Mi-2 HOPLITE - Development
Being a product of the 1940s, the Mi-1 light helicopter, despite all its merits, was falling behind the state of the art by the end of the following decade. A number of new light rotorcraft came into being in other countries, notably in France; they were superior in performance to their Soviet counterpart. This was due primarily to the introduction of a radically new powerplant - the turboshaft engine. The Mil OKB was aware of the need to enhance the performance of its firstling; starting in the mid-1950s, several projects were developed entailing a radical modernization of the Mi-1, some of them providing for the installation of a gas turbine instead of a piston engine. The concept of upgrading the existing model instead of developing a new one from scratch seemed promising at the time because it was expected to save time and make use of the tried and tested parts and assemblies that were well established in production. In the process of developing a project of a single-engined gas turbine-powered successor to the Mi-1, which was allocated the designation V-5, the OKB designers came to the conclusion that a twin-turbine helicopter would be a better option since this would ensure considerably greater reliability and flight safety. The twin-turbine helicopter project was designated V-2.
At first it was the Civil Aviation authorities that displayed the greatest interest in the V-2, but before long it attracted the attention of military customers as well. As a result, on 30th May 1960 the Mil OKB was tasked by the Government to develop this helicopter in agricultural, passenger, transport/ambulance and training versions. The work on the new machine was supervised by Deputy Chief Designer V. A. Kuznetsov. A. Kh. Serman was appointed chief project engineer (later succeeded by A. A. Britvin), the engineer in charge of flight testing was V. V. Makarov. When developing the V-2 the Mil OKB designers strove to use as many as possible the Mi-1's components and assemblies: the main rotor, parts of the main gearbox, the transmission etc.
The design of a powerplant for the V-2 was tackled by the Leningrad-based OKB-117 design bureau headed by Sergey P. Izotov, successor to Vladimir Ya. Klimov; development of such low-power gas turbines was quite a new task for this OKB. This work resulted in the GTD-350 gas turbine rated at 400 shp. The specific parameters of the GTD-350 were markedly inferior to those of foreign engine types, yet the emergence of this engine enabled the Mil OKB to rapidly develop a new second-generation light helicopter similar in its dimensions to the Mi-1 but capable of transporting more passengers (eight instead of three) and possessing considerably better performance. In January 1961 the State Commission approved the full-size mock-up, and in August of the same year the workers of the assembly shop at Plant No. 329 completed the construction of the first prototype.
The layout chosen for the V-2 was typical for all turboshaft-powered helicopters designed by Mil. The powerplant was placed in a large fairing above the fuselage; the two GTD-350 engines were mounted ahead of the three-stage main gearbox, with the cooling fan placed above the engines. The forward fuselage provided accommodation for a pilot and a passenger, as well as for DC batteries and other items of equipment. Behind them was a cargo/passenger cabin; placed centrally on its floor was a fuel tank container which also served as the base for two three-seat benches. A tip-up seat for the eighth passenger was attached to the aft wall of the cabin. In the ambulance version the cabin could accommodate four stretchers and a seat for a medical attendant. Two supplementary fuel tanks could be mounted on the fuselage sides. The helicopter was equipped with a hook for carrying slung loads weighing up to 800 kg (1,764 lb); it was also provided with a hoist and a boom.
A steerable stabilizer was mounted at the end of the tailboom; its variable incidence was correlated with the collective pitch of the main rotor. The main rotor blades of rectangular planform had a pressed duralumin spar and honeycomb trailing-edge sections; they were attached to the rotor head in a traditional way - by drag, flapping and feathering hinges. Hydraulic dampers were installed in the rotation plane. A two-blade all-metal pusher-type tail rotor featuring a single slanted flapping hinge served for directional control and torque compensation. The main and anti-torque rotor blades and the cockpit windshield were provided with an electro-thermal de-icing system. Control of the main rotor collective and cyclic pitch was effected with the help of hydraulic actuators, but there was no need to have a back-up hydraulic system because in the event of a hydraulics failure the pilot could switch over to manual controls (the loads on the control levers were moderate). The three-unit landing gear comprised two main units and the nose leg. The undercarriage legs were fitted with single-chamber oleo-pneumatic shock absorbers. Skis could be mounted instead of wheels during winter operations.
On 22th September 1961 test pilot G. V. Alfyorov performed the first hover in ground effect on the V-2 and a 15-minute low speed flight. In the following month the helicopter was presented for joint State trials.
The military customers regarded the V-2 primarily as a transport and ambulance machine, whereas the Civil Air Fleet needed an agricultural version as a matter of priority. It was in this version that the second prototype was completed by the experimental production facility of Plant No. 329 at the end of 1961. In February 1962 the agricultural version of the V-2 was also submitted for the State trials. It was intended for spraying and dusting forest areas and crops. The chemicals were filled into two hoppers mounted externally either side of the fuselage, each of them holding 400 litres (88 Imp gal). Spraying was effected with the help of large-span transverse spraying bars; they were actuated by special fans and pumps mounted at the lower part of the hoppers. Later, concurrently with the modernization of the helicopter, its agricultural equipment was also upgraded. In 1963-65 the V-2 prototype successfully passed operational tests in agricultural guise, performing crop spraying and dusting work in the Borets (Protagonist) collective farm in the Moscow region. Later it received favorable attention when displayed at the "Chemistry" and "Modern agricultural equipment and machinery" international exhibitions.
On 14th May 1963, when the V-2 was still undergoing flight testing, test pilot B. N. Anopov set a speed record for light helicopters; it was subsequently bettered by T. V. Russiyan, a woman sports pilot, on a helicopter of the same type.
On 20th September 1963 the State Commission adopted a decision recommending the V-2 to be put into series production under the designation Mi-2. It was envisaged that production would be organised in Poland. As early as September 1962 the first prototype of the V-2 was demonstrated to members of the Soviet Government and representatives of the Polish People's Republic. At that time the question was discussed of this helicopter replacing the Mi-1 (SM-1) in series production at the WSK Swidnik helicopter plant. Preparations for Mi-2 production in Poland got underway in late 1963. The official licensing agreement was signed in January 1964. Polish engineers together with the Mil OKB designers worked out production drawings and documents and introduced the machine into large-scale production. In 1965 the first production helicopter left the assembly line at Âwidnik. The first production machine which was assembled in Poland from Soviet-manufactured parts took to the air on 26th August; the first machine assembled from Polish-produced parts followed on 4th November 1965. All "Polish" Mi-2s were immediately sent to the USSR for evaluation . Two years later the Polish helicopter industry demonstrated the Mi-2 at the 26th Paris Air Show in Le Bourget. Poland supplied the Mi-2 not only to the Soviet Union but also to Bulgaria, Czechoslovakia, Cuba, East Germany, Hungary, Iraq, Lesotho, Libya, Nicaragua, North Korea and Romania. At present the Mi-2 has become appreciably more widespread geographically due to resales. Production at Swidnik totalled 5,418 Mi-2s, 16 PZL Kanias (a Mi-2 derivative, see below) and two single prototypes of the Mi-2M1 and Mi-2M2 (see later). From 1974 onwards the Mi-2 helicopter was manufactured by the Swidnik plant with full responsibility for the design and quality.
After the transfer of all production rights to the Swidnik plant Polish designers, aided by their Soviet colleagues, put a lot of effort into upgrading the Mi-2. In the course of this work many of the helicopter's parts and assemblies were improved. This included the introduction of glassfibre main and tail rotor blades, new agricultural equipment and many other improvements. In 1971 the Mil Moscow Helicopter Plant tested the first air intake dust filters on the Mi-2. A number of Mil OKB specialists were awarded orders and medals of the Polish People's Republic for the assistance they had rendered to the Polish helicopter industry. Among them, M. L. Mil and N. S. Otdelentsev were awarded the Commander's Cross of the Order of Poland's Resurrection.
The Mi-2 possessed a number of advantages, yet its flight performance and economic efficiency suffered considerably due to the insufficiently high parameters of the powerplant. Not only was the GTD-350 turboshaft inferior to foreign engines as far as specific parameters are concerned; it also required a lengthy gestation period. In the course of the flight-testing of the Mi-2 it became apparent that it was necessary to move the engines a little farther apart to ensure better access for maintenance; this inevitably led to a redesign of the transmission and the upper part of the fuselage. It proved difficult to put into practice the concept of the widest possible commonality with the Mi-1. In the course of the V-2's development the main rotor which had been borrowed from the Mi-1 had to be completely redesigned because increased RPM (as compared to the Mi-1) led to greater centrifugal forces on the blades. The much more powerful engines dictated the need for a new anti-torque rotor with a greater thrust. An attempt to retain gears from the Mi-1 resulted in an overweight main gearbox. The wish to retain the Mi-1's overall dimensions prevented the designers from using the passenger-carrying capacity of the new helicopter to the full.
Compared to similar class foreign helicopters, all of which were single-engined, the twin-turbine V-2 offered considerably greater flight safety. It is owing to the V-2 that the twin-turbine layout came into widespread use on light rotorcraft; starting in the 1970s, new helicopters of this class with twin-turbine powerplants began appearing abroad.
The need to redesign many parts and assemblies and deal with the new engine's teething troubles caused lengthy delays in the testing of the new helicopter. The trials program was not completed until 1967. Due to its drawbacks the Mi-2 saw only limited operational use in the Soviet armed forces.
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