ATA 49 – APU
Reference APU: Honeywell 131-9 (A)
- APU Supply –
- Electrical power for the A/C systems,
- Bleed air for engine starting and air conditioning on the ground,
- Bleed air for air conditioning/pressurization and wing anti-ice in flight.
- APU is designed to operate throughout the entire flight envelope.
- Electric power – available whenever the APU operates.
- Pneumatic power – available up to 20000 feet.
- APU is installed in the tail section of the fuselage.
- APU control and monitor by ECB.
- ECB – aft cargo compartment, right side.
- APU master switch, APU start switch – cockpit.
- Inlet
- Air intake flap – electrically operated
- Air intake duct
- Compressor
- Single-stage centrifugal compressor with a 7.5:1 pressure ratio
- Centrifugal compressor is less likely to suffer blade or disc failure than an axial flow compressor.
- Combustion chamber
- Reverse-flow annular combustion-chamber
- 1 igniter plug
- 10 fuel nozzles (flow divider > primary and/or secondary fuel manifold)
- Turbine – two-stage axial-flow turbine
- Exhaust – exhaust pipe
- Load compressor
- Single-stage centrifugal compressor with a compressor ratio of 4:1
- Inlet guide vanes (IGVs) are installed at the entrance of the compressor housing to control the compressor output to the aircraft pneumatic system.
- 16 IGVs are moved simultaneously by a gear train operated by an actuator.
- An APU load control valve and a surge control valve are installed on the outlet orifices of the bleed air T-duct.
- Load control valve (LCV) stops or permits the bleed air flow from the APU to the pneumatic system of the aircraft.
- APU load control valve and APU bleed valve are same thing.
- LCV is a pneumatically actuated butterfly valve.
- Surge control valve (SCV) prevents a load compressor surge. The excess air passes through the valve to the exhaust cone.
- SCV is a hydraulically (Fuel Pressure) actuated butterfly valve.
- Accessory drive gearbox
- Starter motor
- AC generator
- Fuel control unit (FCU)
- Lubrication unit – wet-sump lubrication system
- Cooling air fan >> air > Oil cooler
- Fuel Feed System
- Fuel pump (115V AC, 400Hz, single phase),
- LP valve,
- APU inlet LP switch,
- Fuel drain and vent system.
- FUEL >> LH Crossfeed Duct >> Fuel Feed System > Fuel Control Unit
- Drain system
- Drain Tank – 1
- KISS Seal – 3
- Drain Mast
- Drain Tank > Drain Mast — Suction effect at 200 kts
