(6)
The yaw damper module controls the rudder to maintain directional control during gusting and dutch roll frequencies. It also provides turn coordination when making turns at low airspeeds.
(7)
The three spoiler control modules drive spoiler power control actuators which augment roll authority and act as speed brakes.
P. Hydraulic Power Control Actuators and Servos (Fig. 15)
(1)
Hydraulic Actuators for Manual Control
(a) Elevators, ailerons, spoilers, and rudder are driven by Power Control Actuators (PCAs). Each PCA uses hydraulic power from one of the three main hydraulic systems. 1) Each elevator (2) uses three PCAs. 2) Each aileron (2) uses two PCAs. 3) Each spoiler (12) uses one PCA. 4) The rudder uses three PCAs.
(2)
Hydraulic Actuators For Automatic Stability Control
(a) Two Yaw Damper System (YDS) servos provide stability control through the rudder. The YDS servos are in the vertical fin below the rudder PCAs.
(3)
Hydraulic Actuators for Autopilot Control
(a) Autopilot control of the ailerons is through the Autopilot Lateral Control Servos (ALCSs). The ALCSs use autopilot electrical inputs to drive the aileron PCAs.
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PCA = POWER CONTROL ACTUATOR
Hydraulic Power Control Actuators and Servos Figure 15
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(b)
Three Autopilot Pitch Control Servos (APCSs) drive the elevator PCAs. The APCSs are aft of the stabilizer.
(c)
Three Autopilot Rollout Guidance Servos (ARGSs) drive the rudder PCAs. The ARGSs are in the vertical fin.
(d)
The PCAs are the same ones used with manual control of the airplane.
Q. Aileron Control System (Fig. 16)
(1)
Primary lateral control (roll) is provided by one aileron on each wing. The ailerons are controlled by inputs from either pilots' control wheel. The inputs are transmitted to the left and right aileron actuators via mechanical control paths. Each aileron is positioned by its two Power Control Actuators (PCAs). The captains and first officers control paths are interconnected but are separated via override devices in case of a jam.
(2)
Control wheel inputs are conditioned by the lateral feel, trim, and center mechanism. The assembly provides a sense of feel and centering for the pilots' control wheels.
(3)
The flight control computers provide electrical inputs to the Autopilot Lateral Control Servos (ALCSs). The ALCSs then drive the PCAs for roll control and back-drive the control cables to turn the control wheels.
(4)
AIRPLANES WITH CONTROL WHEEL STEERING; the aileron control force transducers provide separate electrical inputs to each Flight Control Computer (FCC). The input is in proportion to force applied to a control wheel. When the autopilot control wheel steering (CWS) configuration is engaged, manual control of the ailerons is allowed through the autopilot. The FCCs provide electrical inputs to the ALCSs. The ALCSs then move the primary system for roll control and back-drive control cables to turn the control wheels.
R. Lateral Feel, Trim and Centering
(1) The lateral feel, trim and centering mechanism is part of the left aft quadrant. It is mounted on the lower part of the left wheel well forward bulkhead. The assembly provides a sense of feel and centering for the pilots control wheels. Artificial feel is necessary because aerodynamic pressure is interrupted by the hydraulic power control units.
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