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GF0510_002
APU INLET DOOR
APU ACCESS DOORS
APU EXHAUST
EXHAUST DISCHARGE
EXHAUST BAFFLE
INLET DUCT
APU INLET DOOR
INLET OIL COOLER
OIL COOLER
APU Compartment
The APU is mounted in the tail cone by a multiaxis
suspension rod system, securing it in all axes.
The APU compartment is completely sealed from the atmosphere with the exception of the inlet to
the oil cooler system and the APU air inlet. The APU utilizes exhaust flow to pump cooling air
through the oil cooler and to the APU and its associated components. The APU compartment is
also isolated from the rest of the airplane for fire protection.
Cooling of the APU compartment is accomplished by an air to oil heat exchanger and by air flow
over the APU through the enclosure (via the APU inlet). The airflow through the inlet splits in two
sections. One section allows air to flow to the inlet plenum (to the compressor), while the other
section allows the air to flow through the oil cooler to provide cooling for the APU oil. The air
flowing through the oil cooler then passes through the compartment to cool the APU and its
mounted components. This air is then exhausted overboard via the APU eductor. This air is the
exausted overboard.
AUXILIARY POWER UNIT
Flight Crew Operating Manual Rev 2A, Apr 11, 2005
CSP 700−5000−6
Volume 2
05−10−2
APU GENERAL ARRANGEMENT
The APU consists of the following:
· Inlet Door − Variable position. The door schedules are sequenced as a function of
weightonwheels,
airplane MACH number and APU speed.
· Compressor − Is a single stage centrifugal impeller. Delivers approximately 52 psia bleed
pressure at normal operating speed.
· Combustor − Contains 10 fuel nozzles and 2 igniters.
· Turbine − Two stage axial flow turbine which drives the compressor/gearbox.
· Gearbox − Provides the sump for the lubrication system and mounting of component and
accessories.
· Exhaust − The flow across the APU and oil cooler is created by utilizing the exhaust discharge
velocity.
· Monitor zones for fire/overheat/smoke events, FIDEEX system health and status.
APU SYSTEM SCHEMATIC
BLEED AIR
APU COMPARTMENT AIRFLOW
OIL
OUT
OIL
IN
AIR/OIL COOLER
TO APU
COMPARTMENT
GEARBOX
TO AIRCRAFT
BLEED AIR
SYSTEM
LOAD CONTROL
VALVE
ELECTRICAL CIRCUITS
THE AIR SYSTEM IS SHOWN WITH AN APU BLEED LOAD
FROM/TO APU
SYSTEMS
FROM/TO
AIRCRAFT
SYSTEMS
FADEC
BLEED AIR
DUCT
BLEED AIR
CHECK VALVE
SURGE VALVE SURGE DUCT
BLEED
DIFFUSER
AIRCRAFT
SKIN
EXHAUST
TURBINE
COMPRESSOR
COMBUSTION
INLET
NOTE
EDUCTOR
INLET AIR
STARTER
GEN
FUEL CONTROL
UNIT
OIL
PUMP
GF0510_003
AUXILIARY POWER UNIT
Rev 3, Apr 25, 2005 Flight Crew Operating Manual
CSP 700−5000−6
Volume 2
05−10−3
APU SYSTEM SCHEMATIC (CONT'D)
Lubrication
The lubrication system incorporates an integral oil reservoir. The two main areas that are
lubricated are the gearbox and turbine bearings.
The gearbox sump is the reservoir and can be filled through the fill cap. The APU can also be
serviced on ground only, using the airplane remote oil replenishment system, simplifying post flight
maintenance actions.
The lubrication system consists of the following components:
· Oil filters − Lube and generator scavenge.
· Oil temperature sensor − Sends an input to the FADEC for both minimum oil temperature
and high oil temperature protection. When oil temperature increases to a high
predetermined value for 10 seconds, the APU (on ground only) will shut down.
· Low Oil Pressure (LOP) switch − When pressure drops below a predetermined PSIG after
the APU has reached onspeed
(not less than 99%) for 15 seconds, the APU (on ground
only) will shut down automatically.
· Oil cooler − Will bypass oil at a predetermined lower than normal operating temperature and
flow through the cooler when temperatures are above the normal operating range.
· Magnetic Chip Collector (visual inspection) − Provides visual indication of metal particles
within the system.
Oil Pressure
On the prestart BITE check, the LOP switch is checked by the FADEC. During operation, if oil
pressure decreases below a predetermined PSIG for approximately 15 seconds (on ground),
automatic shutdown will occur. An “APU OIL LO PRESS” caution message will come on for 15
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