Jet engine total efficiency indicates the efficiency at which ?
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Which statement is correct for a gas turbine engine with a constant speed propeller and free power turbine when the power setting is decreased I The HP spool speed decreases II The EGT decreases ?

The FADEC of a gas turbine engine consists of ?

The bypass ratio i the ratio of inlet air mass flow to exhaust air mass flow ii can be determined from bypass air mass flow and hp compressor mass flow I incorrect, ii correct, i correct, ii incorrect, i incorrect, ii incorrect, i correct, ii correct. bypass ratio = bypass mass flow / hp compressor mass flow. the bypass ratio can be determined from inlet air mass flow the bypass mass flow. The fadec of a gas turbine engine normally includes An engine overspeed and/or an egt protection function, an overheat protection the electronic engine control unit, engine fire loops, an excessive fuel flow detection function. In a gas turbine engine propelling jet generated 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 individual stages. compressed heated gas at an initial velocity passes through blade to blade channels of nozzle assembly where, in course of expansion, part of available heat drop converted into kinetic energy of exhaust flow. further gas expansion conversion of heat drop into useful work take place in blade to blade channels of rotor. the gas flow acting on rotor blades develops torque on turbine's shaft. as a result, absolute velocity of gas reduced. the lower this velocity, larger part of available gas energy that converted into mechanical work on shaft. the rotor blades receive forces produced a change in direction of gas velocity flowing around them (impulse flow effect) by acceleration of gas flow relative to movement in blade to blade channels (reaction flow effect). The internal geometry of a turbofan intake a subsonic commercial aeroplane Divergent in order to reduce airflow velocity increase static pressure in front of fan, convergent in order to increase airflow velocity reduce static pressure in front of fan, divergent in order to increase both airflow velocity static pressure in front of fan, convergent in order to reduce airflow velocity in front of fan. in a divergent intake, flow speed decreases the static pressure increases. dynamic pressure decreases total pressure remains unchanged. Question Turbine Engines 33 Answer 8
The turbine in a gas turbine engine generates shaft power using Expansion of hot gas followed conversion of kinetic energy (velocity) into (mechanical) work, compression of hot gas followed conversion of kinetic energy into (mechanical) work, compression of hot gas followed conversion of potential energy (pressure) into kinetic energy (velocity), expansion of hot gas followed conversion of potential energy (pressure) into (mechanical) work. The expansion the drop of pressure. like a venturi tube, velocity must increase to keep same mass flow. this kinetic energy of hot gases converted into useful rotational, mechanical energy the turbine. this increased velocity (kinetic energy), what drives shaft. Question Turbine Engines 33 Answer 9
The principle of aeroplane propulsion to generate a propelling force Accelerating air or gas in order to obtain a reaction force, generating a high velocity jet pushing against outside air, pressurising air or gas in order to obtain a reaction force, heating up air in order to obtain a reaction force. Question Turbine Engines 33 Answer 10
Which statement correct a gas turbine engine with a constant speed propeller and free power turbine when power setting increased i the gas generator speed decreases ii the egt remains constant I incorrect, ii incorrect, i correct, ii incorrect, i correct, ii correct, i incorrect, ii correct. Hp spool speed, egt gas generator speed all increase a gas turbine engine with a constant speed propeller free power turbine, when power setting increased. Question Turbine Engines 33 Answer 11
Which statement correct a gas turbine engine with a constant speed propeller and free power turbine when power setting increased i the gas generator speed decreases ii the egt decreases I incorrect, ii incorrect, i correct, ii incorrect, i correct, ii correct, i incorrect, ii correct. Hp spool speed, egt gas generator speed all increase a gas turbine engine with a constant speed propeller free power turbine, when power setting increased. Question Turbine Engines 33 Answer 12
The primary performance indicator cockpit instrument the thrust of a turbofan engine Either epr or n , either nor n2, either nor fuel flow, either torque or rpm. Primary engine indications n1, epr egt are primary engine indications on a turbofan engine. secondary engine indications n2, fuel flow, oil pressure, oil temperature, oil quantity, engine vibration are secondary engine indications. a turbofan engine a dual rotor, axial flow turbofan. the n1 rotor consists of a fan, a low pressure compressor a low?pressure turbine. the n2 rotor consists of a high pressure compressor a high pressure turbine. the n1 n2 rotors are mechanically independent. epr, engine pressure ratio. it compares pressure in engine inlet, with pressure in exhaust nozzle. n1 the speed of first stage engine compressor. this used as a power setting in most jet engines. Question Turbine Engines 33 Answer 13
If air tapped from a gas turbine hp compressor effect on engine pressure ratio epr and exhaust gas temperature egt that Epr decreases egt increases, epr decreases egt remains constant, epr remains constant egt increases, both epr egt decrease. If you bleed air from compressor, you are reducing pressure inside compressor, therefore turbine outlet pressure will be reduced. if inlet pressure remains same, outlet pressure reduced, then epr decreases. since hot air tapped directly from a compressor stage, temperature will rise in turbine, egt increases. Question Turbine Engines 33 Answer 14
An abortive hung start the term used to describe an attempt to start in which engine Lights up, but fails to accelerate sufficiently, fails to light up, commences initial rotation, but fails to receive any fuel, will not rotate. After normal light up sequence (until starter 'cut out'), a hung start identified light off followed abnormally slow acceleration rpm stabilization below idle. a hung start may be result of fuel scheduling being either too lean or too rich. a lean hung start associated with low fuel flow proportionally low egt. a rich condition can be recognized a high fuel flow an egt rise which may tend to develop into an over temperature condition possible compressor stall. hung starts may be caused 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 variable stators. turbine section damage. Question Turbine Engines 33 Answer 15
On a fadec jet engine meaning of f a d e c on a gas turbine engine Full authority digital engine control, failure analysis / dispatch evaluation computer, fool adapter dual electronic computer, failsafe adapter direct effect computation. Question Turbine Engines 33 Answer 16
The blades in an axial flow compressor decrease in size from Low pressure to high pressure stages in an attempt to sustain axial velocity, high pressure to low pressure stages in order to allow expansion at increased velocity, root to tip in order to increase tip clearance, root to tip in order to maintain a constant angle of attack. the blades size reduces from inlet until output of compressor. Question Turbine Engines 33 Answer 17
Regarding a jet engine i the maximum thrust decreases slightly as pressure altitude decreases ii the specific fuel consumption increases slightly as pressure altitude decreases at constant tas I incorrect, ii correct, i correct, ii correct, i correct, ii incorrect, i incorrect, ii incorrect. Jet engines are more efficient at higher altitudes because less fuel needed a given thrust, due to reduction in lift drag, lower temperatures through inlet cause a significant reduction in specific fuel consumption, up to tropopause. specific fuel consumption the amount of fuel burnt per unit of thrust. for jets, it reduces with altitude up to tropopause. notice as pressure altitude decreases means 'at a lower altitude'. Question Turbine Engines 33 Answer 18
Which of following statements correct about flow in a divergent subsonic gas turbine engine intake i the speed decreases in flow direction ii the total pressure decreases in flow direction I correct, ii incorrect, i correct, ii correct, i incorrect, ii correct, i incorrect, ii incorrect. In a divergent intake, flow speed decreases the static pressure increases. dynamic pressure decreases total pressure remains unchanged. Question Turbine Engines 33 Answer 19
Which of following statements correct about flow in a divergent subsonic gas turbine engine intake i the static pressure increases in flow direction ii the total temperature increases in flow direction I correct, ii incorrect, i correct, ii correct, i incorrect, ii correct, i incorrect, ii incorrect. Question Turbine Engines 33 Answer 20
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 intermittent ii theoretically combustion occurs at constant volume I incorrect, ii incorrect, i correct, ii correct, i incorrect, ii correct, i correct, ii incorrect. piston engine combustion process intermittent, governed the rythm of back forth movements of piston in a cylinder. the combustion occurs at constant volume in cylinder. turbine engine combustion process continuous occurs at constant pressure. Question Turbine Engines 33 Answer 21
Which of following statements correct about flow in a divergent subsonic gas turbine engine intake i the speed remains constant in flow direction ii the total pressure remains constant in flow direction I incorrect, ii correct, i correct, ii correct, i correct, ii incorrect, i incorrect, ii incorrect. There a velocity decrease as air flows from a small inlet to a larger outlet. Question Turbine Engines 33 Answer 22
Which statement correct about flow in a divergent jet engine inlet i the static pressure remains constant in flow direction ii the total temperature remains constant in flow direction I incorrect, ii correct, i correct, ii correct, i correct, ii incorrect, i incorrect, ii incorrect. Question Turbine Engines 33 Answer 23
Which of these statements about compressor stall are correct or incorrect i a compressor stall most likely to occur in a compressor designed a high pressure ratio operating at low rpm ii a compressor stall most likely to occur when air flow stagnates in rear stages of compressor I correct, ii correct, i correct, ii incorrect, i incorrect, ii correct, i incorrect, ii incorrect. Like stall of a wing, compressor stall caused a breakdown of airflow. if your wing suitable high speed, you fly at low speed large angle of attack, stall most likely to occur. a compressor stall most likely to occur when air flow stagnates in rear stages of compressor. a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow. when incoming speed low angle of attack will be high. when angle of attack gets too high blade stalls. so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow). you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question Turbine Engines 33 Answer 24
In a compressor stage if axial air velocity increases more than rotor blade velocity Stall margin increases, stall margin decreases, pressure ratio will be too high, relative air velocity becomes supersonic. compressor stall occurs when compressor sucks too much air the turbine wheels to handle. excessive pressure then builds aft of compressor, the compressor blades stall. a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow. when incoming air flow speed high blade angle of attack will be low, stall margin increases (there less risk to encounter a compressor stall). Question Turbine Engines 33 Answer 25
Which of these statements about compressor stall are correct or incorrect i a compressor stall most likely to occur in a compressor designed a high pressure ratio operating at high rpm ii a compressor stall most likely to occur when air flow stagnates in rear stages of compressor I incorrect, ii correct, i correct, ii incorrect, i incorrect, ii incorrect, i correct, ii correct. Like stall of a wing, compressor stall caused a breakdown of airflow. if your wing suitable high speed, you fly at low speed large angle of attack, stall most likely to occur. a compressor stall most likely to occur when air flow stagnates in rear stages of compressor. a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow. when incoming speed low angle of attack will be high. when angle of attack gets too high blade stalls. so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow). you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question Turbine Engines 33 Answer 26
With regard to a twin spool turbofan an abortive start hung start will result in N2 speed stabilising at a lower than normal rpm a subsequent increase in egt, n2 speed stabilising at a higher than normal rpm a subsequent increase in egt, n2 speed stabilising at a lower than normal rpm a subsequent decrease in egt, n2 speed stabilising at a higher than normal rpm a subsequent decrease in egt. after normal light up sequence (until starter 'cut out'), a hung start identified light off followed abnormally slow acceleration rpm stabilization below idle. a hung start may be result of fuel scheduling being either too lean or too rich. a lean hung start associated with low fuel flow proportionally low egt. a rich condition can be recognized a high fuel flow an egt rise which may tend to develop into an over temperature condition possible compressor stall. hung starts may be caused 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 variable stators. turbine section damage. Question Turbine Engines 33 Answer 27
Which of following statements correct about flow in a divergent subsonic gas turbine engine intake i the dynamic pressure increases in flow direction ii the static temperature increases in flow direction I incorrect, ii correct, i correct, ii incorrect, i correct, ii correct, i incorrect, ii incorrect. Question Turbine Engines 33 Answer 28
One of functions of a gas turbine engine subsonic intake to Decrease airflow velocity, increase total pressure, increase airflow velocity, decrease static temperature. Question Turbine Engines 33 Answer 29
One of advantages of multiple spool jet engine designs that A smaller air starter driving only a single spool can be used, if one spool seizes, 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 possibly most popular starting system presently in use. it light, simple to use very economical utilizing low pressure air. the air starter motor fastened to accessory gearbox of engine. the sources of air available 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 used. air from one of these sources fed through an electrically controlled start valve to air inlet to rotate turbine rotor 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 other spools. Question Turbine Engines 33 Answer 30
Which of these statements about compressor stall are correct or incorrect i a compressor stall most likely to occur in a compressor designed a high pressure ratio operating at high rpm ii a compressor stall most likely to occur when air flow stagnates in front stages of compressor I incorrect, ii incorrect, i correct, ii incorrect, i incorrect, ii correct, i correct, ii correct. Like stall of a wing, compressor stall caused a breakdown of airflow. if your wing suitable high speed, you fly at low speed large angle of attack, stall most likely to occur. a compressor stall most likely to occur when air flow stagnates in rear stages of compressor. a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow. when incoming speed low angle of attack will be high. when angle of attack gets too high blade stalls. so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow). you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question Turbine Engines 33 Answer 31
After a successful start of a high bypass turbofan engine air starter Is disengaged the coupling between engine n2 spool starter the use of centrifugal forces, disengaged using a clutch that controlled the main engine control, disengaged the coupling between engine nspool starter the use of centrifugal forces, remains engaged rotates continuously with n2 spool. Air starting used on most commercial some military jet engines. it has many advantages over other starting systems, is comparatively light, simple economical to operate. 10. an air starter motor transmits power through a reduction gear clutch to starter output shaft which connected to engine. the starter turbine rotated 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 starter controlled an elec trically operated control pressure reducing valve that opened when an engine start selected is automatically closed at a predetermined starter speed. the clutch also automatically disengages as engine accelerates up to idling rpm the rotation of starter ceases. Question Turbine Engines 33 Answer 32
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 continuous ii theoretically combustion occurs at constant volume I correct, ii incorrect, i incorrect, ii incorrect, i incorrect, ii correct, i correct, ii correct. piston engine combustion process intermittent, governed the rythm of back forth movements of piston in a cylinder. the combustion occurs at constant volume in cylinder. turbine engine combustion process continuous occurs at constant pressure. Question Turbine Engines 33 Answer 33
Which of these statements about compressor stall are correct or incorrect i a compressor stall most likely to occur in a compressor designed a high pressure ratio operating at low rpm ii a compressor stall most likely to occur when air flow stagnates in front stages of compressor I correct, ii incorrect, i incorrect, ii incorrect, i incorrect, ii correct, i correct, ii correct. Like stall of a wing, compressor stall caused a breakdown of airflow. if your wing suitable high speed, you fly at low speed large angle of attack, stall most likely to occur. a compressor stall most likely to occur when air flow stagnates in rear stages of compressor. a compressor blade hitting oncoming airflow at an angle of attack that determined a combination of rotational speed the incoming airflow. when incoming speed low angle of attack will be high. when angle of attack gets too high blade stalls. so when axial flow in a compressor backs up blades stall (pressure increase in rear stages this slows down flow). you can prevent this dumping some late stage air to atmosphere (via bleed valves). Question Turbine Engines 33 Answer 34
The following problems may occur when starting a twin spool turbofan engine No nrotation, although n2 may accelerate normally, no n2 rotation, although nmay 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, compressor very inefficient. if engine experiences more than usual difficulty accelerating (due to such problems as early starter cut out, fuel mis scheduling, or strong tailwinds), engine may spend a considerable time at very low rpm (sub idle). normal engine cooling flows will not be effective during sub idle operation, turbine temperatures may appear relatively high. this known as a hot start. Question Turbine Engines 33 Answer 35
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 intermittent ii theoretically combustion occurs at constant pressure I incorrect, ii correct, i incorrect, ii incorrect, i correct, ii correct, i correct, ii incorrect. piston engine combustion process intermittent, governed the rythm of back forth movements of piston in a cylinder. the combustion occurs at constant volume in cylinder. turbine engine combustion process continuous occurs at constant pressure. Question Turbine Engines 33 Answer 36
The most unfavourable conditions adequate inlet air flow of a turbofan engine are Maximum take off thrust, zero forward speed 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 ground during take off. Question Turbine Engines 33 Answer 37
If a twin spool gas turbine engine controlled a conventional n2 control system rupture of lp shaft may result in Overspeed of lp turbine, n2 epr increase, nn2 increase, ndecrease epr increase. In a twin spool engine lp turbine connected to lp compressor, hp turbine connected to hp compressor. the lp turbine drives lp compressor, if a rupture occurs, it may result in an overspeed of lp turbine. Question Turbine Engines 33 Answer 38
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 Limits damage to blades due to vibration, limits fod damage, limits damage due to creep, facilitates easy assembly removal. Question Turbine Engines 33 Answer 39
For a turbine engine self sustaining speed relates to minimum rpm at which engine Will continue to operate without any starter motor assistance, designed to idle after starting, operates most efficiently in cruise, will enable generators to supply bus bar voltage. Question Turbine Engines 33 Answer 40
The primary function of diffuser located between compressor and combustion chamber of a gas turbine engine to Decrease flow velocity, increase total pressure, convert kinetic energy into mechanical energy, increase temperature of compressed air. Before combustion can proceed, air velocity must be greatly reduced. air leaves compressor through exit guide vanes, which convert radial component of air flow out of compressor to straight line flow. the air then enters diffuser section of engine, which a very divergent duct. the primary function of diffuser structure aerodynamic. the divergent duct shape converts most of air's velocity (pi) into static pressure (ps). as a result, highest static pressure lowest velocity in entire engine at point of diffuser discharge combustor inlet. other aerodynamic design considerations that are important in diffuser section arise from need a short flow path, uniform flow distribution, low drag loss.
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