Subject S - Turbine Powered Auxiliary Power Units Flashcards
What is the typical relationship between an aircraft auxiliary power unit (APU) generator and the engine driven generator?
They are identical
Where does the APU fuel supply normally come from?
The airplanes main fuel supply.
How is the APU rotated during startup?
With an electric starter
What is the function of an APU air inlet Plenum?
It is to stabilize the pressure of air before it enter the compressor.
When operating at high loads what is the speed of an APU?
The APU remains at or near rated speed regardless of load condition.
What is the effect of the pneumatic power when being used in conjunction with maximum APU shaft power output?
The pneumatic loading will be automatically regulated
to maintain a safe exhaust gas temperature.
Before shut down how would APU cooling be accomplished?
By closing the bleed air valve, thus removing the load.
When is most of the load placed on an APU?
When the bleed air is opened.
What regulates fuel scheduling during APU start and under varying pneumatic bleed and electrical loads?
Fuel scheduling is maintained by automatically by the APU fuel control system.
How is most troubleshooting accomplished on modern APU’s?
by gather 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 shut down
3 to 5 minutes
