Baker's General, Airframe, & Powerplant Oral & Practical II

What is the typical relationship between an aircraft's auxiliary power unit (APU) generator and the engine driven generator? - Answer- They are identical. Where does the APU fuel supply normally come from? - Answer- The airplane's main fuel supply. How is the APU rotated during start up? - Answer- With an electric starter. What is the function of an APU air inlet plentum? - Answer- It is to stabilize the pressure of the air before it enters the compressor. When operating at high loads, what is the speed of an APU? - Answer- The APU 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? - Answer- The pneumatic loading will be automatically modulated to maintain a safe EGT. Before shut down, how would APU cooling be accomplished? - Answer- By closing the bleed air valve, thus removing the load When is most of the load placed on an APU? - Answer- When the bleed air is open. What regulates fuel scheduling during APU start and under varying pneumatic bleed and electrical loads? - Answer- Fuel scheduling is maintained automatically by the APU fuel control system. How is most troubleshooting accomplished on modern APUs - Answer- By gathering information from the FADEC What is the primary function of the load compressor on APU's equipped with a free turbine and load compressor? - Answer- To provide bleed air for aircraft pneumatic systems. To prevent rotor seizure "shock cooling", how long should an APU idle before being shut down? - Answer- 3 to 5 minutes. What is the purpose of a propeller? - Answer- To create thrust and either pull or push the airplane through the air.