Multirotor helicopters fall into different groups
according to their rotor configuration. The CH-46,
shown in figure 10-5, is a multirotor helicopter of the
tandem rotor design.
The single-rotor configuration requires the use of
a vertical tail rotor to counteract torque and provide
directional control. The advantages of this con-
figuration are simplicity in design and effective
directional control. In the tandem rotor design, one
rotor is forward of the other. Sometimes the rotor
blades are in the same plane. They may or may not
The design offers good longitudinal
stability since lift occurs at two points, fore and aft.
The tandem rotor has little torque to overcome
because these rotors rotate in opposite directions.
HELICOPTER FLIGHT CONTROLS
Learning Objective: Identify the three
primary flight controls and the basic control
Helicopter flight controls differ drastically from
those found in fixed-wing aircraft. Helicopter flight
controls consist of both cyclic and collective pitch
control systems and the rotary rudder flight control
The hydraulically powered flight control
mechanism, shown in figure 10-6, provides you with
an example of systems common to most helicopters.
These are the systems on which you will most likely
be working. Fairly exact values, such as tolerances,
pressures, and temperatures, are given to provide
instructive coverage. When actually performing the
maintenance procedures, consult the current technical
publications for the latest information and exact
CYCLIC PITCH CONTROL SYSTEM
The cyclic pitch control system provides the
means of controlling the forward, aft, and lateral
movements of the helicopter. Movement of the pilots
or copilots c yclic stick transmits through control rods
and bell cranks.
This movement is sent to the
auxiliary servo cylinders, the mixing unit, and three
primary servo cylinders. These primary servo
cylinders control movement of the rotary-wing
The cyclic system has a stick trim system that
hydraulically operates the controls for automatic
flight. During automatic flight, trim movements are
controlled manually by the cyclic stick grip switch.
The switch is overridden for major control changes by
Moving the cyclic stick forward extends the aft
primary servo cylinder and retracts the forward
primary servo cylinder. Aft movement of the cyclic
stick extends the forward primary servo cylinder and
retracts the aft primary servo cylinder. In both cases,
the helicopter will advance in the direction of stick
Movement of the stick laterally will
move the helicopter right or left, corresponding with
stick movement. This movement occurs by retracting
and extending the left and right lateral primary servo
COLLECTIVE PITCH CONTROL SYSTEM
The collective pitch control system provides
vertical control of the helicopter. Movement of the
collective pitch control stick is sent through control
rods and bell cranks to the appropriate auxiliary servo
cylinder. Movement is sent from the servo cylinder to
the mixing unit.
At the mixing unit, all vertical
movements of the collective sticks are sent to the
primary servo cylinders and the rotary-wing
swashplate. At this point, the pitch of all blades
increases or decreases equally and simultaneously. A
balancing spring attaches to the control rods to help
balance the weight of the collective stick. A friction
lock on the pilots collective stick applies the desired
amount of friction to the tube of the collective stick.
The lock prevents creeping during flight. It also
provides feel for the pilot when operating the
The friction is applied by rotating the
serrated handgrip on the collective stick to its stop.
The grip of each collective stick contains several
switches that are labeled for the function they control.
In the automatic stabilization equipment (ASE) mode
operation, the collective pitch operation controls
through the auxiliary servo cylinder.
ROTARY RUDDER CONTROL SYSTEM
The rotary rudder control system controls the
pitch of the rotary rudder blades. The blades control
the heading of the helicopter. The pedals control the
system through a series of control rods and bell
cranks. These units connect to the directional bank of
the auxiliary servo cylinder and the mixing unit. See
figure 10-6. At the mixing unit, a control rod operates
the forward quadrant.
This quadrant connects by