Topic 05 - Air Systems, Starting, and Ignition

Question 1

air is bled off from various positions on the ______________ of a gas turbine engine and used to ________ the temperature of those internal parts of the engine which may suffer from ______________ heat

Answer 1

compressor, lower, excessive

Question 2

bleed air is also utilized to ______________, which will increase the efficiency of both the compressor and the turbine

Answer 2

pressurize seals

Question 3

air bled from the engine compressor is also used to service many aircraft systems which may include:

Answer 3

• air conditioning or pressurization
• hydraulic reservoir pressurization
• fuel tank pressurization
• domestic water tank pressurization
• thrust reverser actuation
• fuel heaters
• engine or airframe anti-icing

Question 4

for use outside the engine itself, air is typically bled from two sources:

Answer 4

• the first source is an outlet on an early stage compressor, which supplies a continual low pressure bleed
• this continual low pressure bleed can be supplemented by a second source of air taken from the HP compressor through a control component called a high pressure bleed valve

Question 5

during ____________ operation of the engine, the low pressure bleed is usually of sufficient pressure to maintain the air conditioning/pressurization system

Answer 5

high power

Question 6

during ____________ operation, the low pressure bleed will fall and the high pressure bleed valve will open to ensure both an adequate pressure and sufficient airflow

Answer 6

low power

Question 7

the high pressure bleed valve opens when the _____________ is selected because in this situation, the requirement is for hot air and lots of it, the higher the air pressure, the higher the air temperature

Answer 7

anti-icing

Question 8

effects of bleeding air

Answer 8

• reduced thrust
• increase exhaust gas temperature
• increased engine RPM
• increased specific fuel consumption

Question 9

when air is bled from the compressor, it reduces the ____________ of the engine and this will be indicated on the _____ or ______________ gauge

Answer 9

thrust, P7, Engine Pressure Ratio

Question 10

educing the mass flow through the engine will reduce the amount of ________________ the combustion chamber and will have the effect of increasing the exhaust gas temperature

Answer 10

cooling air cooling

Question 11

bleeding air from the compressor reduces the _______ on the turbine, which will have the effect of increasing engine RPM for a _____________

Answer 11

load, given fuel flow

Question 12

air bled from the compressor is used to cool the turbine blades to seal both the ____________ and areas either side of the ______________

Answer 12

bearing chambers, turbine discs

Question 13

when the bleed air has done its job, it is either _____________, or alternatively ejected into the ______________ at the highest possible pressure, thus achieving a small performance recovery

Answer 13

dumped overboard, main gas stream

Question 14

if turbine blades and nozzle guide vanes are continuously cooled, then the temperature of their operating environment can exceed the _______________ of the material from which they are made

Answer 14

melting point

Question 15

some modern turbofan engines use _________________ which works by controlling the temperature of a _________________ which is fitted closely around the turbine casing

Answer 15

active clearance control, tubular shroud

Question 16

air, extracted from the ________________, flows axially through the _______________ between the HP compressor discs and the IP compressor drive shaft, which absorbs heat from the discs which assists in controlling the ________________ of the compressor blades.

Answer 16

IP compressor, annular passage, thermal growth

Question 17

early gas turbine engines used low pressure compressor air in _____________

Answer 17

single pass internal cooling

Question 18

the use of single pass internal cooling retained the temperature of the turbine blade below the critical level at which _______________ would occur

Answer 18

excessive creep

Question 19

turbine blade cooling: when higher gas temperatures were required, passing _________________ compressor air through the blade as well as the _______________ air achieved a reasonable increase in the gas temperature before _____________ was experienced

Answer 19

high pressure, low pressure, blade failure

Question 20

an additional increase in turbine gas temperature was attained by passing air through small holes in the _____________ and ______________ of the blade

Answer 20

leading, trailing edge

Question 21

the film cooling (produced by passing air through small holes in the leading and trailing edge of the blade) created its own ______________ effect which protected the turbine blade from the onslaught of the hot gases coming from the combustion chamber

Answer 21

boundary layer

Question 22

what was the optimum number of times air is allowed to pass through the blade?

Answer 22

five

Question 23

turbine blade cooling: what is presently considered to be state of the art in turbine blade manufacture?

Answer 23

quintuple pass, multi-feed internal cooling with extensive film cooling

Question 24

the nozzle guide vanes use a similar method of cooling to that which is used to cool the turbine blades but the one major difference is that only ___________________ compressor air is used

Answer 24

high pressure

Question 25

heat conduction from the turbine blade to the turbine disc requires that the turbine discs are _________ and prevented from suffering _______________ from uncontrolled ___________________

Answer 25

cooled, thermal fatigue, expansion and contraction

Question 26

the front and rear faces of each of the turbine discs are cooled by _______________ compressor air, the actual pressure in each disc cavity being controlled by _________________

Answer 26

high pressure, inter-stage seals

Question 27

to prevent the leaking of oil or air into spaces where it should be excluded, several different types of seal are in use, where most of these seals work on the principle of the _______________

Answer 27

labyrinth

Question 28

the _______________ consists of fins which rotate within an annulus of oil, or where the exterior of the seal is static, the annulus can consist of either a ________________ material or a _____________ structure

Answer 28

labyrinth seal, soft abradable, honeycomb

Question 29

_________________ are used to either prevent or control leakage of air between sections of the engine which are operating at different pressures

Answer 29

inter-stage seals

Question 30

the amount of pressure dropped across the seal depends upon the number of _______ over which the air must pass

Answer 30

fins

Question 31

more pressure will be dropped by the air passing over the __________ before the low pressure zone, than will be dropped over the ___________ preceding the high pressure zone

Answer 31

five fins, two fins

Question 32

if abradable materials were used in the manufacture of seals between two rotating shafts, there may be friction generated between the fins and the abradable material due to _____________ of the shaft which would create _______________ and the possibility of _______________

Answer 32

flexing, high temperature, shaft failure

Question 33

an ____________________ can be used to provide the seal without risking friction buildup

Answer 33

inter-shaft hydraulic seal

Question 34

the fins of the inter-shaft hydraulic seal rotate close within an __________ of oil, any deflection of the shaft will cause the fin or fins to __________ the oil, and the seal will be maintained without generating any undue friction or heat

Answer 34

annulus, enter

Question 35

air used to seal bearing chambers is taken from the ______________ stages of the compressor through ______________ in the compressor ___________, and passed through communicating passages where it is required

Answer 35

intermediate, air transfer ports, rotor drum

Question 36

when cooling and sealing has been carried out, how is the air disposed of?

Answer 36

- the high pressure air used for cooling is ejected into the exhaust system - the low pressure air is fed out through its own dedicated vent pipe

Question 37

three basic requirements which must be satisfied before a gas turbine engine can start

Answer 37

- compressor/turbine assembly must be rotated to get air into the combustion chambers - fuel must be provided - ignition must be provided to start the air/fuel mixture burning

Question 38

there are other two requirements which satisfy servicing essentials:

Answer 38

- the necessity to motor over the engine with no igniters operating or ‘blowout’ or ‘motoring over’ cycle - the need for the igniters to be operated independent of the start cycle

Question 39

the two most common methods of rotating the high pressure compressor on modern civil aircraft are:

Answer 39

- electric starter motor - air starter motor

Question 40

the original means of starting gas turbine engines, but it has fallen out of favor because of its weight

Answer 40

electric starter motor

Question 41

the electric starter motor is fixed in front of the _______________ and can also be attached to the __________________ which drives the compressor through the gearbox

Answer 41

compressor casing, engine accessory gearbox

Question 42

the most popular starting system on large gas turbine engines which is light, simple to use, and very economical

Answer 42

air starter motor

Question 43

air starter motor utilizes ____________ air as its power source

Answer 43

low pressure

Question 44

air starter motor is attached to the _________________ of the engine

Answer 44

accessory gearbox

Question 45

the sources of air available for engine start, in order of preference are:

Answer 45

- aircraft auxiliary power unit (APU) - ground start unit - cross bleed start

Question 46

air from any of the sources is fed through an ____________________ to the starter motor’s air inlet where it is used to turn the ______________, then the air is subsequently exhausted to the ______________

Answer 46

electrically controlled air start valve, turbine rotor, atmosphere

Question 47

the turbine rotor turns the ______________ which rotates the engine high pressure compressor shaft through a ___________________

Answer 47

reduction gear, ratchet clutch arrangement

Question 48

a __________________ may also be included in the air starter motor system which can be used to de-energize the ___________________

Answer 48

flyweight cutout switch, air start valve

Question 49

all gas turbine engines have two _________________ which each feed a separate ____________

Answer 49

high energy igniter units, igniter plug

Question 50

high energy ignition systems have an output of approximately ______________

Answer 50

twelve joules

Question 51

it may sometimes be necessary to help prevent engine _____________ to have the ignition system selected in circumstances other than engine starting which will cause the ___________ to erode, shortening its working life dramatically

Answer 51

flame out, igniter plug

Question 52

to minimize erosion of the igniter plugs, some aircraft engines are fitted with a combination ignition system which includes a __________________, as well as the ______________________

Answer 52

low energy continuous selection, high energy starting selection

Question 53

in a combination ignition system, the igniters are automatically deactivated at some point after ___________________

Answer 53

self sustaining speed

Question 54

some aircraft have an ___________________ where if an aircraft stall is detected, the aircraft stall warning system will automatically select the __________________

Answer 54

automatic ignition system, continuous ignition system

Question 55

the high energy ignition unit works on the principle of charging up a _______________ and then discharging it across the ___________________

Answer 55

very large capacitor, face of an igniter plug

Question 56

what does HEIU stand for?

Answer 56

high energy ignition unit

Question 57

the HEIU is mounted on the _____________________

Answer 57

side of the engine

Question 58

two types of igniter plugs

Answer 58

- the older of these two types work in similar to a piston engine spark plug but has a much bigger spark gap - the more modern version of the igniter plug is the surface discharge igniter plug