The feel and centering mechanism is in the mechanism of the left shaft assembly, between the flight deck floor and the nose gear wheel well. Access is through the MEC, then along the left side of the nose gear wheel well.
Functional Description
As the left shaft assembly and the cam turn, the cam follower moves, which extends the two springs. The springs supply a feel force to the rudder pedals. The feel force varies from 19.5 lb
(8.8 kg) at breakout to a maximum of 50 lb (22.7 kg) at full displacement of the rudder pedals.
When the pilots release the rudder pedals, the springs force the cam follower back to the cam detent. This returns the system to the neutral trimmed position. The neutral, or zero feel force position, varies with trim input.
During trim operation, the rudder trim actuator moves the lever and the rudder trim position transducer, which then moves the arm and the cam follower assembly. Since the springs keep the cam follower in the cam detent, the trim actuator causes the cam and the left shaft assembly to turn. This also moves the rudder pedals and the rudder pedal position transducers.
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RUDDER CONTROL -FEEL AND CENTERING MECHANISM
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RUDDER CONTROL -RUDDER TRIM CONTROLS AND TRIM ACTUATOR
Purpose
The pilots use two controls to adjust the trim of the airplane about the vertical axis. The two controls are the rudder trim control and the manual trim cancel switch.
The rudder trim control commands the direction and rate of rudder trim. The manual trim cancel switch commands the rudder to the center position and cancels any rudder trim input by the pilot. The manual trim cancel switch does not remove any rudder trim caused by TAC.
The rudder trim actuator extends and retracts to execute the pilot trim commands.
The rudder trim indicator shows the position of the rudder trim actuator.
Location
The two rudder trim controls are on the aft end of the P8 aft aisle stand. The rudder trim position indicator is in front of the trim switches.
The trim actuator is under the flight deck floor.
Trim Controls Physical Description
The rudder trim selector is a self-centering, dual-torque switch. It supplies the L1 and R ACEs with these electrical signals:
EFFECTIVITY
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*
Arm
*
Trim direction (left or right)
*
Trim rate.
The manual trim cancel switch is a momentary push button switch. It sends an electrical signal to the R ACE.
Trim Control Operation
When the pilot turns the rudder trim selector less than 25 degrees, the trim actuator does not move. When the pilot turns the trim selector more than 25 degrees, the trim actuator moves at 0.5 unit per second in the direction selected. When the pilot turns the trim selector more than 40 degrees with greater force, the trim actuator moves at 2 units per second in the direction selected.
When the pilot pushes on the manual trim cancel switch, it causes the rudder trim actuator to center the rudder control system at 2 units per second.
Rudder Trim Actuator Physical Description
The rudder trim actuator is a line replaceable unit (LRU). It weighs 4.1 lb (1.9 kg). Electrical commands limit the stroke of the actuator to 3 inches. Mechanical stops limit the actuator stroke to 3.2 inches.
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RUDDER CONTROL -RUDDER TRIM CONTROLS AND TRIM ACTUATOR
Rudder Trim Position Indicator Physical Description
The rudder trim position indicator is an LRU. It weighs 1.7 lb (0.8 kg).
The rudder trim pointer shows the position of the rudder trim actuator. The indicator scale shows 17 units of actuator trim in both directions. Each unit of pointer movement is equivalent to about 1 degree of rudder movement at low airspeed.
Indications
The warning message CONFIG RUDDER shows on the EICAS display when all of these conditions occur:
*
The rudder trim is not within 2 units from center
*
Either the left or right engine thrust is more than the takeoff threshold
*
The airplane is on the ground.
The status message FLIGHT CONTROL SYS shows on the status display when the rudder trim system is defective.
Training Information Point
In case of a power supply failure to the indicator, the indicator pointer, scale, and nomenclature are not visible. In case of input signal loss, the indicator pointer is not visible but the scale and nomenclature stay visible. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 飞行操纵 Flight Controls 1(50)
