DOC AIRBUS | AMM A320FARTIFICIAL FEEL AND RUDDER TRAVEL LIMITING - ACTUATION - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
A. Rudder Artificial Feel
An artificial feel and trim unit is installed downstream of the cable quadrant.
It consists of a trim screwjack (Ref. 27-22) and a constant-resisting load spring-rod that the trim screwjack holds in the neutral position.
The artificial feel and trim unit also comprises a system which overrides the autopilot.
This system is engaged when the AP mode is selected.
The function of the spring rod is:
An artificial feel and trim unit is installed downstream of the cable quadrant.
Artificial Feel and Trim UnitIt consists of a trim screwjack (Ref. 27-22) and a constant-resisting load spring-rod that the trim screwjack holds in the neutral position.
The artificial feel and trim unit also comprises a system which overrides the autopilot.
This system is engaged when the AP mode is selected.
The function of the spring rod is:
- to provide an artificial feel load proportional to the rudder deflection,
- to provide an accurate centering of the surface to neutral in the absence of a control input,
- to hold the upstream control at neutral when the yaw damper servoactuator supplies signals to the servocontrol.
NOTE: The centering spring force is added to the artificial feel force that the artificial feel and trim unit supplies (Ref. 27-21).
B. Rudder Travel Limiting
The rudder-travel limiting system limits the control inputs to the servocontrols to change the rudder travel in relation to the airspeed (Vc).
The limitation is such that the maximum deflection of the rudder remains lower than the deflection which would induce limit loads on the structure, throughout the flight envelope.
The system is made of a travel limitation unit which is under the control of the Flight Augmentation Computers (FACs) (Ref. ch. 22).
A simplified emergency control system (open loop) brings back automatically the stops to the "low-speed" position when the two FACs are failed and slats are extended.
The rudder-travel limiting system limits the control inputs to the servocontrols to change the rudder travel in relation to the airspeed (Vc).
The limitation is such that the maximum deflection of the rudder remains lower than the deflection which would induce limit loads on the structure, throughout the flight envelope.
The system is made of a travel limitation unit which is under the control of the Flight Augmentation Computers (FACs) (Ref. ch. 22).
A simplified emergency control system (open loop) brings back automatically the stops to the "low-speed" position when the two FACs are failed and slats are extended.
2. Component Location
A. Rudder Artificial Feel
| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||||
| 16CA | SOLENOID-RUDDER ARTF FEEL | 325AL | 325 | 27-23-17 | |
| ** ON A/C NOT FOR ALL | |||||
| 16CA | SOLENOID-RUDDER ARTF FEEL | 325 | 27-23-17 | ||
B. Rudder Travel Limiting
| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 4CC | LIMITATION UNIT-RUDDER TRAVEL | 325DL | 325 | 27-23-51 | |
C. Maintenance and Rigging Facilities.
The item given below is a Line Replaceable Unit (LRU):
The item given below is a Line Replaceable Unit (LRU):
- Electronic assembly
The levers and the casing have rigging holes which materialize the neutral position of the levers, for adjustment of the rods connected to them.
3. Component Description
(1) General
The mechanical design of the TLU is such that a single mechanical failure (rupture or disconnection) cannot cause the loss of the travel limitation function.
The TLU has two brushless electric motors separately controlled by an electronic assembly.
Each motor drives two screws via a reduction gear and permits the symmetrical linear displacement of two nuts used as adjustable stops. (The two nuts have opposite pitches).
A non-locking rotary stop limits the stroke of one of the screw/nut assemblies which are irreversible.
There are two levers on each connection shaft; one is connected to the input rod and the other is used as a punctual stop.
The movement of each screw is transmitted to a transducer unit (RVDT) via a reduction gear which permits to indicate the position of the variable stop.
Two rigging pins are used to set the two levers to the zero position (mid stroke).
To prevent icing, there is a heating system which includes two coils and their regulating thermostats.
The mechanical design of the TLU is such that a single mechanical failure (rupture or disconnection) cannot cause the loss of the travel limitation function.
The TLU has two brushless electric motors separately controlled by an electronic assembly.
Each motor drives two screws via a reduction gear and permits the symmetrical linear displacement of two nuts used as adjustable stops. (The two nuts have opposite pitches).
A non-locking rotary stop limits the stroke of one of the screw/nut assemblies which are irreversible.
There are two levers on each connection shaft; one is connected to the input rod and the other is used as a punctual stop.
The movement of each screw is transmitted to a transducer unit (RVDT) via a reduction gear which permits to indicate the position of the variable stop.
Two rigging pins are used to set the two levers to the zero position (mid stroke).
To prevent icing, there is a heating system which includes two coils and their regulating thermostats.
B. Normal control circuit
The motor itself is a 3-phase asynchronous motor with no brushes:
The motor itself is a 3-phase asynchronous motor with no brushes:
- the associated electronic set supplies the motor windings with variable voltage and variable frequency which are function of the input signal (representative of the position error),
- the system permits to get torque/speed characteristics for the motor equivalent to those obtained with a DC motor,
- a relay isolates the motor windings from the electronic set output when its coil is not energized by the enable signal.
Moreover, in this situation, the output signals are sent back to the monitoring circuits for comparison with fixed thresholds - the command signal that the computer dedicated to each electronic set sends is a DC current which varies between plus or minus 8 mA into a 500-ohm resistor (for the computer, the motor is equivalent to a standard servovalve),
- another relay upstream of the actuator and controlled by the computer supplies the 28VDC power.
C. Emergency control circuit
When the two FACs can no longer achieve normal control (for example if the two electronic power sets of the TLU are failed), an emergency control brings back the stops to the low speed configuration (maximum possible deflection of the rudder) when slats are extended.
For this, the motor is used as a 2-phase asynchronous motor energized by 26 V 400 Hz power.
This control mode is achieved when the coil of a specific relay is energized for a period of 30 s approx (this time is greatly sufficient to bring back the stops to the low speed configuration).
The motor is then able to sustain the energization of the windings during a long period, without any rotation, because the stops are reached.
When the two FACs can no longer achieve normal control (for example if the two electronic power sets of the TLU are failed), an emergency control brings back the stops to the low speed configuration (maximum possible deflection of the rudder) when slats are extended.
For this, the motor is used as a 2-phase asynchronous motor energized by 26 V 400 Hz power.
This control mode is achieved when the coil of a specific relay is energized for a period of 30 s approx (this time is greatly sufficient to bring back the stops to the low speed configuration).
The motor is then able to sustain the energization of the windings during a long period, without any rotation, because the stops are reached.
4. Test
At FAC energization a test is initiated to do the check of at lest 95% of the electronic circuitry without the need of motor rotation.
For this, the test circuitry which receives the output signals when the isolation relay is de-energized compares these signals to two thresholds.
It also energizes a specific relay when the signals correspond to a particular value of the input signal.
One pole of this relay sends a logic information (fault signal) to the upstream computer.
This test proves that the logic output is not permanently set to 1 and that the isolation relay is not closed.
The purpose of this third phase is to prove that the isolation relay is able to close when energized.
At FAC energization a test is initiated to do the check of at lest 95% of the electronic circuitry without the need of motor rotation.
For this, the test circuitry which receives the output signals when the isolation relay is de-energized compares these signals to two thresholds.
It also energizes a specific relay when the signals correspond to a particular value of the input signal.
One pole of this relay sends a logic information (fault signal) to the upstream computer.
- first phase:
the enable signal is equal to zero,
the command signal is equal to zero.
This test proves that the logic output is not permanently set to 1 and that the isolation relay is not closed.
- second phase:
the enable signal is equal to zero,
the command signal is equal to the value which corresponds to the threshold setting.
Then, the computer must verify a logic 1 (ground).
This proves that:
the isolation relay is really open,
the electronic circuitry operates as designed. - third phase:
the isolation relay is energized,
the input signal is equal to zero.
The purpose of this third phase is to prove that the isolation relay is able to close when energized.
NOTE: When the motor is in service there is a monitoring of the current in the windings. If an overcurrent is detected it is indicated by the fault signal (open circuit whereas in normal conditions it should be a ground).