Helicopter: WSK SM-1 (licenced Mi-1, NATO: Hare)

USSR / Poland
utility helicopter
1957

Helicopters were used for the first time on a limited scale during the Second World War by the Germans and Americans. The machines proved themselves well participating in several military operations, drawing the attention of military and aviation specialists, the majority of them predicting a great future to these new flying machines. In the Soviet Union, some designers were also interested in this subject. By the 1930's, first experiments were carried out, but the effects were not promising. That was a reason why they turned their attention towards simpler rotorcraft constructions – autogiros, where lift is caused by a self-propelled rotor (rotor autorotation).

One of the helicopter's designers in the Soviet Union was Mikhail L. Mil. Before the Second World War he worked at the Central Aero and Hydrodynamics Institute in Moscow, where he was busy with the scientific study of issues connected with rotorcraft. Mil also took part in research on autogiros. After the end of the war, he began to design his first helicopter, the EG-1. The necessity of introducing many changes into design led to developing of a new construction in 1948, giving rise to new multipurpose GM-1 helicopter.

The machine was built in a "classic" configuration. The all metal fuselage, in its front part was made in a form of a truss, flowing into the semi stressed tail boom. The cockpit, placed at the front, accommodated the pilot and two passengers. Behind the cockpit was an air cooled radial piston engine. Over the engine, a reduction gear powered the three blade rotor. The tail rotor was made of wood. The fuel tank was placed to the rear of the fuselage. In August 1948, the prototype was almost finished and flew for the first time in September that year. It was powered with a specially designed helicopter radial engine.

Tests showed the necessity of introducing some changes into the design. At the end of 1948, the helicopter crashed due to oil freezing with test pilots bailing out safely. The second GM-1 crashed in 1949. During test flights at a military test site, the transmission shaft, driving the tail rotor, broke due to low quality welding. Military and state tests followed in September 1949. During test flights, there appeared flatter and ground resonance (instability of a helicopter on ground, caused by the rotating main blades). Changes were introduced to manage these problems. In February 1950, the Soviet Board of Ministers made a decision of producing a test series of the GM-1 helicopter in a quantity of 15 examples and changing the name to the Mi-1. In 1951 the Mi-1 helicopter was presented for the first time at the Moscow-Tushino Air Show. On the road to mass production, however, there stood a few political and military notables with narrow imagination. To break their distrust M. Mil decided to show the new helicopter to Stalin. This presentation cleared all the obstacles. The Korean War, where the American helicopters proved their mettle in excellent style performing in many auxiliary roles (air ambulances, liaison, reconnaissance) of significant importance during wartime, also helped make a decision favourable for the Mi-1. The production increased, albeit slowly. In 1952–1960, 1012 examples were manufactured by three different factories.

At the same time, several changes improving the design and durability of the helicopter were introduced. With the first Mi-1 helicopter, the rotor life time was ended at 160 hours. In 1950, the Mi-1U (the GM-1) was developed, equipped with double controls and intended for pilot training. It was then put to mass production. In 1953, the new Mi-1T version appeared. Thanks to the changes in rotor technology, it was now possible to extend the rotor life time up to 300 hours. The more efficient Ai-26 engine, of increased power was used, the horizontal stabiliser was added to the tail boom, de-icing installation was applied and the cockpit doors were enlarged. All these changes improved the helicopter's performace and lowered service costs. Based on the Mi-1T, a few derivatives were developed. Only one version entered production. It was the Mi-1TKR, the artillery spotting version.

The next important Mi-1 modification appeared in 1957. The new version was named Mi-1A. Several significant improvements were made. Main rotor blades were given 600 hours of service time. Mechanical trims were replaced with electric ones, more modern instruments were installed and it was made possible to attach an auxiliary fuel tank. The last version of Mi-1 helicopter was named the MI-1M and entered serial production in 1957. It was based on the experimental Mi-3 helicopter, developed in 1954. The Mi-3 didn't enter production, but its changed fuselage served to build the Mi-1M. Its front part was enlarged to house a more comfortable cockpit. The blades were now of a rectangular shape. There appeared several derivatives of the Mi-1M. The Mi-1NCh was built for civil purposes. It could be used as a three passenger version and as an ambulance it could carry two persons in the containers attached to the fuselage boards. It could be also used as an agricultural machine, spraying chemicals from the attached hoppers.

The most interesting modification resulted from an effort to create a combat version. In 1958–1962 several armament systems were tested on the MI-1. It consisted of large calibre unguided rockets, the anti-tank "Falanga" and "Malyutka" guided rockets, and machine guns. The Soviet Army, however, was not interested in this new kind of weapon. The last Mi-1's were withdrawn from service in 1983. The Mi-1 made its mark in aviation history as the first Soviet helicopter to enter serial production.

In 1954, as a result of Polish-Soviet interstate agreement the Mi-1 was licensed for manufacture in Poland. Production started at Świdnik, near Lublin, in 1956. Licence production of the AI-26 (named the Lit-3) engines began at aircraft engine works in Rzeszów. The helicopter was designated the SM-1. Its first examples were assembled from parts delivered by the Soviet Union, where a group of Polish helicopter pilots were trained as well. At the beginning of 1957, the multipurpose helicopter SM-1/300 went into production. It was a counterpart to the MI-1T variant. It could serve as a liaison, reconnaissance, and executive aircraft. The next variant, the 1/600, a counterpart of Mi-1A, entered the assembly line in 1959. Based on the 1/600, a few derivatives were developed: SM-1Sz – training helicopter with dual controls; SM-1S – air ambulance, capable of carrying sick or injured in a nacelle attached to the fuselage; the SM-1D, a small flying crane; and the SM-1Z, an agricultural aircraft.

In 1960, in cooperation with Soviet specialists, the SM-1W was developed. The design solutions applied were similar to that of the Mi-1M. Agricultural version, the SM-WZ was also developed. The last version to enter production was the SM-1Wb. This featured a hydraulic servo steering system (booster) and all metal rotor blades with 800 hours of life time were applied.

The last SM-1 example was produced at Świdnik at the end of December 1965. In all, 1597 examples were made. Most were delivered to the Soviet Union; however, they were also purchased by other countries. Thanks to the production of the SM-1, Poland became one of the world's largest helicopter manufacturers. The Polish Air Force bought 85 examples. They remained in service until 1983.

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