I85PREP
⌘ K
EASA Module 14 study materials
EASA Module 14 study resources

EASA Module 14 practice questions

One question at a time. Build your EASA Module 14 understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Turbine Engines

In a twin-spool turbofan, which component drives the high-pressure compressor through the HP shaft?

  1. The fan
  2. The low-pressure turbine
  3. The accessory gearbox
  4. The high-pressure turbine Correct answer.

Explanation

The HP (N2) shaft mechanically links the high-pressure turbine to the high-pressure compressor, so the HP turbine extracts energy from the gas stream to drive the HP compressor. The LP turbine drives the fan and LP compressor on a separate concentric shaft.

Question 2Turbine Engines

In a pure turbojet, thrust is produced primarily by:

  1. The pressure of the oil system
  2. The acceleration of the exhaust gases through the nozzle Correct answer.
  3. The static pressure in the combustion chamber alone
  4. The rotation of the compressor blades

Explanation

Thrust in a turbojet comes from the change of momentum of the gas as it is accelerated rearward through the exhaust nozzle. A small additional contribution comes from the pressure difference across the engine, but gas acceleration dominates.

Question 3Turbine Engines

What is the primary function of the diffuser immediately downstream of the centrifugal compressor impeller?

  1. To increase gas velocity before combustion
  2. To meter fuel into the airflow
  3. To cool the compressor bleed air
  4. To convert high gas velocity into static pressure Correct answer.

Explanation

The diffuser slows the high-velocity air leaving the impeller, converting kinetic energy into static pressure with minimal loss. This pressure rise is essential before the air enters the combustion section.

Question 4Turbine Engines

In a can-annular combustion chamber, the cans are:

  1. Completely isolated from each other
  2. Interconnected by flame tubes to allow light-round Correct answer.
  3. Open to the bypass duct
  4. Cooled only by fuel flow

Explanation

Can-annular combustors use interconnecting flame tubes so that ignition from one can propagates to all the others during start (light-round). They combine the can-type liner with an annular casing.

Question 5Turbine Engines

On a typical turbofan, the fan bypass ratio is defined as the ratio of:

  1. Mass flow through the bypass duct to mass flow through the core Correct answer.
  2. Bypass duct pressure to ambient pressure
  3. Core mass flow to bypass mass flow
  4. Fan tip speed to core compressor tip speed

Explanation

Bypass ratio compares the mass of air that passes through the bypass duct with the mass that goes through the engine core. High bypass ratios give better propulsive efficiency at subsonic speeds.

Question 6Turbine Engines

Which turbine blade cooling method uses air bled from the compressor passing through internal passages and exiting through small holes to form a protective layer?

  1. Transpiration cooling
  2. Convection cooling only
  3. Impingement cooling only
  4. Film cooling Correct answer.

Explanation

Film cooling discharges cooling air through small holes in the blade surface, forming a thin insulating film between the hot gas and the metal. Internal convection and impingement are often used together with film cooling.

Question 7Turbine Engines

What is the main purpose of variable inlet guide vanes on an axial compressor?

  1. To increase the compressor pressure ratio at all speeds
  2. To filter foreign objects from the intake
  3. To drive the accessory gearbox
  4. To alter airflow angle and prevent compressor stall at low speeds Correct answer.

Explanation

Variable IGVs change the angle of the incoming air to match the first-stage rotor blades, improving stability and preventing stall or surge at low rotational speeds. They are scheduled by the fuel control or engine control unit.

Question 8Turbine Engines

Which statement best describes the function of the exhaust nozzle in a turbojet engine?

  1. It compresses the exhaust gases before discharge
  2. It cools the exhaust gases before they leave the engine
  3. It expands the hot gases to convert remaining pressure into velocity Correct answer.
  4. It mixes bypass air with core air in all installations

Explanation

The nozzle expands the exhaust gas, converting residual pressure energy into kinetic energy, which increases exhaust velocity and thrust. A convergent nozzle is typical for subsonic exhaust velocities.

Question 9Turbine Engines

An axial compressor stage consists of:

  1. Two rotor rows only
  2. A stator row followed by a rotor row
  3. A rotor row followed by a stator row Correct answer.
  4. A diffuser followed by an impeller

Explanation

In an axial compressor stage, the rotor adds kinetic energy to the air and the following stator diffuses it, converting velocity into static pressure. Each stage therefore comprises one rotor row and one stator row.

Question 10Turbine Engines

During a start, why is the ignition switched off shortly after the engine reaches idle?

  1. Combustion becomes self-sustaining and continuous ignition would waste energy and erode igniters Correct answer.
  2. The igniters would overheat the compressor
  3. Fuel flow cannot be controlled with ignition on
  4. The starter motor requires the ignition circuit

Explanation

Once combustion is stable and self-sustaining, the igniters are no longer needed; leaving them on wastes electrical power and shortens igniter life. Ignition is typically re-selected on for adverse weather or relight capability.

Question 11Turbine Engines

A turbofan engine is fitted with a fuel-oil heat exchanger. Its main purpose is to:

  1. Heat the oil to reduce its viscosity at altitude
  2. Cool the fuel before it reaches the nozzles
  3. Pressurise the fuel system
  4. Warm the fuel and cool the engine oil simultaneously Correct answer.

Explanation

The fuel-oil heat exchanger transfers heat from the hot engine oil to the colder fuel, warming the fuel to prevent ice formation and cooling the oil. This dual function improves efficiency and protects both systems.

Question 12Turbine Engines

Which condition is most likely to cause a compressor surge?

  1. A gradual increase in engine speed at constant altitude
  2. Opening the bleed valves during acceleration
  3. Operating with a clean, unobstructed intake
  4. A rapid reduction in fuel flow at high power with the bleed valves closed Correct answer.

Explanation

Surge occurs when the compressor cannot maintain pressure against downstream demand, often triggered by a rapid fuel reduction or throttle chop at high power. The pressure ratio exceeds stability limits and flow reverses momentarily.

Question 13Turbine Engines

The purpose of the bleed valve on an axial compressor during acceleration is to:

  1. Reduce the turbine inlet temperature
  2. Increase the pressure ratio across the compressor
  3. Supply air to the cabin pressurisation system
  4. Release excess pressure from intermediate stages to improve stability Correct answer.

Explanation

Bleed valves open during acceleration to release air from intermediate stages, lowering the pressure ratio and keeping the compressor within its stable operating range. They close as the engine reaches higher speed.

Question 14Turbine Engines

In a free-turbine turboshaft engine, the output shaft is driven by:

  1. The accessory gearbox through a bevel gear
  2. The starter-generator
  3. The same shaft as the gas generator compressor
  4. A power turbine that is mechanically independent of the gas generator Correct answer.

Explanation

A free-turbine design has a power turbine on its own shaft, aerodynamically coupled to the gas generator but not mechanically connected to it. This allows the rotor or propeller to turn independently of gas generator speed.

Question 15Turbine Engines

What does the term 'light-round' refer to in a multi-can combustion system?

  1. The propagation of flame from one can to the others during start Correct answer.
  2. The sequence of igniter firing across two igniters
  3. The gradual increase of fuel flow during acceleration
  4. The ignition of fuel in the exhaust nozzle

Explanation

Light-round is the process by which combustion initiated in one or two cans spreads through the interconnecting flame tubes to all cans. Successful light-round is indicated by a rapid rise in exhaust gas temperature.

Question 16Turbine Engines

A turboprop engine is operating at constant power while the propeller blade angle is increased. What effect does this have on engine speed if fuel flow is unchanged?

  1. Engine speed increases then stabilises at a higher value
  2. Engine speed remains exactly constant
  3. Engine speed decreases because the propeller absorbs more power Correct answer.
  4. Engine speed increases because the propeller absorbs less power

Explanation

Increasing blade angle increases the power absorbed by the propeller, so at constant fuel flow the engine speed falls. The propeller governor compensates by adjusting fuel or blade angle to maintain the selected speed.

Question 17Turbine Engines

Which parameter is typically used by an engine control unit to limit turbine inlet temperature during acceleration?

  1. Exhaust gas temperature Correct answer.
  2. Fuel nozzle differential pressure only
  3. Oil pressure
  4. Compressor inlet temperature alone

Explanation

Exhaust gas temperature (EGT) is measured by thermocouples downstream of the turbine and used as an indicator of turbine inlet temperature. The control unit schedules fuel to keep EGT within limits during acceleration.

Question 18Turbine Engines

Why is a convergent-divergent nozzle used on some supersonic turbojet engines?

  1. To reduce exhaust noise to acceptable levels
  2. To provide reverse thrust
  3. To increase the pressure at the turbine outlet
  4. To expand the exhaust gas to supersonic velocity efficiently Correct answer.

Explanation

A convergent-divergent nozzle allows the exhaust gas to expand beyond the throat and accelerate to supersonic velocity, improving thrust at high pressure ratios. A simple convergent nozzle can only accelerate the flow to sonic speed at the throat.

Question 19Turbine Engines

What is the function of the stator vanes in the turbine section?

  1. To accelerate and direct the gas onto the rotor blades at the correct angle Correct answer.
  2. To drive the compressor through the shaft
  3. To measure gas temperature
  4. To cool the turbine casing

Explanation

Turbine nozzle guide vanes accelerate the hot gas and turn it to the correct angle before it enters the rotor blades. They also raise the gas velocity so the rotor can extract work efficiently.

Question 20Turbine Engines

In a twin-spool engine, the LP compressor is normally protected from overspeed by:

  1. A relief valve on the fan case
  2. The accessory gearbox clutch
  3. A mechanical fuse on the LP shaft
  4. A control system that schedules fuel and bleed to keep N1 within limits Correct answer.

Explanation

LP spool speed (N1) is limited by the engine control system, which adjusts fuel flow and compressor bleed to keep N1 within certified limits. There is no simple mechanical fuse that limits LP speed.

Question 21Turbine Engines

An engine is fitted with an annular combustion chamber. Which advantage does this give compared with a can-annular design?

  1. Simpler fuel nozzle replacement
  2. Elimination of the need for ignition
  3. A shorter, lighter casing with more uniform outlet temperature Correct answer.
  4. Lower compressor pressure ratio requirement

Explanation

The annular combustor uses a single continuous flame tube around the shaft, giving a shorter and lighter engine with more uniform temperature distribution at the turbine inlet. Can-annular designs are longer and heavier.

Question 22Turbine Engines

A turbofan experiences a fan blade-out event. Which design feature primarily limits the resulting unbalance loads?

  1. The variable inlet guide vanes
  2. Fusible or shear-out fan shaft and engine mount design Correct answer.
  3. The accessory gearbox
  4. The fuel-oil heat exchanger

Explanation

Certification requires the engine to survive a fan blade loss; the design uses shear sections and mount fuses so the resulting unbalance does not propagate catastrophic loads into the airframe. The fan case must also contain the released blade.

Question 23Turbine Engines

Why is turbine blade tip clearance kept as small as possible, and what limits how small it can be?

  1. Small clearance increases thrust, but oil pressure sets the minimum
  2. Small clearance reduces blade weight, but compressor speed sets the minimum
  3. Small clearance reduces leakage losses, but thermal growth and rotor dynamics set a minimum safe gap Correct answer.
  4. Small clearance increases cooling flow, but fuel flow sets the minimum

Explanation

Tip leakage over the turbine blades represents a significant efficiency loss, so clearance is minimised. However, differential thermal expansion and rotor whirl during transients require a minimum running clearance to avoid rub and damage.

Question 24Turbine Engines

A twin-spool turbofan shows a rising EGT and falling thrust at constant fuel flow, with N1 and N2 both slightly low. Which explanation is most consistent?

  1. An open compressor bleed valve
  2. A failed igniter in the combustion chamber
  3. Hot section deterioration such as turbine blade erosion or seal wear Correct answer.
  4. A blocked fuel nozzle causing rich cut-out

Explanation

Deterioration of the turbine (erosion, increased tip clearance, seal wear) reduces turbine efficiency, so more fuel is needed for the same thrust, raising EGT and lowering achievable speed. An open bleed valve or blocked nozzle would produce different signatures.

Question 25Turbine Engines

In a turbofan with a high bypass ratio, why does propulsive efficiency improve at moderate subsonic cruise speeds?

  1. The fan pressure ratio is raised to very high values
  2. The core exhaust velocity is increased to supersonic levels
  3. A large mass of air is accelerated to a modest velocity, reducing wasted kinetic energy in the jet Correct answer.
  4. Bypass air is mixed with fuel before combustion

Explanation

Propulsive efficiency is highest when a large mass of air is given a small velocity increment, because energy lost in the jet is proportional to the square of jet velocity relative to flight speed. High bypass ratio engines therefore perform well at subsonic cruise.

Question 26Turbine Engines

In a single-spool turbojet, which component directly drives the high-pressure compressor?

  1. The accessory gearbox through a radial drive
  2. The starter-generator through a clutch
  3. The exhaust cone through a flexible coupling
  4. The turbine through a concentric shaft Correct answer.

Explanation

In a single-spool turbojet, the turbine and compressor are mounted on the same shaft, so the turbine extracts energy from the gas stream and directly drives the compressor. The accessory gearbox and starter are driven from the spool but do not provide the main drive path. The exhaust cone is a static structure and does not transmit torque.

Question 27Turbine Engines

Which statement describes the primary function of the diffuser in a centrifugal compressor?

  1. It increases the axial velocity of the air before the next stage.
  2. It directs cooling air into the turbine section.
  3. It removes boundary layer air to prevent surge.
  4. It converts kinetic energy of the air leaving the impeller into static pressure. Correct answer.

Explanation

The diffuser receives high-velocity air from the impeller and slows it down, converting dynamic pressure into static pressure. It does not accelerate the flow axially or handle turbine cooling air. Bleed valves, not the diffuser, manage surge margin.

Question 28Turbine Engines

Why are compressor bleed valves opened during engine starting?

  1. To cool the turbine blades during the start cycle.
  2. To increase the mass flow through the turbine for faster acceleration.
  3. To reduce the pressure ratio and prevent compressor stall at low speed. Correct answer.
  4. To supply air to the cabin environmental control system.

Explanation

At low rotational speeds, the front stages of an axial compressor tend to stall because they cannot pass the volume flow demanded by the rear stages. Opening bleed valves reduces the delivery pressure and increases flow through the front stages, keeping the operating point away from the surge line. They are not primarily for turbine cooling or cabin supply during start.

Question 29Turbine Engines

Which type of combustion chamber is characterised by a single annular flame tube with no separate cans?

  1. Can-annular
  2. Reverse-flow can
  3. Multiple-can
  4. Annular Correct answer.

Explanation

An annular combustion chamber uses one continuous annular flame tube around the engine axis, giving a shorter and lighter assembly with a more uniform outlet temperature. Can-annular designs use individual cans linked by interconnectors, and multiple-can designs use separate cans. Reverse-flow describes the direction of gas flow, not the can arrangement.

Question 30Turbine Engines

In a turboprop engine, what is the function of the reduction gearbox?

  1. To drive the accessory gearbox only.
  2. To increase the turbine speed for better efficiency.
  3. To provide thrust augmentation during take-off.
  4. To match the high turbine speed to the lower optimum propeller speed. Correct answer.

Explanation

A turboprop's free turbine or power turbine runs at high speed, while the propeller is efficient at much lower speeds. The reduction gearbox reduces the output speed and increases torque to match the propeller's optimum rpm. It does not increase turbine speed, drive only accessories, or augment thrust.

Question 31Turbine Engines

Which material property is most important for turbine blades operating at high temperature?

  1. High thermal conductivity
  2. Low melting point
  3. High electrical resistivity
  4. Low density and high creep resistance Correct answer.

Explanation

Turbine blades must resist creep deformation under centrifugal load at high temperature, so creep resistance is critical. Low density reduces centrifugal stress and allows higher rotational speeds. High thermal conductivity is not a primary requirement, and a low melting point would be unsuitable.

Question 32Turbine Engines

What is the purpose of the igniter plugs in a gas turbine combustion chamber?

  1. To measure the combustion temperature.
  2. To provide continuous ignition throughout the flight.
  3. To initiate combustion during start and, if selected, for relight. Correct answer.
  4. To inject fuel into the primary zone.

Explanation

Igniter plugs provide the high-energy spark needed to start combustion during engine start and, on some engines, can be selected for continuous ignition in adverse weather. They do not run continuously by default, measure temperature, or inject fuel. Fuel injection is performed by the fuel nozzles.

Question 33Turbine Engines

Which statement best describes the function of the exhaust nozzle in a turbofan engine?

  1. It controls the compressor bleed valves.
  2. It supports the rear bearing of the LP spool.
  3. It accelerates the exhaust gases to produce thrust and directs the flow rearward. Correct answer.
  4. It mixes fan air with core air to reduce noise.

Explanation

The exhaust nozzle expands the exhaust gases, converting remaining pressure into velocity to produce thrust, and directs the flow rearward. Mixing is a function of a separate mixer in some engines, bearing support is structural, and bleed valve control is unrelated.

Question 34Turbine Engines

In a twin-spool turbofan, which spool drives the fan?

  1. The low-pressure spool Correct answer.
  2. The high-pressure spool
  3. The starter spool
  4. The accessory gearbox spool

Explanation

In a twin-spool turbofan, the fan is driven by the low-pressure turbine through the LP shaft, forming the LP spool. The HP spool drives the HP compressor and is separate. The accessory gearbox and starter are not main drive spools.

Question 35Turbine Engines

Which condition can cause a compressor to surge?

  1. A gradual increase in compressor rotational speed
  2. An increase in fuel octane rating
  3. A decrease in turbine inlet temperature
  4. A sudden reduction in engine speed or an obstruction to airflow Correct answer.

Explanation

Surge occurs when the compressor operating point moves beyond the surge line, often due to a sudden reduction in airflow or speed that causes the front stages to stall. A gradual speed increase, lower turbine temperature, or fuel octane change do not directly cause surge. Obstruction or rapid throttle changes are common triggers.

Question 36Turbine Engines

What is the effect of increasing the bypass ratio on the specific fuel consumption of a turbofan at subsonic cruise?

  1. It generally worsens specific fuel consumption.
  2. It increases specific fuel consumption only at high altitude.
  3. It has no effect on specific fuel consumption.
  4. It generally improves specific fuel consumption. Correct answer.

Explanation

A higher bypass ratio increases propulsive efficiency because a larger mass of air is accelerated to a lower velocity, which is more efficient at subsonic speeds. This generally reduces specific fuel consumption. It does not worsen SFC, and the effect is not limited to high altitude.

Question 37Turbine Engines

In a free-turbine turboshaft engine, which component drives the output shaft?

  1. The gas generator turbine
  2. The compressor turbine
  3. The free power turbine Correct answer.
  4. The accessory gearbox

Explanation

In a free-turbine turboshaft, the gas generator turbine drives only the compressor, while a separate free power turbine extracts energy from the exhaust gas and drives the output shaft. The gas generator turbine and compressor turbine are not connected to the output. The accessory gearbox is driven by the gas generator.

Question 38Turbine Engines

Why is a fuel-oil heat exchanger used in a turbofan engine?

  1. To separate water from the fuel.
  2. To heat the fuel and cool the engine oil simultaneously. Correct answer.
  3. To cool the fuel before it enters the combustion chamber.
  4. To increase the fuel pressure for the fuel nozzles.

Explanation

A fuel-oil heat exchanger transfers heat from the hot engine oil to the cooler fuel, which cools the oil and warms the fuel, improving combustion and preventing fuel waxing. It does not primarily cool the fuel, increase pressure, or separate water. Fuel pressure is raised by pumps.

Question 39Turbine Engines

Which parameter is most commonly used to schedule fuel flow for acceleration in a modern turbofan FADEC?

  1. Engine speed (N1 or N2) and turbine gas temperature Correct answer.
  2. Exhaust gas pressure only
  3. Compressor inlet temperature only
  4. Oil temperature

Explanation

A FADEC schedules acceleration fuel flow based on engine speed and turbine gas temperature to avoid exceeding temperature limits and to prevent surge or flameout. Inlet temperature is used for correction but not alone. Exhaust pressure and oil temperature are not primary acceleration scheduling parameters.

Question 40Turbine Engines

What is the purpose of the stator vanes in an axial compressor?

  1. To convert kinetic energy into static pressure and direct flow to the next rotor. Correct answer.
  2. To support the rotor bearings.
  3. To increase the kinetic energy of the air.
  4. To bleed air for turbine cooling.

Explanation

Stator vanes in an axial compressor diffuse the high-velocity air leaving the rotor, converting kinetic energy into static pressure and turning the flow to the correct angle for the next rotor stage. They do not add kinetic energy; that is the rotor's function. Bearing support and bleed air are separate functions.

Question 41Turbine Engines

A turbofan engine has a high bypass ratio. Which statement best explains why it is more fuel-efficient at subsonic cruise than a low-bypass engine?

  1. It accelerates a larger mass of air to a lower velocity, increasing propulsive efficiency. Correct answer.
  2. It produces a higher exhaust velocity for the same thrust.
  3. It uses a smaller fan diameter.
  4. It has a higher turbine inlet temperature.

Explanation

Propulsive efficiency is improved when a large mass of air is accelerated to a modest velocity, which is characteristic of high-bypass turbofans. A low-bypass engine accelerates a smaller mass to a higher velocity, which is less efficient at subsonic speeds. Higher exhaust velocity and smaller fan diameter are not advantages for fuel efficiency.

Question 42Turbine Engines

In a multi-can combustion system, what does a 'light-round' refer to?

  1. The fuel spray pattern from a single nozzle.
  2. The time taken for the engine to reach idle.
  3. The sequence of ignition from can to can through interconnectors. Correct answer.
  4. The cooling air flow around the flame tube.

Explanation

A light-round is the propagation of flame from the ignited can to the adjacent cans through interconnector tubes, ensuring all cans are lit. It is not the time to idle, the spray pattern, or the cooling flow. A successful light-round is essential for smooth starting.

Question 43Turbine Engines

A turboprop is operating at constant power and the propeller blade angle is increased. What is the effect on engine speed?

  1. Engine speed increases.
  2. Engine speed oscillates.
  3. Engine speed decreases. Correct answer.
  4. Engine speed remains constant.

Explanation

Increasing blade angle increases propeller load, so for constant power the engine speed will decrease unless fuel flow is increased. The governor will normally adjust fuel flow to maintain selected rpm, but the immediate effect of increased load is a tendency to slow down. It does not increase or remain constant without a control correction.

Question 44Turbine Engines

Which design feature primarily limits unbalance loads following a fan blade-out event?

  1. The thrust reverser actuators.
  2. The compressor bleed valves.
  3. The accessory gearbox mounts.
  4. The fan containment casing and structural fuselage mounts. Correct answer.

Explanation

Fan blade-out loads are absorbed by the fan containment casing and transmitted through the engine mounts to the airframe structure, which is designed to withstand the resulting unbalance. Thrust reverser actuators, accessory gearbox mounts, and bleed valves are not primary load paths for blade-out unbalance.

Question 45Turbine Engines

A twin-spool turbofan shows rising EGT and falling thrust at constant fuel flow, with N1 and N2 slightly low. Which component is the most likely cause?

  1. A compressor fault causing reduced efficiency. Correct answer.
  2. An open bleed valve.
  3. A faulty igniter plug.
  4. A fuel nozzle blockage increasing fuel flow.

Explanation

Rising EGT with falling thrust and low N1/N2 at constant fuel flow suggests the compressor is not delivering the expected pressure ratio, so the turbine must work harder to drive it, raising EGT. A fuel nozzle blockage would reduce fuel flow, not keep it constant. Igniter and bleed valve faults would not produce this combination.

Question 46Turbine Engines

What is the primary function of variable inlet guide vanes (VIGVs) on an axial compressor?

  1. To provide cooling air to the turbine.
  2. To increase the pressure ratio at high speeds.
  3. To modulate airflow angle and improve surge margin at low speeds. Correct answer.
  4. To reduce the axial velocity of the air.

Explanation

VIGVs change the angle of the incoming air to the first stage, allowing the compressor to operate efficiently and with adequate surge margin at low corrected speeds. They do not primarily increase pressure ratio at high speed or supply cooling air. Their purpose is to adapt the flow angle to varying operating conditions.

Question 47Turbine Engines

In a turbofan engine, what is the purpose of the fan nozzle?

  1. To mix core and bypass air.
  2. To support the LP turbine rear bearing.
  3. To control the variable stator vanes.
  4. To accelerate the bypass air to produce thrust. Correct answer.

Explanation

The fan nozzle expands the bypass air, accelerating it to generate thrust from the fan stream. Mixing is done by a separate mixer in mixed-exhaust engines. Bearing support and stator vane control are unrelated functions.

Question 48Turbine Engines

Which statement best explains why a convergent-divergent nozzle is used on some supersonic turbojet engines?

  1. To increase the pressure ratio of the compressor.
  2. To reduce exhaust noise at take-off.
  3. To provide reverse thrust.
  4. To expand the exhaust gases to supersonic velocity and increase thrust. Correct answer.

Explanation

A convergent-divergent nozzle allows the exhaust gases to expand beyond sonic velocity, converting pressure into velocity and increasing thrust at supersonic flight speeds. It is not primarily for noise reduction, compressor pressure ratio, or reverse thrust. Reverse thrust is achieved by separate reverser mechanisms.

Question 49Turbine Engines

In a twin-spool engine, which parameter is most directly used to protect the LP compressor from overspeed?

  1. Exhaust gas temperature
  2. Fuel flow rate
  3. N1 speed Correct answer.
  4. N2 speed

Explanation

The LP compressor speed is N1, so an N1 overspeed protection system directly limits LP spool speed. N2 protects the HP spool, EGT is a temperature limit, and fuel flow is the control variable. Overspeed protection is based on the relevant spool speed.

Question 50Turbine Engines

What is the main advantage of an annular combustion chamber over a can-annular design?

  1. It requires less cooling air.
  2. It allows easier replacement of individual cans.
  3. It produces a higher pressure drop.
  4. It provides a more uniform outlet temperature and a shorter, lighter assembly. Correct answer.

Explanation

An annular chamber gives a continuous flame volume, resulting in a more uniform temperature distribution at the turbine inlet and a shorter, lighter engine casing. Can-annular designs allow individual can replacement, which is not an advantage of annular. Annular chambers do not necessarily use less cooling air or produce higher pressure drop.