Helicopters were first used on a limited scale during World War II by the Germans and Americans. They proved very effective, taking part in several military operations where they attracted attention. Most aviation specialists predicted a great future for this new type of aircraft. In the USSR as well, some designers attempted to work on such projects. As early as the 1930s, initial helicopter experiments were conducted there, but the results were not impressive. Therefore, attention turned to simpler autogyros, in which lift was generated by a freely rotating or pre-spun rotor (autorotation).
One of the pioneers in helicopter design in the Soviet Union was Mikhail L. Mil. Before the war, he worked at the Central Aerohydrodynamic Institute in Moscow, where he dealt with the scientific study of certain issues related to rotorcraft and participated in autogyro development. After the war, he began designing his first helicopter, the EG-1. The need for many design changes led to the creation of a new design. In 1948, a new multi-purpose helicopter, the GM-1, was developed.
The machine was built in a “classic” configuration. The all-metal fuselage consisted of a space frame truss in the forward section, transitioning into a semi-monocoque tail boom. The cabin, located in the forward fuselage, accommodated the pilot and two passengers. Behind it was the air-cooled radial engine. Above it, the reduction gearbox drove the main rotor consisting of three blades of mixed construction, replaced in the last production version with all-metal ones. The tail rotor was made of wood. At the rear of the fuselage, behind the engine, the fuel tank was located. By August 1948, the first prototype was ready, and it made its first flights in September of the same year. It was powered by a specially designed “helicopter” radial aviation engine, the AI-26V.
Testing revealed the need for design changes. At the end of November 1948, the helicopter suffered an accident caused by frozen grease in the control system. The pilot managed to save himself with a parachute. The second GM-1 crash occurred in March 1949. During a ferry flight to military testing, the tail rotor drive shaft failed due to poor-quality welding. Military and state trials began in September 1949. During test flights, blade flutter and ground resonance (helicopter instability on the ground caused by the rotating main rotor) manifested themselves; design changes prevented their further occurrence. In February 1950, the USSR Council of Ministers passed a resolution to build a trial production run of 15 GM-1 helicopters and to rename it Mi-1. In 1951, the Mi-1 was demonstrated at the Tushino air show. However, some political, economic, and military officials with limited vision stood in the way of mass production. To overcome this resistance, Mil decided to demonstrate the new helicopter to Stalin. This demonstration removed all obstacles. The Korean War also helped, in which American helicopters passed another test with flying colours, performing many auxiliary functions (medical, liaison, reconnaissance) of vital importance to the conduct of military operations. Production of the Mi-1 was gradually increased; between 1952 and 1960, 1,012 units were manufactured at three successive aircraft factories.
During this period, various improvements to the helicopter’s design and durability were successively introduced. In the first Mi-1s, the main rotor’s service life was limited to 150 hours. In 1950, the Mi-1U (GM-2) appeared, equipped with dual controls for pilot training. It was series produced. In 1953, a new version called the Mi-1T (“trekhsotnyi” meaning “three-hundred”) was developed. Thanks to technological changes in the production of the mixed-construction rotor blades, the rotor service life was increased to 300 hours. An improved AI-26 engine with increased power was fitted, a horizontal stabilizer was added to the rear tail boom, and a de-icing system was installed along with enlarged cabin doors. All these changes improved the helicopter’s characteristics and reduced operating costs. Based on the Mi-1T design, several modifications for different purposes were developed. Only one of them entered production in 1956 — the Mi-1TKR, used for artillery fire correction.
The next major modernization of the Mi-1 took place in 1957. The new version was designated Mi-1A. A number of significant changes were introduced. The rotor blades had an increased service life of 600 hours. The previously used mechanical trimmers were replaced with electrical ones, more modern flight instruments were fitted, and it became possible to mount an auxiliary fuel tank on the fuselage side. The final modernization of the multi-purpose helicopter was designated Mi-1M and entered series production in 1957. It was based on the experimental Mi-3 helicopter developed in 1954. The Mi-3 did not enter production, but its modernized fuselage was used in the new Mi-1M. Its forward section was enlarged, allowing for a more comfortable cabin. The helicopter received new blades with a rectangular planform. Several variants based on the Mi-1M were developed. The Mi-1NCh was created for civilian needs. It was used for passenger transport, carrying up to 3 passengers in the cabin. It also served as a medical helicopter, carrying patients in pods attached to the fuselage sides. It could also perform agricultural operations, spraying chemicals from suspended tanks.
The most interesting modernization was the attempt to create an armed variant. Between 1958 and 1962, a number of armament configurations for the Mi-1 were tested. These included large-calibre unguided rockets, “Falanga” and “Malyutka” anti-tank guided missiles, small-calibre aerial bombs, and machine guns. However, the Soviet Army was not interested in this new type of weapon. The last Mi-1 helicopters were retired from service in the USSR in 1983. The Mi-1 went down in history as the first Soviet helicopter approved for mass production.
In 1954, an inter-governmental agreement was negotiated and signed between the Soviet and Polish governments, granting Poland the right to licence-produce the Mi-1 helicopter. Production began in 1956 at the aircraft factory in Swidnik near Lublin. Licence production of the AI-26 engine under the name Lit-3 started in 1956 at the aero engine factory in Rzeszow. The new helicopter was designated SM-1. The first 4 Mi-1s were assembled from parts supplied by the USSR, and a group of Polish helicopter pilots was trained. At the beginning of 1957, production of the SM-1/300 multi-purpose helicopter commenced; it was the equivalent of the Soviet Mi-1T. It could serve for liaison, VIP transport, and reconnaissance purposes.
The next version, the SM-1/600, entered the assembly line in 1959. It was modelled on the Mi-1A. Based on the SM-1/600, the design office at the Swidnik factory developed several new variants for different uses. These were: SM-1Sz – training version with dual controls; SM-1S – medical version with the ability to transport a patient in a special externally-mounted pod; SM-1D – a small flying crane; SM-1Z – agricultural version. In 1960, with the assistance of Soviet specialists, the SM-1W multi-purpose helicopter was developed. Its technical solutions corresponded to the Mi-1M. An agricultural version was also created, designated SM-1WZ. The last helicopter to enter production was the SM-1Wb. It featured a hydraulic power-assisted control system (booster) and metal main rotor blades with an extended service life of 800 hours. The last SM-1 was produced at Swidnik at the end of December 1965. A total of 1,597 SM-1 helicopters were manufactured (according to Russian sources). The majority were delivered to the USSR, but they were also purchased by other countries. Thanks to SM-1 production, Poland joined the world’s list of major helicopter manufacturers.
The Polish military aviation purchased a total of 85 SM-1 helicopters. They were in service until 1983.
| Rotor diameter | 14.35 m |
| Fuselage length | 12.09 m |
| Takeoff weight | 2300 kg |
| Maximum speed | 175 km/h |
| Ceiling | 3000 m |
| Range | 370 km |
| Armament | – |
| Engine | piston, radial AI-26V, 575 hp (423 kW) |
