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CAA NZ Basic Turbine Knowledge (Aeroplane) study materials
CAA NZ Basic Turbine Knowledge (Aeroplane) study resources

CAA NZ Basic Turbine Knowledge (Aeroplane) practice questions

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Question 1Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

In the ideal Brayton cycle used to model a turbofan core, which sequence of processes correctly describes the cycle?

  1. Isentropic compression, constant-volume heat addition, isentropic expansion, constant-pressure heat rejection
  2. Isothermal compression, constant-pressure heat addition, isentropic expansion, constant-volume heat rejection
  3. Constant-volume compression, constant-pressure heat addition, constant-volume expansion, constant-pressure heat rejection
  4. Isentropic compression, constant-pressure heat addition, isentropic expansion, constant-pressure heat rejection Correct answer.

Explanation

The ideal Brayton cycle consists of two isentropic (reversible adiabatic) processes for compression and expansion, linked by two constant-pressure processes for heat addition in the combustor and heat rejection to atmosphere. Constant-volume or isothermal steps belong to the Otto, Diesel or Carnot cycles, not the gas-turbine cycle.

Question 2Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

In a simple turbojet, which station number conventionally identifies the compressor inlet (engine face) in the standard gas-turbine station numbering system?

  1. Station 0
  2. Station 2 Correct answer.
  3. Station 3
  4. Station 4

Explanation

Standard station numbering uses station 1 for the inlet entry, station 2 for the compressor face, station 3 for the compressor delivery/combustor entry and station 4 for the turbine entry. Station 0 is the free stream well ahead of the engine.

Question 3Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

For a turbofan, thrust is produced primarily by which mechanism?

  1. Expansion of bleed air in the environmental control system
  2. Pressure rise inside the combustor acting on the turbine blades
  3. Reaction torque from the rotating spools transferred to the airframe
  4. Momentum change of air accelerated by the fan plus the exhaust jet of the core Correct answer.

Explanation

Thrust arises from Newton's second and third laws: the engine accelerates a mass of air rearward, producing an equal forward reaction. In a high-bypass turbofan, most thrust comes from the fan accelerating bypass air, with the remainder from the core exhaust.

Question 4Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

What is the primary purpose of the diffuser section immediately downstream of the compressor in a gas-turbine engine?

  1. To reduce velocity and raise static pressure before the combustor Correct answer.
  2. To measure fuel flow for the fuel control unit
  3. To accelerate the airflow before combustion
  4. To cool the combustion gases before they reach the turbine

Explanation

The diffuser converts the high-velocity compressor delivery air into a lower-velocity, higher static-pressure flow, which stabilises combustion and reduces pressure loss in the combustor. This diffusion process is essential because combustion requires a low-speed airflow.

Question 5Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which statement best explains why thermal efficiency of an ideal Brayton cycle increases with pressure ratio?

  1. Higher pressure ratio raises the temperature at which heat is added relative to the exhaust temperature Correct answer.
  2. Higher pressure ratio eliminates the need for a turbine
  3. Higher pressure ratio reduces the mass flow through the engine
  4. Higher pressure ratio lowers the compressor work to zero

Explanation

For a given turbine entry temperature, a higher pressure ratio raises the compressor delivery temperature, so heat is added at a higher average temperature while rejection occurs near ambient. Since ideal efficiency depends on the ratio of these absolute temperatures, efficiency rises with pressure ratio.

Question 6Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

A turboprop engine is described as producing thrust mainly through which combination?

  1. Rocket reaction from residual combustor pressure
  2. Propeller thrust with a small residual jet thrust from the exhaust Correct answer.
  3. Fan bypass air with no core contribution
  4. Pure jet exhaust momentum only

Explanation

In a turboprop, most of the gas energy is extracted by the turbine to drive the propeller through a reduction gearbox, so the propeller provides the dominant thrust. A small amount of residual jet thrust remains from the exhaust gases.

Question 7Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

In standard station numbering, which station identifies the turbine inlet (combustor exit)?

  1. Station 4 Correct answer.
  2. Station 5
  3. Station 7
  4. Station 3

Explanation

Station 4 denotes the turbine inlet, where the hot combustion gases leave the combustor and enter the first turbine nozzle guide vanes. Station 3 is compressor delivery, station 5 is turbine exit and station 7 is the exhaust nozzle.

Question 8Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

An engine operating at sea level in a standard atmosphere has an inlet total pressure of 101.3 kPa and a compressor pressure ratio of 12. What is the approximate compressor delivery total pressure, ignoring losses?

  1. About 1216 kPa Correct answer.
  2. About 844 kPa
  3. About 101.3 kPa
  4. About 12.2 kPa

Explanation

Compressor delivery total pressure equals inlet total pressure multiplied by the pressure ratio: 101.3 kPa × 12 ≈ 1216 kPa. Pressure ratio is defined as delivery total pressure divided by inlet total pressure.

Question 9Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

A turbojet takes in 50 kg/s of air and exhausts it at 600 m/s, with the intake air essentially at rest relative to the engine. Ignoring fuel mass flow, what is the approximate gross thrust?

  1. 30 kN Correct answer.
  2. 12 kN
  3. 60 kN
  4. 300 kN

Explanation

Gross thrust equals mass flow multiplied by the change in velocity: 50 kg/s × 600 m/s = 30 000 N, or 30 kN. The fuel mass flow is neglected as stated, so no correction is applied.

Question 10Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which expression correctly represents propulsive efficiency for an engine flying at velocity V with jet velocity Vj, assuming equal mass flows?

  1. 2V / (V + Vj) Correct answer.
  2. Vj / V
  3. (Vj − V) / Vj
  4. (V + Vj) / 2V

Explanation

Propulsive efficiency is the useful work done on the aircraft divided by the kinetic energy added to the jet, which simplifies to 2V/(V + Vj) when mass flows are equal. It approaches unity as jet velocity approaches flight velocity.

Question 11Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Why does a high-bypass turbofan generally have better propulsive efficiency at typical cruise speeds than a low-bypass turbojet of similar thrust?

  1. It eliminates the turbine section entirely
  2. It accelerates a larger mass of air to a lower velocity Correct answer.
  3. It operates at a much higher jet velocity
  4. It burns fuel at a higher combustor temperature

Explanation

Propulsive efficiency improves when a given thrust is produced by moving a large mass of air to a modest velocity rather than a small mass to a high velocity. The high-bypass fan accelerates a large airflow at relatively low jet velocity.

Question 12Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

What does specific fuel consumption (SFC) measure in a gas-turbine engine?

  1. Thrust produced per kilogram of engine mass
  2. Exhaust gas temperature per unit of fuel flow
  3. Fuel mass flow per unit of thrust produced Correct answer.
  4. Total fuel tank capacity divided by range

Explanation

Specific fuel consumption is the rate of fuel use divided by the thrust (or power) produced, giving units such as kg per hour per kN. Lower SFC indicates a more fuel-efficient engine for a given thrust.

Question 13Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

In a twin-spool turbofan, which station typically denotes the fan exit or low-pressure compressor exit?

  1. Station 13
  2. Station 21 Correct answer.
  3. Station 45
  4. Station 25

Explanation

In multi-spool numbering, station 21 commonly denotes the low-pressure compressor or fan exit, with station 25 used for the high-pressure compressor inlet in some conventions. Higher numbers such as 45 denote the high-pressure turbine exit.

Question 14Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

A turbofan has a bypass ratio of 10 and a core mass flow of 50 kg/s. What is the approximate total mass flow through the engine?

  1. 60 kg/s
  2. 550 kg/s Correct answer.
  3. 5 kg/s
  4. 500 kg/s

Explanation

Bypass ratio is bypass mass flow divided by core mass flow, so bypass flow is 10 × 50 = 500 kg/s. Total flow is core plus bypass: 50 + 500 = 550 kg/s.

Question 15Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which factor most directly limits the turbine entry temperature in a modern gas-turbine engine?

  1. The diameter of the exhaust nozzle
  2. The melting point and cooling capability of the turbine nozzle guide vanes and blades Correct answer.
  3. The octane rating of the fuel
  4. The pressure ratio of the fan

Explanation

Turbine entry temperature is limited by the materials and cooling technology of the first-stage nozzle guide vanes and blades, which must survive the hot gas path. Advanced cooling and thermal barrier coatings allow temperatures above the material melting point.

Question 16Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which statement correctly compares the ideal thermal efficiency of a Brayton cycle with the ideal efficiency of a Carnot cycle operating between the same maximum and minimum temperatures?

  1. The Brayton efficiency is always higher than the Carnot efficiency
  2. The Brayton efficiency is lower than the Carnot efficiency for the same temperature limits Correct answer.
  3. The Brayton efficiency is independent of temperature
  4. The two efficiencies are always equal

Explanation

The Carnot cycle is the most efficient cycle possible between two given temperature limits, so a Brayton cycle operating between the same limits must be less efficient. The Brayton efficiency depends on pressure ratio and approaches, but never exceeds, the Carnot value.

Question 17Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

What is the main function of the exhaust nozzle in a turbojet?

  1. To mix fuel with air before combustion
  2. To reduce exhaust noise by slowing the gases
  3. To convert residual pressure and thermal energy into increased exhaust velocity Correct answer.
  4. To drive the accessory gearbox

Explanation

The exhaust nozzle expands the hot gases, converting remaining pressure and thermal energy into kinetic energy so the jet leaves at high velocity. This velocity increase produces the momentum change that generates thrust.

Question 18Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

A turbofan cruises at 250 m/s with an effective exhaust velocity of 500 m/s. Using propulsive efficiency ≈ 2V/(V + Vj), what is the approximate propulsive efficiency?

  1. About 50%
  2. About 33%
  3. About 100%
  4. About 67% Correct answer.

Explanation

Substituting gives 2 × 250 / (250 + 500) = 500 / 750 ≈ 0.67, or about 67 percent. Efficiency rises as jet velocity approaches flight velocity.

Question 19Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which statement best explains why overall efficiency of a turbofan is the product of thermal efficiency and propulsive efficiency?

  1. Propulsive efficiency determines fuel burn while thermal efficiency determines noise
  2. Thermal efficiency converts fuel energy into jet kinetic energy, and propulsive efficiency converts jet kinetic energy into useful thrust work Correct answer.
  3. Both efficiencies are measured directly from fuel flow only
  4. Overall efficiency is independent of the exhaust velocity

Explanation

Thermal efficiency describes how well fuel energy is converted into kinetic energy of the exhaust, while propulsive efficiency describes how much of that kinetic energy becomes useful propulsive work. Their product gives overall efficiency.

Question 20Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

In a convergent exhaust nozzle, the exhaust gases are chocked at the throat. What happens to the mass flow if the upstream total pressure is increased while total temperature remains constant?

  1. Mass flow increases because choked mass flow is proportional to total pressure Correct answer.
  2. Mass flow decreases proportionally
  3. Mass flow becomes zero
  4. Mass flow remains constant because the throat is choked

Explanation

For a choked nozzle, the mass flow is proportional to the upstream total pressure divided by the square root of total temperature. With temperature held constant, raising total pressure increases the choked mass flow.

Question 21Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

An engine is fitted with an afterburner. Which statement correctly describes its effect on the cycle?

  1. It raises exhaust velocity by adding heat downstream of the turbine at near-constant pressure Correct answer.
  2. It reduces the exhaust gas temperature
  3. It increases the compressor pressure ratio
  4. It lowers turbine entry temperature to protect the turbine

Explanation

An afterburner adds fuel and burns it in the exhaust duct downstream of the turbine, raising the exhaust total temperature and therefore the jet velocity for extra thrust. Because the turbine has already extracted work, the added heat primarily increases exhaust kinetic energy.

Question 22Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

A gas-turbine engine operates with a compressor pressure ratio of 16 and a compressor inlet total temperature of 288 K. Assuming an isentropic compressor with γ = 1.4, which value is closest to the ideal compressor delivery total temperature?

  1. About 400 K
  2. About 653 K Correct answer.
  3. About 288 K
  4. About 1150 K

Explanation

For an isentropic compression, T2/T1 = (P2/P1)^((γ−1)/γ). With γ = 1.4 the exponent is 0.2857, so 16^0.2857 ≈ 2.27 and T2 ≈ 288 × 2.27 ≈ 653 K.

Question 23Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Why does a real compressor require more work than an ideal isentropic compressor for the same pressure ratio?

  1. The real compressor operates at a lower pressure ratio than the ideal case
  2. The ideal compressor includes heat loss to the surroundings
  3. The real compressor has a lower mass flow than the ideal case by definition
  4. Friction and flow losses raise the air temperature, increasing the work needed for the same pressure rise Correct answer.

Explanation

Irreversibilities such as friction and flow separation raise the entropy and delivery temperature above the isentropic value, so more work is required to achieve the same pressure ratio. This is captured by the compressor isentropic efficiency being less than one.

Question 24Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering

Which combination of parameters best describes the thrust produced by a convergent nozzle in the choked condition at sea level?

  1. Thrust depends only on the exhaust gas temperature
  2. Thrust depends on the choked mass flow and the velocity plus the pressure thrust term if exit pressure exceeds ambient Correct answer.
  3. Thrust depends only on the nozzle exit area and ambient pressure
  4. Thrust is zero because the flow cannot expand further

Explanation

When the nozzle is choked, the exit velocity is sonic and the mass flow is fixed by upstream conditions. Thrust then comprises the momentum term (mass flow times velocity) plus any pressure thrust from exit pressure exceeding ambient.

Question 25Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

In a single-spool turbojet, which component directly drives the compressor through the main shaft?

  1. The combustor liner
  2. The turbine rotor Correct answer.
  3. The accessory gearbox
  4. The exhaust cone

Explanation

The turbine extracts energy from the hot gas and delivers it via the main shaft to the compressor, which is the only component it mechanically drives on a single-spool engine. The accessory gearbox is driven separately and the exhaust cone only shapes the exhaust flow.

Question 26Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the primary function of the compressor in a gas turbine engine?

  1. To extract work from the exhaust gas
  2. To cool the turbine blades
  3. To raise the pressure of the air before combustion Correct answer.
  4. To add fuel and ignite the mixture

Explanation

The compressor's job is to increase the pressure of the incoming air so that combustion occurs at high pressure, which improves thermal efficiency. Fuel addition, work extraction and blade cooling are handled by other modules.

Question 27Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Which component converts the high-pressure, high-temperature gas into shaft work?

  1. The inlet guide vanes
  2. The combustion chamber
  3. The diffuser
  4. The turbine Correct answer.

Explanation

The turbine expands the hot gas and extracts energy to drive the compressor and accessories. The diffuser slows air to raise static pressure, inlet guide vanes direct flow, and the combustor adds heat rather than extracting work.

Question 28Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

In an axial compressor, what is the purpose of the stator vanes located between rotor stages?

  1. To diffuse the air and redirect it into the next rotor stage Correct answer.
  2. To support the turbine discs
  3. To add heat to the airflow
  4. To accelerate the air to supersonic speed

Explanation

Stator vanes act as diffusers, converting the velocity imparted by the rotor into static pressure and turning the flow to the correct angle for the following rotor row. They do not add heat or drive the turbine.

Question 29Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Why are multiple compressor stages used rather than a single stage?

  1. A single stage cannot achieve the required overall pressure ratio efficiently Correct answer.
  2. Multiple stages eliminate the need for a combustor
  3. A single stage would exceed the turbine temperature limit
  4. Multiple stages reduce the number of bearings needed

Explanation

Each compressor stage can only raise pressure by a limited ratio before flow separation occurs, so many stages are stacked to reach the high overall pressure ratio needed for efficiency. Bearing count and combustor function are unrelated to stage count.

Question 30Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the main advantage of a centrifugal compressor over an axial compressor for a small engine?

  1. It has a higher mass flow capacity for its frontal area
  2. It produces a high pressure rise per stage in a short, robust package Correct answer.
  3. It eliminates the need for a turbine
  4. It requires no diffuser

Explanation

A centrifugal impeller can achieve a large pressure rise in a single stage and is mechanically simple and resistant to foreign object damage, which suits small engines. Axial compressors handle higher mass flows per frontal area and still need diffusion of the flow.

Question 31Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the primary purpose of the combustion chamber in a gas turbine engine?

  1. To cool the turbine inlet gas
  2. To drive the compressor directly
  3. To raise the pressure of the air to its maximum
  4. To add heat energy to the air at constant pressure Correct answer.

Explanation

The combustor burns fuel to raise the total temperature of the gas while pressure stays roughly constant. Pressure rise is the compressor's role, cooling is done by bleed air, and the turbine drives the compressor.

Question 32Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

In an annular combustion chamber, what is the function of the primary zone?

  1. To measure fuel flow
  2. To dilute the gas to a uniform turbine inlet temperature
  3. To provide a stable, recirculating flame for initial combustion Correct answer.
  4. To cool the chamber walls

Explanation

The primary zone creates a recirculation of hot gas that anchors a stable flame, allowing efficient burning of the fuel-air mixture. Dilution and wall cooling occur in the secondary and dilution zones, and fuel flow is measured by the fuel system.

Question 33Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the purpose of the dilution holes in a combustion chamber liner?

  1. To ignite the fuel-air mixture
  2. To reduce the gas temperature to a level the turbine can tolerate Correct answer.
  3. To increase the pressure of the gas before the turbine
  4. To support the flame tube

Explanation

Dilution air lowers the peak gas temperature and evens out the temperature profile before the gas reaches the turbine. It does not raise pressure, ignite the mixture, or provide structural support.

Question 34Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Why is a diffuser fitted at the outlet of the compressor before the combustion chamber?

  1. To cool the compressor blades
  2. To reduce the air velocity so combustion can be stable Correct answer.
  3. To filter debris from the air
  4. To increase the air velocity into the combustor

Explanation

The diffuser slows the high-velocity compressor discharge air, raising static pressure and giving the low-speed flow needed for a stable flame. Filters are fitted at the inlet, and the diffuser does not cool compressor blades.

Question 35Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the function of the turbine nozzle guide vanes?

  1. To cool the compressor
  2. To diffuse the gas and raise its static pressure
  3. To drive the accessory gearbox
  4. To accelerate and direct the gas onto the turbine rotor blades Correct answer.

Explanation

Nozzle guide vanes form the turbine inlet and turn and accelerate the hot gas to the correct angle and velocity for the rotor blades. They do not raise static pressure, cool the compressor, or drive accessories.

Question 36Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Why are turbine blades often manufactured with internal cooling passages?

  1. To eliminate the need for a turbine casing
  2. To increase the pressure ratio of the compressor
  3. To allow operation at gas temperatures above the blade material's melting point Correct answer.
  4. To reduce the weight of the rotor to zero

Explanation

Cooling air bled from the compressor flows through internal passages and film-cooling holes, letting the turbine survive gas temperatures higher than the blade alloy could otherwise withstand. It does not affect compressor pressure ratio or remove the need for a casing.

Question 37Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Which type of bearing is normally used to carry the high axial loads from the compressor and turbine rotors?

  1. A plain journal bearing only
  2. A ball or roller thrust bearing Correct answer.
  3. A spline coupling
  4. A carbon seal

Explanation

Rolling-element thrust bearings, usually ball bearings, take the axial loads while journal bearings take radial loads. Seals and splines transmit or seal but do not carry thrust loads.

Question 38Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the purpose of the squeeze-film damper often fitted around a main engine bearing?

  1. To cool the bearing by forced convection
  2. To carry the axial thrust of the rotor
  3. To increase oil pressure to the bearing
  4. To damp rotor vibration and reduce loads transmitted to the casing Correct answer.

Explanation

A squeeze-film damper uses a thin oil film in a controlled clearance to absorb rotor whirl and reduce vibration transmitted to the engine structure. It does not primarily increase oil pressure, cool the bearing, or take thrust loads.

Question 39Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

In a twin-spool engine, what connects the high-pressure turbine to the high-pressure compressor?

  1. The intermediate casing
  2. The accessory gearbox
  3. The HP shaft Correct answer.
  4. The LP shaft

Explanation

The HP turbine drives the HP compressor through the HP shaft, while the LP turbine drives the LP compressor or fan through the LP shaft. The gearbox and casings do not transmit power between spools.

Question 40Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Why is the LP shaft usually routed inside the HP shaft in a twin-spool engine?

  1. To allow the LP shaft to drive the accessory gearbox
  2. To increase the LP shaft's torque capacity
  3. To reduce the number of bearings to one
  4. To keep both spools concentric and minimise engine length Correct answer.

Explanation

Concentric shafts let the two spools rotate independently within the same engine centreline, keeping the engine short and light. Routing the LP shaft inside does not increase its torque capacity or reduce bearing count to one.

Question 41Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the primary role of the engine casings?

  1. To generate thrust directly
  2. To meter fuel to the nozzles
  3. To contain the gas path and carry structural loads between modules Correct answer.
  4. To cool the combustor

Explanation

Casings define the gas path, contain the air and gas, and carry loads to the engine mounts. Thrust is generated by accelerating the gas, not by the casing, and fuel metering is a fuel system function.

Question 42Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the function of the fan containment casing on a turbofan engine?

  1. To support the LP turbine
  2. To increase the bypass ratio
  3. To cool the HP compressor
  4. To retain a released fan blade and prevent it penetrating the fuselage Correct answer.

Explanation

The containment casing is designed to absorb the energy of a released fan blade and keep it within the engine. Bypass ratio is set by fan and duct design, and the LP turbine is supported by its own bearings and casings.

Question 43Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What does the term 'overall pressure ratio' of a gas turbine engine describe?

  1. The ratio of compressor delivery pressure to compressor inlet pressure Correct answer.
  2. The ratio of fuel flow to air flow
  3. The ratio of turbine inlet pressure to exhaust pressure
  4. The ratio of bypass flow to core flow

Explanation

Overall pressure ratio is measured across the compressor, from inlet to delivery pressure, and is a key indicator of cycle efficiency. Bypass ratio and fuel-air ratio are different parameters, and turbine pressure ratio is measured separately.

Question 44Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

How is a turbine blade root usually attached to the turbine disc?

  1. By a spline on the disc face
  2. By a single central bolt
  3. By a fir-tree root seated in a matching disc slot Correct answer.
  4. By welding to the disc rim

Explanation

Fir-tree roots spread the centrifugal load into the disc and allow blade replacement and thermal growth. Welding would prevent maintenance, and a central bolt or face spline would not carry the blade centrifugal load.

Question 45Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is the purpose of the labyrinth seals between compressor stages and at the shaft ends?

  1. To limit internal air leakage between regions of different pressure Correct answer.
  2. To carry the axial thrust of the rotor
  3. To reduce the compressor pressure ratio
  4. To filter oil from the air

Explanation

Labyrinth seals create a tortuous path that restricts leakage between zones of differing pressure. They do not carry thrust, filter oil, or change the compressor pressure ratio.

Question 46Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is surge in an axial compressor?

  1. A gradual loss of oil pressure
  2. A complete breakdown of flow through the compressor with a rapid pressure rise upstream Correct answer.
  3. A controlled increase in fuel flow
  4. A steady increase in compressor efficiency

Explanation

Surge is a violent instability where the compressor flow reverses momentarily, causing loud bangs and pressure fluctuations that can damage the engine. It is not an efficiency gain, an oil pressure fault, or a fuel scheduling event.

Question 47Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

What is rotating stall in an axial compressor?

  1. A local stall cell that travels around the annulus from blade to blade Correct answer.
  2. A stall of the turbine rotor
  3. A stall of the whole compressor simultaneously
  4. A stall of the accessory gearbox

Explanation

Rotating stall is a localised region of separated flow that propagates around the compressor annulus at a fraction of rotor speed. Full-annulus breakdown is surge, and the turbine and gearbox are not the subject of compressor stall.

Question 48Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Why are variable inlet guide vanes used on some axial compressors?

  1. To adjust the flow angle and improve stall margin at low speeds Correct answer.
  2. To drive the accessory gearbox
  3. To increase the maximum turbine temperature
  4. To reduce the number of compressor stages to one

Explanation

Variable inlet guide vanes change the incidence onto the first rotor stages, improving stall margin and efficiency at part-speed conditions. They do not affect turbine temperature limits or drive accessories.

Question 49Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

Which statement best describes the function of the intermediate casing in a twin-spool engine?

  1. It houses bearings and seals and carries loads between the compressor and turbine sections Correct answer.
  2. It supports the fan blades at their tips
  3. It meters fuel flow to the combustor
  4. It mixes bypass and core flow before the exhaust

Explanation

The intermediate casing is a structural module that contains bearings and seals and transmits loads between the compressor and turbine sections. Flow mixing occurs in the exhaust, fan blade tips run in the fan casing, and fuel metering is a fuel system function.

Question 50Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings

In a can-annular combustion chamber, how are the individual flame tubes arranged relative to the engine centreline?

  1. They are mounted around the engine centreline in a circular array. Correct answer.
  2. They are stacked in a single axial row along the top of the engine.
  3. They are arranged in a spiral around the turbine casing.
  4. They are grouped in pairs on opposite sides of the accessory gearbox.

Explanation

A can-annular (or cannular) combustor uses several cylindrical flame tubes spaced evenly around the engine axis, each with its own liner and fuel nozzle. The tubes are enclosed within a common outer casing, combining features of the can and annular types. This arrangement allows individual cans to be removed for maintenance while sharing a common air supply.