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Mi-10 Harke - Development

The successful use of rotorcraft for airlifting bulky loads on a sling in-spired the Mil OKB engineers in the 1950s to create a "flying crane" helicopter. According to the designers' concept, the intended mission obviated the need for a large cargo hold and hence for a large fuselage; this would simplify the airframe design, reducing structural weight considerably. A "flying crane" helicopter did not have to carry much fuel. It was presumed that the helicopter would transport cargoes over short distances and would often operate within ground effect. All of this was expected to increase the payload by no less than 10 to 12% compared to helicopters of a similar class with a traditional fuselage. The engineers considered the possibility of carrying loads attached to the underside of the fuselage, the weight of which would be reduced to a minimum. Such loads would include various specialised containers: a passenger module, a cargo container, a fuel tank, an ambulance/operating theatre module, a mobile laboratory etc. Besides, the helicopter was to "straddle" the cargo, which would simplify and speed up loading. Such a machine could be used with great efficiency for unloading ships moored at the roadstead at some distance from the shore.

Development of this helicopter, which was designated V-10 (manufacturer's designation "izdeliye 60", article 60), began in the Mil OKB shortly after the first flight of the Mi-6. The project work was accompanied by wind tunnel research with a view to choosing the optimum parameters of the fuselage, landing gear and cargo suspension system. Development of the V-10, as well as of the Mi-6, was supervised by N. G. Roosanovich and M. N. Pivovarov. L. N. Babushkin was appointed chief project engineer. The Government directive calling for the development of a crane helicopter was issued on 20th February 1958. The machine was intended for airlifting bulky cargoes weighing up to 12 tonnes (26,455 lb) to a distance of 250 km (155 miles) and 15 tonnes (33,068 lb) to shorter distances.

The "flying crane" was evolved from the Mi-6, with the intention to ensure maximum structural commonality. The powerplant, the main and tail rotors and the transmission were almost completely borrowed from the V-10's predecessor. The flight control system and the hydraulics were also similar to those of the Mi-6, with the exception of certain features associated with the introduction of a control system for the hydraulic grips. The fuselage of the V-10 was completely new, having a considerably smaller cross-section. The forward fuselage housed the flight deck for a crew of three: two pilots and a flight engineer. The flight deck featured a closed-circuit TV (CCTV) system designed to simplify the operation of "straddling" the cargo and ensure its visual monitoring in flight; the TV camera was attached under the fuselage. Installed under the flight deck was a telescopic escape chute enabling the crew to abandon the machine in an emergency without striking the attached cargo platform. The centre fuselage incorporated a cargo/passenger cabin measuring 15.25 x 1.66 x 2.75 m (50 ft 0.39 in. x 5 ft 5.35 in. x 9 ft 0.26 in.). It could accommodate up to 28 persons accompanying the cargo, or be used for transporting a cargo weighing up to 3 tonnes (6,613 lb) which could be loaded through a side door by means of a hoist. Inside the fuselage, in the area of the main gearbox compartment, the LPG-7 cargo winch and a pulley block were fitted on a mount attached to reinforced frames; they permitted a load weighing up to 15 tonnes (33,068 lb) to be lifted to a height of 30 m (98 ft). The basic fuel load was carried in two external strap-on tanks and a service tank which was located behind the main gearbox. Two auxiliary fuel tanks holding 1,250 litres (275 Imp gal) apiece could be fitted in the cargo hold for ferrying operations.

The V-10 had a curious design feature: the centre fuselage together with the powerplant and main gearbox (and hence the main rotor shaft) was inclined 1 30' to starboard. This caused all the wheels of the four-unit undercarriage to lift off simultaneously, preventing the helicopter from banking and side-slipping during take-off. To retain the flight deck's horizontal position when on the ground, the starboard undercarriage legs were 300 mm (11.8 in) shorter than the port ones.

The design of the V-10's landing gear was similar in its layout to a lumber-hauling truck: it comprised four tall truss-braced legs with oleo-pneumatic shock absorbers and twin wheels. The fuselage had a clearance of 3.75 m (12 ft 3 1.2 in) with the oleo struts fully compressed. Undercarriage track and wheelbase exceeded 6 m (19 ft 8 in.) and 8 m (26 ft 3 in.) respectively. Previously, the Mil OKB had accumulated great experience in eliminating ground resonance in the process of developing the Mi-4 and Mi-6 . This enabled the designers to solve this problem in the case of the V-10 with its unique undercarriage.

According to the original project the load placed under the helicopter was to be hooked up and hoisted into the space under the fuselage and between the undercarriage legs by an LPG-7 winch, whereupon it would be secured by bracing wires. After this the helicopter could take off in ground effect or even with a take-off run. In the course of project development the customer made some changes and additions to the specification. In particular, it was stipulated that provision should be made for airlifting cruise missiles and ballistic missiles. For this purpose the OKB decided to supplement the crane helicopter's winch, with four remote-controlled hydraulic grips which would make it possible to lift containers and items of equipment fitted with appropriate attachment points straight off the ground. Small loads and equipment items lacking such attachment points were to be transported on a special multi-purpose freight platform measuring 8.5 x 3.6 m (26 ft 10.6 in. x 11 ft 9.7 in.) with reinforced sides and tie-down cleats. The platform was to be suspended between the undercarriage legs. It could be moved on its own wheels on the airfield and was provided with an LPG-3 winch for loading operations. Wheeled and tracked vehicles could be rolled onto the platform under their own power, using detachable ramps. The hydraulic grips could be remotely controlled from the flight deck and from the ground with the help of a portable control panel. Besides, as was the case with the Mi-6, the V-10 could be fitted with a hook permitting the carriage of slung loads weighing 8 tonnes (17,636 lb).

Using available parts and assemblies from a production helicopter was not the best solution from the point of view of achieving the maximum payload-to-weight ratio, but it speeded up project development and guaranteed reliability. Design work was completed in 1959, and on 15th June 1960 the helicopter (which had been redesignated Mi-10 by then) took to the air for the first time. The manufacturer's flight test programme was performed by test pilots G. V. Alfyorov and B. V. Zemskov. A special container was built to evaluate the helicopter's performance when operating with bulky loads on the platform. The tests proceeded very smoothly; already in the fourth flight the helicopter covered a distance of 3,000 km (1,863 miles) with intermediate landings. Sadly, in May 1961 the first prototype came to grief: it was destroyed in a ground fire caused by a failure of an oil pump actuator in the main gearbox. The actuators had to be reinforced and replaced both on the Mi-10 prototypes and on all Mi-6s.

The second Mi-10 prototype was ready for testing in July of 1961. This machine took part in the Tushino Air Display of 1961 where it demonstrated to the guests the carriage and delivery of a prefabricated cabin for geological survey teams. The third prototype was delivered to TsAGI for static tests. In the course of factory tests, on 23rd February 1961 a crew captained by B. V. Zemskov set an absolute world payload-to-altitude record by carrying a 15,103-kg (33,296-lb) load to 2,200 m (7,217 ft).

In December 1961 the Mi-10 was presented for joint State trials but was not admitted to these because the customer demanded that the helicopter be fitted with longer-life engines and main gearbox and new faired undercarriage legs, as well as with rotor blades featuring honeycomb filling. When these modifications were effected, it was necessary to conduct new factory tests; it took a full year before the Mi-10 could be presented for Stage A of the joint tests. The results of these tests confirmed that the Mi-10 was capable of airlifting bulky loads weighing up to 15 tonnes (33,068 lb) and measuring up to 20 m (65 ft 7.4 in.) in length, up to 3.5 m (11 ft 5.79 in.) in height and 5 m (16 ft 4.8 in.) in width (up to 10 m/32 ft 9.7 in. if the loads were cruciform), suspended either directly on hydraulic grips or on the special platform (the weight of which was included in the total payload). Besides, it was decided that there was no need to have both the load-lifting system with a winch and the hydraulic grips at the same time. Deletion of the former system made it possible to increase the payload and payload-to-weight ratio.

The joint tests of the Mi-10 were basically completed in 1964, but incorporating various minor improvements demanded by the customer took another three years. These were dictated primarily by the need to reduce vibration levels. The helicopter's thin fuselage compounded this problem. Besides, the flying crane helicopter concept was subject to constant changes; hence the flying crane's entry into series production was constantly delayed, despite the fact that the decision to launch production had been made back in 1961.

In the early 1960s the general view was that the basic mission of a rotorcraft of this kind would consist in ensuring the mobility of missile systems. However, several years later, when the Soviet military doctrine changed, this concept had to be abandoned. The Mil OKB had studied a number of heliborne missile systems and heliborne mobile missile servicing stations based on the Mi-10, but only one of them reached the flight test stage in 1965. It was the 9K74 (S-5V) system with the 9P116 launcher and the 4K95 missile, developed in response to the Government directive of 5th February 1965. The missile launcher weighing 12 tonnes (26,455 lb) could be airlifted to the distance of 200 km (124 miles) and could be prepared for launch within five minutes after the landing. However, the missiles of this type were phased out, and work on the Mi-10RVK (raketno-vertolyotnyy kompleks - heliborne missile system), as the variant came to be known, was discontinued.

The year of 1965 witnessed events which had a dramatic influence on the fate of the Mi-10. On 28th May, using a specially modified Mi-10R (rekordnyy, record-breaking) with a Mi-6-type short tricycle undercarriage instead of the four-unit landing gear, a crew captained by factory test pilot G. V. Alfyorov set an absolute payload-to-altitude record by taking a load of 25,105 kg (55,346 lb) to an altitude of 2,840 m (9,317 ft). Same year the "flying crane", together with the Mi-6, was displayed with great success at the Paris (Le Bourget) Air Show. A year later, in 1966, an air transport company from the Nether-lands purchased a Mi-10 for resale to the US airline Petroleum Helicopters, Inc. American specialists thoroughly tested the "flying crane" and operated it for supporting oil rigs in South America. The Mi-10 was put into production at the Rostov Helicopter Plant No. 168 in 1967, but it had a small production run - only 40 copies were built.

The Mi-10's ability to carry containers attached to the underside of its fuselage led to a number of proposals concerning the use of this helicopter. An experimental version intended for pinpointing enemy radios appeared in 1966 (one of its designations was Mi-10GR). It featured a special container attached to the helicopter by means of hydraulic grips which could deploy antennas to locate radio transmitters.

In 1966 development began of an ECM version of the Mi-10. Four years later the Mi-10P (postanovshchik pomekh - jammer) ECM helicopter was built. It was intended for assisting the combat activities of the Soviet Air Force's tactical arm by jamming the enemy's early-warning and air defence radars. A special Step' (Steppe) container with the mission avionics and antennas of the jammer was attached to the fuselage by means of hydraulic grips. The mission equipment was controlled by an operator sitting in the helicopter's cargo hold. In the mid-1970s nearly two dozen "flying cranes" were converted into ECM variants. One of them was used during the Afghan War. Alongside with these versions, the Mil OKB developed the experimental Mi-10UPL in 1966 for transporting a multi-purpose field laboratory (UPL = ooniversahl'naya polevaya laboratoriya). In 1970 one Mi-10 was fitted experimentally with uprated D-25VF engines delivering 6,500 shp, uprated transmission and new avionics.

The Mi-10 failed to find widespread service in the national economy because all potential cargoes had to be fitted with attachment points matching the helicopter's hydraulic grips to. Besides, bulky loads exposed to the slipstream created strong drag. The massive undercarriage nullified the gains in weight afforded by the lighter fuselage. The high placement of the flight deck impaired visibility for pilots when taxying, and the CCTV monitor proved to be of little use. Mi-10s were used only on special occasions, eg, for transporting the wings of the prototype Tu-144 and Tu-154 airliners.

Foreseeing the problems with the limited operational use of the "long-legged" flying crane, the Mil OKB began development of a "short-legged" version in 1964; this received the designation Mi-10K (K stands for korotkonogiy - short-legged). A. Kh. Serman was the aircraft's chief project engineer. This was a dedicated version for construction jobs and for loading/unloading operations. It had a short four-unit undercarriage; the resultant reduction in empty weight permitted an increase in payload. The Mi-10K was provided with an aft-facing ventral cockpit with a third set of controls and featured new radio equipment. When the helicopter was performing an installation job, one of the pilots descended into the ventral cockpit, facing the cargo, and took the controls. The helicopter's height on ground was reduced from 9.8 m (32 ft 1.8 in.) to 7.8 m (25 ft 7 in.). The strap-on tanks became somewhat shorter because of the redesigned main undercarriage legs. A modernized system for handling underslung loads allowed the helicopter to carry a load of 11.8 tonnes (26,020 lb) externally. The new version was developed within a very short time frame.

On 14th April 1965 the prototype Mi-10K made its maiden flight. During flight tests the crane helicopter was used at construction sites in Leningrad and in the mountains of Dagestan, it attracted attention as an exhibit of the 26th Paris (Le Bourget) Air Show in 1967. Two years later, the Ministry of Civil Aviation officially introduced the machine into its inventory and, after minor improvements to the flight control system and the enlargement of the ventral cockpit, the "short-legged" flying crane was put into series production at the Rostov Helicopter Plant. In all, 15 Mi-10Ks were built and another four were converted from "long-legged" Mi-10s. In the course of the flying cranes' operational use the Mil OKB put much effort into diminishing the vibrations, and in 1975 the Mi-10K was fitted with a system for damping the oscillations of the underslung load.

The Mi-10Ks rendered very useful service until quite recently. They made it possible to considerably speed up construction work at a number of industrial sites and to achieve thereby a substantial reduction of costs. The cost of flying crane operations performed by the Mi-10K proved to be 50% lower than the Mi-6's.

The "short-legged" Mi-10K has vividly demonstrated that helicopters are not only a unique means for transport and combat use; they play an equally unique role in civil engineering. The construction and introduction into operational use of the Mi-10 and Mi-10K gave the OKB invaluable experience of creating heavy-lift flying crane helicopters, and the user organizations obtained operational experience with them.

A group of Mil OKB designers received high Government awards for their part in the creation of the Mi-6 and Mi-10 helicopters. The State Prize was awarded in 1968 to M. L. Mil, V. P. Lapisov, A. V. Nekrasov, M. A. Leikand, P. A. Solov'-yov, M. N. Pivovarov, V. T. Matsitskiy, D. M. Choomachenko, L. N. Mar'yin, G. P. Kalashnikov, I. P. Evich and O. V. Oospenskiy.




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