Powerplant Systems & Components: Turbine Powered Auxiliary Power Units 🔊 Flashcards
What is the typical relationship between an aircraft’s auxiliary power unit (APU) generator and the engine driven generators?
They are identical
Where does the APU fuel supply normally come from?
The aircraft’s main fuel supply
How is the APU rotated during start up?
With an electrical starter
What is the function of an APU air inlet plenum?
To stabilize the pressure of the air before it enters the compressor
When operating at high loads, what is the speed of an APU?
It remains at or near rated speed regardless of the load condition
What is the effect of the pneumatic power when being used in conjunction with maximum APU shaft power output?
Pneumatic loading will be automatically modulated to maintain a safe EGT
Before shutting down, how would APU cooling be accomplished?
By closing the bleed air valve, removing the load
When is most of the load placed on an APU?
When the bleed air valve is opened
What regulates fuel scheduling during APU start and under varying pneumatic bleed and electrical loads?
It is maintained automatically by the APU fuel control system
How is most troubleshooting accomplished on modern APUs?
By gathering information from the FADEC
What is the primary function of the load compressor on APUs equipped with a free turbine and load compressor?
To provide bleed air for aircraft pneumatic systems
To prevent rotor seizure “shock cooling”, how long should an APU idle before being shut down?
3 to 5 minutes
What is the function of the APU on a modern transport category aircraft?
Provides bleed air for engine starting, air conditioning, and deicing
