Turbine engines

Question 1

Explain the main difference and advantage of a turbofan engine over a turbojet engine

Answer 1

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

Question 2

Name the major components in a gas turbine engine

Answer 2

Air inlet, compressor 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

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 rotor blades to the main turbine rotor disc

Answer 5

Dove tail, bulb or fir tree type root

Question 6

What is a split compressor system?

Answer 6

Also called twin or dual 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 disc or by cutting grooves in the disc

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 a 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 a.p.u

Answer 14

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

Question 15

When is the greatest demand placed on an a.p.u?

Answer 15

When supplying bleed air

Question 16

How is an a.p.u generally started?

Answer 16

With its own electrical starter and battery power

Question 17

Where does the a.p.u get it’s fuel supply?

Answer 17

From one of the aircraft’s main fuel tanks

Question 18

At what speed does a gas turbine a.p.u operate and how is the speed maintained?

Answer 18

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

Question 19

What is used to prevent a heavily loaded a.p.u from exceeding it’s maximum egt?

Answer 19

A load control valve modulates the pneumatic load to maintain egts within limits

Question 20

How is an a.p.u shut down and why is this procedure used?

Answer 20

After the a.p.u 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 a.p.u is abruptly shut down without any cool down period, damage could occur as a result of thermal shock

Question 21

What powers the variable inlet guide vanes used on some a.p.us to regulate compressor intake airflow?

Answer 21

Fuel pressure

Question 22

What is fan blade shingling?

Answer 22

It is the overlapping of the mid-span shrouds of the fan blade

Question 23

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

Answer 23

Any rubbing sound or other unusual sounds coming from the engine