2. System Description
__________________
 A. Composition
 The system consists of:

 -An electro-mechanical actuator which comprises two three-phase asynchronous motors connected to a reduction gear by rigid linkage.
 -Two Flight Augmentation Computers (FAC 1 and FAC 2).
 -Four transducer units (RVDT) configured in such a way that a single failure would not affect all the units at the same time.
 -Two engage FLT CTL/FAC pushbutton switches (with FAULT/OFF legend) common to the yaw damper and to the rudder trim (one per FAC).
 -
A rudder-trim control switch located on the RUD TRIM control panel on the center pedestal for manual trim control.

 -
A RUD TRIM/RESET pushbutton switch (this pushbutton switch is not mechanically held), on the RUD TRIM control panel.

 -
A rudder trim indicator with liquid-crystal display located on the left of the rudder-trim control switch.

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 Rudder Trim Function
 Figure 001

 Rudder Trim Function Figure 001A 
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 B. Architecture (Ref. Fig. 002) The system operates using the changeover technique. When the two channels are engaged:
 -
The channel 1 has priority

 -
The channel 2 is synchronized on the position of the actuator through

 the mechanical linkage. The standby channel is not energized (no enable signal, no power-enable signal). The control order is not interrupted. Each channel is duplicated and monitored:

 -
The COMMAND side of the FAC slaves the position of the system

 -
The MONITOR side monitors the system.
 The monitoring orders are equalized on the command orders to reduce
 dispersions due to the use of integrators in the loop.

 Rudder Trim Architecture Figure 002
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 3. Operation
_________

 A. Principle (Ref. Fig. 003) The rudder trim function ensures a trimmed value of the rudder. This value is reproduced at the rudder pedals. This trim is obtained either manually or automatically. The value appears:
 -
On the rudder trim indicator

 -
On the display unit of the ECAM system.
 The resulting deflection is maintained even in case of total loss of the
 function. This permits to have a stabilized value, for example in the
 event of AP loss when an engine failure occurs.
 When the changeover principle is retained:

 -The side 1 has priority through the side 1 signal

 -Interruption of the actuator enable signals on the standby channel

 -Automatic engagement of the standby channel upon loss or disengagement of the channel 1.
 B. Structure of Rudder Trim Control-Law (Ref. Fig. 004) The control law generates a deflection order to control the rudder trim actuator through an integrator which memorizes the required position. This order is generated:
 -
From the position of the position feedback in synchronization

 -
From the control order of the pilot trim (the reset is obtained through the unloading of the trim integrator)

 -
From the ELAC deflection order (Provision only)

 -
From the long-term turn-coordination order for autotrim on the yaw axis

 -
From the generation of an engine failure detection and its

 accomplishment. The engine failure is detected from the lateral acceleration and from the yaw rate through a given threshold. This detection is confirmed by the engine thrust information. Detection is performed by the command and monitoring sides. The first side which is triggered sends a signal to the opposite side in order to lower its threshold and thus ensure synchronized detection. The correction signal (fixed deflection values) is then applied, depending on engine failed. As soon as the engine failure compensation reaches a predetermined threshold, the control law is modified:
 -The engine failure compensation is performed directly by the FG command order and the delta p compensation is boostered. The monitoring side is equalized on the command side to reduce the dispersion of the integrators.

 Rudder Trim Changeover - Logic Figure 003
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 Rudder Trim Actuator - Generation of the Control Order
 Figure 004

 C. Operating Logic

 (1)
 General The operation of the rudder trim function depends on:
　
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