In a gas turbine engine the power changes are normally made by controlling the amount of ?
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Source: Telepilote theorique examen 31
In a free turbine engine ?
During take off the fan in a high by pass ratio turbofan engine produces ?
At constant fuel flow if engine compressor air bled off engine anti icing or a similar system turbine temperature The greater part of thrust. The ratio of tertiary airflow around combustion flame tube that cools turbine decreases thus less cooling flow as warm air diverted anti icing so egt will increase as a result. 
A hung abortive start of a gas turbine engine may be caused A too low pneumatic starter pressure. 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. 
A reverse thrust alert on flight deck occurs when 1 reverser doors are unlocked with reverse lever in stowed position 2 reverser doors are locked with reverse lever in stowed position 3 reverser doors remain stowed with reverse lever in deployed position 4 reverser doors have moved to reverse thrust position with reverse lever in deployed position the combination that regroups all of correct statements A too low pneumatic starter pressure. Boeing fcom thrust reverser each engine equipped with a hydraulically operated thrust reverser consisting of left right translating sleeves aft movement of reverser sleeves causes blocker doors to deflect fan discharge air forward through fixed cascade vanes producing reverse thrust the thrust reverser for ground operations only is used after touchdown to slow airplane reducing stopping distance brake wear when reverse thrust selected an electro mechanical lock releases isolation valve opens the thrust reverser control valve moves to deploy position allowing hydraulic pressure to unlock deploy reverser system an interlock mechanism restricts movement of reverse thrust lever until reverser sleeves have approached deployed position when either reverser sleeve moves from stowed position amber rev indication located on upper display unit illuminates as thrust reverser reaches deployed position rev indication illuminates green the reverse thrust lever can be raised to detent no 2 this position provides adequate reverse thrust normal operations when necessary reverse thrust lever can be pulled beyond detent no 2 providing maximum reverse thrust downward motion of reverse thrust lever past detent no 1 (reverse idle thrust) initiates command to stow reverser when lever reaches full down position control valve moves to stow position allowing hydraulic pressure to stow lock reverser sleeves after thrust reverser stowed isolation valve closes the electro mechanical lock engages if reverser doors are unlocked with reverse lever in stowed position or if reverser doors remain stowed with reverse lever in deployed position reverser light illuminates master caution eng system annunciator lights illuminate. 
In a single spool gas turbine engine compressor rpm The same as turbine rpm. The turbine turning compressor so one turbine one compressor single spool gas turbine engine. Question 31-8
The primary reason a limitation being imposed on temperature of gas flow to Ensure that maximum acceptable temperature at turbine blades not exceeded. The temperatures are highest in combustion chamber but engine most sensitive to high temperatures just behind combustion chamber at turbine high temperatures centrifugal loads can cause turbine blade creep jt9d engine. Question 31-9
One of purposes of bleed valves fitted to axial flow compressors to Reduce tendency to compressor stall. The temperatures are highest in combustion chamber but engine most sensitive to high temperatures just behind combustion chamber at turbine high temperatures centrifugal loads can cause turbine blade creep jt9d engine. Question 31-10
A modern auxiliary power unit apu designed to provide power ground starting of an engine it also supplies both in air subject to certification limitations and on ground Air conditioning electrical services. The temperatures are highest in combustion chamber but engine most sensitive to high temperatures just behind combustion chamber at turbine high temperatures centrifugal loads can cause turbine blade creep jt9d engine. Question 31-11
The disadvantages of axial flow compressors compared to centrifugal flow compressors are 1 more expensive to manufacture2 lower airflow3 greater vulnerability to foreign object damage4 lower pressure ratiothe combination which regroups all of correct answers Air conditioning electrical services. compared to centrifugal flow compressors axial flow compressors are more expensive to manufacture due to design function of a compressor engine's air inlet possibility of ingestion of debris always exists this causes significant damage particularly to compressor turbine sections when this occurs it called foreign object damage (fod) typical fod consists of small nicks dents caused ingestion of small objects from ramp taxiway or runway however fod damage caused bird strikes or ice ingestion can also occur may result in total destruction of an engine example of a centrifugal compressor . Question 31-12
A stage in an axial compressor Consists of a rotor disc followed a ring of stator blades. compared to centrifugal flow compressors axial flow compressors are more expensive to manufacture due to design function of a compressor engine's air inlet possibility of ingestion of debris always exists this causes significant damage particularly to compressor turbine sections when this occurs it called foreign object damage (fod) typical fod consists of small nicks dents caused ingestion of small objects from ramp taxiway or runway however fod damage caused bird strikes or ice ingestion can also occur may result in total destruction of an engine example of a centrifugal compressor . Question 31-13
In a turbo jet purpose of turbine to Drive compressor using part of energy from exhaust gases. compared to centrifugal flow compressors axial flow compressors are more expensive to manufacture due to design function of a compressor engine's air inlet possibility of ingestion of debris always exists this causes significant damage particularly to compressor turbine sections when this occurs it called foreign object damage (fod) typical fod consists of small nicks dents caused ingestion of small objects from ramp taxiway or runway however fod damage caused bird strikes or ice ingestion can also occur may result in total destruction of an engine example of a centrifugal compressor . Question 31-14
The gas turbine illustrated of following type 916 Free turbine centrifugal compressor. For a free power turbine engine turbine driving main rotor transmission mechanically independent from gas generator radial (centrifugal) compressor (located at front of engine). Question 31-15
The control of free turbine engines on turboprops accomplished a propeller control lever used to select 1 propeller rpm2 turbine temperature3 turbine rpm a fuel control lever used to select 4 propeller rpm5 torque6 turbine temperaturethe combination which regroups all of correct statements Free turbine centrifugal compressor. Propeller control lever controls rpm so out of 1 2 3 only 1 correct fuel control lever controls torque turbine temp so out of 4 5 6 both 5 6 are correct the correct answer option then 1 5 6. Question 31-16
The static thrust of a turbo jet at selection of full power 1 equals product of exhaust gas mass flow and exhaust gas velocity2 obtained pressure of exhaust gas on ambient air3 equivalent to zero mechanical power since aeroplane not moving4 independant of outside air temperaturethe combination which regroups all of correct statements Free turbine centrifugal compressor. Static thrust the measured thrust produced when movement prevented thrust in its simplest form is f = m x a thrust (f) = mass flow rate x (jet velocity tas) statement 1 it true 2 it a nonsense statement 3 it true no movement = zero mechanical power statement 4 wrong static thrust dependant of outside air temperature since mass flow will vary with temperature/density. Question 31-17
The purpose of a compressor bleed valve to prevent surging At low compressor rpm. the compressor bleed valve removes excesss volume of air at low compressor rpm to increase flow over front compressor blades reduce flow over latter stages. Question 31-18
Severe compressor stall can be indicated amongst others A rise in turbine gas temperature (tgt) a change in vibration level. A compressor stall means less cooling flow the turbine so egt will increase as a result as a wing vibrations will occur during stall. Question 31-19
In a gas turbine engine compressor blades which are not rigidly fixed in position when engine stationary take up a rigid position when engine running due to The resultant of aerodynamic centrifugal forces. The blades are not rigidly fixed one common mehtod of fitting them with 'fir tree root' rotor blades are strong enought to withstand centrifugal forces they take up a rigid position when engine running due to resultant of aerodynamic centrifugal forces watch videos below >beghfv2y2ry (you can here at 6 00 'clung' noise of blade falling from their casing) >phluddufakg (this for turbine stage but construction similar the compressor stage). Question 31-20
The characteristics of a centrifugal compressor are 1 a high pressure ratio stage2 a large diameter3 a low pressure ratio stage4 a small diameterthe combination containing all of correct statements The resultant of aerodynamic centrifugal forces. axial compressor radial compressor the pressure ratio obtained from a centrifugal compressor stage lower than that which can be obtained from axial flow compressor stage the diameter of a centrifugal compressor usually larger compare to an axial compressor the same flow. Question 31-21
The diffuser in a centrifugal compressor a device in which Pressure rises velocity falls. Diffuser = stator a compressor in case of a compressor velocity falls the pressure increases in stator (the diffuser). Question 31-22
The thrust reversers of jet engines may use clamshell doors in order to Change direction of exhaust gas stream. Diffuser = stator a compressor in case of a compressor velocity falls the pressure increases in stator (the diffuser). Question 31-23
By pass turbine engines are mainly used in commercial aviation because At high subsonic airspeeds they have a better propulsive efficiency than propeller or straight jet engines. Diffuser = stator a compressor in case of a compressor velocity falls the pressure increases in stator (the diffuser). Question 31-24
Engine auxiliary gearboxes Provide drives a wide variety of services may even provide the support of engine in airframe. the accessory gearbox driven a radial shaft that meshes with a bevel gear driven the n2 (or gas producer rotor) is used to drive essential engine components such as fuel pump oil pump fuel control unit generators hydraulic pumps the accessory gear box also used to drive engine rpm feedback tacho generators is means which starter drives engine these are systems which must operate as soon as engine starts structure containing gearbox can be utilised as a support as well each component that attaches to accesssory gearbox has its own mounting pad with its unique gear reduction speed rotational direction. Question 31-25
The greatest risk created a free turbine overspeed Bursting of free turbine disk. In case of turbine overspeed centrifugal force can be so great that turbines rotor blades can detatch during a high powered engine run this 767 had a engine failure piece of turbine seen above lodged in outboard side of engine the photo above shows gash made on lower part of fuselage in air conditioning bay when a piece of turbine exited engine ended up embedding in engine. Question 31-26
The thermal efficiency of a gas turbine engine will increase with a Decrease in ambient air temperature. Thermal efficiency the ratio of useful work to heat put in expressed as a percentage the power output of a gas turbine engine depends on mass airflow a cold air mass has higher density thermal efficiency increases with cold ambient air temperature. Question 31-27
Creep of turbine blades caused High blade temperature whilst under centrifugal loading. Blade creep the increase in length of turbine rotor blades during their operating life due to heat stress. Question 31-28
By pass ratio in a turbine engine the ratio of Cold air mass flow to hot air mass flow. bypass ratio = bypass mass flow / hp compressor mass flow by pass mass flow cold air mass flow hp compressor mass flow the hot air mass flow. Question 31-29
On landing and prior to shut down a gas turbine engine should be r at 'ground idle' a short period this allows The core temperature to diminish. bypass ratio = bypass mass flow / hp compressor mass flow by pass mass flow cold air mass flow hp compressor mass flow the hot air mass flow. Question 31-30
Both gas turbine and piston engines utilise a cycle of induction compression combustion and exhaust however in gas turbine these processes are i and combustion occurs at ii respectively i and ii are (i) continuous (ii) constant pressure. 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 31-31
For a subsonic airflow in a divergent duct Pressure increases velocity decreases temperature increases. 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 31-32
An engine pressure ratio epr can be defined as ratio of Jet pipe total pressure to compressor inlet total pressure. Epr defined as ratio of total turbine outlet pressure to total compressor inlet pressure 'total turbine outlet pressure' 'jet pipe total pressure'. Question 31-33
For a fan jet engine by pass ratio the Cold air mass flow divided the hot air mass flow. bypass ratio = bypass mass flow / hp compressor mass flow by pass mass flow cold air mass flow hp compressor mass flow the hot air mass flow. Question 31-34
The pass air in a pass type gas turbine engine promotes lower specific fuel consumption causing an overall Decrease in exhaust gas flow average velocity higher propulsive efficiency. Bypass engines have a number of advantages the bypass air does not need to be combusted to achieve its acceleration since no fuel needed to heat air design inherently more thermally efficient the bypass air given a smaller acceleration so its propulsive efficiency greater at lower speeds the reason that answer decrease in combustion chamber temperature higher thermal efficiency not correct that although engine more thermally efficient combustion chamber temperatures are not reduced. Question 31-35
In airflow through a single spool axial flow turbo jet engine axial velocity of air greatest On exit from propelling nozzle. single spool axial flow turbo jet engine the term 'single spoo refers to fact that there only one shaft this shaft connects one turbine section to one compressor section all jet engines in current use are axial flow engines meaning that compression phase done axially (parallel to axis of engine) as air flows through compressor axial flow engines are different from early jet engines which compressed air in a centrifugal compressor the axial velocity of air greatest on exit from propelling nozzle (exhaust of propulsive gases). Question 31-36
In a jet engine propelling nozzle Must be designed to obtain correct balance of pressure velocity to prevent flow separation. single spool axial flow turbo jet engine the term 'single spoo refers to fact that there only one shaft this shaft connects one turbine section to one compressor section all jet engines in current use are axial flow engines meaning that compression phase done axially (parallel to axis of engine) as air flows through compressor axial flow engines are different from early jet engines which compressed air in a centrifugal compressor the axial velocity of air greatest on exit from propelling nozzle (exhaust of propulsive gases). Question 31-37
In a multi spool turbofan engine fan driven The rearmost turbine. The high pressure turbine drives high pressure compressor the low pressure turbine drives fan the low pressure compressor therefore we can say that fan driven from rearmost turbine a shaft. Question 31-38
After air has passed through compressor of a gas turbine engine Temperature will be higher than inlet temperature. Compression of air generates heat air warmer after compression 1 compressed air high pressure flows toward low pressure 2 the compressor sections are in front of engine the turbine in rear 3 the compressors are attached to turbines via shafts 4 between compressor turbine sections the combustion chamber where fuel mixed with compressed air iginited the compressor section made up of alternating rows rotating blades stationary vanes that are shaped like wings curved on one side flat on other they function like wings too airflow creates low pressure on curved side high pressure on flat this imparts direction of airflow toward rear of engine high pressure flows toward low pressure the leading edges of these rotating blades face leading edge of stationary blades as air cascades through each pair of rotor stationary vanes it becomes more more compressed the air enters combustion chamber is rapidly heated wants to expand (but there only so much room expansion which another form of compression) so it continues to rear of engine where pressure lower it meets turbines the turbine are like pinwheels the fast flowing compressed air strikes turbines causes it(them) to spin add more fuel more heat compressed air expands faster the turbines spin faster because they are attached to compressor section via shaft compressor spins faster too which compresses incoming air faster even more air does not like to be compressed it likes to be in its normal state so it roars past turbines out back of engine the reaction thrust of exhaust against engine itself causes propulsion. Question 31-39
To achieve reverse thrust on a turbine engine with a high pass ratio generally The fan flow deflected. Compression of air generates heat air warmer after compression 1 compressed air high pressure flows toward low pressure 2 the compressor sections are in front of engine the turbine in rear 3 the compressors are attached to turbines via shafts 4 between compressor turbine sections the combustion chamber where fuel mixed with compressed air iginited the compressor section made up of alternating rows rotating blades stationary vanes that are shaped like wings curved on one side flat on other they function like wings too airflow creates low pressure on curved side high pressure on flat this imparts direction of airflow toward rear of engine high pressure flows toward low pressure the leading edges of these rotating blades face leading edge of stationary blades as air cascades through each pair of rotor stationary vanes it becomes more more compressed the air enters combustion chamber is rapidly heated wants to expand (but there only so much room expansion which another form of compression) so it continues to rear of engine where pressure lower it meets turbines the turbine are like pinwheels the fast flowing compressed air strikes turbines causes it(them) to spin add more fuel more heat compressed air expands faster the turbines spin faster because they are attached to compressor section via shaft compressor spins faster too which compresses incoming air faster even more air does not like to be compressed it likes to be in its normal state so it roars past turbines out back of engine the reaction thrust of exhaust against engine itself causes propulsion. Question 31-40
An aircraft flying in conditions of continuous heavy rain and high ambient temperatures may require precautionary use of The fan flow deflected. Normally in flight no igniters are in use as combustion self sustaining during engine start for take off landing igniters are in use you have to use igniters in case of moderate or severe precipitation turbulence or icing or an in flight relight.
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