15.18 APU Flashcards
what engine is in the APU
small gas turbine (free turbine) turboshaft engine
what does the APU supply
pneumatic bleed air and electrical power to aircraft systems
is the APU housing pressurized or not
unpressurized
what does the APU assist on the aircraft (tasks)
starting engines, pneumatic cabin power, shaft power, backup electrics, electrical power
up to what altitude can the APU operate
40,000ft
what are the 3 main sections of the APU
power section, bleed section, accessory gearbox section
the gearbox drives all the APU accessories such as what
fuel pump, oil pump, cooling fan, AC generator
what is the main function of the compressor in the APU
provide air for combustion
what type of combustion chamber do most APUs have
annular
if there is a fire in an APU what automatically activates
fire extinguishing system
what 2 things does the APU control unit use for constant speed control
APU speed signal, torque motor signal
what is the time for cool down of the APU
0-120 seconds
what 2 subsystems is the APU air system divided into
cooling air, bleed air
what 2 conditions must be met to open the APU bleed valve
APU bleed switch ON, APU start sequence complete
where are external emergency shut off switches
nose landing gear, main wheel well, refuelling station
