Light Turbine Helicopter · Drivetrain

1. The engine. The turboshaft uses one centrifugal compressor, an annular combustion chamber and two axial turbine stages on one shaft. The engine reduction is 5.8025:1. The exhibit uses the maintenance manual’s historical 33,000 rpm comparison point; EASA lists 34,000 rpm for C5/C6 normal operation.
2. Starting and overrunning. A centrifugal starting clutch lets the engine accelerate before loading the rotor. A separate roller freewheel transmits torque in one direction. These are distinct mechanisms: slipping during startup is different from overrunning after an engine cut.
3. The main gearbox. A bevel pair feeds two fixed-ring planetary stages with four and eight planets. The reconstructed tooth counts give a 16.32:1 main reduction and approximately 348 rpm at the rotor. The tail takeoff is downstream of the freewheel.
4. Collective and cyclic. Collective raises the swashplate; cyclic tilts it. A bearing separates its fixed and rotating rings. The three pitch links keep their length while their ball joints move, so each blade’s feathering angle follows from the linkage geometry.
5. Tail rotor control. The shaft runs through supported bearings and couplings to a 95° tail gearbox with a 1.24:1 reduction. The pedals move an axial pitch rod and crosshead, changing both tail blade angles without changing the gear ratio.
6. Inspect the mechanism. Select a close-up, open the covers and reduce simulation speed. Pause and step to inspect engagement and pitch changes. After an engine cut, the rotor and tail drivetrain coast while the freewheel allows the engine to slow independently.

A source-based educational reconstruction, not a factory drawing. Tooth counts, tooth surfaces, dimensions and airfoil detail are reconstructed; bevel teeth approximate the original spiral form. Link lengths and displayed transmission ratios are enforced. The optional point-mass flight demonstration does not model blade aerodynamics, yaw dynamics or sustained autorotation.

Technical references:Maintenance manual, chapters 40.1 / 40.2· EASA E.137