Question 46-1 : An engine pressure ratio epr can be defined as the ratio of ? [ Progression visibility ]

Question 46-2 : For a fan jet engine the by pass ratio is the ?

Cold air mass flow divided by the hot air mass flow.

Img939bypass ratio = bypass mass flow hp compressor mass flowby pass mass flow is cold air mass flowhp compressor mass flow is the hot air mass flow

Question 46-3 : The by pass air in a by pass type gas turbine engine promotes lower specific fuel consumption by causing an overall ?

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 speedsthe 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

Question 46-4 : In the airflow through a single spool axial flow turbo jet engine the axial velocity of the air is greatest ?

On exit from the propelling nozzle.

Single spool axial flow turbo jet engine 912the term single spool refers to the fact that there is only one shaft this shaft connects one turbine section to one compressor sectionall 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 compressoraxial flow engines are different from early jet engines which compressed air in a centrifugal compressorthe axial velocity of the air is greatest on exit from the propelling nozzle exhaust of the propulsive gases

Question 46-5 : In a jet engine the propelling nozzle ?

Must be designed to obtain the correct balance of pressure and velocity to prevent flow separation.

Question 46-6 : In a multi spool turbofan engine the fan is driven by ?

The rearmost turbine.

The high pressure turbine drives the high pressure compressorthe low pressure turbine drives the fan and the low pressure compressor 948therefore we can say that the fan is driven from the rearmost turbine by a shaft

Question 46-7 : After air has passed through the compressor of a gas turbine engine the ?

Temperature will be higher than the inlet temperature.

Compression of air generates heat the air is warmer after compression1 compressed air high pressure flows toward low pressure2 the compressor sections are in the front of the engine and the turbine in the rear3 the compressors are attached to the turbines via shafts4 between the compressor and turbine sections is the combustion chamber where fuel is mixed with the compressed air and iginitedthe compressor section is made up of alternating rows rotating blades and stationary vanes that are shaped like wings curved on one side and flat on the other and they function like wings too airflow creates low pressure on the curved side high pressure on the flat this imparts the direction of the airflow toward the rear of the engine high pressure flows toward low pressurethe leading edges of these rotating blades face the leading edge of the stationary blades and as the air cascades through each pair of rotor and stationary vanes it becomes more and more compressedthe air enters the combustion chamber and is rapidly heated and wants to expand but there is only so much room for expansion which is another form of compression so it continues to the rear of the engine where the pressure is lower and it meets the turbines the turbine are like pinwheels the fast flowing compressed air strikes the turbines and causes it them to spinadd more fuel for more heat the compressed air expands faster and the turbines spin faster because they are attached to the compressor section via shaft the compressor spins faster too which compresses incoming air faster and even moreair does not like to be compressed it likes to be in its normal state so it roars past the turbines out the back of the engine and the reaction thrust of the exhaust against the engine itself causes the propulsion

Question 46-8 : To achieve reverse thrust on a turbine engine with a high by pass ratio generally ?

The fan flow is deflected.

Question 46-9 : An aircraft flying in conditions of continuous heavy rain and high ambient temperatures may require the precautionary use of ?

Engine igniters.

Normally in flight no igniters are in use as the combustion is self sustaining during engine start and for take off and landing igniters are in useyou have to use igniters in case of moderate or severe precipitation turbulence or icing or for an in flight relight

Question 46-10 : The engine type represented in the drawing is a 951 ?

Question 46-11 : When the combustion gases pass through a turbine the ?

Pressure drops.

Question 46-12 : Regarding a jet engine i the maximum thrust decreases as the pressure altitude increasesii the specific fuel consumption is inversely proportional to pressure altitude at constant tas ?

Question 46-13 : Regarding a jet engine i the maximum thrust increases as the pressure altitude decreasesii the specific fuel consumption is proportional to pressure altitude at constant tas ?

I is correct 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 tropopausespecific fuel consumption is the amount of fuel burnt per unit of thrust for jets it reduces with altitude up to the tropopause

Question 46-14 : One of the advantages of an annular combustion chamber is ?

A reduced thermal stress on the turbine.

A combustion chamber is a very complex structure with its divergent convergent passages compare to old multi can combustion system annular combustion chamber are shorter lighter cheaper with improved combustion characteristics more power and greater efficiency the main driver in combustion chamber development is the need to equalise temperature and flow around the whole turbine entry ring in order to reduced thermal stress

Question 46-15 : The correct order of decreasing freezing points of the three mentioned fuels is ?

Jet a jet a 1 jet b.

The accepted minimum fuel temperature for safe flight for jet a is 40°cjet a 1 is 47°cjet b is 65°c

Question 46-16 : Labyrinth seals in the lubrication system of a gas turbine engine are designed to provide a seal that is ?

Not completely tight allowing some movement between rotating and static parts.

Question 46-17 : Regarding a jet engine i the maximum thrust decreases as the pressure altitude increasesii the specific fuel consumption decreases slightly as the pressure altitude increases at constant tas ?

I is correct ii is correct.

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 tropopausespecific fuel consumption is the amount of fuel burnt per unit of thrust for jets it reduces with altitude up to the tropopause

Question 46-18 : The characteristics of an axial compressor are 1 a low pressure ratio by stage2 a high pressure ratio by stage3 the possibility of compressing a large mass airflow4 the inability of compressing a large mass airflowthe combination that regroups all of the correct statements is ?

1 3.

Img914the key word here is by stage a centrifugal compressor will produce about 5 1 ratio per stage ie impeller & diffuser compared to a axial that gives about 12 1 per stage however the use of multi stage axial compressors gives a bigger overall ratio

Question 46-19 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the speed decreases in flow directionii the total pressure remains constant in flow direction ?

I is correct ii is correct.

There is a velocity decrease as air flows from a small inlet to a larger outlet

Question 46-20 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the static pressure increases in flow directionii the total temperature remains constant in flow direction ?

I is correct ii is correct.

In a divergent duct with subsonic flow the static pressure rises as does static temperature but the total temperature remains constant

Question 46-21 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the dynamic pressure decreases in flow directionii the static temperature increases in flow direction ?

I is correct ii is correct.

Question 46-22 : A flat rated turbofan engine has a constant maximum rated thrust level ?

Up to a specific oat.

The term flat rating is so called because of the flat nature of thrust versus the ambient temperature curve the curve shows that from the lowest operating temperature possible to the specified temperature the engine produces full thrust above this temperature full thrust will not be permitteda 'flat rated' turbofan engine is controlled in such a way that at constant ambient air pressure there is no variation of take off thrust with air temperature up to some specified temperature limitabove that limit the engine operates in such a way that either the fan speed or the compressor speed is constant or the turbine inlet temperature is constantand in either case the thrust then decreases with increasing temperature

Question 46-23 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the dynamic pressure decreases in flow directionii the static temperature decreases in flow direction ?

I is correct ii is incorrect.

Question 46-24 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the speed remains constant in flow directionii the total pressure decreases in flow direction ?

I is incorrect ii is incorrect.

The speed flow is reduced static pressure increases dynamic pressure decreases and total pressure remains unchanged there is no total temperature changes but static temperature increases while dynamic temperature decreases

Question 46-25 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the static pressure remains constant in flow directionii the total temperature decreases in flow direction ?

Question 46-26 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the dynamic pressure remains constant in flow directionii the static temperature remains constant in flow direction ?

I is incorrect ii is incorrect.

Static pressure increases dynamic pressure decreases and total pressure remains unchanged there is no total temperature changes but static temperature increases while dynamic temperature decreases

Question 46-27 : Which statement is correct about the flow in a divergent jet engine inlet i the speed increases in flow directionii the total pressure increases in flow direction ?

I is incorrect ii is incorrect.

The flow speed decreases static pressure increases dynamic pressure decreases and total pressure remains unchanged

Question 46-28 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the static pressure decreases in flow directionii the total temperature increases in flow direction ?

I is incorrect ii is incorrect.

Static pressure increases dynamic pressure decreases and total pressure remains unchanged there is no total temperature changes but static temperature increases while dynamic temperature decreases

Question 46-29 : Which of the following statements is correct about the flow in a divergent subsonic gas turbine engine intake i the dynamic pressure increases in flow directionii the static temperature decreases in flow direction ?

I is incorrect ii is incorrect.

Static pressure increases dynamic pressure decreases and total pressure remains unchanged there is no total temperature changes but static temperature increases while dynamic temperature decreases

Question 46-30 : 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 is continuousii theoretically the combustion occurs at constant pressure ?

I is correct ii is correct.

Piston engine the combustion process is intermittent governed by the rythm of the back and forth movements of the piston in a cylinder the combustion occurs at constant volume in the cylinderturbine engine the combustion process is continuous and occurs at constant pressure

Question 46-31 : A twin spool engine with an inlet air mass flow of 220 kgs and a hp compressor mass flow of 220 kgs has a bypass ratio of ?

0.

Img939bypass ratio = bypass mass flow hp compressor mass flow220 220 = 00220 = 0bypass ratio = 0

Question 46-32 : A turbofan engine with an inlet air mass flow of 200 kgs and a hp compressor mass flow of 20 kgs has a bypass ratio of ?

9.

Img939bypass ratio = bypass mass flow hp compressor mass flow200 20 = 18018020 = 9

Question 46-33 : A turbofan engine with an inlet air mass flow of 220 kgs and a hp compressor mass flow of 20 kgs has a bypass ratio of ?

10.

Img939bypass ratio = bypass mass flow hp compressor mass flow220 20 = 200200 20 = 10

Question 46-34 : A turbofan engine with a bypass air mass flow of 200 kgs and a hp compressor mass flow of 20 kgs has a bypass ratio of ?

10.

Img939bypass ratio = bypass mass flow hp compressor mass flow20020 = 10

Question 46-35 : A turbofan engine with an inlet air mass flow of 220 kgs and a bypass mass flow of 200 kgs has a bypass ratio of ?

10.

Img939bypass ratio = bypass mass flow hp compressor mass flow220 200 = 20200 20 = 10

Question 46-36 : The throttle lever angle tla information of a fadec controlled gas turbine engine is provided ?

To the electronic engine control unit by a direct electrical wiring connection.

Tla thrust lever angle indicates the position of the thrust lever in control stand from a reference point usually this is 0° when thrust lever is at idle and increases up to 40° when thrust lever is advanced to take off positionthis thrust lever is connected by mechanical linkages to an electrical resolver synchro sensor called thrust lever angle resolverthe resolver has a stator and rotorthe angle of the rotor with respect to stator reference point changes as thrust lever is moved this angle is called thrust lever resolver angle tra this resolver is connected to electronic engine control eec to control engine thrust for different positions of the thrust lever

Question 46-37 : A twin spool engine with a bypass mass flow of 250 kgs and a hp compressor mass flow of 250 kgs has a bypass ratio of ?

1.

Img939bypass ratio = bypass mass flow hp compressor mass flow250 250 = 1

Question 46-38 : Which of the following statements regarding variable inlet guide vanes vigvs and variable stator vanes vsvs on a high bypass engines is correct ?

Vigvs are located at the front of the hp compressor and together with the vsvs control compressor airflow.

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 952the 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

Question 46-39 : A turbofan engine with an inlet air mass flow of 300 kgs and a hp compressor mass flow of 50 kgs has a bypass ratio ?

5.

Img939bypass ratio = bypass mass flow hp compressor mass flow300 50 = 250250 50 = 5

Question 46-40 : A turbofan engine with a bypass mass flow of 250 kgs and a hp compressor mass flow of 50 kgs has a bypass ratio of ?

5.

Img939bypass ratio = bypass mass flow hp compressor mass flowhp compressor mass flow = 50 bypass = 250250 50 = 5