Helicopter: Mil Mi-4A (NATO: Hound-A)

USSR
utility helicopter

A Soviet piston-engined troop transport helicopter of the 1950s and 1960s.

At the end of the 1940's, Mikhail L. Mil began studying a concept of a large helicopter, powered by the ASh-62 engine, rated at 1000 hp. However, military authorities, placing no interest in the new kind of vehicle, stood in the way. The situation changed during the Korean War, when the American army successfully used large transport helicopters in numerous military operations. In September 1951, at a conference held by Stalin at the Kremlin, a decision was made on "the elimination of the delay in the domain of helicopter production" . For Mil's design, it meant a long awaited go-ahead. In October 1951, the Soviet Board of Ministers issued a resolution ordering Mil's team to develop a transport helicopter in a single year (!). It was to be capable of carrying 12 armed soldiers or 1200 kg of cargo (a jeep or a 57 mm or 76.2 mm cannon) or 1600 kg in the overloaded option. The aircraft received the designation W-12 (WD-12). A helicopter version of the successful ASh-82 engine was to power the helicopter.

The design was based on a "classic" configuration, already proved by the American Sikorsky S-55 helicopter. The engine was placed under the front of the fuselage. Behind the engine, there was a spacious cargo compartment with small side doors and an open rear. Over the cargo bay, a crew compartment and reduction gear was placed, transmitting power into the four-blade main rotor and the three-blade tail rotor. In the control system hydraulic amplifiers were introduced. Under the all-metal semi-stressed construction fuselage, a small nacelle with a 12.7 mm quick-firing machine gun was attached. The helicopter was equipped with a de-icing installation.

The pace of work on designing the W-12 was high, and the last factory drawings were completed in March 1952. At the beginning of April 1952, the first prototype was ready to fly. First takeoff tests were carried out on a tethered machine. At the beginning of June 1952, the first free flight took place. In August factory tests were concluded, however the decision on series production was made before factory and military tests have been concluded. The helicopter was officially designated Mi-4. In 1953, it entered production. The production variant could carry 16 soldiers, the number and type of cargo in comparison with the prototype remained unchanged.

During service several problems were encountered, one being flatter and the other ground resonance. These were gradually overcome. In 1958, production of the improved version, the Mi-4A, started. Modifications included new rotor blade construction with the service span extended to 600 hours. The area of the horizontal stabilizer was enlarged and an auto-pilot was applied. Several military and civil versions were developed based on that design.

In 1958, the tests of the Mi-4AW army support helicopter started. Initially, various unguided rocket armament was envisaged. The Soviet Army High Command was not interested in this new weapon. Yet they had to change their minds by 1967 due to the Vietnam War. Then, at last, the new armament was agreed upon. It was the K-4W unit, consisting of four anti-tank radio guided "Falanga" (NATO reporting name: AT-2 Swatter) rockets and six unguided rocket launchers (96 rockets in all), which could be replaced by bombs. The Mi-4AW eventually became the army support helicopter. 185 Mi-4A examples were then converted into the Mi-4AW.

Poland was among many operators of the Mi-4's. 17 Mi-4A transport and 4 Mi-4ME were bought. They became obsolete with the introduction of Mi-8, however some remained in use till the early 1980s.

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