YAW DAMPER ACTUATION - DESCRIPTION AND OPERATION
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1.
General
_______ (Ref. Fig. 001) Two electrohydraulic yaw damper servo-actuators under the control of the FACs (Ref. 22-61) are installed between the artificial feel and trim unit and the travel limitation unit (TLU). They drive the aft control via a differential linkage. The yaw damper servo-actuator orders are added to those of the pilots up to the maximum travel that the TLU permits. One of the two servo-actuators is active, the other remains in standby (bypass mode). In the event of a double hydraulic failure, a centering spring rod sets the two yaw damper servo-actuators to the neutral position.
2.
Component Location
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(Ref. Fig. 002)
-------------------------------------------------------------------------------FIN | FUNCTIONAL DESIGNATION | PANEL|ZONE|ACCESS | ATA | | | | DOOR | REF.
-------------------------------------------------------------------------------3CC1 SERVO ACTR-YAW DAMPER, 1 325 325BL 27-26-51 3CC2 SERVO ACTR-YAW DAMPER, 2 325 325BR 27-26-51
3. Component Description
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A. Yaw Damper Servo-Actuator
(Ref. Fig. 003)
(1) General The two electrohydraulic servo-actuators are interchangeable. Each servo-actuator includes : - one piston with a transducer unit (LVDT) isolated from the
hydraulic fluid
- one valve group which includes mainly :
one servovalve (2)
two solenoid valves (1)
two mode selector valves (3)
one pressure switch (5)
The design is such that a single failure cannot prevent the selection of the bypass mode.
4. Operation_________ (Ref. Fig. 003)
A. Normal operation with the actuator pressurized The servo-actuator pressurization directly involves the supply of the servovalve (2) by the HP system.
(1)
Yaw damper in the active mode The two solenoid valves (1) must be energized to set the two selector valves (3) to the active mode ; i.e to connect the two piston chambers to the servovalve outputs. Then, the servo-actuator is put in the active mode and the pressure switch (5) is not activated. The feedback transducer (LVDT) (4) provides the servoloop feedback.
(2)
Yaw damper in the bypass mode (standby configuration) The two solenoid valves (1) are de-energized and the associated selector valves (3) are set to the bypass mode under the action of their spring. This permits the interconnection of the two piston chambers. In this case, the pressure switch (5) is not activated.
B. Operation in case of a simple electrical failure One solenoid valve is de-energized and the operation is identical to that of para. 2 (b). But the pressure switch is activated because the two selector valves are not in the same position.
C. Operation after a hydraulic failure With no hydraulic pressure, the two selector valves (3) are set to the bypass mode under the action of their springs, thus the two chambers of the piston are interconnected. In this case, the pressure switch (5) is not activated.
D. Maintenance and rigging facilities
The maintenance is "on condition".
The items below are Line Replaceable Units :
-filter
-servovalve
-solenoid valves
-pressure switch
No rigging operation is necessary to replace the yaw damper.
Yaw Damper Servo-Actuators - General
Figure 001
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Yaw Damper Servo-Actuator - Location
Figure 002
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Yaw Damper Servo Actuator
Figure 003
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YAW DAMPER ACTUATION - DEACTIVATION/REACTIVATION
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TASK 27-26-00-040-001
Deactivation of the Yaw Damper Servo-Actuator 3CC1 (3CC2)
WARNING : PUT THE SAFETY DEVICES AND THE WARNING NOTICES IN POSITION BEFORE YOU
_______ START A TASK ON OR NEAR:
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THE FLIGHT CONTROLS
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THE FLIGHT CONTROL SURFACES
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THE LANDING GEAR AND THE RELATED DOORS
-COMPONENTS THAT MOVE.
1. Reason for the Job
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Refer to the MMEL TASK: 22-63-01
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