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Report > OACI : Jet engine total efficiency indicates the efficiency at which ?

Question 33-1 : Chemical power in the fuel is transformed into propulsive power t x v chemical power in the fuel is transformed into an increase of jet kinetic energy per second the increase of jet kinetic energy is transformed into propulsive energy potential energy in the jet is transformed into propulsive energy

exemple 133 chemical power in the fuel is transformed into propulsive power (t x v).chemical power in the fuel is transformed into propulsive power (t x v).

Which statement is correct for a gas turbine engine with a constant speed ?

Question 33-2 : I is correct ii is correct i is correct ii is incorrect i is incorrect ii is incorrect i is incorrect ii is correct

Hp spool speed egt and gas generator speed all decrease for a gas turbine engine with a constant speed propeller and free power turbine when the power setting is decreased exemple 137 i is correct, ii is correct.i is correct, ii is correct.

The fadec of a gas turbine engine consists of ?

Question 33-3 : An electronic engine control unit and its peripherals fuel metering actuators electrical wiring sensors an electronic engine control unit only all electronic engine control units installed on the aircraft an electronic engine control unit and the engine display units in the cockpit

exemple 141 an electronic engine control unit and its peripherals (fuel metering, actuators, electrical wiring, sensors).an electronic engine control unit and its peripherals (fuel metering, actuators, electrical wiring, sensors).

The bypass ratio.i is the ratio of inlet air mass flow to exhaust air mass ?

Question 33-4 : I is incorrect ii is correct i is correct ii is incorrect i is incorrect ii is incorrect i is correct ii is correct

939..bypass ratio = bypass mass flow / hp compressor mass flow.the bypass ratio can be determined from the inlet air mass flow and the bypass mass flow exemple 145 i is incorrect, ii is correct.i is incorrect, ii is correct.

The fadec of a gas turbine engine normally includes ?

Question 33-5 : An engine overspeed and/or an egt protection function an overheat protection for the electronic engine control unit the engine fire loops an excessive fuel flow detection function

exemple 149 an engine overspeed and/or an egt protection function.an engine overspeed and/or an egt protection function.

In a gas turbine engine the propelling jet is generated by ?

Question 33-6 : Expansion of hot gases resulting in a conversion of potential energy pressure into kinetic energy velocity expansion of hot gases resulting in a conversion of potential energy pressure into mechanical work compression of hot gases resulting in a conversion of kinetic energy velocity into mechanical work compression of hot gases resulting in a conversion of potential energy pressure into kinetic energy velocity

The process of energy conversion in a multistage turbine consists of a number of successive processes in the individual stages.compressed and heated gas at an initial velocity passes through the blade to blade channels of the nozzle assembly where in the course of expansion part of the available heat drop is converted into kinetic energy of the exhaust flow further gas expansion and conversion of the heat drop into useful work take place in the blade to blade channels of the rotor.the gas flow acting on the rotor blades develops torque on the turbine's shaft as a result the absolute velocity of the gas is reduced the lower this velocity the larger the part of the available gas energy that is converted into mechanical work on the shaft.the rotor blades receive the forces produced by a change in the direction of the gas velocity flowing around them impulse flow effect and by acceleration of the gas flow relative to the movement in the blade to blade channels reaction flow effect exemple 153 expansion of hot gases resulting in a conversion of potential energy (pressure) into kinetic energy (velocity).expansion of hot gases resulting in a conversion of potential energy (pressure) into kinetic energy (velocity).

The internal geometry of a turbofan intake for a subsonic commercial aeroplane ?

Question 33-7 : Divergent in order to reduce airflow velocity and increase static pressure in front of the fan convergent in order to increase airflow velocity and reduce static pressure in front of the fan divergent in order to increase both airflow velocity and static pressure in front of the fan convergent in order to reduce airflow velocity in front of the fan

953..in a divergent intake the flow speed decreases and the static pressure increases .dynamic pressure decreases and total pressure remains unchanged exemple 157 divergent in order to reduce airflow velocity and increase static pressure in front of the fan.divergent in order to reduce airflow velocity and increase static pressure in front of the fan.

The turbine in a gas turbine engine generates shaft power using ?

Question 33-8 : Expansion of hot gas followed by conversion of kinetic energy velocity into mechanical work compression of hot gas followed by conversion of kinetic energy into mechanical work compression of hot gas followed by conversion of potential energy pressure into kinetic energy velocity expansion of hot gas followed by conversion of potential energy pressure into mechanical work

The expansion is the drop of pressure like a venturi tube the velocity must increase to keep the same mass flow this kinetic energy of the hot gases is converted into useful rotational mechanical energy by the turbine this increased velocity kinetic energy is what drives the shaft exemple 161 expansion of hot gas followed by conversion of kinetic energy (velocity) into (mechanical) work.expansion of hot gas followed by conversion of kinetic energy (velocity) into (mechanical) work.

The principle of aeroplane propulsion is to generate a propelling force by ?

Question 33-9 : Accelerating air or gas in order to obtain a reaction force generating a high velocity jet pushing against the outside air pressurising air or gas in order to obtain a reaction force heating up air in order to obtain a reaction force

exemple 165 accelerating air or gas in order to obtain a reaction force.accelerating air or gas in order to obtain a reaction force.

Which statement is correct for a gas turbine engine with a constant speed ?

Question 33-10 : I is incorrect ii is incorrect i is correct ii is incorrect i is correct ii is correct i is incorrect ii is correct

Hp spool speed egt and gas generator speed all increase for a gas turbine engine with a constant speed propeller and free power turbine when the power setting is increased exemple 169 i is incorrect, ii is incorrect.i is incorrect, ii is incorrect.

Which statement is correct for a gas turbine engine with a constant speed ?

Question 33-11 : I is incorrect ii is incorrect i is correct ii is incorrect i is correct ii is correct i is incorrect ii is correct

Hp spool speed egt and gas generator speed all increase for a gas turbine engine with a constant speed propeller and free power turbine when the power setting is increased exemple 173 i is incorrect, ii is incorrect.i is incorrect, ii is incorrect.

The primary performance indicator cockpit instrument for the thrust of a ?

Question 33-12 : Either epr or n1 either n1 or n2 either n1 or fuel flow either torque or rpm

Primary engine indications .n1 epr and egt are the primary engine indications on a turbofan engine.secondary engine indications .n2 fuel flow oil pressure oil temperature oil quantity and engine vibration are the secondary engine indications.a turbofan engine is a dual rotor axial flow turbofan the n1 rotor consists of a fan a low pressure compressor and a low pressure turbine the n2 rotor consists of a high pressure compressor and a high pressure turbine the n1 and n2 rotors are mechanically independent .epr is engine pressure ratio it compares the pressure in the engine inlet with pressure in the exhaust nozzle .n1 is the speed of the first stage engine compressor this is used as a power setting in most jet engines exemple 177 either epr or n1.either epr or n1.

If air is tapped from a gas turbine hp compressor the effect on the engine ?

Question 33-13 : Epr decreases and egt increases epr decreases and egt remains constant epr remains constant and egt increases both epr and egt decrease

If you bleed air from the compressor you are reducing the pressure inside the compressor therefore turbine outlet pressure will be reduced if inlet pressure remains the same and outlet pressure is reduced then epr decreases .since hot air is tapped directly from a compressor stage the temperature will rise in the turbine egt increases

An abortive hung start is the term used to describe an attempt to start in ?

Question 33-14 : Lights up but fails to accelerate sufficiently fails to light up commences initial rotation but fails to receive any fuel will not rotate

After the normal light up sequence until the starter 'cut out' a hung start is identified by light off followed by abnormally slow acceleration and rpm stabilization below idle a hung start may be result of fuel scheduling being either too lean or too rich a lean hung start is associated with low fuel flow and proportionally low egt a rich condition can be recognized by a high fuel flow and an egt rise which may tend to develop into an over temperature condition and possible compressor stall.. hung starts may be caused by . starter air pressure too low to accelerate engine to self sustaining speed.. premature starter deactivation. fod foreign object debris to compressor. faulty pressurizing valves not opening at scheduled fuel pressure setting. incorrect scheduling of hp compressor igv and variable stators. turbine section damage exemple 185 lights up, but fails to accelerate sufficiently.lights up, but fails to accelerate sufficiently.

On a fadec jet engine the meaning of f a d e c on a gas turbine engine is ?

Question 33-15 : Full authority digital engine control failure analysis / dispatch evaluation computer fool adapter dual electronic computer failsafe adapter direct effect computation

The blades in an axial flow compressor decrease in size from the ?

Question 33-16 : Low pressure to the high pressure stages in an attempt to sustain axial velocity high pressure to the low pressure stages in order to allow for expansion at increased velocity root to the tip in order to increase tip clearance root to the tip in order to maintain a constant angle of attack

914..the blades size reduces from the inlet until the output of the compressor exemple 193 low pressure to the high pressure stages in an attempt to sustain axial velocity.low pressure to the high pressure stages in an attempt to sustain axial velocity.

Regarding a jet engine.i the maximum thrust decreases slightly as the pressure ?

Question 33-17 : I is incorrect ii is correct i is correct ii is correct i is correct ii is incorrect i is incorrect ii is incorrect

Jet engines are more efficient at higher altitudes because less fuel is needed for a given thrust due to reduction in lift and drag and lower temperatures through the inlet cause a significant reduction in specific fuel consumption up to the tropopause .specific fuel consumption is the amount of fuel burnt per unit of thrust for jets it reduces with altitude up to the tropopause.notice as the pressure altitude decreases means 'at a lower altitude' exemple 197 i is incorrect, ii is correct.i is incorrect, ii is correct.

Which of the following statements is correct about the flow in a divergent ?

Question 33-18 : I is correct ii is incorrect i is correct ii is correct i is incorrect ii is correct i is incorrect ii is incorrect

In a divergent intake the flow speed decreases and the static pressure increases dynamic pressure decreases and total pressure remains unchanged exemple 201 i is correct, ii is incorrect.i is correct, ii is incorrect.

Which of the following statements is correct about the flow in a divergent ?

Question 33-19 : I is correct ii is incorrect i is correct ii is correct i is incorrect ii is correct i is incorrect ii is incorrect

exemple 205 i is correct, ii is incorrect.i is correct, ii is incorrect.

Both gas turbine and piston engines use a cycle made up of induction ?

Question 33-20 : I is incorrect ii is incorrect i is correct ii is correct i is incorrect ii is correct i is correct ii is incorrect

.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 cylinder.turbine engine the combustion process is continuous and occurs at constant pressure exemple 209 i is incorrect, ii is incorrect.i is incorrect, ii is incorrect.

Which of the following statements is correct about the flow in a divergent ?

Question 33-21 : I is incorrect ii is correct i is correct ii is correct i is correct ii is incorrect i is incorrect ii is incorrect

There is a velocity decrease as air flows from a small inlet to a larger outlet exemple 213 i is incorrect, ii is correct.i is incorrect, ii is correct.

Which statement is correct about the flow in a divergent jet engine inlet .i ?

Question 33-22 : I is incorrect ii is correct i is correct ii is correct i is correct ii is incorrect i is incorrect ii is incorrect

exemple 217 i is incorrect, ii is correct.i is incorrect, ii is correct.

Which of these statements about compressor stall are correct or incorrect.i a ?

Question 33-23 : I is correct ii is correct i is correct ii is incorrect i is incorrect ii is correct i is incorrect ii is incorrect

Like the stall of a wing compressor stall is caused by a breakdown of airflow .if your wing is suitable for high speed and you fly at low speed and large angle of attack the stall is most likely to occur.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 221 i is correct, ii is correct.i is correct, ii is correct.

In a compressor stage if the axial air velocity increases more than the rotor ?

Question 33-24 : Stall margin increases stall margin decreases pressure ratio will be too high relative air velocity becomes supersonic

.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 .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 air flow speed is high the blade angle of attack will be low the stall margin increases there is less risk to encounter a compressor stall exemple 225 stall margin increases.stall margin increases.

Which of these statements about compressor stall are correct or incorrect.i a ?

Question 33-25 : I is incorrect ii is correct i is correct ii is incorrect i is incorrect ii is incorrect i is correct ii is correct

Like the stall of a wing compressor stall is caused by a breakdown of airflow .if your wing is suitable for high speed and you fly at low speed and large angle of attack the stall is most likely to occur.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 229 i is incorrect, ii is correct.i is incorrect, ii is correct.

With regard to a twin spool turbofan an abortive start hung start will result in ?

Question 33-26 : N2 speed stabilising at a lower than normal rpm and a subsequent increase in egt n2 speed stabilising at a higher than normal rpm and a subsequent increase in egt n2 speed stabilising at a lower than normal rpm and a subsequent decrease in egt n2 speed stabilising at a higher than normal rpm and a subsequent decrease in egt

.after the normal light up sequence until the starter 'cut out' a hung start is identified by light off followed by abnormally slow acceleration and rpm stabilization below idle a hung start may be result of fuel scheduling being either too lean or too rich a lean hung start is associated with low fuel flow and proportionally low egt a rich condition can be recognized by a high fuel flow and an egt rise which may tend to develop into an over temperature condition and possible compressor stall..hung starts may be caused by. starter air pressure too low to accelerate engine to self sustaining speed.. premature starter deactivation. fod foreign object debris to compressor. faulty pressurizing valves not opening at scheduled fuel pressure setting. incorrect scheduling of hp compressor igv and variable stators. turbine section damage exemple 233 n2 speed stabilising at a lower than normal rpm and a subsequent increase in egt.n2 speed stabilising at a lower than normal rpm and a subsequent increase in egt.

Which of the following statements is correct about the flow in a divergent ?

Question 33-27 : I is incorrect ii is correct i is correct ii is incorrect i is correct ii is correct i is incorrect ii is incorrect

exemple 237 i is incorrect, ii is correct.i is incorrect, ii is correct.

One of the functions of a gas turbine engine subsonic intake is to ?

Question 33-28 : Decrease airflow velocity increase total pressure increase airflow velocity decrease static temperature

One of the advantages of multiple spool jet engine designs is that ?

Question 33-29 : A smaller air starter driving only a single spool can be used if one spool seizes the remaining spool s will continue to operate normally a compressor stall cannot occur under any condition engine length can be reduced

.the air starter motor is possibly the most popular starting system presently in use it is light simple to use and very economical utilizing low pressure air the air starter motor is fastened to the accessory gearbox of the engine the sources of air available for engine start in order of preference they are the aircraft apu. the ground power unit. a cross bleed start where air from an already started engine is used .air from one of these sources is fed through an electrically controlled start valve to the air inlet to rotate the turbine rotor and is then exhausted .on a multiple spool jet engine a small air starter motor can drive a single spool which when started permits to start the other spools exemple 245 a smaller air starter driving only a single spool can be used.a smaller air starter driving only a single spool can be used.

Which of these statements about compressor stall are correct or incorrect.i a ?

Question 33-30 : I is incorrect ii is incorrect i is correct ii is incorrect i is incorrect ii is correct i is correct ii is correct

Like the stall of a wing compressor stall is caused by a breakdown of airflow .if your wing is suitable for high speed and you fly at low speed and large angle of attack the stall is most likely to occur.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

After a successful start of a high bypass turbofan engine the air starter ?

Question 33-31 : Is disengaged by the coupling between engine n2 spool and starter by the use of centrifugal forces is disengaged by using a clutch that is controlled by the main engine control is disengaged by the coupling between engine n1 spool and starter by the use of centrifugal forces remains engaged and rotates continuously with the n2 spool

Air starting is used on most commercial and some military jet engines it has many advantages over other starting systems and is comparatively light simple and economical to operate 10 an air starter motor transmits power through a reduction gear and clutch to the starter output shaft which is connected to the engine.the starter turbine is rotated by air taken from an external ground supply an auxiliary power unit a p u or as a cross feed from a running engine the air supply to the starter is controlled by an elec trically operated control and pressure reducing valve that is opened when an engine start is selected and is automatically closed at a predetermined starter speed the clutch also automatically disengages as the engine accelerates up to idling rpm and the rotation of the starter ceases exemple 253 is disengaged by the coupling between engine n2 spool and starter by the use of centrifugal forces.is disengaged by the coupling between engine n2 spool and starter by the use of centrifugal forces.

Both gas turbine and piston engines use a cycle made up of induction ?

Question 33-32 : I is correct ii is incorrect i is incorrect ii is incorrect i is incorrect ii is correct i is correct 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 cylinder.turbine engine the combustion process is continuous and occurs at constant pressure exemple 257 i is correct, ii is incorrect.i is correct, ii is incorrect.

Which of these statements about compressor stall are correct or incorrect.i a ?

Question 33-33 : I is correct ii is incorrect i is incorrect ii is incorrect i is incorrect ii is correct i is correct ii is correct

Like the stall of a wing compressor stall is caused by a breakdown of airflow .if your wing is suitable for high speed and you fly at low speed and large angle of attack the stall is most likely to occur.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 261 i is correct, ii is incorrect.i is correct, ii is incorrect.

The following problems may occur when starting a twin spool turbofan engine ?

Question 33-34 : No n1 rotation although n2 may accelerate normally no n2 rotation although n1 may accelerate normally a hung abortive start with no light up indication after 'fuel on' selection a hung abortive start with fuel flow indication zero after 'fuel on' selection

.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 exemple 265 no n1 rotation, although n2 may accelerate normally.no n1 rotation, although n2 may accelerate normally.

Both gas turbine and piston engines use a cycle made up of induction ?

Question 33-35 : I is incorrect ii is correct i is incorrect ii is incorrect i is correct ii is correct i is correct ii is incorrect

.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 cylinder.turbine engine the combustion process is continuous and occurs at constant pressure exemple 269 i is incorrect, ii is correct.i is incorrect, ii is correct.

The most unfavourable conditions for adequate inlet air flow of a turbofan ?

Question 33-36 : Maximum take off thrust zero forward speed and strong crosswind conditions maximum thrust during climb out with strong crosswind idle thrust zero forward speed with no wind maximum thrust at rotation speed on the ground during take off

exemple 273 maximum take-off thrust, zero forward speed and strong crosswind conditions.maximum take-off thrust, zero forward speed and strong crosswind conditions.

If a twin spool gas turbine engine is controlled by a conventional n2 control ?

Question 33-37 : Overspeed of the lp turbine n2 and epr increase n1 and n2 increase n1 decrease and epr increase

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 exemple 277 overspeed of the lp turbine.overspeed of the lp turbine.

The rotor blades of an axial compressor of a gas turbine engine are often ?

Question 33-38 : Limits damage to the blades due to vibration limits fod damage limits damage due to creep facilitates easy assembly and removal

exemple 281 limits damage to the blades due to vibration.limits damage to the blades due to vibration.

For a turbine engine the self sustaining speed relates to the minimum rpm at ?

Question 33-39 : Will continue to operate without any starter motor assistance is designed to idle after starting operates most efficiently in the cruise will enable the generators to supply bus bar voltage

exemple 285 will continue to operate without any starter motor assistance.will continue to operate without any starter motor assistance.

The primary function of the diffuser located between the compressor and the ?

Question 33-40 : Decrease the flow velocity increase total pressure convert kinetic energy into mechanical energy increase the temperature of the compressed air

Before combustion can proceed the air velocity must be greatly reduced .air 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 exemple 289 decrease the flow velocity.decrease the flow velocity.

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