Question 48-1 : Which of these statements about compressor stall are correct or incorrect i a compressor stall is most likely to occur in a compressor designed for a high pressure ratio operating at low rpmii a compressor stall is most likely to occur when the air flow stagnates in the front stages of the ? [ Result LAPL ]

Question 1

Question 48-1 : Which of these statements about compressor stall are correct or incorrect i a compressor stall is most likely to occur in a compressor designed for a high pressure ratio operating at low rpmii a compressor stall is most likely to occur when the air flow stagnates in the front stages of the ? [ Result LAPL ]

Answer

I is correct ii is incorrect

Question 2

Question 48-2 : The following problems may occur when starting a twin spool turbofan engine ?

Answer

No n1 rotation although n2 may accelerate normally.

During engine start the compressor is very inefficient if the engine experiences more than the usual difficulty accelerating due to such problems as early starter cut out fuel mis scheduling or strong tailwinds the engine may spend a considerable time at very low rpm sub idle normal engine cooling flows will not be effective during sub idle operation and turbine temperatures may appear relatively high this is known as a hot start

Question 3

Question 48-3 : Both gas turbine and piston engines use a cycle made up of induction compression combustion and exhaust phases which of these statements about a gas turbine are correct or incorrect i the process in a gas turbine engine is intermittentii theoretically the combustion occurs at constant pressure ?

Answer

I is incorrect ii is correct.

Piston engine the combustion process is intermittent governed by the rythm of the back and forth movements of the piston in a cylinder the combustion occurs at constant volume in the cylinderturbine engine the combustion process is continuous and occurs at constant pressure

Question 4

Question 48-4 : The most unfavourable conditions for adequate inlet air flow of a turbofan engine are ?

Answer

Maximum take off thrust zero forward speed and strong crosswind conditions.

Question 5

Question 48-5 : If a twin spool gas turbine engine is controlled by a conventional n2 control system rupture of the lp shaft may result in ?

Answer

Overspeed of the lp turbine.

In a twin spool engine the lp turbine is connected to the lp compressor the hp turbine is connected to the hp compressor the lp turbine drives the lp compressor if a rupture occurs it may result in an overspeed of the lp turbine

Question 6

Question 48-6 : The rotor blades of an axial compressor of a gas turbine engine are often mounted on a disk or drum using a 'loose fit' because this ?

Answer

Limits damage to the blades due to vibration.

Question 7

Question 48-7 : For a turbine engine the self sustaining speed relates to the minimum rpm at which the engine ?

Answer

Will continue to operate without any starter motor assistance.

Question 8

Question 48-8 : The primary function of the diffuser located between the compressor and the combustion chamber of a gas turbine engine is to ?

Answer

Decrease the flow velocity.

Before combustion can proceed the air velocity must be greatly reducedair leaves the compressor through exit guide vanes which convert the radial component of the air flow out of the compressor to straight line flow the air then enters the diffuser section of the engine which is a very divergent duct the primary function of the diffuser structure is aerodynamic the divergent duct shape converts most of the air's velocity pi into static pressure ps as a result the highest static pressure and lowest velocity in the entire engine is at the point of diffuser discharge and combustor inlet other aerodynamic design considerations that are important in the diffuser section arise from the need for a short flow path uniform flow distribution and low drag loss

Question 9

Question 48-9 : A fadec on a gas turbine engine ?

Answer

Is single fault tolerant.

Single input data failure will not affect the normal operation a 'full authority digital engine control' is single fault tolerant a fadec is an engine control system in which the primary functions use digital electronics and the electronic engine control eec unit has full range authority over the engine power or thrust

Is a single channel system. is a three channel system. consists of two identical channels cross linked through an non engine related aircraft computer.

Question 10

Question 48-10 : When a turbo prop aeroplane decelerates during the intial part of the landing roll a constant speed propeller within the beta range ?

Answer

Produces negative thrust.

Question 11

Question 48-11 : Most high bypass unmixed turbofan engines are equipped with a cold exhaust reverser fan reverser only in order to ?

Answer

Save costs and mass at the expense of a reduction in available reverse thrust.

High bypass turbofan engines are equipped with a cold exhaust reverser only in order to save costs and massit is not impossible to reverse the hot exhaust gas but it is complex the gain in reverse thrust will be less than 20% for an increase in maintenance costs and a higher inflight consumption due to weight of the system typical high bypass thrust reversers 1052

Prevent disturbance of cold exhaust reversed airflow by the hot exhaust reversed gas flow. reduce the risk of exhaust gas re-ingestion. prevent extra fuel consumption due to operation of the hot exhaust reverser (turbine reverser).

Question 12

Question 48-12 : A booster or lp compressor in a twin spool turbofan ?

Answer

Rotates at the same rotor speed as the fan.

If the engine is a twin spool turbofan it is highly likely that there will be a hp compressor lp compressor and a fan the lp comp and the fan will be driven from the same turbine on the same shaft and will therefore be at the same speed 948

Question 13

Question 48-13 : The function of the swirl vanes round the fuel nozzles is to 1 increase air pressure at the fuel nozzles2 reduce the average axial flow speed in order to stabilise the flame front3 generate a swirl of incoming air to enhance mixing of the fuel with airthe combination that regroups all of the ?

2 3.

exemple 196: 2 3 — 1, 2. 1, 2, 3. 1 only.

Answer

Reduce maintenance costs.

Answer

Should commence prior to fuel entering the combustion chamber.

Answer

Prevent seizure of the rotor blades in their seals.

This allows to the gas generator and the power turbine discs more time to cool than if the engines were immediately shut down the danger is that the rotor will cool and will shrink more rapidly than the blades and they could be seized in their seals

Answer

Prevent fan stall and lp compressor stall during engine start and low rotor speeds.

A bypass valve is another name for a bleed valve it can also be called a blow off valve anti stall valve or an acceleration valve

Answer

Rise.

The oil in the fueloil heat exchanger located in the tanks is always at a higher pressure than the fuel but the question states located downstream of the hp fuel pump so it is a secondary fueloil heat exchanger in order to avoid fuel icing in the fuel regulation system in this heat exchanger you will have high pressure fuel and relatively low pressure oil so any internal leak will transfer fuel to the oil system raising the indicated oil level

Answer

Number of stages.

Answer

A compressor stall.

Like the stall of a wing compressor stall is caused by a breakdown of airflowa compressor stall is most likely to occur when the air flow stagnates in the rear stages of the compressor a compressor blade is hitting the oncoming airflow at an angle of attack that is determined by a combination of the rotational speed and the incoming airflowwhen the incoming speed is low the angle of attack will be high when the angle of attack gets too high the blade stalls so when the axial flow in a compressor backs up the blades stall pressure increase in the rear stages this slows down the flow you can prevent this by dumping some late stage air to atmosphere via bleed valves

Answer

Total temperature.

Answer

T = m vj vv.

Answer

T = m vj vv + a pj p0 .

Thrust = air mass flow jet exhaust velocity true air speed + exhaust cross sectional area jet exhaust static pressure static ambient pressure thrust is equal to the change in momentum of the air entering and leaving it is measured by the acceleration of the air through the engine

Answer

The power output of a turbine stage is higher than the power consumption of a compressor stage.

Answer

The fadec power source s on the engine.

The fadec has its own independent power supply generator which is separate from the aircraft generator to ensure that the fadec system has electrical power as long as the engine is running regardless of any problems or faults with the aircraft system

Answer

Secondary air is required for cooling of the inner casing.

The combustion system's purpose is to provide a smooth stream of uniformly heated gas with the least loss of pressure and the maximum release of heat 1047the combustion chamber is made from two tubes one is the flame tube which is inside the air casing between the two is an air gap through which any air that does not go into the combustion chamber passes secondary air air enters the combustion chamber at around 500 ftsec and is diffused to around 80 ftsec even at this speed the slow flame at 12 ftsec would be blown away so a region of low pressure is created round it to keep it alright

Answer

The engine continues to operate normally.

Answer

Ignition is activated before fuel is delivered by the hpsov to the fuel nozzles.

Answer

Reduced low cycle fatigue damage.

Low cycle fatigue is where the stress is high enough for deformation to occur this deformation will occur in the turbine since it is most sensitive to high temperatures

Answer

1 4.

Img938 axial compressor 915 radial compressor a centrifugal compressor will provide a compression ratio of 5 1 per stage maximum which is relatively high compared to an axial compressor that achieves a ratio of only 12 1 per stage

Answer

Will rise.

Gorny21 the ratio of the tertiary airflow around the combustion flame tube that cools the turbine decreases thus less cooling flow as the warm air is diverted for anti icing so the egt will increase as a result

Answer

Low cycle fatigue damage is more severe.

It is commonly known that a metal subjected to repetitive or flunctuating stress will fail at a stress much lower than its ultimate strength failures occuring under cyclic loading are generally termed 'fatigue'the endurance of the gas turbine engine to high temperature is particularly marked by the creep resistance of hp turbine blade alloyin turbine engines low cycle fatigue is generally caused by repeated loading cycles caused by operation ie starting or takeoff conditions if a turbine blade goes through one takeoff max power setting it may be fine if it is subjected to 8000 of them it may fail due to fatigue

Answer

A tendency to stall in the front stages.

Img938 axial compressor 915 radial compressor the stall of a blade occurs in the same way as a wing stalls and if the angle of attack exceeds a set value the bladewing will stallthe first stage of blades on a compressor are rotor blades when it turns air is push rearwards increasing the velocity onto the blades behind but also the pressure if the horizontal flow is low it results in a large angle of attack as this is most likely at the front of the compressor it will tend to stall at the front

Answer

The mountings and the resultant of aerodynamic and centrifugal forces.

Answer

Because one stage does not generate sufficient shaft power.

Answer

The combustion chamber and front part of the hp turbine.

Usually titanium alloy is the material used for the combustion chamber and high pressure turbine

Question 14

Question 48-14 : The take off of a jet aeroplane may be performed with 'reduced thrust' in order to ?

Question 15

Question 48-15 : In an ignition system during a normal start of a gas turbine engine igniter activation ?

Question 16

Question 48-16 : A gas turbine engine is run at ground idle for a period of time prior to shutdown to ?

Question 17

Question 48-17 : The purpose of variable by pass valves in a high bypass turbofan engine between the lp compressor and the hp compressor hpc is to ?

Question 18

Question 48-18 : If a gas turbine engine fueloil heat exchanger is located downstream of the hp fuel pump internal leakage of the heat exchanger will cause the oil level to ?

Question 19

Question 48-19 : The compressor pressure ratio of an axial flow compressor is primarily determined by the ?

Question 20

Question 48-20 : In a theoretical gas turbine cycle combustion takes place at constant ?

Pressure.

Question 21

Question 48-21 : When a gas turbine engine accelerates from idle to take off thrust and the compressor rpm is too high in comparison with the air inlet velocity this may result in ?

Question 22

Question 48-22 : Which of the following parameters remains constant in a divergent subsonic gas turbine engine intake ?

Question 23

Question 48-23 : The most favourable conditions to apply the flexible take off procedure are 1 high take off mass2 low take off mass3 high outside temperature4 low outside temperature5 high atmospheric pressure6 low atmospheric pressurethe combination grouping all the correct answers is ?

2 4 5.

exemple 236: 2 4 5 — 1, 3, 5. 2, 3, 6. 2, 4, 6.

Question 24

Question 48-24 : Assuming the jet pipe is not choked the equation to calculate jet engine thrust t with mass flow m airspeed vv and jet velocity vj is ?

Question 25

Question 48-25 : Given p0 = static ambient pressure t0 = static ambient temperaturem = air mass flowvv = true air speedvj = jet efflux exhaust velocitypj = jet efflux exhaust static pressuretj = jet efflux exhaust static temperaturea = exhaust cross sectional areathe thrust t of a jet engine is ?

Question 26

Question 48-26 : The axial compressor of a gas turbine engine usually has more stages than its driving turbine because ?

Question 27

Question 48-27 : On a fadec gas turbine engine during normal flight the power for the fadec's sensors comes from ?

Question 28

Question 48-28 : In a gas turbine combustion chamber ?

Question 29

Question 48-29 : If there is a single input data failure on a fadec gas turbine engine ?

Question 30

Question 48-30 : Concerning the fuel system high pressure shut off valve hpsov of a gas turbine engine ?

Question 31

Question 48-31 : Derated or reduced take offs save engine life primarily due to ?

Question 32

Question 48-32 : The diagram shown in annex represents a twin spool turbofan positions before and after air intake are located at numbers 1054 ?

1 and 2.

Question 33

Question 48-33 : What is the average compression ratio of a centrifugal compressor ?

Question 34

Question 48-34 : If engine compressor air is bled off for engine anti icing or a similar system the turbine temperature ?

Question 35

Question 48-35 : Increasing the frequency of variations in thrust setting during normal operation is detrimental to the life of hp turbine blades because ?

Question 36

Question 48-36 : An axial compressor when operating below its design speed has ?

Question 37

Question 48-37 : The compressor blades in a rotating gas turbine engine are held in position by ?

Question 38

Question 48-38 : Some gas turbine engines have multiple stages in the hp and lp turbines ?

Question 39

Question 48-39 : In which part of a gas turbine engine are high temperature requirements most critical for the materials used ?

Question 40

Question 48-40 : A twin spool engine with an inlet air mass flow of 500 kgs and a hp compressor mass flow of 250 kgs has a bypass ratio of ?

1.

Img939bypass ratio = bypass mass flow hp compressor mass flow500 250 = 250250 250 = 1