Gas turbine engine D-25V was developed in 1959 for heavy transport helicopters Mi-6, Mi-10, Mi-10K created in Mikhail Mil’s design bureau. The engine was based on the D-20P gas turbine engine core. For developing the D-25V-based helicopter propulsion unit, P.A. Solovyov, his deputy I.P. Evich and project engineer G.P. Kalashnikov were awarded with the USSR State Prize.

The D-25V engine with 5 500 horsepower output, had a high gas dynamic resistance to environment factors. The maximum power remained unchanged at heights of up to 3000 meters and at temperatures of up to +40°С during on-ground operation.

A free turbine allowed for the opportunity to establish its rpm regardless of the mode of the turbo-compressor section of the engine. This feature provides for a number of design and operational advantages including:

  • getting the desired rpm of the helicopter rotor shaft for flight modes and heights regardless of the engine turbine-compressor section rpm;
  • reaching the optimal fuel consumption at different conditions of the engine operation;
  • providing for an easy start of the engine;
  • no necessity to equip the helicopter propulsion unit with a friction clutch (feed clutch).

The R-7 gearbox created by the Perm Design Bureau specialists for the propulsion units of Mi-6 and Mi-10/10K with two D-25V, had been second to none in the world’s gearbox development industry for a quarter of a century.

The D-25VF uprated version was developed in 1965 for world’s heaviest helicopter V-12 with the maximum output of 6 500 hp.

In 1970, the State Committee recommended to start the serial production of the V-12 helicopter powered by Pavel Solovyov’s engines. One year on, this unique rotary-wing machine was destined to become a “spice” of the 29th International Aviation and Space Show in Les Bourget (France).