may all be
you should consult the current maintenance instruction
shown in one drawing.
manual (MIM).
The aft sector is essentially the same as the forward
sector, and it acts as a slave to the forward sector.
FLIGHT CONTROL SYSTEMS
Cables from the forward sector attach to the aft edges
of the aft sector. A push-pull tube from the aft sector
LEARNING OBJECTIVE: Identify the
connects to the elevator fitting assembly.
types of flight control systems.
The elevator fitting assembly, commonly called
A flight control system includes all the
the elevator "horn," is built onto the elevators and
components required to control the aircraft about each
extends outward (and usually downward) from the
of the three flight axes. A simple flight control system
elevator surface at right angles to the plane of rotation
may be all mechanical; that is, operated entirely
and the chord line of the elevator surfaces. As the
through mechanical linkage and cable from the control
fitting assembly is moved fore or aft, the elevators are
stick to the control surface. Other more sophisticated
moved up or down.
flight control systems may use electrical or hydraulic
power to provide some or all of the "muscle" in the
system. Still others combine all three methods.
MECHANICAL (UNBOOSTED) FLIGHT
CONTROL SYSTEM
A typical, simple, mechanical (unboosted) flight
control system is the one used in flight training aircraft.
The flight control surfaces (ailerons, elevators, and
Figure 16-1.--Mechanical (unboosted) flight control system.
rudder) are moved manually through a series of
16-1
