In the stator of a turbine the gas velocity v and static pressure ps vary as ? [ Report OACI ]

Question 33-1 : V increases ps decreases v increases ps increases v decreases ps increases v decreases ps decreases

exemple 133 V increases, ps decreases. — If you have multiple stage turbines there is a set of guide vanes between each turbine disc to redirect the flow again before the next turbine blade they are stationary so are sometimes called stators .with the turbine you want a high velocity so turbine blades are designed to extract power from the hot expanding gasses to turn the compressor by using the high velocity hitting the turbine blade the guide vanes straighten the flow before the next set of turbine blades but in effect it decreases the pressure and increases the velocity this also prevents excessive backpressure which could work its way forward and affect the combustion process .the compressor on the other hand is designed to increase the pressure through each of the stages so you can deliver a good mass flow to the combustion chambers however the increasing pressure will try to reverse the flow so the convergent duct is designed to keep the velocity constant through the whole compressor so that the momentum of the airflow prevents reverse flow in effect the velocity is therefore increased in each rotor section .velocity increases and decreases through each set of rotors and stators and by using a convergent duct the velocity therefore stays constant but the pressure is steadily increasing through each stage V increases, ps decreases.

Epr can be defined as the ratio of ?

Question 33-2 : The total turbine outlet pressure to the total compressor inlet pressure the total turbine outlet pressure to the total compressor outlet pressure the total turbine inlet pressure to the total compressor outlet pressure the total turbine inlet pressure to the total compressor inlet pressure

exemple 137 The total turbine outlet pressure to the total compressor inlet pressure. — Img911 The total turbine outlet pressure to the total compressor inlet pressure.

A gas turbine engine turbine section may employ active clearance control ?

Question 33-3 : To provide enhanced clearances between the blade tips and the casing in order to cool the disc in order to reduce 'creep' in the blades as a method of attaching the stators and rotors to the hub of the disc

exemple 141 To provide enhanced clearances between the blade tips and the casing. — .active clearance control acc is a method used in gas turbines to improve fuel efficiency this is achieved by controlling the tip clearance it is particularly effective on turbofans since they are required to respond quickly to changes of the thrust setting .the active clearance control consists of the acc valve which receives the air from the bypass duct and routes the air to flow over the pipes surrounding the turbine casing which in turn reduces the thermal expansion of the turbine case and maintains the accurate clearance between the turbine case and the blade tip this clearance should be maintained accurately which is essential for the engine efficiency and its performance the acc valve opening is adjusted automatically by the fadec system depending on the throttle position To provide enhanced clearances between the blade tips and the casing.

In a gas turbine engine the maximum gas temperature is attained ?

Question 33-4 : Within the combustion chamber at the turbine entrance in the cooling airflow around the flame tube at the entry to the exhaust unit

exemple 145 Within the combustion chamber. — Within the combustion chamber.

A pressure relief valve that does not fit on its seat properly would result in ?

Question 33-5 : Low oil pressure high oil pressure low oil temperature excessive oil consumption

exemple 149 Low oil pressure. — To prevent too high a pressure a pressure release valve is fitted it comprises a stainless steel ball bearing and a spring .the ball is forced by the spring against an oil port when the oil pressure is sufficiently high the ball if forced off its seat and oil is allowed to bypass this restriction thus making sure that the pressure never gets too high .if the pressure relief valve is not hermetic there will be a leak and the pressure decreases Low oil pressure.

In a gas turbine engine the power changes are normally made by controlling the ?

Question 33-6 : Fuel supplied air entering the compressor air entering the compressor and fuel entering the combustion chambers air leaving the compressor by the opening or closing of bleed valves

exemple 153 Fuel supplied. — Fuel supplied.

In a free turbine engine ?

Question 33-7 : There is no mechanical connection between the compressor and the power output shaft its shaft may be connected to either a compressor or another turbine the air enters the compressor via the input turbine the compressor and power output shaft are mechanically connected

exemple 157 There is no mechanical connection between the compressor and the power output shaft. — There is no mechanical connection between the compressor and the power output shaft.

During take off the fan in a high by pass ratio turbofan engine produces ?

Question 33-8 : The greater part of the thrust no thrust half the thrust the lesser part of the thrust

exemple 161 The greater part of the thrust. — The greater part of the thrust.

At constant fuel flow if engine compressor air is bled off for engine anti ?

Question 33-9 : Will rise will be unchanged will fall may rise or fall depending on which stage of the compressor is used for the bleed and the rpm of the engine at the moment of selection

exemple 165 Will rise. — The ratio of the tertiary airflow around the combustion flame tube that cools the turbine decreases thus less cooling flow as the warm air is diverted for anti icing so the egt will increase as a result Will rise.

A hung abortive start of a gas turbine engine may be caused by ?

Question 33-10 : A too low pneumatic starter pressure compressor surging the starter cutting out early in the starting sequence before the engine has accelerated to the required rpm for ignition failure of the fuel to ignite in the starting sequence after the engine has been accelerated to the required rpm by the starter

exemple 169 A too low pneumatic starter pressure. — .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 A too low pneumatic starter pressure.

A reverse thrust alert on the flight deck occurs when .1 the reverser doors ?

Question 33-11 : 1 3 2 4 1 4 2 3

exemple 173 1, 3. — Boeing fcom .thrust reverser .each engine is equipped with a hydraulically operated thrust reverser consisting of left and right translating sleeves aft movement of the reverser sleeves causes blocker doors to deflect fan discharge air forward through fixed cascade vanes producing reverse thrust the thrust reverser is for ground operations only and is used after touchdown to slow the airplane reducing stopping distance and brake wear .when reverse thrust is selected an electro mechanical lock releases the isolation valve opens and the thrust reverser control valve moves to the deploy position allowing hydraulic pressure to unlock and deploy the reverser system an interlock mechanism restricts movement of the reverse thrust lever until the reverser sleeves have approached the deployed position when either reverser sleeve moves from the stowed position the amber rev indication located on the upper display unit illuminates as the thrust reverser reaches the deployed position the rev indication illuminates green and the reverse thrust lever can be raised to detent no 2 this position provides adequate reverse thrust for normal operations when necessary the reverse thrust lever can be pulled beyond detent no 2 providing maximum reverse thrust .downward motion of the reverse thrust lever past detent no 1 reverse idle thrust initiates the command to stow the reverser when the lever reaches the full down position the control valve moves to the stow position allowing hydraulic pressure to stow and lock the reverser sleeves after the thrust reverser is stowed the isolation valve closes and the electro mechanical lock engages .if the reverser doors are unlocked with the reverse lever in the stowed position or if the reverser doors remain stowed with the reverse lever in the deployed position the reverser light illuminates the master caution and eng system annunciator lights illuminate 1, 3.

In a single spool gas turbine engine the compressor rpm is ?

Question 33-12 : The same as turbine rpm independent of turbine rpm greater than turbine rpm less than turbine rpm

exemple 177 The same as turbine rpm. — The turbine is turning the compressor so one turbine and one compressor . 912. single spool gas turbine engine The same as turbine rpm.

The primary reason for a limitation being imposed on the temperature of the gas ?

Question 33-13 : Ensure that the maximum acceptable temperature at the turbine blades is not exceeded ensure that the maximum acceptable temperature within the combustion chamber is not exceeded prevent damage to the combustion chamber from overheating prevent damage to the jet pipe from overheating

The temperatures are highest in the combustion chamber but the engine is most sensitive to high temperatures just behind the combustion chamber at the turbine high temperatures and centrifugal loads can cause turbine blade creep . 913. jt9d engine

One of the purposes of the bleed valves fitted to axial flow compressors is to ?

Question 33-14 : Reduce the tendency to compressor stall enable an external air supply to spin up the compressor for engine starting spill compressor air should the engine overspeed thus controlling the speed control the acceleration time of the engine

exemple 185 Reduce the tendency to compressor stall. — Reduce the tendency to compressor stall.

A modern auxiliary power unit apu is designed to provide power for ground ?

Question 33-15 : Air conditioning and electrical services either air conditioning or electrical services but never both at the same time air conditioning and electrical services on the ground electrical and hydraulic back up services in the air air conditioning and thrust in the event of engine failure

The disadvantages of axial flow compressors compared to centrifugal flow ?

Question 33-16 : 1 and 3 1 and 2 2 and 4 2 and 3

exemple 193 1 and 3. — Img914.compared to centrifugal flow compressors axial flow compressors are more expensive to manufacture .due to the design and function of a compressor engine's air inlet the possibility of ingestion of debris always exists this causes significant damage particularly to the compressor and turbine sections when this occurs it is called foreign object damage fod typical fod consists of small nicks and dents caused by ingestion of small objects from the ramp taxiway or runway .however fod damage caused by bird strikes or ice ingestion can also occur and may result in total destruction of an engine .example of a centrifugal compressor . 915 1 and 3.

A stage in an axial compressor ?

Question 33-17 : Consists of a rotor disc followed by a ring of stator blades has a compression ratio in the order of 2 1 consists of a ring of stator blades followed by a rotor disc has a compression ration in the order of 0 8

exemple 197 Consists of a rotor disc followed by a ring of stator blades. — Consists of a rotor disc followed by a ring of stator blades.

In a turbo jet the purpose of the turbine is to ?

Question 33-18 : Drive the compressor by using part of the energy from the exhaust gases clear the burnt gases the expansion of which provide the thrust compress the air in order to provide a better charge of the combustion chamber drive devices like pumps regulator generator

exemple 201 Drive the compressor by using part of the energy from the exhaust gases. — Drive the compressor by using part of the energy from the exhaust gases.

The gas turbine illustrated is of the following type . 916 ?

Question 33-19 : Free turbine and centrifugal compressor free turbine and axial compressor single shaft turbine and centrifugal compressor single shaft turbine and axial compressor

exemple 205 Free turbine and centrifugal compressor. — For a free power turbine engine the turbine driving the main rotor transmission is mechanically independent from the gas generator . 915. radial centrifugal compressor located at the front of the engine Free turbine and centrifugal compressor.

The control of free turbine engines on turboprops is accomplished by . a ?

Question 33-20 : 1 5 and 6 1 3 and 5 3 4 and 6 2 4 and 5

exemple 209 1, 5 and 6. — Propeller control lever controls rpm so out of 1 2 and 3 only 1 is correct .fuel control lever controls torque and turbine temp so out of 4 5 and 6 both 5 and 6 are correct .the correct answer option is then 1 5 6 1, 5 and 6.

The static thrust of a turbo jet at the selection of full power .1 equals the ?

Question 33-21 : 1 and 3 4 only 1 and 2 2 and 3

exemple 213 1 and 3. — Static thrust is the measured thrust produced when movement is prevented .thrust in its simplest form is .f = m x a.thrust f = mass flow rate x jet velocity tas .statement 1 it is true .2 it is a nonsense .statement 3 it is true no movement = zero mechanical power .statement 4 wrong static thrust is dependant of the outside air temperature since mass flow will vary with temperature/density 1 and 3.

The purpose of a compressor bleed valve is to prevent surging ?

Question 33-22 : At low compressor rpm generated by foreign object ingestion of the first compressor stages with altitude

exemple 217 At low compressor rpm. — .the compressor bleed valve removes excesss volume of air at low compressor rpm to increase the flow over the front compressor blades and reduce the flow over the latter stages At low compressor rpm.

Severe compressor stall can be indicated amongst others by ?

Question 33-23 : A rise in turbine gas temperature tgt and a change in vibration level an increase in engine pressure ratio epr and a decrease in tgt and fuel flow a decrease in tgt and a change in vibration level a rise in tgt and an increase in fuel flow

exemple 221 A rise in turbine gas temperature (tgt) and a change in vibration level. — A compressor stall means less cooling flow for the turbine so the egt will increase as a result as for a wing vibrations will occur during the stall A rise in turbine gas temperature (tgt) and a change in vibration level.

In a gas turbine engine compressor blades which are not rigidly fixed in ?

Question 33-24 : The resultant of aerodynamic and centrifugal forces thermal expansion blade creep oil pressure

exemple 225 The resultant of aerodynamic and centrifugal forces. — The blades are not rigidly fixed one common mehtod of fitting them is with the 'fir tree root' rotor blades are strong enought to withstand centrifugal forces they take up a rigid position when the engine is running due to the resultant of aerodynamic and centrifugal forces .watch the videos below . >beghfv2y2ry. you can here at 6 00 the 'clung' noise of the blade falling from their casing . >phluddufakg. this is for the turbine stage but construction is similar for the compressor stage The resultant of aerodynamic and centrifugal forces.

The characteristics of a centrifugal compressor are .1 a high pressure ratio ?

Question 33-25 : 1 and 2 1 and 4 2 and 3 3 and 4

exemple 229 1 and 2. — Img938. axial compressor . 915. radial compressor .the pressure ratio obtained from a centrifugal compressor by stage is lower than that which can be obtained from the axial flow compressor by stage .the diameter of a centrifugal compressor is usually larger compare to an axial compressor for the same flow 1 and 2.

The diffuser in a centrifugal compressor is a device in which the ?

Question 33-26 : Pressure rises and velocity falls pressure rises at a constant velocity velocity pressure and temperature rise velocity rises and pressure falls

exemple 233 Pressure rises and velocity falls. — Diffuser = stator for a compressor .in the case of a compressor the velocity falls and the pressure increases in the stator the diffuser Pressure rises and velocity falls.

The thrust reversers of jet engines may use clamshell doors in order to ?

Question 33-27 : Change the direction of the exhaust gas stream stop the flow of the exhaust gas stream reduce the pressure of the exhaust gas stream by diffusing it to atmosphere absorb any surge in engine thrust

exemple 237 Change the direction of the exhaust gas stream. — Change the direction of the exhaust gas stream.

By pass turbine engines are mainly used in commercial aviation because ?

Question 33-28 : At high subsonic airspeeds they have a better propulsive efficiency than propeller or straight jet engines they produce less noise they are lighter than straight jet engines twin spool or triple spool jet engines require a high by pass ratio

Engine auxiliary gearboxes ?

Question 33-29 : Provide the drives for a wide variety of services and may even provide for the support of the engine in the airframe always provide drives for fuel pumps oil pumps speed sensing and torque sensing never provide a torque sensing facility are driven by the output from the free power turbine

exemple 245 Provide the drives for a wide variety of services and may even provide for the support of the engine in the airframe. — Img908. 909.the accessory gearbox is driven by a radial shaft that meshes with a bevel gear driven by the n2 or gas producer rotor and is used to drive essential engine components such as the fuel pump oil pump fuel control unit generators and hydraulic pumps .the accessory gear box is also used to drive engine rpm feedback tacho generators and is the means by which the starter drives the engine these are systems which must operate as soon as the engine starts .structure containing the gearbox can be utilised as a support as well .each component that attaches to the accesssory gearbox has its own mounting pad with its unique gear reduction for speed and rotational direction Provide the drives for a wide variety of services and may even provide for the support of the engine in the airframe.

The greatest risk created by a free turbine overspeed is ?

Question 33-30 : Bursting of the free turbine disk a surge of the gas generator creep of the turbine blades an engine overtemperature

In case of turbine overspeed centrifugal force can be so great that the turbines rotor blades can detatch .. 942.during a high powered engine run this 767 had a engine failure . 943.piece of the turbine is seen above lodged in the outboard side of the engine . 944.the photo above shows the gash made on the lower part of the fuselage in the air conditioning bay when a piece of the turbine exited the engine and ended up embedding in the engine

The thermal efficiency of a gas turbine engine will increase with a ?

Question 33-31 : Decrease in ambient air temperature increase in ambient air temperature increase in humidity decrease in ambient air pressure

exemple 253 Decrease in ambient air temperature. — Thermal efficiency is the ratio of useful work to the heat put in expressed as a percentage .the power output of a gas turbine engine depends on mass airflow and a cold air mass has higher density thermal efficiency increases with cold ambient air temperature Decrease in ambient air temperature.

Creep of turbine blades is caused by ?

Question 33-32 : High blade temperature whilst under centrifugal loading prolonged idling at low rpm bending stresses set up by gas pressure static imbalance of the blades

exemple 257 High blade temperature whilst under centrifugal loading. — Blade creep is the increase in length of turbine rotor blades during their operating life due to heat and stress High blade temperature whilst under centrifugal loading.

By pass ratio in a turbine engine is the ratio of the ?

Question 33-33 : Cold air mass flow to the hot air mass flow speed of the combusted air to the speed of the by pass air intake air pressure to the turbine delivery air pressure tertiary air mass flow to the primary air mass flow

exemple 261 Cold air mass flow to the hot air mass flow. — Img939.bypass ratio = bypass mass flow / hp compressor mass flow .by pass mass flow is cold air mass flow .hp compressor mass flow is the hot air mass flow Cold air mass flow to the hot air mass flow.

On landing and prior to shut down a gas turbine engine should be run at 'ground ?

Question 33-34 : The core temperature to diminish the turbine blade temperature to reduce only the engine to be compressor washed cool oil flushing of bearings particularly those in the turbines

exemple 265 The core temperature to diminish. — The core temperature to diminish.

Both gas turbine and piston engines utilise a cycle of induction compression ?

Question 33-35 : I continuous ii constant pressure i continuous ii constant volume i intermittent ii constant pressure i intermittent ii constant volume

exemple 269 (i) continuous (ii) constant pressure — 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 (i) continuous (ii) constant pressure

For a subsonic airflow in a divergent duct the ?

Question 33-36 : Pressure increases velocity decreases and temperature increases pressure decreases velocity increases and temperature increases pressure increases velocity decreases and temperature decreases pressure decreases velocity increases and temperature decreases

exemple 273 Pressure increases, velocity decreases and temperature increases. — Pressure increases, velocity decreases and temperature increases.

An engine pressure ratio epr can be defined as the ratio of ?

Question 33-37 : Jet pipe total pressure to compressor inlet total pressure jet pipe total pressure to combustion chamber pressure combustion chamber pressure to compressor inlet total pressure compressor outlet pressure to compressor inlet total pressure

exemple 277 Jet pipe total pressure to compressor inlet total pressure. — Epr is defined as the ratio of the total turbine outlet pressure to the total compressor inlet pressure . 947.'total turbine outlet pressure' is 'jet pipe total pressure' Jet pipe total pressure to compressor inlet total pressure.

For a fan jet engine the by pass ratio is the ?

Question 33-38 : Cold air mass flow divided by the hot air mass flow hot air mass flow divided by the cold air mass flow hot air mass flow divided by the fuel flow fuel flow divided by hot air mass flow

exemple 281 Cold air mass flow divided by the hot air mass flow. — Img939.bypass ratio = bypass mass flow / hp compressor mass flow .by pass mass flow is cold air mass flow .hp compressor mass flow is the hot air mass flow Cold air mass flow divided by the hot air mass flow.

The by pass air in a by pass type gas turbine engine promotes lower specific ?

Question 33-39 : Decrease in exhaust gas flow average velocity and higher propulsive efficiency decrease in combustion chamber temperature and higher thermal efficiency increase in exhaust gas flow average velocity thus increasing engine pressure ratio increase in the mean jet temperature and increase in thermal efficiency

exemple 285 Decrease in exhaust gas flow average velocity and 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 is needed to heat the air the design is inherently more thermally efficient . the bypass air is given a smaller acceleration so its propulsive efficiency is greater at lower speeds .the reason that answer decrease in combustion chamber temperature and higher thermal efficiency is not correct is that although the engine is more thermally efficient combustion chamber temperatures are not reduced Decrease in exhaust gas flow average velocity and higher propulsive efficiency.

In the airflow through a single spool axial flow turbo jet engine the axial ?

Question 33-40 : On exit from the propelling nozzle as it leaves the compressor within the combustion chamber as it leaves the turbine

exemple 289 On exit from the propelling nozzle. — Single spool axial flow turbo jet engine . 912.the term 'single spool' refers to the fact that there is 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 the compression phase is done axially parallel to the axis of the engine as the air flows through the compressor .axial flow engines are different from early jet engines which compressed air in a centrifugal compressor .the axial velocity of the air is greatest on exit from the propelling nozzle exhaust of the propulsive gases On exit from the propelling nozzle.

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1279 Free Training Exam Other source study: Ppl exam examen 33