DOC AIRBUS | AMM A320FROTOR ACTIVE CLEARANCE CONTROL SYSTEM (RACC) - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
The engine Rotor Active Clearance (RAC) and Start Bleed (SB) control system uses High Pressure Compressor (HPC) air from stage 5 to control compressor clearance at altitude, and stage 9 HPC bleed air to unload the compressor during starts and accelerations. The function of the RAC system is to improve compressor efficiency during cruise and the function of the SB system is to improve stall margin during engine starting and acceleration.
** ON A/C NOT FOR ALL The engine Rotor Active Clearance (RAC) and Start Bleed (SB) control system uses High Pressure Compressor (HPC) air from stage 5 to control compressor clearance at altitude, and stage 9 HPC bleed air to unload the compressor during starts and accelerations. The function of the RAC system is to improve compressor efficiency during cruise and the function of the SB system is to improve stall margin during engine starting and acceleration.
RACSB Schematic2. Description
The RACSB is an open loop system. The RAC control system ducts 5th stage compressor bleed air to the HPC bore cavity. The 5th stage air causes the rotor to expand and reduces HPC clearances. The increased efficiency of the HPC results in lower fuel consumption.
The SB function is used during engine starting and acceleration from low speed. During transients, the 9th stage bleed increases engine stall margin.
On engine start, the RACSB valve moves to a 9th stage bleed position which unloads the HPC to improve engine acceleration. At steady speeds above idle, at low altitudes, the RACSB valve is in the no air position. At high altitudes, the RACSB valve bleeds 5th stage air to heat the HPC bore which tightens compressor clearances and improves compressor efficiency. When the engine is shut down, the valve extends to a failsafe no air position.
** ON A/C NOT FOR ALL The RACSB is an open loop system. The RAC control system ducts 5th stage compressor bleed air to the HPC bore cavity. The 5th stage air causes the rotor to expand and reduces HPC clearances. The increased efficiency of the HPC results in lower fuel consumption.
The SB function is used during engine starting and acceleration from low speed. During transients, the 9th stage bleed increases engine stall margin.
On engine start, the RACSB valve moves to a 9th stage bleed position which unloads the HPC to improve engine acceleration. At steady speeds above idle, at low altitudes, the RACSB valve is in the no air position. At high altitudes, the RACSB valve bleeds 5th stage air to heat the HPC bore which tightens compressor clearances and improves compressor efficiency. When the engine is shut down, the valve extends to a failsafe no air position.
3. RACSB Valve Description
The RACSB valve has integrated dual butterfly valves driven by a single fuel powered actuator. Position feedback to the ECU is provided by a dual channel LVDT attached on the actuator. One butterfly valve controls the flow of 5th stage compressor bleed while the other butterfly valve controls the flow of the 9th stage compressor bleed. The 5th stage air is ducted to the compressor bore cavity while the 9th stage air is ducted to the LPT cavity. The main valve modes are defined in the table that follows:
The RACSB valve has integrated dual butterfly valves driven by a single fuel powered actuator. Position feedback to the ECU is provided by a dual channel LVDT attached on the actuator. One butterfly valve controls the flow of 5th stage compressor bleed while the other butterfly valve controls the flow of the 9th stage compressor bleed. The 5th stage air is ducted to the compressor bore cavity while the 9th stage air is ducted to the LPT cavity. The main valve modes are defined in the table that follows:
| --------------------------------------------------------------------------- |
| ! Actuator ! Mode ! 5th Stage ! 9th Stage ! |
| ! Stroke ! ! Butterfly ! Butterfly ! |
| !-------------------------------------------------------------------------! |
| ! 0 percent ! No Air ! Closed ! Closed ! |
| ! Failsafe ! ! ! ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 19 percent ! Transient ! Closed ! Fully open ! |
| ! ! Bleed/ ! ! ! |
| ! ! Start Bleed ! ! ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 52.5 percent ! No Air ! Closed ! Closed ! |
| !-----------------!---------------!-------------------!-------------------! |
| ! 52.5-100 ! Rotor Active ! Intermediate ! Closed ! |
| ! percent ! Clearance ! ! ! |
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