ATPL Bgt Quiz

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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."

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.

A turbofan engine is a type of jet engine that consists of two main components: the core and the bypass. The core is responsible for combustion and generating thrust, while the bypass directs air around the core to provide additional thrust. In this question, it is stated that 20% of the total air intake passes through the core. Therefore, the remaining 80% bypasses the core. To determine the bypass ratio, we compare the amount of air bypassing the core to the amount passing through it. In this case, the bypass ratio is 80:20, which can be simplified to 4:1. Therefore, the correct answer is 4:1.

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.

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.

Increasing the engine operating temperature can improve the performance of a jet engine. This is because higher temperatures allow for more efficient combustion of fuel, leading to increased thrust and power output. Additionally, higher operating temperatures can also improve the overall efficiency of the engine by increasing the thermal efficiency and reducing specific fuel consumption. However, it is important to note that increasing the engine operating temperature also poses challenges in terms of materials and cooling systems to prevent overheating and damage to the engine components.

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.

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.