Chapter 3

Question 1

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

Answer 1

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

Question 2

Name the major components in a gas turbine engine.

Answer 2

Air inlet, compressor section, diffuser section, combustion section, turbine section, exhaust section, gearbox and accessory section.

Question 3

What determines the amount of airflow through a turbine engine?

Answer 3

The forward speed of the aircraft, compressor speed, and air density.

Question 4

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

Answer 4

Axial and centrifugal flow compressors.

Question 5

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

Answer 5

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

Question 6

What is a split compressor system?

Answer 6

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

Question 7

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

Answer 7

Can, annular, can-annular, and reverse flow annular.

Question 8

What prevents the combustion chambers from burning?

Answer 8

Cooling air along the inside of the liner.

Question 9

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

Answer 9

For flame propagation during start.

Question 10

What functions do axial flow turbine nozzles perform?

Answer 10

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

Question 11

How is thermal stress relieved on a turbine disc?

Answer 11

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

Question 12

What are carbon seals used for in turbine engines?

Answer 12

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

Question 13

What is shaft horsepower?

Answer 13

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

Question 14

Name the main components of a typical APU.

Answer 14

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

Question 15

When is the greatest demand place on an APU?

Answer 15

When supplying bleed air.

Question 16

Where does an APU get its fuel supply?

Answer 16

From one of the aircraft’s main fuel tanks.

Question 17

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

Answer 17

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

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

Answer 18

A load control valve modulates the pneumatic load to maintain EGTs within limits.

Question 19

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

Answer 19

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

What powers the variable inlet guide vanes used on some APUs to regulate compressor intake airflow?

Answer 20

Fuel pressure.

Question 21

What is fan blade shingling?

Answer 21

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

Question 22

When a turbofan or turbojet engine is shut down, what should a mechanic listen for during shutdown?

Answer 22

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

Question 23

How is an APU generally started?

Answer 23

With its own electrical starter and battery power.