DOC AIRBUS | AMM A320FBLUE AUXILIARY HYDRAULIC POWER - DESCRIPTION AND OPERATION
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** ON A/C NOT FOR ALL
** ON A/C NOT FOR ALL
1. General
The Blue auxiliary hydraulic power system (referred to as the Blue auxiliary system) supplies hydraulic power from the ram air turbine (RAT) to the Blue main hydraulic power system (referred to as the Blue main system).
The RAT produces also electrical power through the constant speed motor/generator (CSM/G).
The RAT is installed in the belly fairing on the left side. When necessary, an actuator (RAT actuator) extends the RAT into the airflow. The actuator extends the RAT into the airflow automatically when there is:
It is possible to extend the RAT into the airflow at any point in the flight envelope of the aircraft.
** ON A/C NOT FOR ALL The Blue auxiliary hydraulic power system (referred to as the Blue auxiliary system) supplies hydraulic power from the ram air turbine (RAT) to the Blue main hydraulic power system (referred to as the Blue main system).
The RAT produces also electrical power through the constant speed motor/generator (CSM/G).
The RAT is installed in the belly fairing on the left side. When necessary, an actuator (RAT actuator) extends the RAT into the airflow. The actuator extends the RAT into the airflow automatically when there is:
- A failure of both engines, or
- A failure of one engine together with a failure of the electrical generator of the other engine
- A total AC failure.
It is possible to extend the RAT into the airflow at any point in the flight envelope of the aircraft.
NOTE: The automatic function only operates when the speed of the aircraft is more than 100 kts.
The flight and maintenance crews can also extend the RAT from the flight compartment. It is only possible to retract the RAT when the aircraft is on the ground. 2. Component Location
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Location of Mechanical Components| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 1GE | EJECTION ACTUATOR | 147 | 29-22-00 | ||
| ** ON A/C NOT FOR ALL | |||||
| 2GE | RAT | 147BB | 147 | 29-22-00 | |
| ** ON A/C NOT FOR ALL | |||||
| 2GE | RAT | 147 | 29-22-00 | ||
| ** ON A/C ALL | |||||
| 3GE | RAT CTL PNL | 195 | 29-22-00 | ||
3. System Description
In an emergency the Blue auxiliary system supplies hydraulic power to the aircraft. Electrical power can also be supplied through the Blue auxiliary system by the constant speed motor generator (CSMG). The system supplies hydraulic power in less than 4.5 seconds from the time it gets the electrical command to extend the RAT. The hydraulic power available from the RAT is sufficient to supply the flight controls and the CSMG (for electrical power). The RAT is available and will operate through the entire flight envelope. The RAT has a stall protection device which prevents a RAT stall below the governed speed range. The stall protection device limits the maximum power the pump can take from the turbine. When the stall protection device is in operation, the pump displacement is adjusted to get a constant RAT speed not related to the aircraft speed.
The RAT has a de-icing device which is installed in the nose of the turbine hub. The de-icing device produces heat which keeps the nose temperature to 3 deg.C (37.40 deg.F) minimum. This temperature prevents icing conditions at the turbine hub when the RAT is in operation.
The de-icing device does not use external power sources. The heat is produced by the eddy current heating device. The heating device has two basic components, an electrically conductive aluminium plate and an even number of samarium cobalt magnets. The magnets are cicumferrentially mounted on a stationary magnetic plate. When relative rotation take place, the flux field, when it passes through the aluminium plate, produces a current. As aluminium has an electrical resistance, power is generated which is than dissipated in the form of heat.
The main components of the Blue auxiliary system are:
All the components are in the left belly fairing. This does not include the RAT control panel and the selector switches. The RAT control panel is part of the ground-service panel of the Blue hydraulic system, and the selector switches are in the flight compartment.
The drain port of the RAT gearbox has a leakage drain line which transfers hydraulic fluid from the internal reservoir of the RAT pump to an external drain tank. The location of the drain tank is behind a cover plate on the left side of the RAT bay.
A P/BSW (2805GE) is installed on the hydraulic control panel 40VU in the cockpit. This switch permits the pilot to manually select the deployment of the RAT.
When it is on stand-by, the RAT (2GE) stays retracted in its stow compartment. In an emergency, the RAT is deployed (automatically or manually) to supply hydraulic power to the Blue main hydraulic system.
The turbine is a constant-speed variable-pitch unit with two blades. The mechanical governor and the pitch-change mechanism are installed in the hub. The turbine is attached to the lower end of the leg assembly and operates the gearbox which drives the hydraulic pump. The hydraulic pump has a stall protection which makes sure that the power demand from the pump does not exceed the power available from the turbine.
An index mechanism installed on the front of the leg assembly locks the turbine hub assembly in the correct position. The turbine hub has markings which allows easy alignment between the turbine hub and the index mechanism. This then permits the RAT to be stowed.
During the deployment of the RAT, the index mechanism disengages from the turbine hub when the leg is not more than 10 deg. before full extension. The RAT retracts hydraulically with the hydraulic supply from the Blue electric pump or from a ground supply. The retraction of the RAT is operated by the RAT control panel (3GE). The RAT can retract only if the turbine is in the correct position and the index mechanism is engaged. If the index mechanism is not engaged, it is necessary to turn the turbine manually until the index mechanism engages. The RAT will also not retract if the ground test tool is still attached.
The RAT actuator is attached to the top end of the leg assembly and the RAT mounting frame. The RAT actuator extends the RAT into the airflow with the force of a spring. Therefore no hydraulic power is necessary to extend the RAT. Hydraulic power is required to retract the RAT. You can retract the RAT only when the aircraft is on the ground.
Two solenoids and one proximity switch are installed on the top of the RAT actuator. The two solenoids release a lock and the RAT extends. The RAT extends when both or one solenoid is energized. An extend lock keeps the RAT in the extended position.
A stow proximity switch gives a signal to the ECAM system if the RAT actuator is extended. Two links attach the RAT compartment doors to the leg assembly and open the doors when the RAT extends. The two links also keep the RAT doors closed when the RAT is in its normal stow position. The stowed proximity sensor sends a signal to the RAT control panel and the indicator light RAT STOWED comes on when the RAT is locked in its retracted position.
The RAT control panel (3GE) is part of the ground-service panel of the Blue hydraulic in the left rear belly fairing. The control panel (3GE) has the controls which operate the RAT retraction.
** ON A/C NOT FOR ALL In an emergency the Blue auxiliary system supplies hydraulic power to the aircraft. Electrical power can also be supplied through the Blue auxiliary system by the constant speed motor generator (CSMG). The system supplies hydraulic power in less than 4.5 seconds from the time it gets the electrical command to extend the RAT. The hydraulic power available from the RAT is sufficient to supply the flight controls and the CSMG (for electrical power). The RAT is available and will operate through the entire flight envelope. The RAT has a stall protection device which prevents a RAT stall below the governed speed range. The stall protection device limits the maximum power the pump can take from the turbine. When the stall protection device is in operation, the pump displacement is adjusted to get a constant RAT speed not related to the aircraft speed.
The RAT has a de-icing device which is installed in the nose of the turbine hub. The de-icing device produces heat which keeps the nose temperature to 3 deg.C (37.40 deg.F) minimum. This temperature prevents icing conditions at the turbine hub when the RAT is in operation.
The de-icing device does not use external power sources. The heat is produced by the eddy current heating device. The heating device has two basic components, an electrically conductive aluminium plate and an even number of samarium cobalt magnets. The magnets are cicumferrentially mounted on a stationary magnetic plate. When relative rotation take place, the flux field, when it passes through the aluminium plate, produces a current. As aluminium has an electrical resistance, power is generated which is than dissipated in the form of heat.
The main components of the Blue auxiliary system are:
- The RAT
- The leg assembly with its pivot
- The hydraulic pump
- The RAT Actuator
- The RAT control panel and
- Selector switches to extend the RAT from the flight compartment.
All the components are in the left belly fairing. This does not include the RAT control panel and the selector switches. The RAT control panel is part of the ground-service panel of the Blue hydraulic system, and the selector switches are in the flight compartment.
The drain port of the RAT gearbox has a leakage drain line which transfers hydraulic fluid from the internal reservoir of the RAT pump to an external drain tank. The location of the drain tank is behind a cover plate on the left side of the RAT bay.
A P/BSW (2805GE) is installed on the hydraulic control panel 40VU in the cockpit. This switch permits the pilot to manually select the deployment of the RAT.
When it is on stand-by, the RAT (2GE) stays retracted in its stow compartment. In an emergency, the RAT is deployed (automatically or manually) to supply hydraulic power to the Blue main hydraulic system.
The turbine is a constant-speed variable-pitch unit with two blades. The mechanical governor and the pitch-change mechanism are installed in the hub. The turbine is attached to the lower end of the leg assembly and operates the gearbox which drives the hydraulic pump. The hydraulic pump has a stall protection which makes sure that the power demand from the pump does not exceed the power available from the turbine.
An index mechanism installed on the front of the leg assembly locks the turbine hub assembly in the correct position. The turbine hub has markings which allows easy alignment between the turbine hub and the index mechanism. This then permits the RAT to be stowed.
During the deployment of the RAT, the index mechanism disengages from the turbine hub when the leg is not more than 10 deg. before full extension. The RAT retracts hydraulically with the hydraulic supply from the Blue electric pump or from a ground supply. The retraction of the RAT is operated by the RAT control panel (3GE). The RAT can retract only if the turbine is in the correct position and the index mechanism is engaged. If the index mechanism is not engaged, it is necessary to turn the turbine manually until the index mechanism engages. The RAT will also not retract if the ground test tool is still attached.
The RAT actuator is attached to the top end of the leg assembly and the RAT mounting frame. The RAT actuator extends the RAT into the airflow with the force of a spring. Therefore no hydraulic power is necessary to extend the RAT. Hydraulic power is required to retract the RAT. You can retract the RAT only when the aircraft is on the ground.
Two solenoids and one proximity switch are installed on the top of the RAT actuator. The two solenoids release a lock and the RAT extends. The RAT extends when both or one solenoid is energized. An extend lock keeps the RAT in the extended position.
A stow proximity switch gives a signal to the ECAM system if the RAT actuator is extended. Two links attach the RAT compartment doors to the leg assembly and open the doors when the RAT extends. The two links also keep the RAT doors closed when the RAT is in its normal stow position. The stowed proximity sensor sends a signal to the RAT control panel and the indicator light RAT STOWED comes on when the RAT is locked in its retracted position.
The RAT control panel (3GE) is part of the ground-service panel of the Blue hydraulic in the left rear belly fairing. The control panel (3GE) has the controls which operate the RAT retraction.
4. Power Supply
The DC system of the aircraft delivers the electrical power to the RAT system.
The Hot Battery Bus 701PP supplies 28 V DC to the deploy solenoid 1 on the RAT actuator when the OVRD HYD switch 2805GE is operated.
The battery No. 2 supplies 28 V DC to the deploy solenoid 2 when the OVRD ELEC switch 24XE is operated.
DC Essential Bus 401PP supplies 28 V DC to the RAT stow panel. The supply to the RAT stow panel is used for:
** ON A/C NOT FOR ALL The DC system of the aircraft delivers the electrical power to the RAT system.
The Hot Battery Bus 701PP supplies 28 V DC to the deploy solenoid 1 on the RAT actuator when the OVRD HYD switch 2805GE is operated.
The battery No. 2 supplies 28 V DC to the deploy solenoid 2 when the OVRD ELEC switch 24XE is operated.
DC Essential Bus 401PP supplies 28 V DC to the RAT stow panel. The supply to the RAT stow panel is used for:
- The stow solenoid
- The pressure switch
- The stow proximity switch
- The interlock proximity switch.
5. Component Description
A. Ram Air Turbine (RAT)
The turbine is a constant-speed variable-pitch unit with two blades. The hub size and shape of the turbine is designed to avoid icing problems on the RAT.
The diameter of the hub assembly with the two turbine blades has an overall diameter of 1003 mm (39.4882 in.). The rotation speed of the turbine is kept between 4.800 and 6.540 revolutions per minute (RPM) because of the blade pitch angle adjustment. A governor mixes the blade counterweight, the governor, the spring and the aerodynamic forces to adjust the blade pitch angle.
An index mechanism locks the rotary assembly (turbine blade and hub) in the stowed position and during extension. During extension the rotary assembly is locked until not more than 10 deg. before full extension. A clearance of 19 mm (0.7480 in.) between the RAT doors and turbine blades is given.
The hub has markings to make sure that the index mechanism and the hub align easily for the retraction of the RAT. It is not possible to retract the RAT more than 10 deg. if the rotary assembly is not correctly locked or if the ground tool is installed. The index mechanism therefore prevents damage to the RAT, the RAT doors and the aircraft structure.
The gearbox drain port has a leakage drain line which transfers hydraulic fluid from the internal reservoir of the RAT pump to an external drain tank.
The turbine is a constant-speed variable-pitch unit with two blades. The hub size and shape of the turbine is designed to avoid icing problems on the RAT.
The diameter of the hub assembly with the two turbine blades has an overall diameter of 1003 mm (39.4882 in.). The rotation speed of the turbine is kept between 4.800 and 6.540 revolutions per minute (RPM) because of the blade pitch angle adjustment. A governor mixes the blade counterweight, the governor, the spring and the aerodynamic forces to adjust the blade pitch angle.
An index mechanism locks the rotary assembly (turbine blade and hub) in the stowed position and during extension. During extension the rotary assembly is locked until not more than 10 deg. before full extension. A clearance of 19 mm (0.7480 in.) between the RAT doors and turbine blades is given.
The hub has markings to make sure that the index mechanism and the hub align easily for the retraction of the RAT. It is not possible to retract the RAT more than 10 deg. if the rotary assembly is not correctly locked or if the ground tool is installed. The index mechanism therefore prevents damage to the RAT, the RAT doors and the aircraft structure.
The gearbox drain port has a leakage drain line which transfers hydraulic fluid from the internal reservoir of the RAT pump to an external drain tank.
B. Leg Assembly
The leg assembly is the mechanical and hydraulic connection between the pump assembly and the aircraft.
The main part of the leg assembly is a one-piece forging which includes attachments for other components. At the bottom end, the leg assembly holds the turbine. The top of the leg assembly has a pivot where it is attached to the aircraft structure. The pivot includes swivel connections for the hydraulic supply to and from the pump.
The stationary part of the hydraulic system is connected to the movable part by a swivel joint (pivot).The swivel joint has a check valve in the pump discharge line and a device which gives a warm-up flow to the actuator only in the RAT stow condition.
The cascade-type orifice for the warm-up flow is protected by self-cleaning filters.
The leg assembly is the mechanical and hydraulic connection between the pump assembly and the aircraft.
The main part of the leg assembly is a one-piece forging which includes attachments for other components. At the bottom end, the leg assembly holds the turbine. The top of the leg assembly has a pivot where it is attached to the aircraft structure. The pivot includes swivel connections for the hydraulic supply to and from the pump.
The stationary part of the hydraulic system is connected to the movable part by a swivel joint (pivot).
The leg assembly is the mechanical and hydraulic connection between the pump assembly and the aircraft.
The main part of the leg assembly is a one-piece forging which includes attachments for other components. At the bottom end, the leg assembly holds the turbine. The top of the leg assembly has a pivot where it is attached to the aircraft structure. The pivot includes swivel connections for the hydraulic supply to and from the pump.
The stationary part of the hydraulic system is connected to the movable part by a swivel joint (pivot).The swivel joint has a check valve in the pump discharge line and a device which gives a warm-up flow to the actuator only in the RAT stow condition.
The cascade-type orifice for the warm-up flow is protected by self-cleaning filters.
The leg assembly is the mechanical and hydraulic connection between the pump assembly and the aircraft.
The main part of the leg assembly is a one-piece forging which includes attachments for other components. At the bottom end, the leg assembly holds the turbine. The top of the leg assembly has a pivot where it is attached to the aircraft structure. The pivot includes swivel connections for the hydraulic supply to and from the pump.
The stationary part of the hydraulic system is connected to the movable part by a swivel joint (pivot).
C. Hydraulic Pump
The hydraulic pump is a standard axial piston-type pump. The pump has a cylinder barrel with nine pistons. An external power supply drives the barrel. The pistons turn against a face cam and are held by a hold-down plate. When the cylinder barrel turns, the pistons slide in and out of their cylinders. Movement of the pistons causes hydraulic fluid to move in and out through the pump ports. The change in the position angle of the face cam controls the volume of hydraulic fluid from the hydraulic pump.
The angle position of the face cam is changed by a stroking piston. The stroking piston is controlled by a pressure compensator valve. The changes to the angle of the face cam make the pump output fulfil the flow-demand of the aircraft hydraulic system.
The hydraulic pump also includes an anti-stall system. The anti-stall system makes sure that the pump holds the fluid pressure on the primary aircraft hydraulic system at the start-up of the turbine, when the flow-demand is more than the available flow, and maintains the hydraulic power related to the available airflow as the airspeed decreases on approach for landing.
The anti-stall valve permits the turbine to get to the operational speed in less time. This is because the piston pump is constrained to a minimum output until the pump gets to the preset speed. When the aircraft approaches for landing, the anti-stall valve holds the pump output in balance to the airspeed at the turbine.
The output of the gerotor pump is applied to the anti-stall valve. The compensator valve can not operate fast enough to fulfil the demand when the turbine RPM is less than the governed operation range. When the pressure drops across an orifice in the pump, it causes the piston in the anti-stall valve to move. Thus it applies case drain pressure to the stroking piston. The stroking piston then moves the face cam to the maximum output position. As the output changes, the compensating valve takes control of the stroking piston and adjusts the output to fulfil the demand.
The hydraulic pump is a standard axial piston-type pump. The pump has a cylinder barrel with nine pistons. An external power supply drives the barrel. The pistons turn against a face cam and are held by a hold-down plate. When the cylinder barrel turns, the pistons slide in and out of their cylinders. Movement of the pistons causes hydraulic fluid to move in and out through the pump ports. The change in the position angle of the face cam controls the volume of hydraulic fluid from the hydraulic pump.
The angle position of the face cam is changed by a stroking piston. The stroking piston is controlled by a pressure compensator valve. The changes to the angle of the face cam make the pump output fulfil the flow-demand of the aircraft hydraulic system.
The hydraulic pump also includes an anti-stall system. The anti-stall system makes sure that the pump holds the fluid pressure on the primary aircraft hydraulic system at the start-up of the turbine, when the flow-demand is more than the available flow, and maintains the hydraulic power related to the available airflow as the airspeed decreases on approach for landing.
The anti-stall valve permits the turbine to get to the operational speed in less time. This is because the piston pump is constrained to a minimum output until the pump gets to the preset speed. When the aircraft approaches for landing, the anti-stall valve holds the pump output in balance to the airspeed at the turbine.
The output of the gerotor pump is applied to the anti-stall valve. The compensator valve can not operate fast enough to fulfil the demand when the turbine RPM is less than the governed operation range. When the pressure drops across an orifice in the pump, it causes the piston in the anti-stall valve to move. Thus it applies case drain pressure to the stroking piston. The stroking piston then moves the face cam to the maximum output position. As the output changes, the compensating valve takes control of the stroking piston and adjusts the output to fulfil the demand.
D. RAT Actuator
Hydraulic power is not necessary to extend the RAT. A spring forces the RAT to extend. In the stow position, the spring is compressed and an internal uplock segment keeps the actuator cylinder in the retracted position.
Two solenoids operate the lock release mechanism for the deployment of the RAT actuator 1GE. If one solenoid has a malfunction, this will not prevent the deployment of the RAT actuator. One solenoid is enough to deploy the RAT. The two solenoids for the ejection release are attached externally to the upper end of the RAT actuator.
A stowed switch gives a signal to tell you if the RAT is in the correct stow position or not.
Hydraulic power is not necessary to extend the RAT. A spring forces the RAT to extend. In the stow position, the spring is compressed and an internal uplock segment keeps the actuator cylinder in the retracted position.
Two solenoids operate the lock release mechanism for the deployment of the RAT actuator 1GE. If one solenoid has a malfunction, this will not prevent the deployment of the RAT actuator. One solenoid is enough to deploy the RAT. The two solenoids for the ejection release are attached externally to the upper end of the RAT actuator.
A stowed switch gives a signal to tell you if the RAT is in the correct stow position or not.
E. RAT Control Panel
The RAT control panel is a switch box for the retraction of the RAT on the ground.
The RAT control panel has:
The RAT control panel has a protective cover. The cover is spring-loaded to the open position and is safetied with a quick-release fastener in the closed position. A small window in the protective cover makes the warning light visible when the cover is closed.
The STOW/RESET switch operates the retraction of the RAT. The STOW/RESET switch is spring-loaded and thus moves to the center position when released.
The ON/OFF switch which switches off the 28 V DC is a toggle switch with a safety guard. It is only possible to close the protective cover when the switch and the safety guard are in the OFF position.
A pushbutton switch is installed to test the warning/ indicator lights.
The RAT control panel is a switch box for the retraction of the RAT on the ground.
The RAT control panel has:
- an ON/OFF switch to switch off 28 V DC,
- a STOW/RESET switch,
- a residual pressure warning light,
- a RAT stow indicator light,
- an interlock warning light,
- a lamp test switch,
- a ground connector.
The RAT control panel has a protective cover. The cover is spring-loaded to the open position and is safetied with a quick-release fastener in the closed position. A small window in the protective cover makes the warning light visible when the cover is closed.
The STOW/RESET switch operates the retraction of the RAT. The STOW/RESET switch is spring-loaded and thus moves to the center position when released.
The ON/OFF switch which switches off the 28 V DC is a toggle switch with a safety guard. It is only possible to close the protective cover when the switch and the safety guard are in the OFF position.
A pushbutton switch is installed to test the warning/ indicator lights.
F. Electrical and Hydraulic Override Pushbutton Switches (24XE, 2805GE)
The elec ovrd (24XE) and hyd ovrd (2805GE) pushbutton switches are installed in the flight compartment. The hyd ovrd pushbutton switch is on the HYD section of the overhead panel 40VU. The elec ovrd pushbutton switch is on the EMER PWR section of the overhead panel 21VU. Both pushbutton switches make it possible for the flight crew to extend the RAT from the flight compartment. Both pushbutton switches have guards to stop accidental operation.
The hyd ovrd pushbutton switch (identified as RAT/MAN/ON in the flight compartment) when operated connects the 28 V DC supply from HOT BUS 1, 701PP directly to solenoid 1.
The elec ovrd pushbutton switch (identified as RAT & EMER GEN/MAN ON/AUTO in the flight compartment) when operated connects the 28 V DC supply from No. 2 BATTERY through circuit breaker 6XE to solenoid 2. At the same time the 28 V DC is supplied to the control unit of the CSM/G 8XE.
The elec ovrd (24XE) and hyd ovrd (2805GE) pushbutton switches are installed in the flight compartment. The hyd ovrd pushbutton switch is on the HYD section of the overhead panel 40VU. The elec ovrd pushbutton switch is on the EMER PWR section of the overhead panel 21VU. Both pushbutton switches make it possible for the flight crew to extend the RAT from the flight compartment. Both pushbutton switches have guards to stop accidental operation.
The hyd ovrd pushbutton switch (identified as RAT/MAN/ON in the flight compartment) when operated connects the 28 V DC supply from HOT BUS 1, 701PP directly to solenoid 1.
The elec ovrd pushbutton switch (identified as RAT & EMER GEN/MAN ON/AUTO in the flight compartment) when operated connects the 28 V DC supply from No. 2 BATTERY through circuit breaker 6XE to solenoid 2. At the same time the 28 V DC is supplied to the control unit of the CSM/G 8XE.
A. Retracted Position
In the retracted position, the RAT is kept in the RAT stow compartment with the doors closed. The leg assembly has two links which are attached to the stow compartment doors and keep them closed. The internal lock in the RAT actuator locks the RAT in the retracted position. The index mechanism on the leg assembly locks the turbine blades so that they can not turn. The turbine blades are at the fine pitch. A calibrated flow of warm oil is supplied to the leg assembly and the pump.
In the retracted position, the RAT is kept in the RAT stow compartment with the doors closed. The leg assembly has two links which are attached to the stow compartment doors and keep them closed. The internal lock in the RAT actuator locks the RAT in the retracted position. The index mechanism on the leg assembly locks the turbine blades so that they cannot turn. The turbine blades are at the fine pitch.
In the retracted position, the RAT is kept in the RAT stow compartment with the doors closed. The leg assembly has two links which are attached to the stow compartment doors and keep them closed. The internal lock in the RAT actuator locks the RAT in the retracted position. The index mechanism on the leg assembly locks the turbine blades so that they can not turn. The turbine blades are at the fine pitch. A calibrated flow of warm oil is supplied to the leg assembly and the pump.
In the retracted position, the RAT is kept in the RAT stow compartment with the doors closed. The leg assembly has two links which are attached to the stow compartment doors and keep them closed. The internal lock in the RAT actuator locks the RAT in the retracted position. The index mechanism on the leg assembly locks the turbine blades so that they cannot turn. The turbine blades are at the fine pitch.
B. Extension
The extension of the RAT is controlled by the:
When the RAT receives an automatic or manual command to extend, one of the two deploy solenoids operates and releases the internal lock. Spring pressure causes the RAT actuator to extend, which extends the RAT into the airflow. The RAT compartment doors open with the extension of the RAT. When the RAT extends, the stowed switch operates and sends a signal to the ECAM system where the legend RAT OUT appears.
The index mechanism disengages automatically when the RAT is 8 degrees from its fully extended position. As the RAT is caught by the airstream, the actuator operates as a shock absorber which prevents high-shock loads on the RAT and aircraft structure. When the rod of the actuator is at its maximum extension, movement of the turbine assembly stops.
The extension of the RAT is controlled by the:
- Manual operation of the pushbutton switch OVRD HYD 2805GE on the HYD section of the overhead panel 40VU, or
- Manual operation of the pushbutton switch OVRD ELEC 24XE on the overhead panel 21VU, or
- Automatic control in the event of a total failure of the AC busbars 1XP and 2XP.
When the RAT receives an automatic or manual command to extend, one of the two deploy solenoids operates and releases the internal lock. Spring pressure causes the RAT actuator to extend, which extends the RAT into the airflow. The RAT compartment doors open with the extension of the RAT. When the RAT extends, the stowed switch operates and sends a signal to the ECAM system where the legend RAT OUT appears.
The index mechanism disengages automatically when the RAT is 8 degrees from its fully extended position. As the RAT is caught by the airstream, the actuator operates as a shock absorber which prevents high-shock loads on the RAT and aircraft structure. When the rod of the actuator is at its maximum extension, movement of the turbine assembly stops.
C. RAT Operation
As the turbine assembly extends into the airstream, a stationary stop on the pivot operates a control cable. The cable is attached to the index lock plunger. The index lock releases the turbine hub at approximately 8 degrees from the fully extended position of the turbine assembly. The airstream then causes the turbine blades to turn. A bevel gear inside the gearbox assembly transmits the rotation of the turbine to operate the hydraulic pump.
When the turbine is released to spin, it accelerates without pump load. As the turbine speed gets to the operational range, the pitch cam changes the angle of the blades to the intermediate or the coarse-pitch position. The rotation speed of the turbine is opposed to the force of the governor spring, the blade and the counterweight.
As the speed of the turbine increases, the blades move to the coarse-pitch position for less air load. When the blades move to coarse-pitch, the governor spring is compressed. As the air load on the turbine blades decreases, the turbine speed decreases. The governor spring, which is compressed, expands and overcomes the torques of the blades and the counterweight. Then the pitch cam adjusts the blades to a finer pitch position and the speed of the turbine increases. Thus the turbine is kept at a constant speed in its operation range between 92 and 135 knots equivalent air speed (KEAS) by the governor.
When the airspeed is less than 92 KEAS, the turbine speed decreases less than the governor operation range of 4.750 RPM. When the RPM is between 3.800 and 4.200 RPM, the anti-stall system then keeps the output of the pump in balance to the airspeed at the turbine. As the airspeed and the turbine speed continue to decrease, the output pressure of the pump decreases to zero.
The bevel gearset in the gearbox supplies power to the hydraulic pump through the turbine. Attached to the RAT hub is a directly-driven shaft. An internal spline is on the aft end of the drive shaft which drives the turbine and the pump during the ground test of the RAT system. To test the turbine, the transmission, the pump and the actuator, a ground test tool is attached to the back of the RAT.
As the turbine assembly extends into the airstream, a stationary stop on the pivot operates a control cable. The cable is attached to the index lock plunger. The index lock releases the turbine hub at approximately 8 degrees from the fully extended position of the turbine assembly. The airstream then causes the turbine blades to turn. A bevel gear inside the gearbox assembly transmits the rotation of the turbine to operate the hydraulic pump.
When the turbine is released to spin, it accelerates without pump load. As the turbine speed gets to the operational range, the pitch cam changes the angle of the blades to the intermediate or the coarse-pitch position. The rotation speed of the turbine is opposed to the force of the governor spring, the blade and the counterweight.
As the speed of the turbine increases, the blades move to the coarse-pitch position for less air load. When the blades move to coarse-pitch, the governor spring is compressed. As the air load on the turbine blades decreases, the turbine speed decreases. The governor spring, which is compressed, expands and overcomes the torques of the blades and the counterweight. Then the pitch cam adjusts the blades to a finer pitch position and the speed of the turbine increases. Thus the turbine is kept at a constant speed in its operation range between 92 and 135 knots equivalent air speed (KEAS) by the governor.
When the airspeed is less than 92 KEAS, the turbine speed decreases less than the governor operation range of 4.750 RPM. When the RPM is between 3.800 and 4.200 RPM, the anti-stall system then keeps the output of the pump in balance to the airspeed at the turbine. As the airspeed and the turbine speed continue to decrease, the output pressure of the pump decreases to zero.
The bevel gearset in the gearbox supplies power to the hydraulic pump through the turbine. Attached to the RAT hub is a directly-driven shaft. An internal spline is on the aft end of the drive shaft which drives the turbine and the pump during the ground test of the RAT system. To test the turbine, the transmission, the pump and the actuator, a ground test tool is attached to the back of the RAT.
D. Retraction
It is only possible to retract the RAT when the aircraft is on the ground. Retraction is operated from the RAT control panel which is in the ground service panel of the Blue system. The system must be in the subsequent condition to retract the RAT:
When the 28V DC switch is set to the ON position, electrical power is supplied to the STOW/RESET selector switch. To retract the RAT you must set the spring-loaded STOW/RESET selector switch to the STOW position and hold it there for approximately 20 seconds, then:
When the STOW/RESET switch is released and is in the neutral position:
When the ON/OFF switch is set to the OFF position:
When the STOW/RESET switch is released before the RAT is fully retracted, the RAT will immediately stop and return in the fully extended position. This occurs because the supply of electrical power to the solenoid of the RAT ground retraction module is stopped. The RAT ground retraction module goes to the flight position and the RAT extends because of the RAT actuator spring pressure.
Also the RAT will not retract but return to its fully extended position when the RAT retract lock does not engage. If the marks on the turbine hub and the leg are not aligned and the STOW/RESET switch is set to STOW, the RAT will start to retract but:
Before you do the retraction again, you must do the subsequent:
When the STOW/RESET switch is released and is in the neutral position:
When the ON/OFF switch is set to the OFF position:
When the STOW/RESET switch is released before the RAT is fully retracted, the RAT will immediately stop and return to the fully extended position. This occurs because the supply of electrical power to the solenoid of the RAT ground retraction-module is stopped. The RAT ground retraction-module goes to the flight position and the RAT extends because of the RAT actuator spring pressure.
Also, the RAT will not retract, but return to its fully extended position when the RAT retract lock does not engage. If the marks on the turbine hub and the leg are not aligned and the STOW/RESET switch is set to STOW, the RAT will start to retract but:
Before you do the retraction again, you must do the subsequent:
It is only possible to retract the RAT when the aircraft is on the ground. Retraction is operated from the RAT control panel which is in the ground service panel of the Blue system. The system must be in the subsequent condition to retract the RAT:
- The ground test equipment is not attached
- The cover plate is installed correctly
- The position arrows on the hub and the lower leg gearbox align (the turbine is then in the index position)
- The 28V DC switch on the RAT control panel is in the ON position (28 V DC is supplied to the RAT stow panel)
- The INTERLOCK WARNING lamp on the RAT control panel is off
- The Blue main-hydraulic system is pressurized.
NOTE: You must manually turn the turbine to the index position.
The RAT is retracted hydraulically with the hydraulic supply from the Blue electric pump or from a ground supply. When the 28V DC switch is set to the ON position, electrical power is supplied to the STOW/RESET selector switch. To retract the RAT you must set the spring-loaded STOW/RESET selector switch to the STOW position and hold it there for approximately 20 seconds, then:
- The solenoid operates and connects the high pressure supply of the aircraft to the retract side of the RAT actuator
- The high pressure fluid operates the pressure switch and the ACTUATOR PRESSURE indicator lamp comes on to indicate that the RAT actuator is pressurized
- The high pressure supply releases the RAT actuator extend lock and retracts the RAT into the stow compartment
- The return fluid from the RAT actuator goes directly into the low-pressure system of the aircraft.
- The retract lock of RAT actuator engages and holds the RAT in place
- The stowed proximity sensor on the RAT actuator operates
- The STOWED indicator lamp comes on.
When the STOW/RESET switch is released and is in the neutral position:
- The RAT actuator is depressurized
- The ACTUATOR PRESSURE indicator lamp goes off.
When the ON/OFF switch is set to the OFF position:
- The power supply is stopped
- The STOWED indicator lamp goes off.
When the STOW/RESET switch is released before the RAT is fully retracted, the RAT will immediately stop and return in the fully extended position. This occurs because the supply of electrical power to the solenoid of the RAT ground retraction module is stopped. The RAT ground retraction module goes to the flight position and the RAT extends because of the RAT actuator spring pressure.
Also the RAT will not retract but return to its fully extended position when the RAT retract lock does not engage. If the marks on the turbine hub and the leg are not aligned and the STOW/RESET switch is set to STOW, the RAT will start to retract but:
- When the RAT is approximately 8 degrees from full extension the interlock proximity switch operates
- The INTERLOCK WARNING indicator lamp comes on
- The high pressure supply to the RAT actuator stops
- The RAT returns to its fully extended position.
Before you do the retraction again, you must do the subsequent:
- Press the warm up flow indicator in
- Align the index marks of the hub with the index marks on the leg so that the index is in the correct position
- Put the STOW/RESET switch to the RESET position to reset the interlock logic in the stow panel.
- The retract lock of the RAT actuator engages and holds the RAT in position
- The stowed proximity sensor on the RAT actuator operates
- The STOWED indicator lamp comes on.
When the STOW/RESET switch is released and is in the neutral position:
- The RAT actuator is depressurized
- The ACTUATOR PRESSURE indicator lamp goes off.
When the ON/OFF switch is set to the OFF position:
- The power supply is stopped
- The STOWED indicator lamp goes off.
When the STOW/RESET switch is released before the RAT is fully retracted, the RAT will immediately stop and return to the fully extended position. This occurs because the supply of electrical power to the solenoid of the RAT ground retraction-module is stopped. The RAT ground retraction-module goes to the flight position and the RAT extends because of the RAT actuator spring pressure.
Also, the RAT will not retract, but return to its fully extended position when the RAT retract lock does not engage. If the marks on the turbine hub and the leg are not aligned and the STOW/RESET switch is set to STOW, the RAT will start to retract but:
- When the RAT is approximately 8 degrees from full extension the interlock proximity switch operates
- The INTERLOCK WARNING indicator lamp comes on
- The high pressure supply to the RAT actuator stops
- The RAT returns to its fully extended position.
Before you do the retraction again, you must do the subsequent:
- Align the index marks of the hub with the index marks on the leg. This makes sure that the index is in the correct position
- Put the STOW/RESET switch to the RESET position to reset the interlock logic in the stow panel.
7. Test
A. RAT Functional Test
During the functional test you can test the mechanical governor and the hydraulic pump of the RAT on the ground. To do the test, a RAT ground test tool and a hydraulic ground-power supply are necessary.
During the functional test you can test the mechanical governor and the hydraulic pump of the RAT on the ground. To do the test, a RAT ground test tool and a hydraulic ground-power supply are necessary.
B. Retraction Test
The RAT retraction test is operated through the RAT control panel which is installed in the Blue ground-service panel.
The RAT retraction test is operated through the RAT control panel which is installed in the Blue ground-service panel.