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MAINTENANCE MANUAL
NO. 4 SYS 1 TO RUDDER (TYP)
ELEVATOR POWER CONTROL PACKAGE RH OUTBD
NO. 4 SYS RUDDER & ELEVATOR HYDRAULIC SUPPLY SHUTOFF
NO. 3 SYS STANDPIPE
NO. 3 SHUTOFF NO. 4) (SAME AS STATIC PITOT ACTUATOR ELEV FEEL ELEVATOR POWER CONTROL PACKAGE RH INBD
NO. 3 NO. 2 SYS SYS ELEV FEEL COMPUTER
SHUTOFF NO. 4) (SAME AS NO. 2 STATIC PITOT ELEVATOR POWER CONTROL PACKAGE LH INBD
STANDPIPE
NO. 2 SYS
NO. 1 SYS
NO. 1 SYS 2 POWER LH OUTBD ELEVATOR CONTROL PACKAGE
NO. 1 SHUTOFF NOTE:____ SYSTEM OPERATION. NO. 1 SHOWN CLOSED TO ILLUSTRATE ALL SHUTOFFS NORMALLY OPEN
Figure 4 Elevator Hydraulic System Schematic
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL
(4)
When the control columns are moved, the aft quadrant translates the fore and aft cable movement into lateral control rod movement to transmit the motion to the main control valve linkage on each inboard elevator power control package. The resulting movement of each inboard elevator activates the attached slave control linkage. This results in the movement of the main control valve linkage on the corresponding outboard elevator PCP, causing simultaneous movement of that surface in the same direction.
(5)
Stops limit the travel of the crank at the end of the control column torque tube. These stops, and stops in the PCPs, constrain elevator travel. The inboard elevator rig neutral position is at 1.0 |0.2 degrees up and the outboard elevator rig neutral position is at
1.0 |0.5 degree down. Surface position transmitters connected to the inboard and the outboard elevators provide electrical signals to the aft surface digitizer circuit card. This is then displayed on EICAS to show relative displacement and positions of the elevators.
(6)
In manual operation, the inboard and outboard elevator PCPs function similarly. On the inboard elevator PCP, pressure from both associated hydraulic systems is applied to two separate pressure ports. The functions performed by both systems on the inboard elevator PCP are identical, but complete hydraulic isolation is maintained between the two systems. On the outboard elevator PCP, only one hydraulic system is active.
(7)
The fluid from each system enters the pressure port and passes through a filter and a pressure check valve to the main control servo valve. On inboard elevator PCPs, pressure is applied simultaneously to a time delay valve. This valve consists of a self-cleaning orifice which delays pressurization of the linkage overtravel mechanism by 0.75 second to prevent stick kick at the control column when hydraulic power is turned on. No time delay is required on the outboard elevator PCPs, because they are not directly connected to the control column and because the outboard elevators are balanced.
(8)
On both inboard and outboard elevator PCPs, pressurization of the over- travel mechanism provides a hydraulically supported pivot for the control linkage, arming the linkage. With the linkage armed, control inputs are applied to the main control servo valve. When the control system demands elevator movement, the main control valve directs fluid to and from the appropriate chambers of the actuator. Feedback linkage from the actuator returns the control valve to neutral when the commanded amount of elevator movement is achieved. When no hydraulic system associated with a particular unit is pressurized, the input lever has unrestricted travel for any position of the actuator. A bias spring holds the pivot in place firmly enough to transmit small operating forces to the control valve in this condition. Outboard units contain a centering mechanism to ensure that an outboard elevator returns to neutral if connection with the associated inboard elevator is lost.
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