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Mi-1 HARE - Variants

In all, 1,683 Mi-1s in various versions were produced in Poland (including 86 examples of the locally designed SM-2 derivative). Most of them were delivered to the Soviet Union. The last Mi-1 in the USSR was officially retired in 1983.

In the course of production and operational use numerous modifications and improvements were progressively introduced into the design of the helicopter. Special attention was paid to improving the design and enhancing the reliability of the rotor blades which are some of the helicopter's most difficult components to manufacture, and embodies a lot of scientific research. The blades' tapered steel-tube spars originally built in three parts with telescopic joints were replaced in 1956 by spars made of a single cold-rolled variable-section, variable-thickness steel tube. A year later the first all-metal blades for the Mi-1 featuring a pressed duralumin spar were developed. At that time the Soviet metallurgic industry had no experience in pressing long closed-contour extrusions, and the specialists of Plant 329 (or OKB-329, as the Mil Design Bureau came to be known) had to develop the production methods for manufacturing such structural sections together with the metallurgists.

Introduction of all-metal blades led to the inclusion of aerodynamic compensators (balance tabs) and then of irreversible hydraulic actuators into the helicopter's control system. After the Mi-4's rotor hub featuring considerable im-provements was tested, radical alterations were introduced into the Mi-1's rotor hub as well. The separate pitch and throttle controls were combined in a single pitch/throttle control collective pitch lever. Improvements incorporated in the Mi-1 during the 1950s included the fitting of a steerable variable-incidence stabilizer, the installation of a sling system capable of transporting a 500-kg (1,102-lb) load externally, the introduction of de-icing on the rotor blades, new avionics etc. In 1952 the AP-5 autopilot originally designed for fixed-wing aircraft was tested on a Mi-1. Subsequently this helicopter was used on many occasions as a flying testbed for testing various new items of equipment.

In 1950 the baseline communications liaison helicopter was followed by a two-seat training version with dual controls, the Mi-1U (oochebnyy; original manufacturer's designation GM-2); the pilot and the instructor were seated side-by-side. In 1951-1952 the next baseline version of the Mi-1 was developed (temporarily known in-house as the GM-3). Besides an uprated AI-26GRF engine, it featured a number of minor alterations in the design and formed the basis for developing in the following year yet another baseline version, the Mi-1T (tryokhsotchasovoy, ie, with a 300-hour service life), possessing a 300-hour design life of the main assemblies. On this machine the AI-26GRF engine was replaced by an improved version, the AI-26V delivering 575 hp at take-off; the cabin doors were enlarged, the helicopter was fitted with a stabilizer and a de-icing system. The new model was adopted as a standard for series production in 1955. Its two-seat training version was allocated the designation Mi-1TU (Mi-1T-oochebnyy - training).

In 1954 two Mi-1T helicopters were modified for operations from icebreakers in the Arctic Ocean; that year development also began of the Mi-1KR (later Mi-1TKR) artillery spotting version (KR = korrektirovschchik-razvedchik) which was put into production in 1956. In the same year of 1956 the prototype of the Mi-1NKh made its appearance. This version was intended for the use in national economy (NKh stands for narodnoye khoziaistvo - national economy). In the mid-1950s the Soviet Navy tried to use the Mi-1 as an ASW helicopter, but the power of the AI-26V engine proved insufficient for carrying the search equipment and anti-submarine armament. A project of a shipborne version of the Mi-1 with folding rotor blades and tail boom, developed in the OKB, progressed no further than the drawing board. In 1957 one Mi-1T was modified and tested with equipment for laying telephone lines for Army use.

When the industry mastered the production of the radically new type of rotor blades featuring a one-piece variable-section extruded spar, this formed the basis for creating a new baseline model of the Mi-1 in 1957. It received the designation Mi-1A (the original factory designation was Mi-1R; the R stands for resoorsny = longer service life). The service life of the model's assemblies was increased to 600 hours. The modernized model differed from the Mi-T in having electromechanical trim tabs instead of spring tabs, new avionics and an attachment point on the fuselage side for an auxiliary fuel tank. A training two-seater version was allocated the designation Mi-1AU, while a version equipped with periscopic observation device and an aerial camera for artillery spotting was named Mi-1AKR. The service life of the helicopter's main assemblies was constantly increased; by the end of 1950s it reached 1,000 hours, increasing to 2,000 hours by the mid-1960s and 3,000 hours 10 years later.

The Mi-1T and the Mi-1A represented a direct development of the GM-1 helicopter. A more profound modernization of the Mi-1 was started when the OKB, in compliance with an order from military customers, developed an ambulance version which was allocated the factory designation Mi-3. It featured a new four-bladed main rotor, a more comfortable cabin, a modified fuselage structure and was equipped with two detachable external panniers housing casualty stretchers. The front part of the panniers was glazed and they were connected with the cabin by tunnels, which allowed the medical attendant to be in touch with the patients and to give them medicines in case of need. This model's performance was superior to that of the production Mi-1T, and it was recommended for series production.

However, introduction of the Mi-3 into squadron services was halted because of the difficulties connected with the manufacturing of both three-bladed and four-bladed main rotors at the same time. Nevertheless, the experience gained by the OKB in designing and developing this model was put to good use when the Mil team embarked on developing the modernized Mi-1M version which was built in 1957. Compared to the Mi-1A, it differed in having attachment points on the sides for detachable panniers and containers, a less "snub-nosed" forward fuselage (the upper fairing of the nose housed the cabin ventilation system), larger and more comfortable cabin, equipment for all-weather operations, wheels with brakes, a baggage compartment and some other refinements. In the same year of 1957 series production of the Mi-1M was started at Plant No. 168 in Rostov. This army helicopter was used in communications transport and ambulance roles and, in its turn, served as a basis for producing the Mi-1MU two seat training version and the Mi-1MRK for reconnaissance and artillery spotting (razvedchik-korrektirovschchik). Two examples of the Mi-1M were equipped with flotation gear; designated Mi-1MG or Mi-1G (ghidro-, = hydro-), they were placed on board the vessels of the "Slava" (Glory) whaling fleet in 1958.

The Mi-1M served as a basis for a new version developed in 1957 for the use in the national economy and designated Mi-1MNKh. It took into account the experience gained in the process of designing the Mi-1NKh and was developed in five versions: passenger version with a rear bench for three passengers; ambulance version with detachable side panniers; mail-carrying version with detachable containers; agricultural version; ferry configuration with an auxiliary fuel tank. When used for crop spraying and dusting, the agricultural version was equipped with detachable hoppers for chemicals and spray bars mounted on the sides of the fuselage. In production and in service the Mi-1MNKh was referred to simply as Mi-1NKh; from 1959 onwards it bore the popular name Moskvich (Muscovite). One Moskvich fitted out as a VIP machine was used by the President of Finland. Starting in the early 1960s, all production Mi-1Ms and Mi-1NKhs were powered by boosted AI-26VF engines and featured all-metal main rotor blades and hydraulic actuators in the control system. In 1963 the Mi-1MGs serving on board whaling vessels were upgraded to Mi-1KF standard (KF = kitoboynyy flot - whaling fleet).

In the second half of the 1950s armed combat helicopters appeared in other countries. In the Soviet Union the development of such machines was initiated in 1958 on the basis of the Mi-1MU. Mounted on the sides of this helicopter were outriggers carrying two cassettes with 12 TRS-132 rocket projectiles (TRS = toorboreaktivnyy snaryad, literally 'turbo-rocket projectile', the 'turbo' referring to the rotation imparted to the projectile by canted nozzles in order to stabilise it). In the following year new versions were developped, their armament comprising infantry machine-guns designed by Nikitin or Kalashnikov; the same year saw the appearance of the first Soviet version armed with the Falanga (Solifuge) anti-tank guided missile system which included two or four guided rockets.

In 1961-1962 a tank-busting version of the Mi-1MU armed with four 3M11 Falanga ATGMs successfully passed State acceptance trials and was recommended for entry into service with the Armed Forces. However, at that time the Armed Forces command possessed no clear-cut concept of the use of combat rotary-wing machines, and the type did not go into series production. Three years later, new combat versions of the Mi-1MU were developed, armed with four 9M17 Falanga ATGMs or six 9M14 Malyutka (Little one, or Baby) missiles, but they were not adopted for squadron services, because the production of the Mi-1 was coming to a close. Other armament configurations for this helicopter provided for the installation of heavy-calibre aviation machine-guns in detachable containers on the fuselage sides, but they went no further than the drawing board.

In 1957 another modernized version was tested - the military handler of telephone lines of communication Mi-1T. On its sides hung containers with coils of telephone wire, which allowed to lay in one flight a communication line up to 13 km long.

In addition, in the mid-1950s, a deck modification was developed with a folding tail beam and blades, but the engine power was insufficient to lift special search equipment and weapons. The projects of the helicopter GM-3 of the longitudinal scheme with two screw installations and B-5 (Mi-5) with a gas turbine engine were also not realized.

Another modification of the Mi-1 which, likewise, failed to materialize was the version developed at the Plant No. 329 in 1960 and intended for the Spetsnaz (commando) troops. Four troopers were accommodated in the cabin, and the fifth one was placed in a special compartment fitted out in the aft fuselage under the tailboom.

The Mi-1T, Mi-1TU, Mi-1MNKh and Mi-1A were built under license in Poland at the WSK Swidnik plant as the SM-1/300, SM-1Sz (szkolny), SM-1Z and SM-1/600 respectively. In 1959 Polish designers assisted by engineers from the Mil OKB developed their own versions based on the Mi-1T: the SM-1S ambulance version and the SM-1D flying crane. In 1960 the Polish plant terminated the production of the Mi-1A and switched over to the manufacture of the Mi-1M and Mi-1NKh (Mi-1MNKh) under the designations SM-1W and SM-1WZ accordingly. The Mi-1M helicopters built there between 1963 and 1965 were equipped with all-metal main rotor blades and boosters in the control system, bearing the designation SM-1Wb. Polish-produced Mi-1s were used by the Polish Aviation Research Institute (Instytut Lotnictwa) as testbeds for new avionics, oil prospecting equipment etc.; they were also used as glider tugs. In 1971 the specialists of this Polish aviation research centre fitted an SM-1/300 with wings of trapezoidal platform spanning 8 m (26.24 ft) and conducted thorough studies of this layout of a rotary wing aircraft.

In 1959 the Mi-1 helicopter was used by Polish helicopter constructors as a basis for the development of a modernized version called SM-2 which featured an enlarged cabin for 5 persons with wide sliding door on each side. The fourth passenger was seated to starboard of the pilot seat. The wide door facilitated rescue operations. In the ambulance version the stretcher was placed inside the cabin. However, the SM-2's performance proved to be inferior to that of the Mi-1, and the modernized machine saw only a limited production run. A number of SM-2s was exported to Czechoslovakia.

The first helicopter developed by the Mil Design Bureau laid the foundation for large-scale production and widespread operational use of helicopters in the USSR, as well as in a number of other nations.