Turbines

Question 1

What are the two basic sections of a turbine engine?

Answer 1

The hot section and the cold section.

Question 2

What are the two basic types of compressors that are used in aircraft turbine engines?

Answer 2

Axial-flow and centrifugal.

Question 3

What is the purpose of the stators in an axial-flow compressor?

Answer 3

The stators convert velocity energy into pressure energy and direct air to hit the next row of blades at the right angle

Question 4

What are three types of combustors used on aircraft turbine engines?

Answer 4

Can-type, annular-type, and can-annular-type.

Question 5

How many igniters are there normally in an aircraft turbine engine?

Answer 5

Two.

Question 6

What is the main purpose of the turbine nozzle in an aircraft turbine engine?

Answer 6

Directs the hot gas as it leaves the combustor so it will turn the turbine wheel with maximum efficiency.

Question 7

What is meant by a free-turbine turboshaft engine?

Used on turboprops and helos.

Answer 7

A turboshaft engine that has a turbine wheel that is not used to drive the compressor of the gas generator section of the engine.

Question 8

Why do some axial-flow turbine engines have more than one set of turbines and compressors?

Answer 8

A two-spool turbine engine has a low pressure and a high pressure compressor, each driven by its own turbine. The two independent systems operate at the speed at which they are most efficient.

Question 9

What kind of bearings are used to support the rotor shaft of an aircraft turbine engine?

Answer 9

Ball bearings or roller bearings.

Question 10

What is meant by a turbofan engine?

Answer 10

A turbine engine in which the first stage of compressor blades are lengthened, so they can force air around the outside of the gas generator portion of the engine.

Question 11

Why is it important that a turbojet engine be allowed to cool before it is shut down after it has been operated at a high power setting?

Answer 11

The shroud could contract around the turbine wheel and seize the rotor.

Question 12

What is meant by a hung start in a turbine engine?

Answer 12

A start in which ignition occurs, but the engine does not accelerate to a self-sustaining speed.

Question 13

What is meant by a hot start in a turbine engine?

Answer 13

A start in which ignition occurs, but the internal temperatures go high enough that they can damage the engine.

Question 14

What is meant by creep of the turbine blades?

Answer 14

A condition of permanent elongation of the turbine blades. Creep is caused by the high temperatures and the high centrifugal stress on blades.

Question 15

Where is water injected into a turbine engine for cooling purposes?

Answer 15

Into the compressor inlet and into the engine diffuser case.

Question 16

At what point in a turbine engine is the temperature the highest?

Answer 16

At the inlet to the turbine.

Question 17

What is the function of the interconnect tubes between the cans of a turbine engine that uses can-type combustors?

Answer 17

These tubes allow the flame to travel from the cans that contain the igniters to all of the other cans when the engine is being started.

Question 18

What are two types of thrust reversers that are used on turbojet engines?

Answer 18

The mechanical blockage-type and the aerodynamic blockage-type.

Question 19

What is meant by trimming a turbojet engine?

Answer 19

Adjusting the fuel control to get the correct idling and maximum-thrust RPM.

Question 20

What are two sources of compressed air from an APU?

Answer 20

From bleed air from the APU turbine compressor, or from a load compressor driven by a free turbine in the engine.

Question 21

What is EPR, and what does it indicate?

Answer 21

Engine Pressure Ratio is the ratio of the turbine discharge pressure to the inlet air pressure, it indicates amount of thrust being produced.

Question 22

What are two factors that EPR readings can be affected by?

Answer 22

altitude and outside air temperature.

Question 23

What are the three parts of a centrifugal compressor?

Answer 23

Impeller, diffusor, manifold.

Question 24

What are the two main components of an axial flow compressor?

Answer 24

Rotors and stators.

Question 25

In a dual spool axial flow compressor, what is the front spool called?

Answer 25

A low speed, low pressure, or N1 compressor.

Question 26

In a dual spool compressor, which section is governed?

Answer 26

The high speed or N2.

Question 27

What is a compressor stall?

Answer 27

When an imbalance occurs between compressor blade rotation speed and inlet air velocity.

Question 28

What are the results of a compressor stall?

Answer 28

Air can slow down, stagnate, or reverse direction in the compressor.

Question 29

How can a compressor stall be fixed?

Answer 29

* Variable inlet guide vanes, * stator vane positioning controlled by the FCU * or bleeding off air.

Question 30

What are the two types of air flow in a combustor, and what do they do?

Answer 30

The primary and secondary. **Primary air goes through the center of the combustor**, **secondary** travels around the periphery creating a **cooling blanket** of air and centering the flame.

Question 31

What are the four basic elements that make up the turbine section?

Answer 31

Case, stator, shroud, rotor.

Question 32

What are three factors that affect the thermal efficiency of a turbine engine?

Answer 32

Turbine inlet temperature, the compression ratio, and turbine/compressor efficiency.

Question 33

What is stagnation density?

Answer 33

A combination of three variables (temperature, altitude, airspeed) that affect the production of thrust in a gas turbine engine.

Question 34

What is ram recovery?

Answer 34

the air inlet recovers as much of the total pressure of the airstream as possible to deliver that air to the compressor

Question 35

What is the main advantage of turbofans over turbojets?

Answer 35

The fan provides additional thrust without increasing fuel flow.

Question 36

What are the major components of a turbine engine?

Answer 36

An inlet, compressor, combustor, turbine, exhaust, gearbox and accessory.

Question 37

What are carbon seals used for in turbine engines?

Answer 37

Oil seals for the rotor shaft bearings.

Question 38

What is shaft horsepower?

Answer 38

An indication of torque developed by turboprop or turboshaft engines.

Question 39

What prevents a heavily loaded APU from exceeding its maximum EGT?

Answer 39

A load control valve.

Question 40

Why are compressor washes performed?

Answer 40

To **remove contaminants** from the compressor and **improve engine performance.**

Question 41

What methods are commonly used for compressor washes?

Answer 41

Fluid wash and abrasive grit.

Question 42

How can you tell if a turbofan or turbojet engine is out of trim?

Answer 42

High EGT at the target engine pressure ratio for takeoff power.

Question 43

What kind of markers can be used to mark the parts in hot and cold sections during repair?

Answer 43

Layout dye, felt tip marker, chalk.

Question 44

What criteria determines replacement of a life limited part in a turbine engine?

Answer 44

Number of cycles, hours, or calendar time.

Question 45

How are gas turbine engine tachometers calibrated?

Answer 45

Percent RPM.

Question 46

How is EGT measured?

Answer 46

Thermocouples near the turbine exit.

Question 47

Can the EGT system on a turbine engine be checked without running the engine?

Answer 47

Yes, by checking the resistance of the thermocouples.

Question 48

What is the thrust ratio of a turbofan engine?

Answer 48

a comparison of the thrust produced by the fan to the thrust produced by the engine core exhaust

Question 49

What is the bypass ratio of a turbofan engine?

Answer 49

the ratio of incoming air that bypasses the core to the amount of air that enters the core

Question 50

What are the three classifications of turbofans based off of their bypass ratio?

Answer 50

low bypass (1:1) medium bypass (2:1 oer 3:1) high bypass (4:1 or greater)

Question 51

What are the three types of ratios in regards to turbofan engines?

Answer 51

bypass ratio, thrust ratio, fan pressure ratio

Question 52

What is fan pressure ratio in a turbofan engine?

Answer 52

the ratio of the air pressure leaving the fan to the air pressure entering the fan

Question 53

What are the two types of flameouts turbine engines can have?

Answer 53

lean die out and rich blowout

Question 54

What is the most common way of attaching turbine blades?

Answer 54

fir tree slots

Question 55

What is the term for the type of turbine blade cooling that involves bleed air directed through hollow blades and out through holes in the tip?

Answer 55

convection or film cooling

Question 56

What is the term for the type of turbine blade cooling that involves ducting bleed air into the stationary nozzle vanes and exits through porous material?

Answer 56

transpiration cooling

Question 57

What is the primary function of the compressor section of a gas turbine engine?

Answer 57

to supply enough air to **support combustion** and **produce thrust**

Question 58

What two factors determine the angle of attack of a compressor blade?

Answer 58

inlet air velocity, compressor RPM

Question 59

When is a turbine engine trimmed?

Answer 59

after you change an engine or fuel control unit, or whenever an engine is not producing its maximum thrust

Question 60

What can be used to check the accuracy of an engine's EGT and RPM readings?

Answer 60

Jetcal Analyzer

Question 61

What are the three stages of blade creep? Explain each

Answer 61

1. primary: occurs during an engine's first run 2. secondary: occurs during many hours of operation 3. tertiary: occurs at an acclerated rate after a period of secondary creep. Attributed to hot starts and overtemperature events

Question 62

What are the five most common types of atomizing fuel nozzles used in a turbine engine?

Answer 62

spill type, variable port, air spray, simpex, duplex

Question 63

What is the purpose of water injection in a turbine engine?

Answer 63

it cools the airflow and increases air density to the engine