A Soviet transport and assault helicopter with a piston engine, used in the 1950s and 1960s.
In the late 1940s, Mikhail L. Mil began design studies on a large helicopter powered by an ASz-82 engine rated at 1,000 hp. An obstacle to the new design was the military’s reluctance toward this type of air transport.
A turning point came during the Korean War, where the American Army successfully used large (by contemporary standards) transport helicopters in numerous military operations. In September 1951, a meeting led by Stalin was held in the Kremlin, at which the decision was made to “eliminate the backlog in helicopter production.” The long-awaited green light for Mil’s new project was finally given.
In October 1951, the Council of Ministers issued a resolution tasking Mil’s team with developing within one year (!) a transport and assault helicopter capable of carrying 12 armed soldiers or other cargo weighing 1,200 kg (a small off-road vehicle or a 57 mm or 76.2 mm cannon), or 1,600 kg in an overloaded variant. The project was named V-12 (VD-12). The ASz-82V engine was selected for it, a helicopter version of a successful powerplant used in several Soviet aircraft.
The helicopter’s design employed the “classic” concept proven on the American S-55. In the lower front section of the fuselage, the engine was located, followed by a spacious cargo compartment with small doors and an opening rear. Above it were the crew cabin and the reduction gearbox, which transmitted power to the four-blade main rotor and the three-blade tail rotor mounted at the end of a long tail boom. Hydraulic boosters were incorporated into the control system. Beneath the fuselage, which was of semi-monocoque metal construction, a small gondola housed a heavy, rapid-fire 12.7 mm calibre machine gun. The helicopter was equipped with a de-icing system.
Design work on the V-12 progressed rapidly; in March 1952, the last workshop drawings were completed. By the end of April, the first V-12 prototype was ready for flight, and initial tethered hover tests were conducted. At the beginning of June 1952, the first free flight was made. In August, factory trials were completed. The decision to begin series production was taken before factory and military trials were finished. The helicopter received the official designation Mi-4. In 1953, it was accepted into service. The production version could carry 16 soldiers in the cargo compartment; the quantity and type of cargo compared to the initial design remained unchanged.
Service use of the helicopter revealed a number of problems, the most serious of which were rotor blade flutter and ground resonance. These were solved through the joint efforts of designers, manufacturers, and research institutes.
In 1958, production of an improved version designated Mi-4A began. Changes were made to the rotor blade construction, extending their service life to 600 hours. The horizontal stabilizer area was increased, and an autopilot was fitted. Based on the Mi-4 and Mi-4A, a number of variants with different purposes were developed for both military and civilian aviation.
In 1958, trials of a fire support helicopter designated Mi-4AV began. Initially, the armament was to consist of various unguided rockets. The Soviet Army command showed no interest in the new weapon. A change of position on this matter did not come until 1967 (influenced by the experience of the Vietnam War). Only then was the new Mi-4AV armament package accepted. It was the K-4V system, consisting of 4 radio-guided “Falanga” anti-tank guided missiles and 6 unguided rocket launchers (96 rockets), which could be replaced by aerial bombs. The Mi-4AV finally became a fire support helicopter for ground forces, and 185 Mi-4A units were converted for this purpose.
The Mi-4 was produced in numerous versions between 1952 and 1966, first in Saratov and then in Kazan. A total of 3,307 helicopters were built. In 1956, a production licence for the Mi-4 was granted to the People’s Republic of China, where it was produced between 1963 and 1979 under the designation Z-5. A total of 545 units were built. Among the many countries using the Mi-4 was Poland, which purchased 17 transport and assault Mi-4A and 4 Mi-4ME helicopters. They were replaced by Mi-8 helicopters and derivative versions, although some Mi-4s continued flying into the early 1980s.
| Rotor diameter | 21.0 m |
| Fuselage length | 16.79 m |
| Takeoff weight | 7300 kg |
| Maximum speed | 185 km/h |
| Ceiling | 5650 m |
| Range | 425 km |
| Armament | 1x 12.7 mm machine gun |
| Engine | piston, 14-cylinder double-row radial, air-cooled ASz-82V, 1250 kW (1700 hp) |
