I85PREP
⌘ K
EASA Part-66 Module12 helicopter systems foundations study materials
EASA Part-66 Module12 helicopter systems foundations study resources

EASA Part-66 Module12 helicopter systems foundations practice questions

One question at a time. Build your EASA Part-66 Module12 helicopter systems foundations understanding.

First 50 of 190 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 1Rotary-wing aerodynamic and hub principles

In forward flight, the advancing blade of a single main rotor travels faster through the air than the retreating blade, producing unequal lift across the rotor disc. What is this phenomenon called?

  1. Coriolis effect
  2. Translating tendency
  3. Dissymmetry of lift Correct answer.
  4. Gyroscopic precession

Explanation

Dissymmetry of lift is the unequal lift across the rotor disc in forward flight, caused by the advancing blade having a higher relative airspeed than the retreating blade. It is compensated by blade flapping (and cyclic feathering).

Question 2Rotary-wing aerodynamic and hub principles

A helicopter is established in a high descent rate at low forward airspeed with power applied, and the pilot reports rising sink rate, increasing vibration and reduced cyclic authority. The rotor is descending into its own downwash. Which condition is this?

  1. Retreating blade stall
  2. Vortex ring state Correct answer.
  3. Ground resonance
  4. Dynamic rollover

Explanation

Vortex ring state (settling with power) occurs at high rate of descent, low airspeed and with power applied, as the rotor recirculates its own downwash; symptoms include increasing sink rate, vibration and loss of cyclic authority. Recovery is forward cyclic or lowering collective to fly out of the recirculating air.

Question 3Rotary-wing aerodynamic and hub principles

As an articulated rotor blade flaps upward, its centre of mass moves closer to the axis of rotation. To conserve angular momentum the blade tends to accelerate. What is this effect, which is accommodated by the lead-lag (drag) hinge?

  1. Gyroscopic precession
  2. Coriolis effect Correct answer.
  3. Dissymmetry of lift
  4. Phase lag

Explanation

The Coriolis effect causes a flapping blade to speed up (lead) as its mass moves inboard and slow down (lag) as it moves outboard, conserving angular momentum. Articulated heads provide a lead-lag hinge and dampers to accommodate this.

Question 4Rotary-wing aerodynamic and hub principles

During autorotation following a power loss, what provides the energy to keep the main rotor turning?

  1. Residual torque stored in the freewheel unit
  2. Stored hydraulic accumulator pressure
  3. Upward airflow through the rotor disc as the helicopter descends Correct answer.
  4. Tail rotor windmilling driving the main gearbox

Explanation

In autorotation the freewheel unit disconnects the failed engine and the upflow of air through the descending rotor disc drives the blades, maintaining rotor RPM. The disc divides into driven, driving and stall regions along the span.

Question 5Rotary-wing aerodynamic and hub principles

A single main rotor helicopter tends to drift laterally in a stable hover because of the thrust produced by the tail rotor. What is this tendency, and how is it commonly corrected by the designer?

  1. Coning, corrected by increasing blade weight
  2. Translating tendency, corrected by rigging the rotor mast or controls to a slight lateral tilt Correct answer.
  3. Ground effect, corrected by raising the skids
  4. Phase lag, corrected by advancing the swashplate

Explanation

Translating tendency (tail rotor drift) is the sideways drift caused by tail rotor thrust in the hover. Designers correct it by offsetting the mast/transmission, biasing the cyclic rigging, or raising one side of the gearbox so the disc is slightly tilted to oppose the drift.

Question 6Rotary-wing aerodynamic and hub principles

A helicopter hovering close to the ground requires less power than the same hover at altitude. The cushion of higher-pressure air beneath the disc that reduces induced drag and downwash is known as:

  1. Vortex ring state
  2. Translational lift
  3. Ground effect Correct answer.
  4. Coning

Explanation

Ground effect occurs when the rotor is within roughly one rotor diameter of the surface; the restricted downwash reduces induced velocity and induced drag, lowering the power required to hover.

Question 7Rotary-wing aerodynamic and hub principles

On the retreating side of the rotor disc in high-speed forward flight, a region near the blade root experiences airflow that strikes the trailing edge first. What is this region called?

  1. Driving region
  2. Stall region
  3. Reverse flow region Correct answer.
  4. Negative coning region

Explanation

The reverse flow region is the area near the root of the retreating blade where the blade is moving rearward more slowly than the forward airspeed, so air meets the trailing edge first. It grows with forward speed and contributes to the high-speed limits.

Question 8Rotary-wing aerodynamic and hub principles

A two-bladed main rotor that flaps as a single unit about a central hinge, like a see-saw, is described as a:

  1. Fully articulated rotor
  2. Hingeless rotor
  3. Semi-rigid teetering rotor Correct answer.
  4. Coaxial rotor

Explanation

A semi-rigid (teetering) rotor uses two blades rigidly connected and free to teeter about a single flapping hinge; as one blade flaps up the other flaps down. It has no individual lead-lag hinges, simplifying the head.

Question 9Rotary-wing aerodynamic and hub principles

Coning of the main rotor blades is the upward angle the blades assume in flight and results from the balance between:

  1. Drag and thrust
  2. Torque and anti-torque
  3. Lift acting upward and centrifugal force acting outward Correct answer.
  4. Bleed air and ram air pressure

Explanation

Coning angle is set by the equilibrium between the lift force bending the blades upward and the centrifugal force tending to hold them in the plane of rotation; higher loading or lower RPM increases coning.

Question 10Rotary-wing aerodynamic and hub principles

A flapping hinge on a fully articulated rotor head is provided principally to:

  1. Allow blades to change pitch
  2. Drive the swashplate
  3. Lock the blades for transport
  4. Allow each blade to move up and down independently, relieving bending stress and helping equalise lift Correct answer.

Explanation

The flapping hinge lets each blade rise and fall independently, which relieves root bending stresses and automatically helps compensate for dissymmetry of lift as the advancing blade flaps up and the retreating blade flaps down.

Question 11Rotary-wing aerodynamic and hub principles

Torque reaction on a single main rotor helicopter causes the fuselage to tend to rotate:

  1. In the opposite direction to the main rotor Correct answer.
  2. In the same direction as the main rotor
  3. Forward along the flight path
  4. Vertically about the lateral axis

Explanation

By Newton's third law, the torque driving the main rotor produces an equal and opposite reaction on the fuselage, tending to spin it in the opposite direction. The tail rotor (or equivalent) provides the anti-torque thrust to counter this.

Question 12Rotary-wing aerodynamic and hub principles

Loss of tail rotor effectiveness (LTE) on a single main rotor helicopter is most likely to occur:

  1. At high forward speed in still air
  2. During cruise descent
  3. At low airspeed, high power, with certain relative wind directions in the hover or low-speed flight Correct answer.
  4. Only on the ground

Explanation

LTE arises in low-airspeed, high-power conditions where wind from particular directions disturbs tail rotor thrust (e.g. weathercock instability, main rotor disc vortex interference), reducing yaw control and allowing an uncommanded yaw.

Question 13Controls, drivetrain and anti-torque

In a single main rotor helicopter, raising the collective lever to increase total rotor thrust changes the pitch of the main rotor blades in what way?

  1. It increases the pitch of only the advancing blades
  2. It increases the pitch of all blades equally and simultaneously Correct answer.
  3. It tilts the rotor disc forward
  4. It increases blade pitch cyclically once per revolution

Explanation

Collective control raises the entire non-rotating swashplate, increasing the pitch of all blades by the same amount at the same time, which increases total rotor thrust. Cyclic, by contrast, tilts the swashplate to vary pitch once per revolution.

Question 14Controls, drivetrain and anti-torque

The non-rotating (stationary) part of the swashplate is connected to which control inputs?

  1. The main rotor blade grips only
  2. The tail rotor pitch-change spider
  3. The pilot's cyclic and collective controls Correct answer.
  4. The freewheel unit and rotor brake

Explanation

The stationary swashplate is moved by the pilot's cyclic and collective inputs (via servos), while the rotating swashplate transmits those movements through pitch links to the rotating blades. This separates non-rotating input from rotating output.

Question 15Controls, drivetrain and anti-torque

On a conventional single main rotor helicopter, the anti-torque pedals primarily control the helicopter by varying:

  1. Main rotor collective pitch
  2. Cyclic disc tilt
  3. Main rotor RPM
  4. Tail rotor blade pitch (thrust) Correct answer.

Explanation

The yaw (anti-torque) pedals change the pitch of the tail rotor blades, varying tail rotor thrust to counter main rotor torque and control the helicopter's heading about the vertical axis.

Question 16Controls, drivetrain and anti-torque

Lead-lag (drag) dampers fitted to a fully articulated main rotor head are primarily provided to:

  1. Control in-plane blade oscillations and help prevent ground resonance Correct answer.
  2. Increase the maximum forward speed of the rotor
  3. Increase collective pitch range
  4. Lubricate the pitch-change bearings

Explanation

Lead-lag dampers restrain and damp the in-plane (drag-hinge) motion of articulated blades caused by Coriolis and aerodynamic forces; correctly serviced dampers are essential to avoid ground resonance.

Question 17Controls, drivetrain and anti-torque

On a helicopter with fully powered (irreversible) hydraulic flight controls, what is the purpose of the artificial feel system?

  1. To prevent hydraulic fluid contamination
  2. To provide the pilot with control-force feedback proportional to control displacement Correct answer.
  3. To increase rotor RPM during manoeuvres
  4. To automatically track the main rotor blades

Explanation

With fully powered controls the pilot is isolated from aerodynamic loads, so an artificial feel unit (often spring-based) reintroduces a force/displacement relationship so the pilot can sense control inputs and avoid over-controlling.

Question 18Controls, drivetrain and anti-torque

The freewheel (sprag) unit in a helicopter drive train is essential because it:

  1. Increases engine torque to the rotor
  2. Allows the rotor to overrun the engine, enabling autorotation after an engine failure Correct answer.
  3. Brakes the rotor on shutdown
  4. Filters metal particles from the gearbox oil

Explanation

The freewheel/one-way (sprag) clutch transmits drive from engine to rotor but disengages if the rotor turns faster than the engine, allowing the rotor to overrun and autorotate after an engine failure. Without it, a stopped engine would stop the rotor.

Question 19Controls, drivetrain and anti-torque

A warning light driven by a magnetic chip detector located in the main gearbox sump illuminates. This most directly indicates:

  1. Metallic debris collecting in the gearbox oil Correct answer.
  2. Low rotor RPM
  3. Excessive tail rotor pitch
  4. Loss of hydraulic pressure

Explanation

A magnetic chip detector attracts ferrous particles; bridging across its gap completes a circuit and lights the warning, indicating internal wear or impending failure of gearbox components and prompting inspection of the captured debris.

Question 20Controls, drivetrain and anti-torque

Long tail rotor drive shafts running through the tail boom are supported at intervals by hanger bearings primarily to:

  1. Prevent the shaft from whirling or bowing at high RPM Correct answer.
  2. Increase the shaft rotational speed
  3. Provide an emergency disconnect
  4. Cool the gearbox oil

Explanation

Hanger (support) bearings space the long tail rotor drive shaft along the boom to keep it concentric and prevent whirl/bowing at operating RPM, which would otherwise cause severe vibration or failure. Flexible couplings accommodate misalignment.

Question 21Controls, drivetrain and anti-torque

In a helicopter drive train, where is the freewheel unit normally located?

  1. Between the tail rotor gearbox and the tail rotor
  2. Between the engine output and the main rotor transmission Correct answer.
  3. Inside the swashplate assembly
  4. Within the main rotor hub

Explanation

The freewheel unit is positioned between the engine output and the main transmission so that, if the engine fails or slows, the rotor can overrun and continue turning for autorotation while the engine is disconnected from the rotor.

Question 22Controls, drivetrain and anti-torque

A helicopter main gearbox typically uses which method to reduce the high engine RPM to the much lower main rotor RPM?

  1. A single direct-drive coupling with no reduction
  2. A friction belt drive
  3. A hydraulic torque converter only
  4. Multiple stages of gear reduction, often including bevel and planetary gears Correct answer.

Explanation

Main gearboxes use several stages of reduction (commonly a bevel/spiral-bevel stage to change drive direction followed by a planetary/epicyclic stage) to step turbine RPM down to a few hundred rotor RPM while carrying high torque.

Question 23Controls, drivetrain and anti-torque

The pitch links (pitch-change rods) in a helicopter control system connect the:

  1. Engine to the gearbox
  2. Battery to the starter
  3. Rotating swashplate to the blade pitch horns Correct answer.
  4. Fuel tank to the boost pump

Explanation

Pitch links transmit the up-and-down motion of the rotating swashplate to the blade pitch horns, changing each blade's feathering angle. Their length is adjustable for setting blade angle during rigging and track.

Question 24Controls, drivetrain and anti-torque

On many single main rotor helicopters the collective and yaw controls are interconnected so that raising the collective automatically adds tail rotor pitch. This mixing is provided to:

  1. Increase rotor RPM
  2. Reduce fuel consumption
  3. Compensate for the increased main rotor torque so the pilot needs less pedal correction Correct answer.
  4. Prevent retreating blade stall

Explanation

Raising collective increases main rotor torque, demanding more anti-torque thrust. A collective-to-yaw mixing unit feeds in tail rotor pitch automatically, reducing the pedal input the pilot must make and improving handling.

Question 25Controls, drivetrain and anti-torque

A fixed horizontal stabiliser fitted to a helicopter tail boom is provided mainly to:

  1. Improve pitch stability and reduce fuselage pitch attitude changes in forward flight Correct answer.
  2. Generate the majority of the lift in the hover
  3. Drive the tail rotor
  4. Act as an air brake

Explanation

The horizontal stabiliser (stabilator) provides an aerodynamic pitching moment in forward flight that improves longitudinal stability and helps keep the fuselage at a favourable attitude, reducing pilot workload.

Question 26Controls, drivetrain and anti-torque

In a fly-by-wire helicopter flight control system, pilot control inputs are:

  1. Connected mechanically through push-pull rods to the swashplate
  2. Transmitted hydraulically without any computer
  3. Converted to electrical signals processed by flight control computers that drive the actuators Correct answer.
  4. Pneumatically signalled through bleed air

Explanation

Fly-by-wire replaces mechanical linkages with electrical signalling: sensors read the pilot inputs, flight control computers process them (applying control laws and limits) and command the servo-actuators that move the swashplate and tail rotor.

Question 27Controls, drivetrain and anti-torque

Rigging the helicopter flight controls includes setting the blade pitch angles using rigging pins and a protractor/incidence board. The purpose of using rigging pins is to:

  1. Lock the controls permanently
  2. Measure rotor RPM
  3. Hold the controls at known neutral/reference positions so linkages can be adjusted to the correct datum Correct answer.
  4. Bleed the hydraulic system

Explanation

Rigging pins lock the control system at defined neutral or reference positions so that the lengths of links and the blade angles can be adjusted to match the manufacturer's rigging datum, ensuring correct control travel and blade tracking baseline.

Question 28Controls, drivetrain and anti-torque

A spiral-bevel input gear stage in a helicopter main gearbox is used principally to:

  1. Filter the oil
  2. Pressurise the cabin
  3. Detect chips
  4. Change the direction of drive from the horizontal engine shaft to the vertical rotor mast and provide reduction Correct answer.

Explanation

A spiral-bevel gear set turns the drive through about 90 degrees (from a typically horizontal engine output to the vertical mast) while also providing a stage of speed reduction, before further planetary reduction to rotor RPM.

Question 29Controls, drivetrain and anti-torque

On a twin-engine helicopter, the main gearbox combines power from both engines. If one engine fails, drive continuity is maintained because:

  1. The tail rotor takes over driving the main rotor
  2. Both engines must keep running or the rotor stops
  3. The rotor brake automatically engages
  4. The remaining engine drives the rotor through its own freewheel unit while the failed engine's freewheel disengages Correct answer.

Explanation

Each engine drives the combining gearbox through its own freewheel unit. If one engine fails, its freewheel disengages so it does not become a drag, and the live engine continues to drive the rotor through its freewheel, allowing continued flight.

Question 30Controls, drivetrain and anti-torque

An intermediate gearbox part-way along a helicopter tail rotor drive is fitted mainly to:

  1. Increase the tail rotor RPM above the engine speed
  2. Detect ice
  3. Store hydraulic fluid
  4. Change the angle of the drive shaft as it follows the tail boom up to the tail rotor Correct answer.

Explanation

An intermediate (mid) gearbox redirects the tail rotor drive shaft through the angle where the boom rises to meet the tail pylon/fin, maintaining drive alignment; the tail rotor gearbox at the end provides final angle change and reduction.

Question 31Controls, drivetrain and anti-torque

Flexible couplings (e.g. flexible disc or diaphragm couplings) in a helicopter tail rotor drive shaft are fitted to:

  1. Allow the shaft to be disconnected in flight
  2. Detect chips
  3. Store oil for the gearbox
  4. Accommodate small misalignments and airframe flexing while transmitting torque Correct answer.

Explanation

Flexible couplings transmit torque between drive shaft sections while accommodating angular and axial misalignment and airframe/tail-boom flexing, avoiding the wear and vibration of rigid connections and the maintenance demands of universal joints.

Question 32Controls, drivetrain and anti-torque

The Fenestron-type anti-torque device differs from a conventional tail rotor in that it:

  1. Uses bleed air ejected through the boom
  2. Has no moving blades
  3. Encloses a multi-bladed fan within a shroud (duct) in the vertical fin Correct answer.
  4. Drives the main rotor

Explanation

A Fenestron is a ducted (shrouded) fan with many small blades housed inside the tail fin; the shroud reduces tip losses and noise and protects the blades and ground personnel, while still providing anti-torque thrust.

Question 33Controls, drivetrain and anti-torque

Before applying the rotor brake during shutdown, the technician notes the manufacturer specifies a maximum rotor RPM for application. Applying the rotor brake above this RPM risks:

  1. Overcharging the battery
  2. Overheating and damaging the brake disc/pads and overstressing the drive train Correct answer.
  3. Inflating the floats
  4. Resetting the avionics

Explanation

Applying the rotor brake above the specified maximum RPM generates excessive heat and friction loads, which can warp or burn the disc/pads and overstress the drive components; the brake must only be applied once RPM has decayed below the published limit.

Question 34Tracking, vibration, inspection and monitoring

A persistent lateral (side-to-side) one-per-revolution vibration felt strongest in the cabin of a helicopter is most commonly caused by:

  1. Main rotor out of balance Correct answer.
  2. Tail rotor imbalance
  3. Engine compressor stall
  4. A leaking hydraulic servo

Explanation

A main rotor that is out of span or chordwise balance produces a low-frequency one-per-revolution (1/rev) vibration, typically felt as a lateral shake; main rotor track and balance corrects it. Tail rotor faults give a higher-frequency vibration.

Question 35Tracking, vibration, inspection and monitoring

During main rotor track and balance, the term blade tracking refers to checking that:

  1. All blade tips pass through the same plane (tip-path plane) during rotation Correct answer.
  2. Each blade weighs exactly the same
  3. The blades are set to the maximum collective pitch
  4. The rotor RPM is within governed limits

Explanation

Tracking verifies that all blade tips follow the same tip-path plane for a given control setting; a blade flying high or low is out of track and produces vertical 1/rev vibration. Balance corrects mass distribution; the two are adjusted together.

Question 36Tracking, vibration, inspection and monitoring

When using an electronic balancer, an azimuth (phase) reference for the once-per-revolution signal is most commonly generated by:

  1. A pitot probe in the rotor wash
  2. A magnetic pickup sensing an interrupter on the rotating swashplate or mast Correct answer.
  3. The chip detector circuit
  4. A fuel flow transducer

Explanation

A magnetic pickup mounted on the non-rotating structure senses a ferrous interrupter on the rotating mast/swashplate, producing one electrical pulse per revolution. This 1/rev reference lets the balancer relate vibration phase to blade azimuth.

Question 37Tracking, vibration, inspection and monitoring

A higher-frequency vibration that occurs at a multiple of rotor speed, such as four-per-revolution on a four-bladed rotor, is generally described as an:

  1. 1/rev vibration
  2. Sub-harmonic flutter
  3. n/rev vibration Correct answer.
  4. Ground resonance mode

Explanation

Vibrations occurring at an integer multiple of rotor RPM (number of blades per revolution) are called n/rev vibrations; on a four-bladed rotor the dominant blade-passing frequency is 4/rev. They are distinct from the low-frequency 1/rev balance vibration.

Question 38Tracking, vibration, inspection and monitoring

A helicopter main rotor blade or hub component whose total fatigue life is strictly limited and which must be retired at a fixed number of hours or cycles regardless of condition is known as a:

  1. On-condition item
  2. Consumable item
  3. Redundant component
  4. Life-limited (safe-life) component Correct answer.

Explanation

Highly stressed dynamic components such as rotor blades, hubs and pitch links are typically safe-life (life-limited) items: they must be removed from service at their published life limit even if they appear serviceable, because fatigue failure would be catastrophic.

Question 39Tracking, vibration, inspection and monitoring

A helicopter equipped with a Health and Usage Monitoring System (HUMS) primarily uses accelerometer and sensor data to:

  1. Detect developing faults in rotor, transmission and engine components by trend monitoring of vibration and usage Correct answer.
  2. Replace the need for any scheduled maintenance
  3. Control the autopilot
  4. Manage cabin temperature

Explanation

HUMS continuously records vibration, rotor track/balance, exceedances and usage cycles, enabling trend analysis that flags developing gearbox, bearing or rotor faults early and supports condition-based maintenance.

Question 40Tracking, vibration, inspection and monitoring

A trim tab fitted to the trailing edge of a main rotor blade is adjusted during track and balance to:

  1. Change the colour-coded blade identification
  2. Alter the blade's aerodynamic pitching moment so it flies higher or lower in track Correct answer.
  3. Increase the chord of the blade
  4. Provide anti-icing

Explanation

Bending the trailing-edge trim tab changes the local aerodynamic pitching moment and effective angle of attack of that blade, raising or lowering its track height without altering the mechanical pitch link, allowing fine track adjustment.

Question 41Tracking, vibration, inspection and monitoring

Anti-resonance or vibration absorbers such as a bifilar absorber fitted to a rotor head are tuned to:

  1. Increase rotor thrust
  2. Provide emergency lift
  3. Reduce specific in-plane n/rev vibrations transmitted from the rotor to the airframe Correct answer.
  4. Cool the main gearbox

Explanation

A bifilar (pendulum) absorber mounted on the rotor hub is tuned to counter in-plane n/rev hub forces, reducing the vibration passed into the fuselage. It is a passive vibration-control device, not a lift or cooling device.

Question 42Tracking, vibration, inspection and monitoring

Helicopter rotor blades and dynamic components are frequently inspected for cracks using which non-destructive method that reveals surface-breaking flaws in non-ferrous and ferrous parts respectively?

  1. Visual inspection only
  2. Tap testing only
  3. X-ray for all materials only
  4. Dye (liquid) penetrant for non-ferrous and magnetic particle for ferromagnetic parts Correct answer.

Explanation

Liquid penetrant inspection reveals surface cracks in non-magnetic materials, while magnetic particle inspection is used on ferromagnetic steels; eddy current and ultrasonic methods supplement these for subsurface or specific defects in critical rotor parts.

Question 43Tracking, vibration, inspection and monitoring

On-board maintenance systems on modern helicopters store fault data in non-volatile memory so that maintenance staff can:

  1. Refuel the aircraft faster
  2. Retrieve a record of detected faults and exceedances for diagnosis and rectification Correct answer.
  3. Adjust the rotor track in flight
  4. Increase engine power limits

Explanation

On-board maintenance/central maintenance systems capture and store fault messages, exceedances and BITE results, which technicians download to identify failed line-replaceable units quickly and accurately, reducing troubleshooting time.

Question 44Airframe, power, fluid and protection systems

Helicopter airframes incorporate firewalls around the engine and certain other zones. The primary purpose of a firewall is to:

  1. Reduce airframe weight
  2. Provide structural lift
  3. Resist and contain fire and prevent its spread to adjacent areas for a defined period Correct answer.
  4. Shield the avionics from lightning

Explanation

A firewall is a fire-resistant barrier (typically stainless steel or titanium) that separates designated fire zones such as the engine bay from the rest of the airframe, resisting flame penetration for the certification-required time to protect structure and occupants.

Question 45Airframe, power, fluid and protection systems

Modern helicopter main rotor blades are frequently constructed from composite materials rather than all-metal. A key maintenance advantage of composite blades is that they:

  1. Require no inspection at all
  2. Resist corrosion and can offer improved fatigue performance and damage tolerance Correct answer.
  3. Are immune to lightning strikes
  4. Need no balancing

Explanation

Composite blades resist corrosion, can be tailored for good fatigue and damage-tolerance characteristics, and often allow longer or unlimited life with inspection, compared with metal blades; they still require inspection, balancing and lightning protection.

Question 46Airframe, power, fluid and protection systems

A helicopter tail boom and fuselage built as a stressed-skin structure where the external skin carries a major part of the load is described as which type of construction?

  1. Monocoque or semi-monocoque Correct answer.
  2. Truss (space-frame)
  3. Geodesic
  4. Sandwich-honeycomb only

Explanation

Most modern helicopter fuselages and tail booms are semi-monocoque: the stressed skin carries much of the load, supported by frames, stringers and longerons. Pure monocoque relies on the skin alone, while truss structures carry loads in a framework.

Question 47Airframe, power, fluid and protection systems

Where main rotor blades attach to the hub through pitch-change bearings and retention bolts, these highly stressed attachment fittings are critical because they:

  1. Carry only aerodynamic drag
  2. Only support the blade weight on the ground
  3. Are non-structural fairings
  4. Transmit the full centrifugal, flapping and lead-lag loads of the blade to the hub Correct answer.

Explanation

Blade attachment fittings transmit enormous centrifugal force plus flapping and lead-lag loads from the blade into the hub. They are life-limited, carefully torqued and inspected because failure would release a blade.

Question 48Airframe, power, fluid and protection systems

A helicopter cabin air conditioning system that uses an air-cycle machine derives its cooling air supply principally from:

  1. Battery-heated air
  2. Ram air only
  3. The hydraulic reservoir
  4. Engine compressor bleed air Correct answer.

Explanation

An air-cycle (bootstrap) system draws hot, high-pressure bleed air from the engine compressor, cools it in heat exchangers and expands it through a turbine to provide conditioned cabin air; vapour-cycle systems instead use a refrigerant compressor.

Question 49Airframe, power, fluid and protection systems

A vapour-cycle cooling system fitted to a helicopter cabin removes heat by:

  1. Expanding bleed air through a turbine
  2. Venting cabin air overboard through an outflow valve
  3. Passing air over the gearbox oil cooler
  4. Evaporating and condensing a refrigerant in a closed loop with a compressor Correct answer.

Explanation

A vapour-cycle air conditioning system uses a compressor, condenser, expansion device and evaporator to circulate refrigerant; the refrigerant absorbs cabin heat as it evaporates and rejects it at the condenser, like a domestic refrigerator.

Question 50Airframe, power, fluid and protection systems

In a typical light helicopter DC electrical system, the engine-driven generator/alternator output is regulated and the battery serves principally to:

  1. Power the rotor during autorotation
  2. Cool the avionics
  3. Provide energy for engine starting and act as an emergency reserve and bus stabiliser Correct answer.
  4. Drive the hydraulic pump

Explanation

The battery supplies the high current needed for starting, stabilises bus voltage, and provides emergency power if the generator fails. The generator/alternator with a voltage regulator supplies the loads and recharges the battery in normal operation.