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Question 1Airframes, Structures and Aircraft Systems

Under the applicable airworthiness design requirements, the ultimate load factor used for aircraft structural design is obtained by multiplying the limit load factor by:

  1. 1.5 Correct answer.
  2. 1.15
  3. 2.0
  4. 2.5

Explanation

Airworthiness codes such as CS-23 and CS-25 define limit loads as the maximum loads expected in service, which the structure must sustain without detrimental permanent deformation. Ultimate load is 1.5 times the limit load, and the structure must withstand it for at least three seconds without failure. The design ultimate load factor is therefore 1.5 times the limit load factor.

Question 2Airframes, Structures and Aircraft Systems

In a semi-monocoque fuselage, the frames (formers) primarily:

  1. provide the principal path for fuselage shear loads
  2. react the wing bending moments into the centre section
  3. carry the axial bending loads of the fuselage shell
  4. maintain the cross-sectional shape and carry concentrated local loads Correct answer.

Explanation

In semi-monocoque construction the skin and stringers form the primary load path and carry shear, bending and pressurisation loads. The frames maintain the cross-sectional shape, support the stringers against buckling and carry concentrated loads such as floor beams and attachment fittings. They are therefore shaping and local-load members rather than the main bending path.

Question 3Airframes, Structures and Aircraft Systems

Pneumatic de-icing boots fitted to a wing leading edge remove ice by:

  1. bleeding hot engine air over the skin surface
  2. cyclically inflating to crack and shed the accumulated ice Correct answer.
  3. supplying a continuous film of anti-icing fluid
  4. heating the leading edge with electrical resistance mats

Explanation

Pneumatic boots are inflated cyclically by engine bleed air or a pump, and the resulting change in profile cracks the ice layer so that aerodynamic forces shed it. They are a de-icing rather than an anti-icing system, so some ice is allowed to form between inflation cycles. Operation is normally timed by a cycling valve or timer.

Question 4Airframes, Structures and Aircraft Systems

The primary function of a hydraulic accumulator in an aircraft hydraulic system is to:

  1. filter contaminants from the fluid before it reaches the actuators
  2. raise the nominal system pressure to the relief-valve setting
  3. store fluid under pressure to meet peak demands and damp surges Correct answer.
  4. cool the fluid returning from the actuators before it enters the reservoir

Explanation

The accumulator contains a gas charge separated from the hydraulic fluid by a piston or bladder. It stores energy so that short-term peak flow demands are met without an excessive pressure drop, damps pressure pulses from pumps and valves, and provides a limited fluid supply if the pump fails. It does not itself generate or regulate system pressure.

Question 5Airframes, Structures and Aircraft Systems

The shimmy damper fitted to a nose landing gear is intended to:

  1. damp nose-wheel steering inputs made by the pilot
  2. absorb the vertical landing loads before the oleo closes
  3. suppress oscillations of the nose wheel about its steering axis Correct answer.
  4. prevent the nose wheel from casting during retraction

Explanation

Shimmy is a self-excited oscillation of the wheel about the steering axis, driven by tyre scrub interacting with landing-gear flexibility. The shimmy damper introduces hydraulic or friction damping at the steering collar to suppress that oscillation and keep the wheel stable during take-off and landing runs. It should not restrict normal steering inputs from the pilot.

Question 6Airframes, Structures and Aircraft Systems

In a pressurised aircraft, the cabin outflow valve controls cabin pressure by:

  1. controlling the speed of the cabin recirculation fan
  2. regulating the bleed air entering the cabin
  3. metering the rate at which air leaves the cabin Correct answer.
  4. dumping excess pressure through the negative relief valve

Explanation

In most transport aircraft the inflow of conditioned bleed air is controlled only loosely, and cabin pressure is regulated by the outflow valve. By opening or closing the valve the pressure controller meters the mass of air leaving the cabin, and hence sets the cabin altitude and the rate of change. Closing the valve increases cabin pressure; opening it reduces it.

Question 7Airframes, Structures and Aircraft Systems

Fuel tanks on a transport aircraft are vented primarily to:

  1. provide a path for fuel to transfer between tanks during cross-feed
  2. keep the tank at approximately ambient pressure as fuel is burned or added Correct answer.
  3. allow vapour to escape so the tank cannot over-pressurise during refuelling only
  4. supply air to the fuel pumps so that fuel can be delivered under pressure

Explanation

Venting keeps the tank close to ambient pressure as fuel is burned and during refuelling or defuelling, so the structure is not loaded by differential pressure and the pumps can feed continuously. Air is allowed in as fuel is used, preventing a vacuum that would stop fuel flow. The vent therefore works in both directions.

Question 8Airframes, Structures and Aircraft Systems

In a typical aircraft DC generating system, the generator control unit (GCU):

  1. regulates field excitation and protects the bus from generator faults Correct answer.
  2. limits the current drawn by each individual DC load circuit
  3. rectifies the AC output of the generator to supply the DC bus
  4. selects which generator supplies the essential bus automatically

Explanation

The GCU controls generator field current so that bus voltage stays within limits, and it monitors the generator for over-voltage, under-voltage, over-frequency and over-current conditions. On sensing a fault it trips the generator contactor and illuminates the appropriate warning, protecting the bus. Voltage regulation and protection are therefore combined in the same unit.

Question 9Airframes, Structures and Aircraft Systems

Ailerons are frequently rigged with differential deflection, in which the up-going aileron travels further than the down-going one, in order to:

  1. prevent the wing from exceeding its limit load factor during a roll
  2. increase the total roll rate at low speed without raising wing loading
  3. compensate for aileron float caused by aerodynamic hinge moments
  4. reduce the adverse yaw produced by the higher-drag down-going aileron Correct answer.

Explanation

When the ailerons are deflected, the down-going aileron produces more lift but also more induced drag on the outer wing, which yaws the aircraft away from the intended turn, an effect known as adverse yaw. Rigging the up-going aileron to travel further reduces the effective lift and drag of the down-going side and helps balance that yaw. Less rudder input is then needed to coordinate the turn.

Question 10Airframes, Structures and Aircraft Systems

In a wing torsion box, the spar flanges and the spar web respectively carry:

  1. bending loads and shear loads Correct answer.
  2. shear loads and torsional loads
  3. shear loads and bending loads
  4. torsional loads and bending loads

Explanation

The spar flanges are the top and bottom booms of the spar and carry the bending moments as tension and compression, because they lie farthest from the neutral axis. The spar web connects the flanges and carries the shear force, reacting it as a shear flow between the booms. In a closed torsion box the skin panels carry most of the torsion.

Question 11Airframes, Structures and Aircraft Systems

In a conventional semi-monocoque wing, the primary purpose of the wing ribs is to:

  1. Provide a fuel-tight boundary within the integral tank
  2. Transmit engine thrust to the wing spar
  3. Carry the bending loads along the span to the wing root
  4. Maintain the aerofoil contour and support the skin panels Correct answer.

Explanation

Wing ribs define the aerofoil section, support the skin and stringers, and transfer local aerodynamic loads to the spars. Bending loads along the span are carried mainly by the spar flanges, not by the ribs.

Question 12Airframes, Structures and Aircraft Systems

The torque links (scissors) fitted to an oleo-pneumatic nose landing gear strut mainly:

  1. Provide steering actuation through the rudder pedals
  2. Dampen shimmy oscillations during taxi
  3. Transmit the vertical landing loads from the wheel into the airframe structure
  4. Keep the piston aligned and stop wheel rotation about the strut axis Correct answer.

Explanation

Torque links connect the lower piston to the fixed cylinder and allow the strut to compress while preventing the piston from rotating. This keeps the wheel assembly correctly aligned with the aircraft centreline during taxi and landing.

Question 13Airframes, Structures and Aircraft Systems

In an aircraft hydraulic system, the pressure relief valve is fitted to:

  1. Limit system pressure by returning excess fluid to the reservoir Correct answer.
  2. Stop the engine-driven pump from cavitating at high altitude
  3. Direct fluid to the standby system when main system pressure falls
  4. Maintain a constant pump output flow regardless of the hydraulic demand

Explanation

A pressure relief valve opens at a preset pressure and returns excess fluid to the reservoir, protecting pumps, seals and lines from overpressure. It is a safety device and does not normally regulate system flow or select the standby supply.

Question 14Airframes, Structures and Aircraft Systems

Ground spoilers are deployed immediately after touchdown primarily to:

  1. Provide a nose-down pitching moment to keep the nosewheel on the ground
  2. Dump lift and increase the load on the main wheels, improving braking effectiveness Correct answer.
  3. Reduce the aerodynamic drag so that the landing roll is shortened
  4. Increase the lift coefficient so that the aircraft settles gently on the runway

Explanation

Ground spoilers destroy a large part of the wing lift after touchdown, which increases the weight on the wheels and allows the brakes to be applied more effectively. They also add drag, but their main landing-roll benefit is the increase in wheel loading.

Question 15Airframes, Structures and Aircraft Systems

A balance tab on an aircraft control surface is designed to:

  1. Move in the same direction as the control surface and increase the aerodynamic damping
  2. Move opposite to the control surface and reduce the force needed to hold the deflection Correct answer.
  3. Trim the aircraft in pitch by adjusting the neutral position of the elevator with a screw jack
  4. Prevent flutter by locking the control surface at high airspeed

Explanation

A balance tab is linked so that it deflects opposite to the control surface, creating an aerodynamic moment that assists the pilot's input and reduces stick force. A trim tab adjusts the neutral setting, while an anti-balance tab moves in the same direction to increase feel.

Question 16Airframes, Structures and Aircraft Systems

The yaw damper fitted to a transport aircraft is primarily intended to:

  1. Suppress Dutch roll by automatic rudder inputs opposing the yaw rate Correct answer.
  2. Increase the available rudder authority during a single-engine go-around at high altitude
  3. Limit rudder deflection at high airspeed to prevent structural overload of the fin
  4. Hold the aircraft on the runway centreline during the take-off roll in a crosswind

Explanation

Dutch roll is a coupled rolling and yawing oscillation, and the yaw damper senses yaw rate and commands small rudder movements to oppose it. This improves ride comfort and reduces the workload on the human pilot.

Question 17Airframes, Structures and Aircraft Systems

In a pressurised aircraft, the negative pressure relief valve protects the fuselage structure by:

  1. Preventing the external pressure from exceeding the cabin pressure by a safe margin Correct answer.
  2. Opening to supply additional bleed air when cabin pressure falls below schedule
  3. Closing the outflow valve automatically when the positive differential pressure reaches its maximum limit
  4. Venting cabin air overboard when the cabin altitude exceeds 10,000 ft

Explanation

The negative pressure relief valve opens when external pressure is higher than cabin pressure, preventing the fuselage from being loaded in the reverse direction. Positive differential pressure is controlled by the outflow valve, not by the negative relief valve.

Question 18Airframes, Structures and Aircraft Systems

A fuel boost pump installed in an aircraft fuel tank is normally used to:

  1. Supply fuel to the engine-driven pump at positive pressure and prevent vapour lock Correct answer.
  2. Jettison fuel overboard in an emergency
  3. Measure the quantity of fuel remaining in the tank by sensing the pump delivery pressure
  4. Transfer fuel from the outer wing tanks to the centre tank during cruise

Explanation

The boost pump provides a positive fuel pressure at the inlet of the engine-driven pump, which helps prevent cavitation and vapour lock at high altitude or high fuel temperature. It is not used for measuring quantity or for normal fuel jettison.

Question 19Airframes, Structures and Aircraft Systems

In a cylindrical pressurised fuselage, the hoop stress in the skin caused by cabin differential pressure is:

  1. Approximately twice the longitudinal stress Correct answer.
  2. Approximately equal to the longitudinal stress
  3. Independent of the fuselage diameter
  4. Approximately half the longitudinal stress

Explanation

For a thin-walled cylinder, hoop stress is pd/2t and longitudinal stress is pd/4t, so the hoop stress is twice the longitudinal stress. Hoop stress therefore generally drives the skin thickness and joint design in a pressurised fuselage.

Question 20Airframes, Structures and Aircraft Systems

In fail-safe structural design philosophy, a structure is designed so that:

  1. The component is retired from service after a fixed number of flight hours regardless of condition
  2. Cracks are prevented from initiating by keeping stresses below the fatigue limit indefinitely
  3. All principal load paths are made from a single material with a known safe life
  4. Failure of one load path is detected before residual strength falls below the required level Correct answer.

Explanation

Fail-safe design provides multiple load paths or crack-stopping features so that a crack or failure in one element is detected during inspection before the structure loses its required residual strength. Safe-life design, by contrast, retires a component after a fixed life.

Question 21Airframes, Structures and Aircraft Systems

In a truss-type fuselage, the primary flight and ground loads are carried mainly by:

  1. the cabin floor beams acting in torsion
  2. closely spaced frames acting in bending
  3. the outer skin acting in shear and hoop tension
  4. longitudinal members and diagonal struts acting in tension and compression Correct answer.

Explanation

A truss fuselage is a triangulated framework of tubes or members; axial tension and compression in these members carry the loads, while the fabric or light skin is largely non-structural fairing. This is why truss structures are common on light aircraft but less efficient for pressurised fuselages.

Question 22Airframes, Structures and Aircraft Systems

Static dischargers fitted to the trailing edges of an aircraft's wings and tail surfaces are intended to:

  1. increase the radar cross-section for identification
  2. warn the crew of St Elmo's fire
  3. dissipate precipitation static by providing a controlled discharge path Correct answer.
  4. add trailing-edge mass to reduce flutter

Explanation

Static dischargers provide a sharp point from which accumulated static charge can bleed into the atmosphere, reducing radio interference caused by precipitation static. They do not eliminate lightning strikes or add structural damping.

Question 23Airframes, Structures and Aircraft Systems

In an aircraft pneumatic bleed-air system, the purpose of a check valve is to:

  1. cool the bleed air before it reaches the manifold
  2. regulate the bleed-air pressure to a constant value
  3. shut off bleed air in the event of an overheat
  4. allow flow in one direction while preventing reverse flow Correct answer.

Explanation

A check valve is a one-way valve; it permits bleed air to flow toward the consumer and blocks reverse flow when upstream pressure falls. Pressure regulation and overheat shutoff are performed by other components such as regulators and shutoff valves.

Question 24Airframes, Structures and Aircraft Systems

In a fuel system, a fuel/oil heat exchanger is normally used to:

  1. increase the fuel's octane rating before combustion
  2. warm the fuel to prevent ice blockage while cooling the engine oil Correct answer.
  3. cool the fuel before it enters the engine fuel control unit
  4. separate water from the fuel by centrifugal action

Explanation

The fuel/oil heat exchanger transfers heat from hot engine oil to the colder fuel, which cools the oil and warms the fuel sufficiently to prevent ice crystals from blocking fuel filters. It does not chemically alter the fuel or act as a water separator.

Question 25Airframes, Structures and Aircraft Systems

An artificial feel unit is required in a hydraulically powered flight control system because:

  1. the hydraulic actuators cannot move the control surface without it
  2. the pilot would otherwise receive no natural aerodynamic feedback proportional to speed Correct answer.
  3. it prevents the control surface from reaching full deflection
  4. it trims the aircraft without moving the control column

Explanation

In a fully powered system the pilot's control input is not directly connected to aerodynamic hinge moment, so an artificial feel unit generates a resisting force that increases with airspeed and control deflection. This restores a conventional control feel and helps prevent overstressing the structure.

Question 26Airframes, Structures and Aircraft Systems

In a pressurised aircraft, the cabin pressure controller schedules cabin altitude primarily as a function of:

  1. the outside air temperature only
  2. the engine bleed-air temperature
  3. aircraft altitude, with a selected cabin altitude schedule and differential pressure limit Correct answer.
  4. the number of passengers on board

Explanation

The controller compares selected cabin altitude and rate with actual aircraft altitude and modulates the outflow valve to follow a schedule while respecting the maximum differential pressure. Passenger load and bleed temperature do not define the cabin altitude schedule.

Question 27Airframes, Structures and Aircraft Systems

In a typical DC generating system, the reverse current cut-out protects the system by:

  1. limiting generator output current to a safe value
  2. disconnecting the generator when its voltage exceeds the bus voltage
  3. opening the generator field circuit when current flows from the battery into the generator Correct answer.
  4. preventing the generator from over-speeding

Explanation

If generator voltage falls below battery voltage, current would flow from the battery back through the generator; the reverse current cut-out senses this reverse flow and opens the generator contactor. Overcurrent protection and voltage regulation are separate functions.

Question 28Airframes, Structures and Aircraft Systems

In the upper skin of a semi-monocoque wing, stringers are provided mainly to:

  1. provide attachment points for the wing ribs only
  2. carry the torsional shear between the front and rear spars
  3. stabilise the skin against buckling and carry part of the spanwise bending load Correct answer.
  4. support the leading-edge de-icing system

Explanation

Stringers run spanwise and stiffen the wing skin, raising its buckling resistance in compression and contributing to bending strength. Torsional shear is carried mainly by the skin and spar webs, not by the stringers alone.

Question 29Airframes, Structures and Aircraft Systems

In a wing spar, vertical stiffeners attached to the web are primarily intended to:

  1. prevent buckling of the web under shear loading Correct answer.
  2. increase the bending strength of the spar flanges
  3. provide a path for lightning current
  4. carry the fuel load in an integral tank

Explanation

A thin spar web can buckle under shear; vertical stiffeners divide the web into smaller panels and raise its critical buckling load. They do not significantly increase flange bending strength or carry fuel loads.

Question 30Airframes, Structures and Aircraft Systems

In a landing gear oleo-pneumatic strut, the recoil valve is fitted to:

  1. prevent the strut from extending after the aircraft becomes airborne
  2. lock the strut in the compressed position during taxiing
  3. meter the flow of hydraulic fluid equally in compression and extension
  4. allow the strut to extend freely while restricting the rate of rebound Correct answer.

Explanation

The recoil valve is a one-way restrictor arrangement that permits relatively free extension of the oleo strut but restricts the rebound flow, so the strut does not top out violently after compression. Compression damping is handled by the main metering orifice.

Question 31Airframes, Structures and Aircraft Systems

The shimmy damper fitted to an aircraft nose landing gear is primarily intended to:

  1. hold the nose gear in the retracted position after gear selection
  2. absorb vertical landing loads before the oleo strut operates
  3. damp oscillation of the nose wheel about its steering axis Correct answer.
  4. prevent the nose wheel from touching down before the main wheels

Explanation

Shimmy is a self-excited oscillation of a castoring or steerable nose wheel about its steering axis. The damper adds hydraulic resistance to that motion, so the oscillation dies out instead of building up; it does not carry vertical landing loads.

Question 32Airframes, Structures and Aircraft Systems

In an aircraft hydraulic system, the accumulator is normally provided to:

  1. remove air and solid contamination from the hydraulic fluid before it reaches the actuators
  2. increase the system operating pressure above the setting of the pump relief valve
  3. automatically select the alternate hydraulic system after a pump failure has occurred
  4. store fluid under pressure to meet peak demands and supply limited emergency operation Correct answer.

Explanation

The accumulator contains fluid under gas pressure and acts as a hydraulic spring. It supplies extra flow during high transient demand, damps pressure pulses, and gives a limited emergency supply if the pump fails.

Question 33Airframes, Structures and Aircraft Systems

Differential aileron movement, in which the up-going aileron deflects through a larger angle than the down-going aileron, is used mainly to:

  1. prevent the wing from stalling when a large aileron input is applied
  2. provide artificial feel that increases progressively with indicated airspeed
  3. reduce adverse yaw by decreasing drag on the down-going aileron's wing Correct answer.
  4. increase the maximum rate of roll achieved at high indicated airspeed

Explanation

The down-going aileron increases lift but also increases induced drag on that wing, producing adverse yaw. Rigging it to move through a smaller angle than the up-going aileron reduces that drag and the yaw, improving co-ordinated roll.

Question 34Airframes, Structures and Aircraft Systems

In a pressurised aircraft, the cabin outflow valve regulates cabin pressure by:

  1. opening only when cabin differential pressure exceeds the positive relief valve setting
  2. modulating the rate at which air escapes from the cabin to atmosphere Correct answer.
  3. controlling the flow of conditioned air entering the cabin from the bleed-air system
  4. dumping cabin air overboard when the cabin altitude warning operates

Explanation

The outflow valve is the controlled exit for cabin air. The pressure controller positions it to regulate the discharge rate, thereby scheduling cabin altitude and differential pressure; inflow is set by the bleed-air supply.

Question 35Airframes, Structures and Aircraft Systems

The vent system fitted to an aircraft fuel tank is required to:

  1. maintain near-ambient pressure inside the tank during refuelling, climb and descent Correct answer.
  2. allow fuel vapour to drain overboard during normal pressurised flight at altitude
  3. prevent fuel from flowing to the engine if the engine-driven boost pump fails
  4. indicate the quantity of fuel remaining in the tank to the flight deck

Explanation

Fuel tanks are vented so that the pressure above the fuel stays close to ambient. This prevents overpressure during refuelling and prevents negative pressure or cavitation during climb and descent as fuel is consumed.

Question 36Airframes, Structures and Aircraft Systems

The upper and lower caps (booms) of a wing spar are designed primarily to carry:

  1. shear loads from the wing skin panels
  2. bending moments in tension and compression Correct answer.
  3. concentrated loads from the engine attachment fittings
  4. torsional loads produced by aileron deflection

Explanation

The spar caps are placed at the top and bottom of the spar, far from the neutral axis. Bending of the wing puts one cap in tension and the other in compression, so they are sized mainly for bending moment.

Question 37Airframes, Structures and Aircraft Systems

Pneumatic de-ice boots fitted to a wing leading edge remove accumulated ice by:

  1. heating the leading edge with bleed air to melt the accumulated ice
  2. inflating and deflating to crack and shed the ice layer Correct answer.
  3. reducing the local air pressure so that the ice sublimates directly
  4. spraying de-icing fluid through small holes in the boot surface

Explanation

Pneumatic boots are inflated by engine bleed air or a pump and then deflated. The inflation cracks the ice layer and the airflow sheds it; the boots are cyclic de-icing devices, not continuous anti-icing.

Question 38Airframes, Structures and Aircraft Systems

An aircraft anti-skid braking system controls brake pressure in order to:

  1. prevent the brakes from being applied until the nose wheel is on the ground
  2. apply full braking immediately after touchdown regardless of runway condition
  3. maintain a constant brake torque at all ground speeds after touchdown
  4. limit wheel slip so that the tyre retains grip and does not lock Correct answer.

Explanation

Anti-skid senses wheel speed and releases brake pressure when a wheel approaches lock. This keeps tyre slip near the value that gives maximum braking friction and preserves directional control on slippery runways.

Question 39Airframes, Structures and Aircraft Systems

In a damage-tolerant aircraft structure, the design philosophy requires that:

  1. cracks are detectable and the remaining structure can carry design loads until repair Correct answer.
  2. the structure must be proof-tested to ultimate load after every flight
  3. the structure is designed so that a single failure cannot reduce its ultimate strength
  4. all structural components are replaced at fixed intervals before any crack can initiate

Explanation

Damage tolerance assumes that cracks can exist and uses fracture mechanics and inspection to manage them. The structure must retain the required residual strength with a detectable crack until it is found and repaired.

Question 40Airframes, Structures and Aircraft Systems

A hydraulic fuse installed in an aircraft hydraulic system is intended to:

  1. isolate the system pump when the fluid temperature exceeds a set limit
  2. stop the loss of hydraulic fluid if a downstream line ruptures Correct answer.
  3. filter fine particles from the fluid before it reaches the actuator
  4. relieve excessive pressure by returning fluid to the reservoir

Explanation

A hydraulic fuse senses flow and closes when flow exceeds a set value, as happens if a downstream line ruptures. It confines the leak and preserves fluid for the rest of the system; some types reset when pressure equalises.

Question 41Aircraft Engines and Propellers

In a normally aspirated four-stroke aircraft piston engine, which sequence correctly describes the order of the operating strokes?

  1. Compression, induction, power, exhaust
  2. Induction, compression, exhaust, power
  3. Induction, power, compression, exhaust
  4. Induction, compression, power, exhaust Correct answer.

Explanation

The four-stroke cycle always follows the order induction, compression, power and exhaust. The intake valve opens during induction, both valves are closed for compression and power, and the exhaust valve opens for the exhaust stroke. Reversing compression and power would make the engine unable to produce useful work.

Question 42Aircraft Engines and Propellers

What is the primary function of a magneto in an aircraft piston engine ignition system?

  1. It regulates the charging current supplied to the battery.
  2. It provides low-tension current to the starter motor.
  3. It reduces battery voltage before it reaches the spark plugs.
  4. It generates the spark voltage independently of the aircraft battery. Correct answer.

Explanation

A magneto is a self-contained generator that produces high-tension voltage for the spark plugs as soon as the engine turns. Because it does not rely on the aircraft battery, ignition continues even if the electrical system fails. This independence is the reason magnetos are used instead of a battery-fed coil ignition.

Question 43Aircraft Engines and Propellers

In propeller terminology, geometric pitch is best described as which quantity?

  1. The angle between the blade chord and the plane of rotation.
  2. The theoretical forward distance advanced per revolution. Correct answer.
  3. The forward distance travelled by the aircraft per second.
  4. The actual forward distance travelled per revolution.

Explanation

Geometric pitch is the distance the propeller would advance in one revolution if it screwed through a solid medium without slip. It is a design property of the blade angle and radius. Effective pitch is the actual forward distance covered, which is smaller because of slip.

Question 44Aircraft Engines and Propellers

Carburettor icing is most likely to occur under which combination of conditions?

  1. High-power cruise with very low humidity
  2. Low-power descent in warm, humid air Correct answer.
  3. High-power climb in cold, dry air
  4. Take-off at full throttle in freezing rain

Explanation

Carburettor icing results from cooling caused by fuel vaporisation and the pressure drop in the venturi. Low power settings reduce the heat available from the engine to counteract this cooling, and humid air provides the moisture that freezes. Descent at reduced power in humid air is therefore a classic icing situation.

Question 45Aircraft Engines and Propellers

In a constant-speed propeller system, what does the governor do when engine RPM tends to rise above the selected value?

  1. It feathers the propeller to limit RPM.
  2. It decreases blade pitch to reduce the load on the engine.
  3. It opens the wastegate to reduce manifold pressure.
  4. It increases blade pitch so the propeller absorbs more power. Correct answer.

Explanation

The governor senses an overspeed condition and directs oil pressure to increase blade pitch. A larger blade angle increases the aerodynamic load on the propeller, which absorbs more power and brings RPM back to the selected value. Decreasing pitch would reduce the load and allow RPM to rise further.

Question 46Aircraft Engines and Propellers

For obtaining maximum power from a piston engine at a given altitude, the fuel-air mixture should normally be set to which condition?

  1. Fully rich regardless of altitude
  2. Lean of peak exhaust gas temperature
  3. Exactly at peak exhaust gas temperature
  4. Slightly rich of peak exhaust gas temperature Correct answer.

Explanation

Best-power mixture is reached slightly rich of peak EGT, typically about 100 to 150 degrees Fahrenheit rich of peak on the exhaust gas temperature gauge. This setting provides a little excess fuel for cooling and ensures all available oxygen is consumed. Leaning further toward or beyond peak reduces power and raises cylinder temperatures.

Question 47Aircraft Engines and Propellers

Which set of operating conditions most strongly promotes detonation in an aircraft piston engine?

  1. Rich mixture, low cylinder head temperature and retarded ignition timing
  2. High manifold pressure, high intake temperature and low fuel octane rating Correct answer.
  3. High RPM at low power with a lean mixture and cold cylinders
  4. Low manifold pressure, low intake temperature and high fuel octane rating

Explanation

Detonation occurs when the unburnt end gas ignites spontaneously ahead of the normal flame front. High manifold pressure and high intake temperature raise the pressure and temperature during compression, while a low octane fuel resists knock poorly. Together these conditions make uncontrolled secondary ignition much more likely.

Question 48Aircraft Engines and Propellers

In a turbojet engine, which event is most likely to trigger compressor surge?

  1. Steady operation at high RPM with a clean, undistorted intake
  2. An abrupt throttle movement that disturbs airflow through the compressor Correct answer.
  3. A gradual increase in turbine inlet temperature at constant RPM
  4. A decrease in exhaust gas temperature during cruise

Explanation

Compressor surge is a breakdown of smooth airflow through the compressor, often caused by a rapid throttle change or airflow distortion. Abrupt acceleration increases fuel flow and can raise pressure downstream faster than the compressor can deliver air, causing the flow to reverse momentarily. The result is the familiar bang and fluctuating RPM associated with a surge.

Question 49Aircraft Engines and Propellers

Why is valve overlap, in which the intake and exhaust valves are both open briefly around top dead centre, used in piston engines?

  1. To reduce the risk of detonation at high manifold pressure
  2. To allow the valves to cool between successive strokes
  3. To prevent exhaust gas from entering the intake at low RPM
  4. To improve scavenging and cylinder filling at high RPM Correct answer.

Explanation

During overlap the outgoing exhaust gases help draw fresh mixture into the cylinder, and the incoming charge helps push residual gases out. This scavenging effect improves volumetric efficiency, particularly at high RPM where gas inertia is greatest. At low RPM the effect is small, which is why overlap is matched to the engine's operating range.

Question 50Aircraft Engines and Propellers

For a fixed-pitch propeller turning at constant RPM, what happens to the blade angle of attack as true airspeed increases?

  1. It decreases, reducing thrust. Correct answer.
  2. It increases, producing more thrust.
  3. It becomes negative at all cruise speeds.
  4. It remains constant because RPM is constant.

Explanation

At constant RPM the propeller advances a fixed theoretical distance per revolution, but as true airspeed rises the aircraft moves forward faster. The relative airflow therefore meets the blade at a smaller angle, so the angle of attack decreases and thrust falls. This is why a fixed-pitch propeller is efficient only over a limited speed range.