Turbine Powered Auxilary Power Units

Question 1

1. What is the typical relationship between aircrafts auxiliary power unit generator and the engine Driven generator?

Answer 1

Identical

Question 2

2. Where does the APU fuel supply normally come from?

Answer 2

Airplanes main fuel supply

Question 3

3. How does the APU rotate during start up?

Answer 3

Electric starter

Question 4

4. What is the function of an APU air inlet plenum?

Answer 4

To stabilize pressure of air before it enters compressor

Question 5

5. When operating at high loads, what is the speed of an APU?

Answer 5

At or near constant speed regardless of load

Question 6

6. What is the effect of the pneumatic power when being used in conjunction with maximum APU shaft power output?

Answer 6

Pneumatic loading will automatically modulate to maintain safe EGT

Question 7

7. Before shutting down, how would APU cooling be accomplished?

Answer 7

Closing the bleed air valve

Question 8

8. When is most of the load placed on an APU?

Answer 8

Bleed air is opened

Question 9

9. What regulates fuel scheduling during APU start and under varying pneumatic bleed and electrical loads?

Answer 9

APU fuel control stystem

Question 10

10. How is most troubleshooting accomplished on modern APUs?

Answer 10

FADEC

Question 11

11. What is the primary function of the load compressor on APUs equipped with a free turbine and load compressor?

Answer 11

Provide bleed air for pneumatic systems

Question 12

12. To prevent rotor seizure shock cooling how long should an APU idle before being shut down?

Answer 12

3-5 minutes

Question 13

13. What is the function of the APU on a modern transport category aircraft?

Answer 13

Provides bleed air for engine starting, air conditioning, and de icing