AI-4, G.A.Ivchenko

"V" stays for "Vertoliotnyj", designed to power helicopters (or 'Val', Shaft); it was the second engine in the USSR (after AI-26GR), specially equipped to power helicopters. It had an 'integrated' cooling fan, 2-stage gearbox and combined clutch. First stage of the gearbox loweredRPM's to desired value and the second one distributed power to two coaxial counter-rotating rotors.

AI-4V