United Engine Corporation (UEC, part of Rostec) has revealed in detail the operation of one of the most important components of a helicopter engine – the main gearbox. As explained by the UEC press service, the power plant and the main rotor operate in completely different speed ranges, and connecting them directly without an intermediary is impossible.
The main problem is the huge difference in revolutions. The free turbine of a helicopter gas turbine engine, which does not create jet thrust, spins up to 12-15 thousand revolutions per minute. These are absolutely unacceptable values for the main rotor, whose rotation speed is limited: for example, on the Mi-8 it is only about 192 revolutions per minute, and on the Mi-24 – about 240. Without a gearbox, the rotor would simply break, so a mechanical transmission is introduced into the design to match speeds and convert torque.
The gearbox itself is designed on the principle of a multi-stage transmission. Gear wheels of different diameters mesh with each other, forming several stages, and due to the gear ratio, they reduce the revolutions from tens of thousands to the required values. At the same time, the gearbox not only transmits power to the main and tail rotors but also distributes it to key units: the generator, hydraulic pumps, and oil pump – that is, it ensures the operation of all onboard hydraulics and electrics.
In the UEC product line, this unit is primarily used on turboshaft engines. In fact, the corporation emphasizes the role of mechanical processing in engine building: it is the high precision of gearbox manufacturing that determines the service life of the power plant, the level of vibrations, and flight safety in general.
Within the UEC, the production of such units is carried out at enterprises with deep competencies in metalworking and heat treatment, including "Krasny Oktyabr", where, for example, the TV3-117 engine gearbox is produced.
