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A twin spool engine with a bypass mass flow of 250 kg/s and a hp compressor ? [ Understand DGAC ]

Question 47-1 : 1 2 0 0 5

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.250 / 250 = 1 exemple 147 1.1.

Which of the following statements regarding variable inlet guide vanes vigvs ?

Question 47-2 : Vigvs are located at the front of the hp compressor and together with the vsvs control compressor airflow vigvs are located in the front of the fan and control both fan and compressor air flow vsvs are used in the compressor only and are used to increase pressure ratio vigvs prevent lp compressor stall and vsvs prevent hp compressor stall if vigvs move towards the open position vsvs move towards the closed position

The compression system is usually split into two units a low pressure lp compressor mounted on one shaft followed by an high pressure hp compressor mounted on the hp shaft and driven by its own hp turbine . 952.the fan blades of the general electric engine on a boeing 747 800 behind the fan the compressor inlet guide vanes inner circle and variable stator vanes outer circle can be seen exemple 151 Vigvs are located at the front of the hp compressor and, together with the vsvs, control compressor airflow.Vigvs are located at the front of the hp compressor and, together with the vsvs, control compressor airflow.

A turbofan engine with an inlet air mass flow of 300 kg/s and a hp compressor ?

Question 47-3 : 5 6 1 7

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.300 50 = 250.250 / 50 = 5 exemple 155 5.5.

A turbofan engine with a bypass mass flow of 250 kg/s and a hp compressor mass ?

Question 47-4 : 5 6 1 4

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.hp compressor mass flow = 50 .bypass = 250.250 / 50 = 5 exemple 159 5.5.

A turbofan engine with an inlet air mass flow of 300 kg/s and a bypass mass ?

Question 47-5 : 5 6 1 2

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.inlet = 300.bypass = 50.hp compressor mass flow 300 50 = 250.bypass ratio = 250 / 50 = 5 exemple 163 5.5.

A turbofan engine with a bypass mass flow of 888 kg/s and a hp compressor mass ?

Question 47-6 : 8 9 1 12 7

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.888 / 111 = 8 exemple 167 8.8.

Bleeding air from the hp compressor of a turbofan whilst maintaining thrust ?

Question 47-7 : Egt and fuel flow hp compressor discharge pressure and n2 n2 and fuel flow egt and n1

Oscarjp .if there is less air flow coming in egt will rise in function of that and because there is a loss on efficiency due to the bleed more work is demanded to the system and so fuel flow increases exemple 171 Egt and fuel flow.Egt and fuel flow.

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

Question 47-8 : 1 2 0 3

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.inlet = 500.bypass = 250 > compressor = 250.250 / 250 = 1 exemple 175 1.1.

Compressor stall is due to ?

Question 47-9 : An excessively high angle of attack of the rotor blades an excessively low angle of attack of the rotor blades an excessively high axial velocity an inadequate fuel flow

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 179 An excessively high angle of attack of the rotor blades.An excessively high angle of attack of the rotor blades.

A turbofan engine with an inlet air mass flow of 1000 kg/s and a hp compressor ?

Question 47-10 : 8 01 9 01 1 12 10 01

Img939.bypass ratio = bypass mass flow / hp compressor mass flow.bypass mass flow = 1000 111 = 889.889 / 111 = 8 01 exemple 183 8.01.8.01.

Which of these statements about an reaction turbine are correct or incorrect .i ?

Question 47-11 : I is correct ii is incorrect i is correct ii is correct i is incorrect ii is correct i is incorrect ii is incorrect

There is a pressure drop and a velocity increase across the stator of a reaction turbine exemple 187 I is correct, ii is incorrect.I is correct, ii is incorrect.

The electronic engine control of a fadec gas turbine engine checks ?

Question 47-12 : All input and output data active channel input and output data only input data only output data only

The full authority digital engine control system fadec receives all the necessary data for engine operation and takes over virtually all of the steady state and transient control functions which includes compressor airflow control vigv's vsv's etc exemple 191 All input and output data.All input and output data.

Jet engine total efficiency indicates the efficiency at which ?

Question 47-13 : 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 195 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 47-14 : 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 199 I is correct, ii is correct.I is correct, ii is correct.

The fadec of a gas turbine engine consists of ?

Question 47-15 : 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 203 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 47-16 : I is incorrect ii is correct i is correct ii is incorrect i is incorrect ii is incorrect i is correct ii is correct

Img939.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 207 I is incorrect, ii is correct.I is incorrect, ii is correct.

The fadec of a gas turbine engine normally includes ?

Question 47-17 : 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 211 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 47-18 : 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 215 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 47-19 : 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

Img953.in a divergent intake the flow speed decreases and the static pressure increases .dynamic pressure decreases and total pressure remains unchanged exemple 219 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 47-20 : 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 223 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 47-21 : 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 227 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 47-22 : 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 231 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 47-23 : 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 235 I is incorrect, ii is incorrect.I is incorrect, ii is incorrect.

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

Question 47-24 : 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 239 Either epr or n1.Either epr or n1.

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

Question 47-25 : 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 47-26 : 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 247 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 47-27 : Full authority digital engine control failure analysis / dispatch evaluation computer fool adapter dual electronic computer failsafe adapter direct effect computation

exemple 251 Full authority digital engine control.Full authority digital engine control.

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

Question 47-28 : 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

Img914.the blades size reduces from the inlet until the output of the compressor exemple 255 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 47-29 : 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 259 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 47-30 : 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 263 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 47-31 : 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 267 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 47-32 : 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 271 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 47-33 : 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 275 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 47-34 : 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 279 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 47-35 : 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 283 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 47-36 : 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 287 Stall margin increases.Stall margin increases.

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

Question 47-37 : 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 291 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 47-38 : 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 295 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 47-39 : 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 299 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 47-40 : Decrease airflow velocity increase total pressure increase airflow velocity decrease static temperature

exemple 303 Decrease airflow velocity.Decrease airflow velocity.

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