Jeppesen Chapter 3 - Turbine Engines - (23 items)

Question 1

Q1. Explain the main difference and advantage of turbofan over turbojet engines.

Answer 1

A1. A turbofan engine uses a fan to bypass some air around the engine air core to provide thrust. The advantage is that this provides additional thrust without increasing fuel flow.

Question 2

Q3. What determines the amount of airflow through a turbine engine?

Answer 2

A3. (1)The forward speed of the aircraft, (2)Compressor speed, (3)Air density

Question 3

Q4. Name the two types of compressors commonly used in turbine engines.

Answer 3

A4. Axial and Centrifugal flow compressors.

Question 4

Q5. Name two different methods for attaching turbine engine rotor blades to the rotor disks.

Answer 4

A5. Dovetail-type root, or Bulb-type root, or Fir tree-type root.

Question 5

Q6. What is a split compressor system?

Answer 5

A6. Also called dual or twin compressors, these are connected to the turbine section with two rotor shafts, one inside the other.

Question 6

Q7. What are the different types of combustion chambers used in turbine engines?

Answer 6

A7. (1)Can, (2)Annular, (3)Can-Annular, and (4)reverse flow annular

Question 7

Q8. What prevents the combustion chambers from burning?

Answer 7

A8. Cooling air along the inside of the liner.

Question 8

Q9. What is the purpose of the interconnecting tubes attached between can-type combustion chambers?

Answer 8

A9. For flame propagation during the start.

Question 9

Q10. What functions do axial flow turbine nozzles perform?

Answer 9

A10. They direct the mass airflow to drive the turbine rotor at a specific angle.

Question 10

Q11. How is the thermal stress relieved on a turbine disc?

Answer 10

A11. By directing bleed air onto the face of the disk, or by grooves being cut in the disk.

Question 11

Q12. What are carbon seals used for in turbine engines?

Answer 11

A12. They are used as oil seals for the rotor shaft bearings.

Question 12

Q13. What is shaft horsepower?

Answer 12

A13. It is an indication of the torque developed by a turboprop or turboshaft engine.

Question 13

Q14. Name the main components of a typical APU.

Answer 13

A14. A small power turbine for power and bleed air, and an electrical generator.

Question 14

Q15. When is the greatest demand placed on an APU?

Answer 14

A15. When supplying bleed air.

Question 15

Q16. How is an APU generally started?

Answer 15

A16. With its own electrical starter and battery power.

Question 16

Q17. Where does the APU get its fuel supply?

Answer 16

A17. From one of the aircraft’s main fuel tanks.

Question 17

Q18. At what speed does a gas turbine APU operate and how is this speed maintained?

Answer 17

A18. At or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed.

Question 18

Q19. What is used to prevent a heavily loaded APU from exceeding its maximum EGT?

Answer 18

A19. A load control valve modulates the pneumatic load to maintain EGT’s within limits.

Question 19

Q20. How is an APU shut down and why is this procedure used?

Answer 19

A20. After the APU is unloaded by closing the bleed air valve, it is run for a specified amount of time to allow the EGT to cool and stabilize. This cool down period is typically three minutes. If a heavily loaded APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock.

Question 20

Q21. What powers the variable inlet guide vanes used on some APU’s to regulate compressor intake airflow?

Answer 20

A21. Fuel Pressure.

Question 21

Q22. What is fan blade shingling?

Answer 21

It is the overlapping of the midspan shrouds of the fan blade.

Question 22

Q23. When a turbofan or turbojet engine is shut down, what should a mechanic listen for during a coast coastdown?

Answer 22

A23. Any rubbing sound or other unusual noises from the engine.

Question 23

Q2. Name the major components in a gas turbine engine.

Answer 23

A2. (1)Air inlet, compressor section, (2)combustion section, (3)turbine section, (4)exhaust section, (5)gearbox and accessory section.