Turbine powered auxiliary power unit Flashcards
(13 cards)
Name the main components of a typical APU
A small power turbine for power and bleed air and an electrical generator
What 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 the aircrafts main fuel tanks
At what speed does a gasturbine APU operate and how is the speed maintained?
At or near it’s 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 for exceeding its maximum EGT?
A load control valve modulates the pneumatic load to maintain EGT 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 follow the EGT to cool and stabilize. It takes around three minutes. if a heavily loaded APU is abruptly shut down without any cooling, Damage may occur as a result of thermal shock
What powers the variable inlet guide vanes used on some APU’s to regulate compressor intake airflow?
Fuel pressure
What is the function of an APU on modern transport category aircraft?
Does apply ground electrical and pneumatic power to aircraft systems when the engines are not operating and in some aircraft as a backup source of in flight electrical power
Name at least two uses for APU produced pneumatic power
Engine starting
Ground air conditioning
Anti-icing
How is the cool down for many APU’s accomplished prior to shut down?
By running the APU for at least three minutes, period of time after closing the bleed air valve
What is the operating effect of following a required cooldown period prior:
The APU’s EGT is lowered and stabilized
How is an APU’s operating speed maintained despite variations in the loads imposed?
By the APU’s fuel control automatically adjusting the fuel flow
