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O. auxiliary power

auxiliary power units 15

QuestionAnswer
what is the purpose of the APU? they provide ground electrical and pneumatic power for aircraft systems when the engines are not running. pneumatic power can be used for engine starting, ground heating or air conditioning and anti-icing.
name the main components of a typical APU. a small power turbine for power and bleed air, and or electrical generator.
when is the greatest demand placed on an APU? when supplying bleed air.
how is an APU generally started? with its own electrical starter and battery power.
where does the APU get its fuel supply? from one of the aircraft's main fuel tanks.
at what speed does a gas turbine APU operate and how is this speed maintained? at or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjust the fuel flow to maintain the rated speed.
what is used to prevent a heavily loaded APU from exceeding its maximum EGT? a load control valve modulates the pneumatic load to maintain EGTs within limits.
how is an APU shut down and why is this procedure used? after the APU is unloaded by closing the bleed air valve, it is run for a specified amount of time to allow the EGT to cool and stabilize. cool down period is typically 3 min. damage can occur if APU is shut down without cooldown time.
what powers the variable inlet guide vanes used on some APUs to regulate compressor intake airflow? fuel pressure.
Created by: Justin84