You would expect to find the highest gas velocity in a turbojet engine

at the end of the exhaust nozzle

The purpose of a diffuser in a gas turbine engine

raise pressure and lower velocity

lower pressure and lower temperature

raise velocity and lower temperature

The correct statement regarding the variations of MSL full throttle thrust of a jet engine is

thrust decreases as air temperature increases

thrust increases as air temperature increases

thrust increases as humidity increases

You would expect to find the highest gas pressure in a turbojet engine

at the last stage of the turbine

The 'Engine Core' of a turbofan engine refers to

the compressor, combustion chambers, turbines and exhaust

The maximum thrust output of a turbojet engine will increase with

a decrease in ambient air temperature

a decrease in ambient air pressure

a decrease in ambient air density

The effect an increase in altitude alone will have on the Low Pressure compressor of a gas turbine engine if constant thrust is maintained is

discharge pressure will increase

raises the thrust output of a jet engine as aircraft speed increases

lowers the efficiency of a jet engine as aircraft speed increases

cools the air as it enters the engine intake

In passing through the turbine section of a pure turbojet engine

gas pressure reduces, velocity increases and temperature decreases

gas pressure, velocity and temperature all decrease

gas pressure increases, velocity falls and temperature increases

'Tertiary creep' in a turbine blade of a gas turbine engine means

blade creep to the point where it would be detrimental to continue to run the engine

blade creep experienced on the test bench by the manufacturer

normal blade creep over the life of the engine

Gas turbine engine compressor stall may be caused by

an unstable airflow through the compressor

prolonged ground running with the air intake guard screens fitted

The maximum gas pressure in a gas turbine is obtained

at the entry to the exhaust unit

For a given RPM, thrust output from a gas turbine engine will be greatest

at MSL under ISA plus temperatures

If a compressor blade stall occurs in a gas turbine engine

the smooth flow of air over the blading breaks away and causes an interruption of airflow through the engine

the compressor ceases to rotate

the fuel flow burners will cease immediately

The purpose of variable inlet guide banes in a gas turbine engine is to

prevent compressor blade stall during operation off design RPM

prevent turbine blade stall at high engine RPM

prevent excessive cooling due to large mass air flow through the engine

Turbojet aircraft range increases as altitude increases toward the optimum FL because the high altitude

the engine can operate at design RPM to maintain an efficient wing angle of attack

the decrease in mass airflow permits an increased fuel/air ratio

the higher ambient temperature results in a greater pressure rise through the engine

The use of bleed air from a gas turbine engine compressor for anti-icing equipment will result in

an increase in the gas temperature, reduced thrust and an increase in SFC

an increase in thrust since less air will be mixed with fuel in the combustion chambers

an increase in RPM and a decrease in gas temperature

Maximum gas pressure in a gas turbine engine is found

between the final compressor stage and the inlet to the combustion chamber

at the downstream end of the combustion chamber

The main reason for a limit on the maximum gas temperature in a gas turbine engine is

to prevent overheating of the turbine

to prevent burning of the thermocouples

Burning fuel in the combustion chambers of a gas turbine engine is necessary to

increase the volume and velocity of the gases

raise the pressure and reduce the velocity of the gases

increase the density and reduce the temperature of the gases

On leaving the compressor in a gas turbine engine, the air passes through

divergent ducts which lower the velocity and raise the pressure of the air

nozzles designed to increase velocity of the air

special passages which drop the pressure of the air before combustion occurs

When an aircraft is parked overnight, to reduce fuel tank condensation you would

keep the tanks as full as possible

fill the tank airspace with carbon dioxide

ATPL Bgt Quiz

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Basic Gas Turbine Questions

Questions and Answers

1.

You would expect to find the highest gas velocity in a turbojet engine
- A.
  
  At the face of the compressor
- B.
  
  Leaving the diffuser
- C.
  
  At the end of the exhaust nozzle
Correct Answer
C. At the end of the exhaust nozzle

Explanation
In a turbojet engine, the highest gas velocity is expected to be found at the end of the exhaust nozzle. This is because the exhaust nozzle is designed to accelerate the exhaust gases to maximize thrust. As the gases pass through the engine, they are compressed in the compressor and then expanded in the combustion chamber. The exhaust nozzle then channels the high-pressure, high-temperature gases and further accelerates them, resulting in the highest gas velocity at the end of the nozzle.

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2.

The purpose of a diffuser in a gas turbine engine
- A.
  
  Lower pressure and lower temperature
- B.
  
  Raise pressure and lower velocity
- C.
  
  Raise velocity and lower temperature
Correct Answer
B. Raise pressure and lower velocity

Explanation
A diffuser in a gas turbine engine is designed to raise the pressure and lower the velocity of the airflow. As the high-velocity air enters the diffuser, it is slowed down, which increases its pressure. This is important because the air needs to be at a higher pressure before it enters the combustion chamber. Additionally, by reducing the velocity of the airflow, the diffuser helps to ensure a more efficient combustion process and prevents any potential damage to the engine caused by high-velocity air entering the combustion chamber.

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3.

The correct statement regarding the variations of MSL full throttle thrust of a jet engine is
- A.
  
  Thrust increases as air temperature increases
- B.
  
  Thrust decreases as air temperature increases
- C.
  
  Thrust increases as humidity increases
Correct Answer
B. Thrust decreases as air temperature increases

Explanation
As air temperature increases, the density of the air decreases. This means that there are fewer air molecules available for combustion in the engine, resulting in a decrease in thrust. Therefore, the correct statement is that thrust decreases as air temperature increases.

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4.

You would expect to find the highest gas temperature in a turbojet engine
- A.
  
  In the jet pipe
- B.
  
  At the end of the compressor
- C.
  
  In the combustion chamber
Correct Answer
C. In the combustion chamber

Explanation
The highest gas temperature in a turbojet engine is expected to be found in the combustion chamber. This is because the combustion chamber is where the fuel is burned and mixed with compressed air, resulting in a high-temperature combustion process. The burning fuel releases a large amount of energy, which increases the temperature of the gases in the combustion chamber. This high-temperature gas then expands and drives the turbine, which powers the compressor and the engine. Therefore, the combustion chamber is the location where the highest gas temperature is typically observed in a turbojet engine.

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5.

You would expect to find the highest gas pressure in a turbojet engine
- A.
  
  In the diffuser
- B.
  
  At the last stage of the turbine
- C.
  
  At the inlet of the compressor
Correct Answer
A. In the diffuser

Explanation
In a turbojet engine, the diffuser is the component that slows down and increases the pressure of the incoming air before it enters the combustion chamber. This increase in pressure is essential for efficient combustion and power generation in the engine. Therefore, it is expected to find the highest gas pressure in the diffuser.

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6.

The 'Engine Core' of a turbofan engine refers to
- A.
  
  The fan
- B.
  
  The compressor, combustion chambers, turbines and exhaust
- C.
  
  The accessory drive shaft
Correct Answer
B. The compressor, combustion chambers, turbines and exhaust

Explanation
The 'Engine Core' of a turbofan engine refers to the compressor, combustion chambers, turbines, and exhaust. This is because the engine core is the central part of the engine where the air is compressed, fuel is burned, and the resulting gases are used to drive the turbines and produce thrust. The fan and the accessory drive shaft are not part of the engine core, but rather auxiliary components that support the engine's operation.

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7.

The maximum thrust output of a turbojet engine will increase with
- A.
  
  A decrease in ambient air temperature
- B.
  
  A decrease in ambient air pressure
- C.
  
  A decrease in ambient air density
Correct Answer
A. A decrease in ambient air temperature

Explanation
The maximum thrust output of a turbojet engine will increase with a decrease in ambient air temperature because colder air is denser, meaning there are more air molecules available for combustion. This increased air density allows for a greater fuel-air mixture, resulting in more efficient combustion and a higher thrust output.

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8.

The effect an increase in altitude alone will have on the Low Pressure compressor of a gas turbine engine if constant thrust is maintained is
- A.
  
  It will stall more readily
- B.
  
  Discharge pressure will increase
- C.
  
  RPM will increase
Correct Answer
C. RPM will increase

Explanation
When the altitude increases, the air density decreases. This means that there is less air available for the engine to intake and compress. In order to maintain a constant thrust, the engine needs to compensate for the decrease in air density by increasing the RPM (rotations per minute) of the low-pressure compressor. By increasing the RPM, the engine can maintain the required airflow and compression, allowing it to continue producing the same amount of thrust despite the decrease in air density.

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9.

A pure turbojet engine in comparison to a turbofan engine has
- A.
  
  A bypass ratio less than 1:1
- B.
  
  A bypass ratio more than 1:1
- C.
  
  No bypass air
Correct Answer
C. No bypass air

Explanation
A pure turbojet engine does not have any bypass air. Unlike a turbofan engine, which has a portion of the incoming air bypassing the combustion chamber and going directly to the rear of the engine, a pure turbojet engine relies solely on the air passing through the combustion chamber for propulsion. This lack of bypass air means that all of the air entering the engine is used for combustion and thrust generation, resulting in a higher exhaust velocity and a more efficient propulsion system.

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10.

Subsonic gas flow decreases velocity and increases in pressure when flowing through
- A.
  
  A convergent duct
- B.
  
  A divergent duct
- C.
  
  A helical duct
Correct Answer
B. A divergent duct

Explanation
In a divergent duct, the cross-sectional area increases as the gas flows, causing the gas velocity to decrease. According to the principle of continuity, as the velocity decreases, the pressure increases. This is because the same mass flow rate of gas needs to pass through a larger area, resulting in a decrease in velocity and an increase in pressure. Therefore, in a divergent duct, subsonic gas flow decreases velocity and increases in pressure.

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0
11.

Ram effect
- A.
  
  Lowers the efficiency of a jet engine as aircraft speed increases
- B.
  
  Raises the thrust output of a jet engine as aircraft speed increases
- C.
  
  Cools the air as it enters the engine intake
Correct Answer
B. Raises the thrust output of a jet engine as aircraft speed increases

Explanation
The Ram effect refers to the increase in thrust output of a jet engine as the speed of the aircraft increases. This is because at higher speeds, the engine intakes more air, which leads to a greater mass flow rate through the engine. This increased mass flow rate results in higher thrust production, improving the overall efficiency and performance of the jet engine.

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12.

In passing through the turbine section of a pure turbojet engine
- A.
  
  Gas pressure, velocity and temperature all decrease
- B.
  
  Gas pressure increases, velocity falls and temperature increases
- C.
  
  Gas pressure reduces, velocity increases and temperature decreases
Correct Answer
C. Gas pressure reduces, velocity increases and temperature decreases

Explanation
In the turbine section of a pure turbojet engine, the gas pressure reduces because the energy of the gas is being used to drive the turbine. As the gas expands and loses pressure, its velocity increases due to the conservation of mass. This increase in velocity is necessary to maintain a constant mass flow rate through the engine. Additionally, as the gas expands and loses pressure, its temperature decreases due to the decrease in energy. Therefore, in the turbine section of a pure turbojet engine, gas pressure reduces, velocity increases, and temperature decreases.

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13.

'Tertiary creep' in a turbine blade of a gas turbine engine means
- A.
  
  Blade creep experienced on the test bench by the manufacturer
- B.
  
  Normal blade creep over the life of the engine
- C.
  
  Blade creep to the point where it would be detrimental to continue to run the engine
Correct Answer
C. Blade creep to the point where it would be detrimental to continue to run the engine

Explanation
Tertiary creep in a turbine blade of a gas turbine engine refers to blade creep reaching a critical point where it would be harmful or damaging to continue operating the engine. This suggests that the blade has undergone significant deformation and is at risk of failure if the engine continues to run. It is important to address this issue to prevent potential damage or accidents.

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14.

Gas turbine engine compressor stall may be caused by
- A.
  
  Prolonged ground running with the air intake guard screens fitted
- B.
  
  An unserviceable igniter plug
- C.
  
  An unstable airflow through the compressor
Correct Answer
C. An unstable airflow through the compressor

Explanation
An unstable airflow through the compressor can cause a gas turbine engine compressor stall. When the airflow through the compressor becomes unstable, it disrupts the proper functioning of the compressor blades. This disruption can lead to a decrease in the compressor's efficiency and result in a stall. A stall occurs when the airflow is disrupted to the point where the compressor blades no longer generate enough pressure to maintain combustion in the engine. This can cause a loss of power and potentially damage the engine if not addressed promptly.

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15.

The maximum gas pressure in a gas turbine is obtained
- A.
  
  Within the combustion chamber
- B.
  
  At the entry to the exhaust unit
- C.
  
  At the compressor exit
Correct Answer
C. At the compressor exit

Explanation
The maximum gas pressure in a gas turbine is obtained at the compressor exit. This is because the compressor is responsible for compressing the incoming air, which increases its pressure. As the air passes through the compressor, its pressure gradually increases, reaching its maximum value at the exit of the compressor. From there, the high-pressure air flows into the combustion chamber, where fuel is added and ignited to generate power. Therefore, the highest gas pressure is achieved at the compressor exit before entering the combustion chamber.

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16.

For a given RPM, thrust output from a gas turbine engine will be greatest
- A.
  
  At MSL under ISA conditions
- B.
  
  At high altitudes
- C.
  
  At MSL under ISA plus temperatures
Correct Answer
A. At MSL under ISA conditions

Explanation
The thrust output from a gas turbine engine will be greatest at MSL (Mean Sea Level) under ISA (International Standard Atmosphere) conditions. This is because at MSL, the air density is higher compared to high altitudes, which allows for more efficient combustion and greater thrust production. Additionally, under ISA conditions, the temperature and pressure are standardized, providing a consistent and optimal environment for the engine's performance.

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17.

If a compressor blade stall occurs in a gas turbine engine
- A.
  
  The compressor ceases to rotate
- B.
  
  The smooth flow of air over the blading breaks away and causes an interruption of airflow through the engine
- C.
  
  The fuel flow burners will cease immediately
Correct Answer
B. The smooth flow of air over the blading breaks away and causes an interruption of airflow through the engine

Explanation
When a compressor blade stall occurs in a gas turbine engine, the smooth flow of air over the blading breaks away. This break in the smooth flow causes an interruption of airflow through the engine. This can lead to a decrease in engine performance and potentially cause damage to the engine. The other options, such as the compressor ceasing to rotate or the fuel flow burners ceasing immediately, may or may not happen as a result of the stall, but they are not directly related to the interruption of airflow caused by the break in smooth air flow over the blading.

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18.

The purpose of variable inlet guide banes in a gas turbine engine is to
- A.
  
  Prevent turbine blade stall at high engine RPM
- B.
  
  Prevent compressor blade stall during operation off design RPM
- C.
  
  Prevent excessive cooling due to large mass air flow through the engine
Correct Answer
B. Prevent compressor blade stall during operation off design RPM

Explanation
The purpose of variable inlet guide vanes in a gas turbine engine is to prevent compressor blade stall during operation off design RPM. Compressor blade stall occurs when the angle of attack of the incoming airflow becomes too high, causing a disruption in the airflow and a loss of compressor efficiency. By adjusting the angle of the inlet guide vanes, the airflow can be controlled and optimized to prevent stall, especially during off-design RPM conditions where the engine is operating at speeds other than its maximum designed RPM.

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19.

Turbojet aircraft range increases as altitude increases toward the optimum FL because the high altitude
- A.
  
  The decrease in mass airflow permits an increased fuel/air ratio
- B.
  
  The higher ambient temperature results in a greater pressure rise through the engine
- C.
  
  The engine can operate at design RPM to maintain an efficient wing angle of attack
Correct Answer
C. The engine can operate at design RPM to maintain an efficient wing angle of attack

Explanation
As altitude increases towards the optimum FL, the engine can operate at its design RPM to maintain an efficient wing angle of attack. At higher altitudes, the air density decreases, which means that the engine needs to work harder to maintain the same level of performance. By operating at its design RPM, the engine can maintain the necessary power output to keep the aircraft flying efficiently. Additionally, maintaining an efficient wing angle of attack is crucial for achieving maximum lift and minimizing drag, which ultimately improves the aircraft's range.

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20.

The use of bleed air from a gas turbine engine compressor for anti-icing equipment will result in
- A.
  
  An increase in the gas temperature, reduced thrust and an increase in SFC
- B.
  
  An increase in thrust since less air will be mixed with fuel in the combustion chambers
- C.
  
  An increase in RPM and a decrease in gas temperature
Correct Answer
A. An increase in the gas temperature, reduced thrust and an increase in SFC

Explanation
When bleed air from a gas turbine engine compressor is used for anti-icing equipment, it results in an increase in the gas temperature. This is because the bleed air is hot and when it is used for anti-icing, it transfers some of its heat to the surrounding air. This increase in gas temperature can lead to reduced thrust because the hotter air is less dense, resulting in lower engine performance. Additionally, the use of bleed air for anti-icing can increase the Specific Fuel Consumption (SFC), as some of the air that would have been used for combustion is diverted for anti-icing purposes.

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21.

Maximum gas pressure in a gas turbine engine is found
- A.
  
  Between the final compressor stage and the inlet to the combustion chamber
- B.
  
  In the exhaust unit
- C.
  
  At the downstream end of the combustion chamber
Correct Answer
A. Between the final compressor stage and the inlet to the combustion chamber

Explanation
The maximum gas pressure in a gas turbine engine is found between the final compressor stage and the inlet to the combustion chamber. This is because the compressor stage compresses the incoming air, increasing its pressure, before it enters the combustion chamber where fuel is added and ignited. The pressure at this point is at its highest before it is further expanded and exhausted in the downstream end of the combustion chamber.

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22.

The main reason for a limit on the maximum gas temperature in a gas turbine engine is
- A.
  
  To prevent overheating of the turbine
- B.
  
  To prevent burning of the thermocouples
- C.
  
  To prevent a thermal runaway
Correct Answer
A. To prevent overheating of the turbine

Explanation
The main reason for a limit on the maximum gas temperature in a gas turbine engine is to prevent overheating of the turbine. Excessive heat can cause damage to the turbine blades and other components, leading to reduced performance and potential failure of the engine. By setting a maximum temperature limit, the engine can operate within safe parameters and ensure the longevity and reliability of the turbine.

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23.

Burning fuel in the combustion chambers of a gas turbine engine is necessary to
- A.
  
  Raise the pressure and reduce the velocity of the gases
- B.
  
  Increase the density and reduce the temperature of the gases
- C.
  
  Increase the volume and velocity of the gases
Correct Answer
C. Increase the volume and velocity of the gases

Explanation
Burning fuel in the combustion chambers of a gas turbine engine increases the volume and velocity of the gases. When fuel is burned, it releases energy in the form of heat, which causes the gases to expand and increase in volume. This expansion of gases creates a high-pressure environment, which in turn increases the velocity of the gases as they are expelled from the engine. This increased volume and velocity of the gases are essential for generating thrust and powering the turbine engine.

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24.

On leaving the compressor in a gas turbine engine, the air passes through
- A.
  
  Nozzles designed to increase velocity of the air
- B.
  
  Divergent ducts which lower the velocity and raise the pressure of the air
- C.
  
  Special passages which drop the pressure of the air before combustion occurs
Correct Answer
B. Divergent ducts which lower the velocity and raise the pressure of the air

Explanation
The correct answer is divergent ducts which lower the velocity and raise the pressure of the air. In a gas turbine engine, the compressor increases the pressure of the air. After leaving the compressor, the air passes through divergent ducts, which are designed to gradually increase the cross-sectional area of the flow path. This causes the velocity of the air to decrease and the pressure to increase. This process is necessary to prepare the air for combustion in the combustion chamber.

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25.

When an aircraft is parked overnight, to reduce fuel tank condensation you would
- A.
  
  Leave the fuel filler caps off
- B.
  
  Keep the tanks as full as possible
- C.
  
  Fill the tank airspace with carbon dioxide
Correct Answer
B. Keep the tanks as full as possible

Explanation
Keeping the tanks as full as possible when an aircraft is parked overnight helps to reduce fuel tank condensation. When the tanks are full, there is less empty space for moist air to enter and condense, which can lead to water contamination in the fuel. By keeping the tanks full, the amount of condensation that can occur is minimized, ensuring that the fuel remains clean and free from water.

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26.

In a free turbine turboprop engine, the propellor is driven by
- A.
  
  Both the HP and LP turbines
- B.
  
  Only the front HP turbines
- C.
  
  Only the rear LP turbines
Correct Answer
C. Only the rear LP turbines

Explanation
In a free turbine turboprop engine, the propeller is driven by only the rear LP turbines. The LP turbines are responsible for extracting energy from the exhaust gases and converting it into mechanical energy to drive the propeller. The front HP turbines, on the other hand, are connected to the compressor section and are responsible for driving the compressor to provide compressed air for combustion. Therefore, the correct answer is only the rear LP turbines.

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27.

The action which should be taken if a gas turbine compressor begins to stall during engine acceleration on start-up is
- A.
  
  Open the throttle and watch RPM increase to optimum range
- B.
  
  Close the throttle and manually operate the bleed valves
- C.
  
  Shut off the fuel supply and maintain starter motor rotation
Correct Answer
C. Shut off the fuel supply and maintain starter motor rotation

Explanation
If a gas turbine compressor begins to stall during engine acceleration on start-up, the correct action to take is to shut off the fuel supply and maintain starter motor rotation. This is because stalling can lead to damage to the compressor and other components of the engine. By shutting off the fuel supply, the combustion process is stopped, preventing further damage. Maintaining starter motor rotation ensures that the engine continues to turn over, allowing for a safe restart once the issue is resolved.

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28.

The term SFC (Specific Fuel Consumption) means
- A.
  
  Units of fuel used per unit of thrust per hour
- B.
  
  Distance travelled per unit of fuel
- C.
  
  Amount of fuel used in a specified engine RPM range
Correct Answer
A. Units of fuel used per unit of thrust per hour

Explanation
The term SFC (Specific Fuel Consumption) refers to the amount of fuel used per unit of thrust per hour. It measures the fuel efficiency of an engine by indicating how much fuel is consumed to generate a certain amount of thrust over a specific time period. This measurement is crucial in evaluating the performance and efficiency of aircraft engines, as lower SFC values indicate better fuel efficiency and reduced operating costs.

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29.

Some turbojet engine turbine blades are shrouded at the tips to
- A.
  
  Prevent blade tups rubbing against the shroud ring on expansion
- B.
  
  Prevent gas leaking past blade tips, increase rigidity and reduce vibration
- C.
  
  Prevent hot gases distorting the turbine blades
Correct Answer
B. Prevent gas leaking past blade tips, increase rigidity and reduce vibration

Explanation
The shrouding of turbine blades in turbojet engines serves multiple purposes. One of the main reasons is to prevent gas leakage past the blade tips. This is important because any leakage can lead to a decrease in engine efficiency and performance. Additionally, shrouding helps to increase the rigidity of the blades, making them less prone to bending or deformation under high-speed and high-temperature conditions. Lastly, the shroud also helps to reduce vibration, which is crucial for maintaining the stability and smooth operation of the engine.

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0
30.

The fuel flow in a jet engine is increased. Thrust increases because exhaust gas
- A.
  
  Temperature increases
- B.
  
  Pressure increases
- C.
  
  Velocity increases
Correct Answer
C. Velocity increases

Explanation
When the fuel flow in a jet engine is increased, the thrust increases because the velocity of the exhaust gas increases. This is because the increased fuel flow leads to more combustion and a greater release of energy. As a result, the exhaust gas is expelled from the engine at a higher velocity, producing a greater thrust force. Increased exhaust gas temperature and pressure may also occur, but the main factor contributing to the increased thrust is the higher velocity of the gas.

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31.

The times the surge bleed valve is open and closed during normal gas turbine operation are
- A.
  
  Open from idling to nearly design RPM, then closed up to max RPM
- B.
  
  Closed for idling to nearly design RPM, then opened up to max RPM
- C.
  
  Open over the entire RPM range, unless compressor stall occurs
Correct Answer
A. Open from idling to nearly design RPM, then closed up to max RPM

Explanation
During normal gas turbine operation, the surge bleed valve is initially open from idling to nearly design RPM. This allows excess air to be bled off to prevent compressor surge at lower speeds. Once the turbine reaches nearly design RPM, the valve is then closed to optimize the air flow and increase efficiency. It remains closed up to the maximum RPM to ensure optimal performance and prevent any damage or instability that may occur at higher speeds.

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32.

The propulsive efficiency of a turboprop decreases with an increase in speed because
- A.
  
  Of compressibility effects on the blades
- B.
  
  Blade interference increases
- C.
  
  Blade angle of attack becomes too great
Correct Answer
A. Of compressibility effects on the blades

Explanation
The correct answer is "of compressibility effects on the blades". As the speed of a turboprop increases, the airflow around the blades becomes faster, leading to compressibility effects. These effects cause a decrease in propulsive efficiency as the blades are less able to effectively convert the energy from the airflow into thrust. This decrease in efficiency is due to factors such as shock waves and changes in the flow patterns around the blades, which negatively impact their performance.

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33.

The gas turbine (Brayton) cycle is called an open or continuous cycle because
- A.
  
  All events are occurring at the same time
- B.
  
  The engine is open from end to end
- C.
  
  The cycle can start and stop at any time
Correct Answer
A. All events are occurring at the same time

Explanation
The gas turbine (Brayton) cycle is called an open or continuous cycle because all events are occurring at the same time. This means that the different processes of the cycle, such as compression, combustion, expansion, and exhaust, are happening simultaneously. Unlike a closed cycle where the processes occur in a sequential manner, in an open cycle, the gases flow continuously through the turbine, allowing for a continuous power output. This characteristic of the gas turbine cycle makes it efficient and suitable for applications such as power generation and aircraft propulsion.

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34.

A modest increase in speed in a slow flying jet aircraft leads to a small initial decrease in maximum thrust available because
- A.
  
  Of intake choking
- B.
  
  Combustion chamber back-pressure increasing
- C.
  
  The difference between exhaust and intake velocities is reduced
Correct Answer
C. The difference between exhaust and intake velocities is reduced

Explanation
When a slow flying jet aircraft increases its speed, the difference between the exhaust and intake velocities is reduced. This reduction in velocity difference affects the efficiency of the engine, causing a small initial decrease in maximum thrust available.

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35.

Pressure though the combustion chambers in a gas turbine engine
- A.
  
  Rises steadily
- B.
  
  Is constant or falls slightly
- C.
  
  Rises initially and then falls steadily
Correct Answer
B. Is constant or falls slightly

Explanation
In a gas turbine engine, the pressure through the combustion chambers is either constant or falls slightly. This is because as the fuel is burned, it releases energy and expands the gases, causing an increase in pressure. However, as the gases flow through the combustion chambers and further into the engine, they also lose some of their energy and pressure. Therefore, the pressure in the combustion chambers either remains constant or decreases slightly as the gases move through the engine.

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36.

To prevent melting of the turbine wheels, the hot gases from the combustion chamber in a gas turbine engine are cooled by
- A.
  
  Water
- B.
  
  Fuel
- C.
  
  Air
Correct Answer
C. Air

Explanation
In a gas turbine engine, the hot gases from the combustion chamber need to be cooled to prevent the melting of the turbine wheels. This is achieved by using air as a cooling medium. The high-temperature gases are directed over the turbine blades, and the cool air flow helps to dissipate the heat, keeping the turbine wheels within a safe operating temperature range. Using water or fuel for cooling could be detrimental to the engine's performance and may cause damage or inefficiency.

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37.

Engine Pressure Ratio (EPR) is the ratio of
- A.
  
  Engine compressor inlet pressure to propelling nozzle pressure
- B.
  
  Engine compressor outlet pressure to jet pipe pressure
- C.
  
  Engine compressor inlet pressure to jet pipe pressure
Correct Answer
C. Engine compressor inlet pressure to jet pipe pressure

Explanation
The Engine Pressure Ratio (EPR) is a measure of the pressure difference between the engine compressor inlet and the jet pipe. It is used to evaluate the performance and efficiency of the engine. The correct answer states that the EPR is the ratio of engine compressor inlet pressure to jet pipe pressure, which accurately describes the relationship being measured.

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38.

When climbing in a jet aircraft, the engine parameter which would stay constant if the thrust lever setting remained unchanged is
- A.
  
  RPM
- B.
  
  EPR
- C.
  
  EGT
Correct Answer
A. RPM

Explanation
RPM stands for revolutions per minute, which is a measure of the engine's rotational speed. When climbing in a jet aircraft, if the thrust lever setting remains unchanged, the RPM will stay constant because it is directly related to the engine's rotational speed. The other parameters, EPR (engine pressure ratio) and EGT (exhaust gas temperature), can vary depending on factors such as altitude, airspeed, and thrust settings. Therefore, RPM is the only parameter that would remain constant in this scenario.

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39.

Thrust is produced in a jet engine by
- A.
  
  Reaction to impingement of exhaust gases on the outside atmosphere
- B.
  
  Reaction to the pressure difference between exhaust and intake air pressures
- C.
  
  The force required to accelerate a mass of air through the engine
Correct Answer
C. The force required to accelerate a mass of air through the engine

Explanation
Thrust is produced in a jet engine by the force required to accelerate a mass of air through the engine. This means that the engine takes in air, compresses it, mixes it with fuel, ignites it, and then expels it at high velocity out of the exhaust nozzle. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. As the engine expels the high-velocity exhaust gases, it creates a forward force, known as thrust, that propels the aircraft in the opposite direction.

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40.

Fuel boost pumps in a jet aircraft fuel system are usually located in
- A.
  
  The accessory housing
- B.
  
  The fuel tanks
- C.
  
  The fuel control unit
Correct Answer
B. The fuel tanks

Explanation
Fuel boost pumps in a jet aircraft fuel system are usually located in the fuel tanks. This is because the fuel tanks are responsible for storing the fuel, and the boost pumps are used to provide additional pressure to ensure a steady flow of fuel to the engine. Placing the boost pumps in the fuel tanks allows for a more efficient and direct transfer of fuel to the engine, ensuring proper fuel delivery and engine performance.

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41.

Most modern turbofan engines have two of more spools (shafts) because
- A.
  
  The allows the compressors to run closer to their ideal RPM
- B.
  
  Manufacturing is made simpler and cheaper
- C.
  
  Shaft strength is increased
Correct Answer
A. The allows the compressors to run closer to their ideal RPM

Explanation
Having two or more spools (shafts) in modern turbofan engines allows the compressors to run closer to their ideal RPM. This is because each spool can be optimized for a specific range of RPM, allowing the engine to operate more efficiently and effectively. By dividing the workload between multiple spools, the compressors can maintain their ideal RPM range, resulting in improved performance and fuel efficiency.

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42.

An ideal jet engine air intake delivers air to the compressor with
- A.
  
  No turbulence and pressure lower than ambient
- B.
  
  No turbulence and velocity higher than ambient
- C.
  
  No turbulence and pressure higher than ambient
Correct Answer
C. No turbulence and pressure higher than ambient

Explanation
An ideal jet engine air intake should deliver air to the compressor with no turbulence to ensure smooth and efficient airflow. Additionally, the pressure of the air should be lower than ambient pressure to allow for proper compression and combustion within the engine. If the pressure were higher than ambient, it would create backflow and disrupt the engine's operation. Therefore, the correct answer is "no turbulence and pressure higher than ambient."

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43.

Air that is bypassed in a turbofan engine
- A.
  
  Goes to the rear of the combustion chamber for cooling purposes
- B.
  
  Does not pass through the compressor
- C.
  
  Is used to drive the air turbine
Correct Answer
B. Does not pass through the compressor

Explanation
In a turbofan engine, air that is bypassed does not pass through the compressor. The compressor is responsible for compressing the incoming air before it enters the combustion chamber. However, in the case of bypassed air, it is redirected and flows around the outside of the engine core. This bypassed air is used for cooling purposes at the rear of the combustion chamber or is used to drive the air turbine. Therefore, it does not follow the usual path of passing through the compressor.

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44.

One compressor bleed outlet is for cabin pressurisation and air conditioning. Another is used to
- A.
  
  Reduce combustion chamber back pressure
- B.
  
  Give a balance to the air losses
- C.
  
  Precent compressor stall and surge when operating off design RPM
Correct Answer
C. Precent compressor stall and surge when operating off design RPM

Explanation
The second compressor bleed outlet is used to prevent compressor stall and surge when the engine is operating at a speed other than its designed RPM. Stall and surge can occur when the airflow through the compressor is disrupted, leading to a loss of engine performance and potentially damaging the compressor. By bleeding off a portion of the compressed air, the outlet helps to maintain a stable airflow and prevent these issues, ensuring the engine operates safely and efficiently even at off-design RPMs.

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45.

The row of stator blades after each row of rotating compressor blades is designed to
- A.
  
  Stop the swirl that would otherwise form
- B.
  
  Convert kinetic energy into pressure energy
- C.
  
  Increase the velocity of the air
Correct Answer
B. Convert kinetic energy into pressure energy

Explanation
The row of stator blades after each row of rotating compressor blades is designed to convert kinetic energy into pressure energy. As the air passes through the rotating compressor blades, it gains kinetic energy due to the rotation. However, this kinetic energy needs to be converted into pressure energy in order to increase the overall pressure of the air. The stator blades are specifically designed to achieve this conversion by redirecting the flow and slowing down the air, thereby increasing its pressure. This ensures efficient compression of the air and optimal performance of the compressor.

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46.

The turbofan is more efficient than the turbojet because
- A.
  
  It accelerates a relatively large mass of air to a relatively low velocity
- B.
  
  It accelerates a relatively small mass of air to a relatively high velocity
- C.
  
  It accelerates a relatively large mass of air to a relatively high velocity
Correct Answer
A. It accelerates a relatively large mass of air to a relatively low velocity

Explanation
The turbofan is more efficient than the turbojet because it accelerates a relatively large mass of air to a relatively low velocity. By doing so, the turbofan is able to achieve a higher propulsive efficiency compared to the turbojet. This is because accelerating a larger mass of air at a lower velocity requires less energy compared to accelerating a smaller mass of air at a higher velocity. Additionally, the larger mass of air in the turbofan provides more thrust, making it more efficient in terms of propulsion.

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47.

Apart from bigger, stronger fan blades, a turbofan enjoys better foreign object damage (FOD) protection than a pure turbojet because
- A.
  
  These engines have intake screens
- B.
  
  Most of the air bypasses the engine
- C.
  
  Most foreign objects are smaller than the blades
Correct Answer
B. Most of the air bypasses the engine

Explanation
A turbofan engine enjoys better foreign object damage (FOD) protection than a pure turbojet because most of the air bypasses the engine. This means that a large portion of the incoming airflow is directed around the engine rather than passing through the core, reducing the risk of foreign objects entering and damaging the engine components. The bypass airflow acts as a protective barrier, preventing most of the foreign objects, which are typically smaller than the fan blades, from reaching the engine and causing damage.

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48.

A turbofan is not as efficient as a turboprop at low speeds. This is because the turbofan has
- A.
  
  A lower air mass accelerated to a higher velocity
- B.
  
  A higher air mass accelerated to a higher velocity
- C.
  
  A higher air mass accelerated to a lower velocity
Correct Answer
A. A lower air mass accelerated to a higher velocity

Explanation
A turbofan is not as efficient as a turboprop at low speeds because it accelerates a lower air mass to a higher velocity. In turbofan engines, a significant portion of the air bypasses the combustion chamber and is accelerated by the fan, while a smaller portion passes through the combustion chamber. This bypass air contributes to the overall thrust of the engine but at a lower velocity. In contrast, a turboprop engine uses a propeller to accelerate a larger air mass at a lower velocity, which is more efficient for low-speed operations.

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1
49.

A turboprop cannot operate at the high speeds of a turbofan because the turboprop has
- A.
  
  Inadequate power output
- B.
  
  Gearbox RPM limitations
- C.
  
  Shockwaves at the propeller blade tips at high Mach number
Correct Answer
C. Shockwaves at the propeller blade tips at high Mach number

Explanation
The correct answer is shockwaves at the propeller blade tips at high Mach number. When a turboprop operates at high speeds, the tips of the propeller blades can reach or exceed the speed of sound, resulting in the formation of shockwaves. These shockwaves can cause a loss of efficiency and increased drag, limiting the maximum speed at which a turboprop can operate effectively. In contrast, turbofans are designed to operate at higher speeds and do not experience the same issues with shockwaves at the blade tips.

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50.

A free turbine turboprop uses smaller starter motor than other turboprops because
- A.
  
  Of the simpler design
- B.
  
  Only the engine core is rotated for starting
- C.
  
  The engine as a whole is lighter
Correct Answer
B. Only the engine core is rotated for starting

Explanation
A free turbine turboprop uses a smaller starter motor than other turboprops because only the engine core is rotated for starting. In a free turbine turboprop, the power turbine and the propeller are not directly connected to the engine core. Instead, they are connected through a free turbine, which allows them to rotate independently. During starting, only the engine core needs to be rotated to initiate the combustion process, while the power turbine and propeller remain stationary. This simpler design eliminates the need for a larger starter motor, resulting in a lighter overall engine.

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Quiz Edited by
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Mar 22, 2011

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