The Soviet Mil Mi-1 helicopter's Polish made LiT-3 engine consists of the drive shaft, two speed rev reducer, rotor brake, combined clutch, free spinning device and cooling ventilator, connected by an axle to the main reducer that propels the rotor hub and the mid and tail reducers that move the tail rotor. Since the revs of the rotor are almost constant, performance can be increased or decreased by changing the angle of the rotor blades. The Mi-1 is a multi-purpose light helicopter that served in the Hungarian People's Army between 1961 and 1982. This multi-faceted and reliable machine greatly contributed to the acceptance of helicopters in the Hungarian Air Force.