Under hydraulic pressure, the servo ram then moves in the desired
direction to reposition the rudder actuator servo control valve which, in turn,
results in rudder movement.
As the system moves the rudder, a summing lever / transducer assembly
provides position information to the yaw servo amplifier. The servo
amplifier, in turn, nulls the signal to the transfer valve.
G. Yaw Trim System:
Trim control about the vertical axis is controlled by displacing the entire
rudder surface (there is no rudder trim tab). This is accomplished through
the use of a rudder trim control wheel mounted on the upper aft end of the
center pedestal, shown in Figure 14.
Rotation of the rudder trim control wheel left or right rotates a cable drum
below the cockpit floor through the use of a torque tube. As the drum
rotates, cables transmit the movement to a screw-type rudder trim actuator.
The actuator, in turn, extends and retracts, repositioning the rudder
actuator input cable sector through the trim actuator attachment to the
artificial feel bungee. Movement of the input cable sector provides input to
the rudder actuator servo control valve, thus driving the rudder to effect trim
position.
Since the are no stops incorporated in the rudder trim actuator, total travel
is determined by integral stops in the rudder trim control wheel. Total trim
wheel travel is approximately 6½ turns from stop to stop. This yields a
maximum of 10 units (7.5°) NOSE L (left) and 10 units (7.5°) NOSE R
(right) of rudder deflection from the neutral position.
H. Failure Detection System:
CAA Certified Aircraft Only: A flight control automatic failure detection
system monitors flight control inputs from the rudder pedals and compares
them to the rudder actuator outputs. If the system detects a failure, it
automatically shuts off hydraulic pressure to the actuator and triggers the
appropriate warning on the Crew Alerting System (CAS). Once activated by
a malfunction, hydraulic pressure is inhibited until power to the respective
monitoring system is interrupted, for instance, by pulling and resetting the
appropriate circuit breaker.
The monitoring system is a dual-channel system. One channel controls the
Combined hydraulic system pressure source while the other controls the
Flight hydraulic system pressure source. Power for the system is received
from the 28 VDC Essential DC bus.
A pair of limit switches monitor applied rudder pedal input while a pair of
reed switches monitor actuator output in response to the input.
If a disagreement occurs between rudder pedal input and actuator output,
the associated limit switch and reed switch close to complete a circuit to
the respective hydraulic shutoff delay relay. If the relay remains energized
for more than ½ second, it energizes the respective hydraulic shutoff
control relay. The control relay, in turn, powers its hydraulic shutoff valve to
the closed position. Activation of the shutoff valve also causes an amber
RD CMB HYD OFF (or RD FLT HYD OFF) message to be displayed on
CAS.
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS2A-27-00
Page 34
January 31/02
Revision 6
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