angle changes result from both collective pitch
These linkages and controls transmit force to
stick and rudder pedal movement. The auxiliary
primary and auxiliary hydraulic system servo
servo irreversible transfer of collective pitch
c y l i n d e r s and to the rotary rudder. The
motion will act to displace the rudder. The rudder
mechanical flight controls have two independent
pedal motion will not affect rotary wing collective
systems. They are the rotary wing flight control
pitch blade angle.
and the rotary rudder flight control systems.
The rotary rudder control system controls
The rotary wing flight controls consist of cyclic
helicopter heading by moving control rods and
and collective pitch control sticks, a mixing unit,
bell cranks connected to the auxiliary servo
a balance spring, and linkage. The cyclic controls
cylinder. The auxiliary servo cylinder connects to
give forward, aft, and lateral movement of the
helicopter. The collective controls give vertical
the mixing unit by control rods. At the mixing
control of the helicopter.
unit, a control rod operates a forward quadrant.
From the forward quadrant, cables operate a rear
The rotary rudder flight controls consist of
quadrant in the aft fuselage. A control rod from
pedals, pedal switches, and pedal adjusters for the
the rear quadrant connects, at the pylon hinge
pilot and copilot. Other system components are
a negative force gradient spring and mechanical
line, to the control rods, bell cranks, and pitch
linkage. The rotary rudder compensates for the
control shaft. These units are found in the tail
gearbox. A hydraulic pedal damper in the servo
torque of the rotary wing. The controls provide
cylinder prevents sudden movements of the
a way to change the heading (direction) of the
control pedals from causing rapid changes in
helicopter.
The cyclic pitch control system controls the
blade pitch, which might damage the helicopter.
A typical helicopter flight control system
forward, aft, and lateral movements of the
consists of four subsystems. They are the cyclic
helicopter. Control comes from the pilot's or
pitch control sticks for directional flight, the
copilot's cyclic stick. Control rods and bell cranks
collective pitch control sticks for vertical flight,
connect the stick to the auxiliary servo cylinders,
then to the mixing unit, and three primary servo
the directional heading control (rudder) pedals,
and the throttle. The throttle may be a motor-
cylinders. The primary servo cylinders control
cycle-type grip mounted on the collective pitch
movement of the rotary wing blades through the
stick. The throttle may be lever-type mounted on
swashplate. The swashplate changes the pitch of
the center overhead console. Also included are an
the blades.
auxiliary servo cylinder, a mixing unit, primary
The collective pitch control system provides
servo cylinders, and mechanical linkage.
vertical control of the helicopter. Control comes
The cyclic pitch control stick controls forward,
from the pilot's and copilot's collective pitch
aft, and lateral helicopter movements. The
control sticks. Control rods and bell cranks
collective pitch control stick controls vertical
connect the stick to the auxiliary servo cylinder,
helicopter movement. The directional control
then to the mixing unit. At the mixing unit,
movements of the collective stick are sent to the
pedals control helicopter headings. See figure 7-4.
Movement of the control sticks is sent by
primary servo cylinders and the swashplate. The
mechanical linkage to a hydraulically operated
swashplate increases or decreases the pitch of all
auxiliary servo cylinder for power boost. The
blades equally and simultaneously. A balance
boosted input is sent through a mixing unit for
spring on a control rod helps to balance the weight
coordination with any heading directional control
of the collective stick when the auxiliary servo
inputs. Stick movement is finally sent through the
system is off.
hydraulically actuated primary servo cylinders to
A collective-to-cyclic pitch coupling (fore-and-
the rotary wing head. At the rotary wing head,
aft) is found in the mixing unit. The coupling
blade pitch changes.
automatically applies a nose-down pitching cor-
rection when the collective pitch stick is raised.
When the collective pitch stick is lowered, a
TYPES OF HELICOPTERS
nose-up pitching correction is made. This action
provides attitude control during transitions,
Helicopters are of two basic types. They are
especially during automatic stabilization equip-
the single-rotor and multi-rotor types. The single
ment (ASE) system transitions.
main rotor with a vertical tail rotor is the most
A collective-to-yaw coupling provides
common type of helicopter. The SH-60 or SH-2,
automatic rotary rudder pitch changes to adjust
shown in figure 7-5, are examples of single-rotor
for collective pitch changes. Rotary rudder blade
7-6
