Showing content mapped to EASA Part-66. Change authority in the header.
Rotary-wing aerodynamics
The main rotor produces both lift and thrust; total rotor thrust is tilted by the swashplate to move the aircraft. Blades experience dissymmetry of lift in forward flight — the advancing blade sees higher airspeed than the retreating blade — corrected by blade flapping and cyclic feathering. Retreating blade stall limits forward speed. Coning results from lift versus centrifugal force.
Flight control systems
Collective changes pitch on all blades equally (total thrust). Cyclic changes pitch cyclically to tilt the rotor disc. Anti-torque pedals control tail rotor pitch (or NOTAR/fenestron thrust) to counter main-rotor torque and provide yaw. Correlation/governor units maintain rotor RPM as collective changes. Hydraulic servos and stability augmentation (SAS/AFCS) reduce pilot workload.
Autorotation & flight limits
In autorotation, upward airflow through the disc drives the rotor after power loss; the pilot lowers the collective immediately and flares to convert rotor energy for landing. The height-velocity ('dead man's') curve shows combinations from which autorotation is not possible. Other limits: vortex ring state, ground resonance, mast bumping on teetering rotors, and loss of tail-rotor effectiveness.
Transmission & rotor heads
Drive train: engine → freewheel (overrun) clutch → main gearbox → mast, with a tail-rotor drive shaft and intermediate/tail gearboxes. Rotor head types: fully articulated (flap, drag and feather hinges with dampers), semi-rigid/teetering, and rigid/bearingless using elastomeric bearings. Chip detectors, oil temperature and pressure monitoring, and HUMS/vibration analysis are key maintenance tools.
Rotor track & balance
Out-of-track produces vertical vibration at 1/rev; out-of-balance produces lateral vibration. Track is checked with a strobe/reflector or optical tracker and adjusted using pitch links and trim tabs; balance is adjusted with weights. Tail rotor imbalance shows as high-frequency vibration through the pedals.
Structures & systems
Airframes use semi-monocoque with high-vibration fatigue considerations, and many components are life-limited by hours or cycles. Systems mirror fixed-wing practice — hydraulics, fuel with crash-resistant tanks, electrical, environmental, fire protection, ice protection, floats/skids or wheeled gear, plus instrumentation for rotor RPM, torque and vibration.