Russian production of the aircraft model still continues as of The Mi-8 is the world's most-produced helicopter , [ 2 ] with over 17, units used by over 50 countries. As of , when combined with the related Mil Mi , the two helicopters are the third most common operational military aircraft in the world. Mikhail Mil originally approached the Soviet government with a proposal to design an all-new two-engined turbine helicopter in after the success of the Mil Mi-4 and the emergence and effectiveness of turbines used in the Mil Mi After design and development, the Mi-8 was subsequently introduced into the Soviet Air Force in The Soviet military originally argued against a new helicopter, as they were content with the current Mil Mi Due to the position of the engine, this enabled Mikhail Mil to justify redesigning the entire front half of the aircraft around the single engine.
The prototype, which was named V-8, was designed in [ 4 ] and based on the Mil Mi-4 with a larger cabin. During an official visit to the United States in September , Nikita Khrushchev took a flight in the S presidential helicopter for the first time and was reportedly extremely impressed. However, it would be necessary to have a second engine for reliability. This gave Mikhail Mil the power under the orders of Khrushchev to build the original two-engined helicopter, which for the first time in Soviet history would need purpose-built turbine engines, rather than those adapted from fixed wing aircraft as in the Mil Mi-6 and the first prototype V-8 and an entirely new main rotor gear box that would be designed in-house for the first time.
In May , the order was given for Mikhail Mil to create his twin engine helicopter. The Sergei Isotov Design Bureau accepted the task of creating the engines. The second prototype still equipped with the one turbine engine as the Isotov engines were still under development flew in September Two months after the engines were completed by Isotov, the third prototype designated V-8A equipped with two 1, kW 1, shp Isotov TV2 engines, made its first flight piloted by Nikolai Ilyushin on 2 August , marking the first flight of any Soviet helicopter to fly with purpose built gas turbine engines.
The fourth prototype was designed as a VIP transport, with the rotor changed from four blades to five blades in to reduce vibration, the cockpit doors replaced by blister perspex slides and a sliding door added to the cabin. The fifth and final prototype was a mass production prototype for the passenger market.
In November , all joint testing had been completed and the Soviet government began mass production. Production started in the Kazan Production Plant, with the first aircraft completed by the end of The Soviet military originally showed little interest in the Mi-8 until the Bell UH-1 's involvement in the Vietnam War became widely publicised as a great asset to the United States, allowing troops to move swiftly in and out of a battlefield and throughout the country.
