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 A.  The lower rudder PCP consists of a PCM, two hydraulically driven PCAs, mounting trunnion, and associated hydraulic connections. The PCM consists of duel spool control valve, yaw damper actuator, solenoid valve, and position transducer. Airplane hydraulic systems No. 2 and 4 supply the lower rudder PCM. The PCM then regulates flow to the two hydraulic PCAs attached to the lower rudder front spar. Replaceable filters in the PCM protect the unit from contamination.
 13. Hydraulic Fuse
______________
 A.  A pressure reset - type fuse located on the aft side of the torque box forward bulkhead in section 48, senses flow rate in hydraulic system 4 pressure line upstream of the rudder actuator. The fuse will close to prevent loss of hydraulic fluid in the event of hydraulic line rupture downstream, and thus maintains hydraulic pressure in the system. The fuse automatically resets by spring action once the pressure in the line is equal on both sides of the fuse. The fuse incorporates a time delay to prevent inadvertent fuse setting from pressure surges when the hydraulic system is first activated.
 14. Operation
_________
 A.  Functional Description
 (1)  
Airplane hydraulic systems No. 1, 2, 3 and 4 operate the rudders in response to mechanical, electromechanical, or electrical control inputs. The pilots apply mechanical inputs to either set of rudder pedals; electromechanical inputs through the rudder trim control system; or electrical inputs directly from the autoflight system. The autoflight system provides inputs directly to the upper and lower rudder PCPs. For yaw damper functional description, refer to 22-21-00/001.

 (2)  
In the rudder pedal control mode, fore and aft movement of rudder pedals transmits motion to jackshaft yoke of the forward quadrant by means of two pushrods. Rotary motion of jackshaft yoke is passed to the forward quadrant by means of the jackshaft. The forward quadrant transmits motion to the aft quadrant through a pair of cables. Rotation of the aft quadrant in turn causes rotation of the rudder control torque tube in feel and centering mechanism. As the pedals are displaced progressively from neutral, the rudder feel and centering mechanism imparts a progressively increasing centering force to the control system. When pedal force is removed, the centering mechanism returns the pedals and rudder to their neutral position. The feel and centering mechanism translates the fore and aft cable movement into lateral control rod movement to transmit motion to the lower and upper RRCs. The RRC conveys the controlled input to the main control valve linkage on each PCM. The RRC limits the rudder travel by changing the effective length of the output lever arm in proportion to air speed. For a given condition of airspeed and altitude, the servo unit will hold a fixed moment arm for the RRC output crank. Any movement then will be limited to the restrictions imposed by the servo unit.

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 27-21-00
 ALL  ú ú 02 Page 9 ú Jun 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

UPPER RUDDER 
POWER CONTROL  UPPER 
ACTUATORS  RUDDER 

UPPER RUDDER
RATIO CHANGER

UPPER RUDDER POWER 
CONTROL MODULE 
IDLER CRANK 
RUDDER TRIM 
ACTUATOR  ROLLOUT CAM/ROLLER 
OVERRIDE MECHANISM 
AFT QUADRANT  ROLLOUT PCP
(3 PLACES) 
LOWER RUDDER 
POWER CONTROL 
ACTUATORS 
RUDDER 
PEDALS  FORWARD 
QUADRANT 

LOWER 
RUDDER 
LOWER RUDDER 
RATIO CHANGER 
LOWER RUDDER POWER 
CONTROL MODULE 

Rudder and Rudder Trim Control System Simplified Schematic
Figure 4 (Sheet 1)

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 27-21-00
 ALL  ú ú 02 Page 10 ú Jun 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

NO. 4 SYS
NO. 4 SHUTOFF
NO. 3 SYS
NO. 3 SHUTOFF (SAME AS NO. 4)
NO. 2 SHUTOFF (SAME AS NO. 4)
NO. 2 SYS
NO. 1 SYS
2
NO. 1 SHUTOFF
　
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