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The function of the swirl vanes round the fuel nozzles is to .1 increase air ? [ Exercise Manual ]

Question 35-1 : 2 3 1 2 1 2 3 1 only

exemple 135 2, 3.2, 3.

The take off of a jet aeroplane may be performed with 'reduced thrust' in order ?

Question 35-2 : Reduce maintenance costs save fuel reduce take off noise reduce the risk of engine failure during take off

exemple 139 Reduce maintenance costs.Reduce maintenance costs.

In an ignition system during a normal start of a gas turbine engine igniter ?

Question 35-3 : Should commence prior to fuel entering the combustion chamber should commence after fuel has entered the combustion chamber should commence prior to starter motor engagement to prevent a hot start commences upon starter motor engagement and is deactivated at a rotor speed of approximately 15% below idle rpm

exemple 143 Should commence prior to fuel entering the combustion chamber.Should commence prior to fuel entering the combustion chamber.

A gas turbine engine is run at ground idle for a period of time prior to ?

Question 35-4 : Prevent seizure of the rotor blades in their seals prevent vapour lock in the fuel control and/or fuel lines prevent seizure of the engine bearings allow the engine oil to cool

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 exemple 147 Prevent seizure of the rotor blades in their seals.Prevent seizure of the rotor blades in their seals.

The purpose of variable by pass valves in a high bypass turbofan engine between ?

Question 35-5 : Prevent fan stall and lp compressor stall during engine start and low rotor speeds provide sufficient air to the hp compressor during engine start prevent fan surge at high rotor speeds high rpm prevent hp compressor stall during engine start

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 exemple 151 Prevent fan stall and lp compressor stall during engine start and low rotor speeds.Prevent fan stall and lp compressor stall during engine start and low rotor speeds.

If a gas turbine engine fuel/oil heat exchanger is located downstream of the hp ?

Question 35-6 : Rise rise and the fuel nozzles eventually to become clogged fall fall and the oil jets eventually to become clogged

The oil in the fuel/oil 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 fuel/oil 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 exemple 155 Rise.Rise.

The compressor pressure ratio of an axial flow compressor is primarily ?

Question 35-7 : Number of stages rotor diameter compressor inlet temperature design value compressor inlet pressure design value

exemple 159 Number of stages.Number of stages.

In a theoretical gas turbine cycle combustion takes place at constant ?

Question 35-8 : Pressure energy temperature volume

exemple 163 Pressure.Pressure.

When a gas turbine engine accelerates from idle to take off thrust and the ?

Question 35-9 : A compressor stall stagnation supersonic airflow at the compressor blade trailing edges a compressor blade airflow angle of attack that is too small

Like the stall of a wing compressor stall is caused by a breakdown of airflow .a 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 airflow .when 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 exemple 167 A compressor stall.A compressor stall.

Which of the following parameters remains constant in a divergent subsonic gas ?

Question 35-10 : Total temperature static pressure dynamic pressure static temperature

exemple 171 Total temperature.Total temperature.

The most favourable conditions to apply the flexible take off procedure are .1 ?

Question 35-11 : 2 4 5 1 3 5 2 3 6 2 4 6

exemple 175 2, 4, 5.2, 4, 5.

Assuming the jet pipe is not choked the equation to calculate jet engine thrust ?

Question 35-12 : T = m vj vv t = m vv vj t = m vv + vj t = mvj

exemple 179 T = m(vj - vv)T = m(vj - vv)

Given . p0 = static ambient pressure .t0 = static ambient temperature.m = air ?

Question 35-13 : T = m vj vv + a pj p0 t = m vv vj + a t j t0 t = m vv vj + a pj p0 t = m vj vv + a tj t0

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 exemple 183 T = m(vj -vv ) + a(pj - p0).T = m(vj -vv ) + a(pj - p0).

The axial compressor of a gas turbine engine usually has more stages than its ?

Question 35-14 : The power output of a turbine stage is higher than the power consumption of a compressor stage the compressor consumes much more power than the turbine bleed air is taken from the compressor turbine speed is much higher than compressor speed

exemple 187 The power output of a turbine stage is higher than the power consumption of a compressor stage.The power output of a turbine stage is higher than the power consumption of a compressor stage.

On a fadec gas turbine engine during normal flight the power for the fadec's ?

Question 35-15 : The fadec power source s on the engine the aircraft battery the aircraft generator the apu generator

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 exemple 191 The fadec power source(s) on the engine.The fadec power source(s) on the engine.

In a gas turbine combustion chamber ?

Question 35-16 : Secondary air is required for cooling of the inner casing the gas pressure increases in an axial downstream direction the axial velocity of the gas stream is greatest behind the swirl vanes the gas temperature is highest at the chamber outlet

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 . 1047.the 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 ft/sec and is diffused to around 80 ft/sec even at this speed the slow flame at 1/2 ft/sec would be blown away so a region of low pressure is created round it to keep it alright exemple 195 Secondary air is required for cooling of the inner casing.Secondary air is required for cooling of the inner casing.

If there is a single input data failure on a fadec gas turbine engine ?

Question 35-17 : The engine continues to operate normally the engine stops the engine is set at a fail safe thrust the electronic engine control unit uses a constant data value for computation

exemple 199 The engine continues to operate normally.The engine continues to operate normally.

Concerning the fuel system high pressure shut off valve hpsov of a gas turbine ?

Question 35-18 : Ignition is activated before fuel is delivered by the hpsov to the fuel nozzles the hpsov is located between the hp fuel pump and the fuel control unit manual hpsov control from the cockpit is not possible with fadec equipped engines the hpsov is mounted in the wing front spar near the pylon

exemple 203 Ignition is activated before fuel is delivered by the hpsov to the fuel nozzles.Ignition is activated before fuel is delivered by the hpsov to the fuel nozzles.

Derated or reduced take offs save engine life primarily due to ?

Question 35-19 : Reduced low cycle fatigue damage the maximum oil temperature not being exceeded reduced corrosion of the hp turbine blades reduced creep damage due to higher egt levels during take off

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 exemple 207 Reduced low cycle fatigue damage.Reduced low cycle fatigue damage.

The diagram shown in annex represents a twin spool turbofan positions before ?

Question 35-20 : 1 and 2 1 and 8 2 and 3 5 and 8

exemple 211 1 and 2.1 and 2.

What is the average compression ratio of a centrifugal compressor ?

Question 35-21 : 1 4 1 15 1 60 1 5 10

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 1 2 1 per stage exemple 215 1:4.1:4.

If engine compressor air is bled off for engine anti icing or a similar system ?

Question 35-22 : Will rise will be unchanged may rise or fall depending on which stage of the compressor is used for the bleed and the rpm of the engine at the moment of selection will fall

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 exemple 219 Will rise.Will rise.

Increasing the frequency of variations in thrust setting during normal ?

Question 35-23 : Low cycle fatigue damage is more severe the egt limit would be exceeded more often fatigue due to vibration is more severe creep will be 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 alloy .in turbine engines low cycle fatigue is generally caused by repeated loading cycles caused by operation i e 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 exemple 223 Low cycle fatigue damage is more severe.Low cycle fatigue damage is more severe.

An axial compressor when operating below its design speed has ?

Question 35-24 : A tendency to stall in the front stages a tendency to stall in the rear stages a tendency to stall in the centre stages no tendency to stall

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 blade/wing will stall .the 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 exemple 227 A tendency to stall in the front stages.A tendency to stall in the front stages.

The compressor blades in a rotating gas turbine engine are held in position by ?

Question 35-25 : The mountings and the resultant of aerodynamic and centrifugal forces abradable seals and aerodynamic forces a centrifugal latch the mountings and thermal expansion only

exemple 231 The mountings and the resultant of aerodynamic and centrifugal forces.The mountings and the resultant of aerodynamic and centrifugal forces.

Some gas turbine engines have multiple stages in the hp and lp turbines ?

Question 35-26 : Because one stage does not generate sufficient shaft power to facilitate balancing of the turbine assembly to help stabilise the pressure between the compressor and the turbine to reduce noise in the propelling nozzle

exemple 235 Because one stage does not generate sufficient shaft power.Because one stage does not generate sufficient shaft power.

In which part of a gas turbine engine are high temperature requirements most ?

Question 35-27 : The combustion chamber and front part of the hp turbine the last part of the hp compressor and front part of the hp turbine the turbine and exhaust nozzle the combustion chamber and exhaust nozzle

Usually titanium alloy is the material used for the combustion chamber and high pressure turbine exemple 239 The combustion chamber and front part of the hp turbine.The combustion chamber and front part of the hp turbine.

A twin spool engine with an inlet air mass flow of 500 kg/s and a hp compressor ?

Question 35-28 : 1 0 2 3

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.500 250 = 250.250 / 250 = 1

A 'fan' stage of a ducted fan turbine engine is driven by ?

Question 35-29 : The low pressure turbine airflow drawn across it by the high pressure compressor the high pressure compressor through reduction gearing the high pressure turbine

Img948 exemple 247 The low pressure turbine.The low pressure turbine.

The oil supply to gas turbine engine bearings is maintained in the event of the ?

Question 35-30 : Differential pressure opening the bypass valve of the main oil filter the hp fuel pump the scavenge pumps a back up oil system

exemple 251 Differential pressure opening the bypass valve of the main oil filter.Differential pressure opening the bypass valve of the main oil filter.

One of the purposes of compressor bleed valves is to ?

Question 35-31 : Decrease the airflow across the rear compressor stages whilst that across the early stages is increased limit the acceleration period of the engine increase the airflow across the rear compressor stages whilst that across the early stages is decreased decrease the load on the compressor when the engine is approaching maximum rpm

Bleed valves are fitted to prevent compressors stalling .vdo1055.like the stall of a wing compressor stall is caused by a breakdown of airflow .the bleed valve removes excesss volume of air at low compressor speeds to increase the flow over the front compressor blades and reduce the flow over the latter stages .as speed of the compressor increases the bleed valve closes exemple 255 Decrease the airflow across the rear compressor stages, whilst that across the early stages is increased.Decrease the airflow across the rear compressor stages, whilst that across the early stages is increased.

Turbine blade stages may be classed as either 'impulse' or 'reaction' in an ?

Question 35-32 : I drops ii remains constant i rises ii remains constant i remains constant ii drops i remains constant ii rises

Img940.nozzle guide vanes = stator .the pressure drops across the stator blades and remains constant across the rotor blades exemple 259 (i) drops (ii) remains constant(i) drops (ii) remains constant

One advantage of having three instead of two spools in some high bypass ?

Question 35-33 : Fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at low rotor speeds fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at high rotor speeds there is a lower fuel consumption due to a higher overall pressure ratio there is a lower fuel consumption and more thrust due to higher overall pressure ratio

Variable inlet guide vanes v i g v s are fitted to engines which have a particular problem with inherent compressor stall at low rpm or during engine acceleration or deceleration the vanes are fitted just in front of the first rotor stage they can be automatically pivoted around their own axis to vary the path of the airflow going into the compressor so maintaining the proper relationship between compressor rotational speed and airflow in the front compressor stages at low compressor speeds the v i g v s are angled to impart the greatest amount of swirl to the air thereby correcting the relative airflow to obtain the optimum angle of attack over the rotor blades this optimum angle of attack allows a smooth and rapid engine acceleration .on a three spools high bypass turbofan engine an additional intermediate pressure compressor stage is added and reduces the risk of compressor stall at low rotor speeds exemple 263 Fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at low rotor speeds.Fewer variable stator vanes and variable inlet guide vanes are required to prevent compressor stall at low rotor speeds.

The compressor surge effect during acceleration is prevented by the ?

Question 35-34 : Fuel control unit f c u variable setting type nozzle guide vanes surge bleed valves inlet guide vanes

With modern engines there are various ways to control surge one of them is the use of blow off valves also called compressor bleed valves .on all modern turbine engines with electronic fuel control systems the valves are controlled by the fuel control unit .the end result will be that the blow off valve will reduce the pressure in the compressor to prevent the surge exemple 267 Fuel control unit (f.c.u.).Fuel control unit (f.c.u.).

Creep in a gas turbine engine is ?

Question 35-35 : The permanent increase in length of metal parts due to a combination of tensile stress and high temperatures over a prolonged period expansion of metal parts due to temperature increase the elastic increase in length of metal parts due to tensile stress and high temperatures crack formation in metal parts due to cyclic mechanical loads and high temperatures

exemple 271 The permanent increase in length of metal parts due to a combination of tensile stress and high temperatures over a prolonged period.The permanent increase in length of metal parts due to a combination of tensile stress and high temperatures over a prolonged period.

About a twin spool compressor ?

Question 35-36 : The low pressure spool runs at a lower rpm than the high pressure spool both spools run at the same rpm the low pressure spool runs at a very high rpm thus preventing the onset of compressor stall when operating at very high rpm's the later stages within the high pressure spool will have a large negative angle of attack

exemple 275 The low pressure spool runs at a lower rpm than the high pressure spool.The low pressure spool runs at a lower rpm than the high pressure spool.

In addition to providing 'customer' bleed for aeroplane systems air may be bled ?

Question 35-37 : At low rotor speed at high rotor speed and prevent stall at high rotor speed and recover from stall at high rotor speed

During engine starts most turbojet/turbofan engines use engine bleed air to reduce the possibility of compressor stalls .compressor stall occurs when the compressor sucks too much air for the turbine wheels to handle excessive pressure then builds aft of the compressor and the compressor blades stall also happens with centrifugal type compressor .bleeding air from an engine air is bled just aft of the compressor relieves that excessive pressure and the compressor can more easily 'push' the sucked air behind him exemple 279 At low rotor speed.At low rotor speed.

One reason to fit a tip shroud to a turbine blade is to ?

Question 35-38 : Increase turbine efficiency provide a seal for the cooling airflow prevent blade creep reduce turbine temperatures

The shrouded blades form a band around the perimeter of the turbine which serves to reduce blade vibrations the shrouds improve the airflow characteristics and increase the efficiency of the turbine the shrouds also serve to cut down gas leakage around the tips of the turbine blades exemple 283 Increase turbine efficiency.Increase turbine efficiency.

The most important oil system instrument indication during gas turbine engine ?

Question 35-39 : Oil pressure oil temperature oil quantity oil filter clogged warning signal

exemple 287 Oil pressure.Oil pressure.

Turbine blade stages may be classed as either 'impulse' or 'reaction' in an ?

Question 35-40 : The pressure drops across the stator blades and remains constant across the rotor blades the pressure rises across the stator blades and remains constant across the rotor blades the pressure remains constant across the stator blades and drops across the rotor blades the pressure remains constant across stator blades and rises across the rotor blades

Img940.nozzle guide vanes = stator .the pressure drops across the stator blades and remains constant across the rotor blades exemple 291 The pressure drops across the stator blades and remains constant across the rotor blades.The pressure drops across the stator blades and remains constant across the rotor blades.

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