position. In the event of hydraulic failure, a slip link
fail, the rudder servo cylinders automatically receive
allows movement of the control valve linkage to port
hydraulic power from the backup hydraulic system
hydraulic fluid from the actuating cylinder. Then the
(flight control backup module). The rudder trim
cylinder can be mechanically driven by pilot input
switch on the EXT ENVIRONMENT/THROTTLE
during manual operation. In manual operation, surface
control panel enables trimming of the aircraft in yaw.
travels are reduced by the lost-motion effect of the slip
Setting the switch to L or R provides a trim-left or
link.
trim-right input, respectively, to the rudder trim
The load-feel bungee is also the connecting link
actuator. The actuator provides rudder movement
from the rudder trim actuator to the power mechanism.
through the rudder-feel assembly, the yaw summing
When the trim actuator is operated, the bungee
network, the reversing network, and the rudder servo
r e p o s i t i o n s t h e p ow e r m e c h a n i s m . T h e p ow e r
cylinders.
mechanisms deflect the rudder for nose-left and
nose-right trim. Figure 16-15 is a functional schematic
ELECTRONIC PRIMARY FLIGHT
of the operation of the rudder control system.
CONTROL SYSTEMS
The rudder power mechanism is actuated when
All electronic flight control servo cylinders are
movement from the cable sector assembly is
controlled by electrical impulses from computers. The
transmitted through the push-pull tube to the primary
computers compare all data received from the pilot's
control crank. The crank is connected to the load-feel
control stick, airspeed indicator, altimeter, angle of
bungee, a slip link to the secondary crank, a link and
spring to the pedal position transmitter, and a link to
attack, and other sensors. They configure all flight
the control valve of the actuator assembly. The actuator
controls for best flight characteristics and performance
assembly consists of an electromechanical dual input
of the aircraft. An example of the electrical portion that
control valve, a rudder surface position transmitter,
replaces the mechanical linkages system is shown in
and a power cylinder. When the mechanism linkage is
figure 16-16. Each electric component is duplicated
actuated, the control valve directs hydraulic pressure
two to four times throughout the system. Provisions are
from both the utility hydraulic system and the surface
made to detect a failed component or sensor and
control hydraulic system to the power cylinder. The
remove its influence from the system. These multiple
valve directs the hydraulic pressure to two separate
redundant paths ensure that a single failure has no
chambers in the cylinder. Each chamber has a separate
effect, and multiple failures have minimum effect on
piston that is mounted on as common shaft. The shaft is
controls.
connected to a push-pull tube that moves the rudder.
The actuator assembly normally operates from both
Q16-4. On small or low-speed aircraft, cockpit flight
hydraulic systems. If one system should fail, the other
controls are connected directly to control
supplies sufficient pressure to operate the rudder with
surfaces by what means?
some lost hinge movement. In the event both hydraulic
Q16-5. On high-speed aircraft, what components aid
systems fail, the slip link will allow movement of the
the pilot in moving the flight control surface?
control valve linkage to port hydraulic fluid from the
actuating cylinder.
Q16-6. Current specifications call for what type of
power source for emergency operation of a
When the automatic flight control system is
primary flight control system?
engaged, the actuator initiates the movement of the
rudder system through the electrical impulse received
Q16-7. In an elevator system, what component ports
by the control valve from the surface control amplifier.
hydraulic pressure to the power cylinder?
The pedal position transmitter and the rudder surface
Q16-8. With the stabilizer trimmed nose down, what
transmitter function only when the automatic flight
action does the load-feel bungee add on the
control system is engaged.
elevator?
Rudder pedal movement transfers mechanically to
the left and right rudder servo cylinders through the
Q16-9. Stabilizer trim deflection on an S-3 aircraft is
rudder feel assembly, the yaw summing network, and
from how many degrees down to up?
the reversing network. These servo cylinders, normally
powered by the flight and combined hydraulic power
Q16-10. What is the maximum surface deflection of
each stabilator on an F/A-18 aircraft?
systems, move the rudders. If both hydraulic systems
16-17
