Turbine Engines

Question 1

Define the term “thermal efficiency” in regards to aircraft engines.

Answer 1

The ratio of net work produced by the engine to the chemical energy supplied in the form of fuel

Question 2

What are the major components of a typical gas turbine engine?

Answer 2

Air inlet, compression section, combustion section, turbine section, exhaust section, and accessory section

Question 3

What are the two principle types of compressors used in turbojet aircraft?

Answer 3

Centrifugal and Axial flow

Question 4

What are the four combustion chamber systems?

Answer 4

Can, Annular, Can-Annular, Reverse Flow Annular

Question 5

What is the purpose of the interconnector tubes between can type combustion chambers?

Answer 5

To spread the flame to the combustion chambers that are not equipped with igniter plugs during engine starting

Question 6

What prevents burning of the liner walls in a can type combustion chamber?

Answer 6

Louvers are provided along the axial length of the liners to direct a cooling layer of air along the inside wall of the liner

Question 7

What types of damage may be found when inspecting compressor blades?

Answer 7

Burns, Burrs, Cracks, Dents, Galling, Gouges, Pitting, Scratches

Question 8

What is the location and function of the diffuser section in a turbine engine?

Answer 8

Located between the compressor section and burner cans to change the high velocity compressor discharge air to static pressure

Question 9

Where are stress rupture cracks most likely to occur on turbine blades?

Answer 9

Across the leading or trailing edge of the blades

Question 10

How are compressor blades attached to a disk-type rotor?

Answer 10

By either bulb-type, fir-tree, or dove tail type roots. Blades are then locked by means of screws, peening, locking wires, pins, or keys

Question 11

What is the purpose of the nozzle diaphragm or turbine nozzle?

Answer 11

The turbine nozzle prepares the combustion mass airflow to drive the turbine rotor

Question 12

What is the major difference between turboprop and turbojet engines?

Answer 12

A turboprop engine usually has more turbine stages, and the turbine must also drive a propeller

Question 13

What is a turbofan engine?

Answer 13

It is the same as a turboprop, except that the propeller is replaced with a duct-enclosed axial flow fan

Question 14

What is the effect of air density on the thrust of a turbine engine?

Answer 14

As air density increases thrust increases

Question 15

What are the two most common types of thrust reversers?

Answer 15

Mechanical and Aerodynamic Blockage

Question 16

What is a split compressor system in a turbine engine?

Answer 16

It requires two concentric shafts joining the turbine stages to their respective compressors

Question 17

What is one method of relieving thermal stress on a turbine disk?

Answer 17

Direct cooling bleed air back onto the face of the disk

Question 18

What may be the indicators if a turbojet engine is out of trim?

Answer 18

High Exhaust Gas Temperature

Question 19

What does it mean when you have high exhaust gas temperature, high fuel flow, and low thrust or power?

Answer 19

Pending engine failure or low compression

Question 20

What is a free turbine?

Answer 20

A turbine wheel that, rather than driving the compressor rotor, drives a propeller or helicopter transmission

Question 21

What is the main purpose of thrust reversers?

Answer 21

Slowing the aircraft down to effective braking speeds

Question 22

What are the advantages of turbofan engines over turbojet engines?

Answer 22

Turbofan engines provide additional thrust without increasing fuel flow

Question 23

What methods are commonly used to accomplish turbine engine compressor field cleaning?

Answer 23

Fluid wash and Abrasive Grit Blast

Question 24

What would the possible cause be for a turbojet or turbofan engine having high exhaust gas temperature, low RPM and high fuel at all engine pressure ratio settings?

Answer 24

Possible turbine damage or loss of turbine efficiency

Question 25

What is the purpose of inlet guide vanes on a turbine engine?

Answer 25

Straighten the airflow and direct it into the first stages of the compressor