CAAS SAR-66 AML Module 12 — Helicopter Aerodynamics, Structures and Systems (Singapore)

What aerodynamic phenomenon causes a helicopter to tilt to the left or right during forward flight unless compensated for by cyclic pitch control?

• ADissymmetry of lift
• BVortex ring state
• CTransverse flow effect
• DGround effect

Due to gyroscopic precession, if a force is applied perpendicular to the plane of rotation of a main rotor blade, where does the maximum aerodynamic response (displacement) occur?

• AAt the point of force application
• B90 degrees later in the direction of rotation
• C180 degrees opposite the point of force application
• D45 degrees before the point of force application

In a fully articulated main rotor head, what mechanical component allows the individual rotor blades to move forward and backward in the plane of rotation to absorb acceleration and deceleration forces?

• AFlapping hinge
• BLead-lag (drag) hinge
• CPitch change feathering hinge
• DTeetering pin

What is the primary function of the freewheeling unit (sprag clutch) located between the helicopter engine and the main gearbox?

• ATo disengage the tail rotor during engine starting
• BTo automatically disengage the engine from the transmission in the event of engine failur…
• CTo vary transmission gear ratio according to flight speed
• DTo lock the main rotor blades during ground parking

During autorotation following a engine failure, which region of the main rotor blade along its span acts as the driving region (generating forward aerodynamic force to keep the rotor turning)?

• AThe root region (inner 25%)
• BThe mid-blade region (approximately 25% to 70% span)
• CThe blade tip region (outer 30%)
• DThe entire blade span uniformly

How does raising the collective pitch lever affect the main rotor blades and engine fuel control unit in a turbine helicopter?

• AIt increases the pitch angle of all main rotor blades simultaneously and signals the gove…
• BIt changes blade pitch differentially around the rotor azimuth without altering fuel flow
• CIt decreases rotor blade pitch while increasing engine RPM
• DIt tilts the swashplate assembly laterally without altering collective pitch

A low-frequency lateral vibration occurring at a frequency of 1 per revolution (1:1 rotor speed) in a helicopter is most commonly caused by which discrepancy?

• AMain rotor blade out-of-track (blade flying higher or lower)
• BMain rotor blade mass out-of-balance (weight discrepancy)
• CTail rotor drive shaft unbalance
• DEngine turbine wheel unbalance

What is the function of the swashplate assembly in a helicopter flight control system?

• ATo convert non-rotating flight control inputs from cyclic and collective linkages into ro…
• BTo automatically balance tail rotor thrust against main rotor torque
• CTo disconnect the flight controls during autopilot engagement
• DTo damper blade lead-lag motion in high-speed flight

In a semi-rigid two-bladed teetering rotor system, what dangerous dynamic condition can occur if the helicopter experiences a low-G flight maneuver?

• AGround resonance
• BMast bumping
• CVortex ring state
• DThermal runaway

What type of tail rotor replacement design utilizes a multi-bladed shrouded fan built directly into the vertical tail fin structure?

• ANOTAR (NO TAil Rotor)
• BFenestron (ducted fan)
• CTandem rotor
• DCoaxial rotor

Which component in a helicopter transmission system provides an electrical warning to the cockpit crew when metallic wear particles collect in the lubricating oil?

• AThermostatic bypass valve
• BMagnetic chip detector
• COil pressure transmitter
• DScavenge pump filter bypass indicator

Ground resonance is a severe destructive oscillation most typically associated with which rotor head configuration when touching down on landing gear?

• ASemi-rigid two-bladed rotor head
• BFully articulated rotor head with lead-lag hinges
• CRigid rotor head with hingeless composite blades
• DEnclosed Fenestron ducted fan

What is pitch-flap coupling (often referred to as Delta-Three angle) in rotor head design?

• AA mechanical linkage geometry where a flapping movement of the blade automatically change…
• BThe angle between the main rotor mast and tail boom
• CThe angular difference between cyclic control stick input and swashplate tilt
• DThe phase displacement between blade lag dampers and drag hinges

In a optical or strobe main rotor blade tracking procedure, how is a low-flying main rotor blade adjusted during ground or flight tracking?

• ABy shortening or lengthening the blade pitch control link or bending the trailing edge tr…
• BBy adding lead weights to the tail rotor hub
• CBy increasing engine turbine speed by 10%
• DBy shifting the swashplate mixing unit lateral bias

What is the purpose of the rotor brake installed on the tail rotor drive shaft or main transmission?

• ATo assist in controlling rotor RPM during steep autorotative descents
• BTo rapidly stop main and tail rotor rotation after engine shutdown and prevent windmillin…
• CTo automatically apply brake force whenever collective pitch is raised
• DTo lock the swashplate assembly during high-speed forward flight

Coriolis effect (law of conservation of angular momentum) causes a main rotor blade in an articulated head to do what when it flaps upward?

• ALead forward in its plane of rotation
• BLag backward in its plane of rotation
• CIncrease its pitch angle automatically
• DStop rotating completely

In a hydraulic flight control system on a medium twin-engine helicopter, what safety feature is installed to ensure control remains available if one hydraulic system fails?

• ADual independent hydraulic systems powering dual tandem or parallel control actuators
• BA manual hand pump connected directly to the swashplate
• CA mechanical cable backup that replaces hydraulic pressure automatically
• DPneumatic air bottles that pressurize the hydraulic lines upon failure

What is translational lift in helicopter aerodynamics?

• AThe additional lift obtained when the helicopter transitions into forward flight due to c…
• BThe loss of lift experienced when hovering near a building
• CThe vertical force generated by the tail rotor during hovering
• DThe downward aerodynamic force produced by the stabilizer fin at maximum forward speed

What component connects the tail rotor gearbox to the main transmission across long tail boom structures?

• ASegmented drive shafts supported by rubber-mounted hanger bearings and flexible couplings
• BA continuous solid single-piece steel torque tube with no supports
• CFlexible hydraulic hoses driven by a hydraulic motor
• DHigh-tension stainless steel push-pull cables

In helicopter structural inspections, why is the tail boom attachment joint to the main fuselage considered a critical inspection zone?

• AIt is subject to high cyclic fatigue bending moments from main rotor downwash, tail rotor…
• BIt houses the main passenger cabin pressure bulkhead
• CIt contains the primary electrical power generation bus
• DIt is exposed to engine exhaust gas heat exceeding 800 degrees C continuously

What is the function of a hydraulic lead-lag damper installed on a fully articulated main rotor head?

• ATo restrain and cushion the forward and backward hunting motion of the blade around its d…
• BTo prevent the blade from flapping upward in high winds
• CTo alter blade pitch angle during collective movement
• DTo lock the rotor head during engine starting

Which tail rotor control input is produced when the pilot depresses the right anti-torque pedal in a conventional Western helicopter (main rotor turning counter-clockwise viewed from above)?

• ATail rotor pitch decreases, reducing leftward tail thrust and allowing the nose to yaw to…
• BTail rotor pitch increases, pushing the tail violently to the right and nose to the left
• CMain rotor swashplate tilts right, causing a rolling maneuver
• DFreewheeling unit disengages automatically

What safety system is fitted to emergency floats on offshore helicopters to inflate them prior to water landing?

• ACompressed helium or nitrogen cylinders fired electrically or mechanically via water imme…
• BEngine bleed air tapped directly from the turbine compressor
• CAn electric air blower powered by the main battery
• DHydraulic fluid pressure from System 1

What is vortex ring state (settling with power) and how does it develop?

• AA condition occurring when a helicopter descends vertically or at low forward speed at hi…
• BAn overspeed condition of the main rotor caused by sudden collective pitch reduction
• CA high-speed aerodynamic stall of the advancing blade in dive maneuvers
• DA sudden loss of tail rotor effectiveness in tailwind conditions

What inspection tool is commonly used to inspect internal gear teeth and bearing races inside a helicopter main gearbox without disassembly?

• AOptical flexible or rigid borescope
• BUltrasonic thickness gauge
• CEddy current bolt hole scanner
• DMagnetic particle bench

What type of rotor head uses flexible composite arms or elastomeric bearings to replace mechanical metallic hinges (flapping, lag, and feathering hinges)?

• ARigid / Hingeless or Bearingless rotor head
• BFully articulated metallic head
• CSemi-rigid teetering head
• DFenestron enclosed rotor

What is the primary function of a mixing unit in a helicopter mechanical flight control system?

• ATo combine and coordinate collective, cyclic, and anti-torque pedal inputs so that contro…
• BTo mix hydraulic fluid with engine oil for transmission cooling
• CTo combine fuel from left and right tanks before feeding the engine
• DTo blend static air pressure with pitot pressure for airspeed calculation

Which aerodynamic limitation sets the maximum forward speed ($V_{NE}$) of a conventional helicopter?

• ARetreating blade stall combined with compressibility effects on the advancing blade tip
• BTail rotor overspeed
• CMain gearbox thermal oil limit
• DSkid landing gear drag coefficient

What maintenance action is required when an elastomeric bearing in a main rotor head shows evidence of surface cracking or extrusion of rubber layers during visual inspection?

• AInspect against manufacturer depth/length limit criteria and replace the bearing if limit…
• BApply engine oil to soften the rubber
• CWeld a steel reinforcing strap over the bearing housing
• DTighten the pitch link by 5 turns to compress the rubber

What is the function of droop stops (droop restraints) on a fully articulated main rotor head?

• ATo prevent the blades from sagging downward and striking the tail boom or airframe when t…
• BTo lock the blades at maximum collective pitch during takeoff
• CTo damp out high-frequency vibrations in flight
• DTo prevent the blades from lagging forward during high-speed forward flight

In a Health and Usage Monitoring System (HUMS) installed on modern commercial helicopters, what sensors are primarily placed on gearboxes and bearing housings?

• APiezoelectric accelerometers and magnetic chip detectors
• BPitot tubes and static ports
• CCapacitance fuel quantity probes
• DCarbon monoxide detectors

What is translational drift (tendency to drift laterally during a hover) in a single main rotor helicopter, and how is it compensated for in design?

• AThe sideways push caused by tail rotor thrust; compensated for by mounting the main rotor…
• BThe tendency of the helicopter to turn nose-down in forward flight; compensated for by a…
• CThe spin of the fuselage caused by main rotor drag; compensated for by engine governor
• DThe lateral motion caused by wind gusts; compensated for by auto-hover pitot tubes

Which safety device prevents accidental engagement of the rotor brake while the helicopter engines are operating at flight power?

• AAn electrical or mechanical interlock switch that locks the brake handle when engine cont…
• BA thermal fuse in the rotor brake disc
• CA relief valve in the pitot-static line
• DA spring-loaded tail rotor pitch slider

What structural feature of helicopter skid landing gear absorbs impact energy during hard landings?

• AElastic bending and plastic deformation of the tubular aluminum or steel cross tubes
• BInternal high-pressure oleo-pneumatic struts inside the skids
• CRubber inflatable shock airbags underneath the fuselage
• DHydraulic dampener cylinders filled with brake fluid

In a stability augmentation system (SAS) fitted to a helicopter, how do SAS electro-hydraulic actuators interact with pilot manual control inputs?

• ASAS actuators operate in series with control rods with limited authority (typically 10-15…
• BSAS actuators override pilot inputs completely by moving control sticks to full stops
• CSAS actuators operate only when the collective lever is locked on the floor
• DSAS actuators disconnect flight control rods and operate fly-by-wire only

What is the primary function of a tail rotor intermediate gearbox (42-degree or 90-degree gearbox) in a helicopter tail drive train?

• ATo change the direction of the drive shaft axis along angled tail boom sections while mai…
• BTo disengage tail rotor drive during high-speed forward flight
• CTo automatically adjust tail rotor blade pitch angle
• DTo convert AC electrical power to DC power for tail lights

Ground effect increases rotor efficiency when hovering within how many main rotor diameters above the surface?

• AWithin approximately 0.5 to 1.0 main rotor diameter of the ground
• BWithin 5 to 10 main rotor diameters
• COnly when touch down wheels contact the pavement
• DAt altitudes above 5,000 feet MSL exclusively

What type of rotor hub design uses a single central trunnion bearing allowing two blades to tilt together like a seesaw?

• ASemi-rigid (teetering) rotor head
• BFully articulated rotor head
• CRigid bearingless head
• DTandem dual head

What is the function of pitch links (push-pull control rods) connected between the rotating swashplate and rotor blade pitch horns?

• ATo transmit vertical linear movement from the swashplate to rotate the blades around thei…
• BTo supply lubricating oil to the rotor hub
• CTo hold the main rotor blades rigid during ground towing
• DTo drive the rotor mast rotation

Why are rotor blade trailing edge trim tabs bent during dynamic flight tracking procedures?

• ATo adjust high-speed aerodynamic pitching moments of individual blades so that all blade…
• BTo increase engine torque during climb
• CTo lock the lead-lag hinges in hover
• DTo prevent static electricity build-up on composite blades

What causes retreating blade stall in forward flight at high airspeeds?

• AThe retreating blade must operate at higher angles of attack to equalize lift with the ad…
• BThe advancing blade stops rotating due to tail rotor drag
• CEngine power drops to zero automatically above 100 knots
• DThe swashplate reaches its maximum mechanical stop

What is the purpose of a oil cooler blower (fan) driven by the main transmission in a helicopter lubrication system?

• ATo provide continuous cooling airflow across transmission and engine oil coolers even whe…
• BTo inflate emergency flotation bags
• CTo blow dust off the windscreen
• DTo pressurize the fuel tanks

What type of tail rotor anti-torque system uses internal high-velocity air slots along the tail boom to exploit the Coanda effect?

• ANOTAR (NO TAil Rotor)
• BFenestron
• CConventional open tail rotor
• DTandem counter-rotating rotor

In helicopter main rotor head maintenance, what is the significance of measuring blade grip feathering bearing play or breakaway torque?

• ATo detect brinelling, corrosion, or wear in the blade pitch change bearings before stiffn…
• BTo calculate total fuel burn per hour
• CTo check hydraulic fluid cleanliness
• DTo measure tail boom flex

How is a high-frequency vibration occurring at tail rotor rotational frequency (typically 4:1 to 6:1 ratio relative to main rotor RPM) isolated during vibration troubleshooting?

• ABy placing accelerometers on the tail rotor gearbox and checking tail rotor mass balance…
• BBy adjusting main rotor pitch links
• CBy bleeding the main landing gear oleo struts
• DBy replacing the engine fuel filter

What is the purpose of a main gearbox planetary (epicyclic) gear stage?

• ATo provide high speed-reduction gear ratio in a compact concentric assembly while distrib…
• BTo change the direction of main rotor rotation in flight
• CTo drive the cockpit air conditioning compressor only
• DTo connect the battery to the starter generator

What aerodynamic force causes a helicopter to pitch up automatically when transitioning into autorotation if no pilot cyclic correction is made?

• ARotor disc upward flapping and change in induced flow angle across the rotor disc as powe…
• BEngine exhaust gas pressure pushing the tail down
• CHydraulic system pressure surge locking the elevator
• DTail rotor speed dropping to zero instantaneously

In helicopter electrical power systems, why are generator control units (GCUs) designed to trip a generator off-bus during an overvoltage condition?

• ATo protect sensitive avionics and aircraft battery systems from thermal damage and voltag…
• BTo increase engine horsepower by 25%
• CTo engage the rotor brake automatically
• DTo dump excess fuel overboard