FROM RUDDER
PEDALS AND
TRIM KNOB
PRESSURE
1 VALVE SHOWN OPEN
RETURN
2 VALVE SHOWN CLOSED
PRESSURE
(SUPPLY SHUTOFF)
Rudder and Rudder Trim Control System Simplified Schematic
Figure 4 (Sheet 2)
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A
747-400
MAINTENANCE MANUAL
(3)
In the ratio changer control system, the SRM receives variable air data input and sends electrical signals to the servo units in the ratio changer. Mechanical input and output linkages connect the servo unit to the feel and centering unit and to the rudder PCP. Servo unit travel is limited by mechanical stops. Intermediate servo unit positions are related to the air data input so that each position within the stroke corresponds to a specific airspeed. The positional potentiometer provides a signal proportional to the servo unit stroke.
(4)
In the rudder trim control mode, rotating the rudder trim control switch provides electrical inputs to the rudder trim actuator. The coordination crank of the feel and centering mechanism is connected to the actuator rod end. Linear movement of actuator rod end, causes the rudder feel and centering mechanism to rotate about its shaft. This provides a new neutral position for pedal and the feel and centering mechanism. This motion is transmitted to the rudders by the feel and centering mechanism control rods and the RRCs to provide the indicated trim.
(5)
Stops limit the travel of the rudder pedals at the end of the forward quadrant. There are adjustable stops also at the rig pin bracket in feel and centering mechanism. These stops constrain rudder travel to 32 degrees maximum in either direction. Surface position transmitters connected to rudders provide electrical signals to the aft surface position digitizer circuit card. This is then displayed on EICAS to show relative displacement and position of the rudders.
(6)
In manual operation, the lower and upper rudder PCPs function similarly. On each PCP, pressure from both associated hydraulic systems is applied to two separate pressure ports. The lower rudder PCA installation has two hydraulic supplies driving two PCAs from a dual tandem valve. The upper rudder PCA installation has two hydraulic supplies driving three PCAs from a triple tandem valve to give hydraulic isolation. The functions performed by both systems are identical but complete hydraulic isolation is maintained between the two systems.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
B. Control
(1) Rudder Pedal Control.
WARNING: AILERONS, ELEVATORS, RUDDERS, TRAILING EDGE FLAPS AND
_______ SPOILERS ARE FULLY POWERED. ENSURE PERSONNEL AND EQUIPMENT CLEAR OF ALL CONTROL SURFACES BEFORE PROVIDING HYDRAULIC POWER. RUDDERS WILL MOVE TOWARDS NEUTRAL.
(a) Provide systems No. 1 and 3 hydraulic power for upper rudder and systems No. 2 and 4 hydraulic power for lower rudder.
NOTE: Hydraulic power from only one system for each rudder is
____ required to operate rudders.
(b)
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