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Mi-8 Hip - Further Modifications

In the course of development and operational service of the Mi-8 the design of its parts and assemblies was constantly improved. The helicopter provided for a good basis for testing various experimental designs. One major problem which took a long time to crack was the development of a long-life anti-torque rotor for the Mi-8. The EDB engineers had to conduct a lot of research aimed at improving the design of the rotor and optimizing its performance. Experimental anti-torque rotors of various types were tested on the Mi-8. These included a three-blade rotor with a cardan shaft-mounted hub and glass fibre blades; a four-blade rotor with drag and flapping hinges and elastic links between the blades; a four-blade and a five-blade semi-rigid rotors. The latter type was recommended for series production but never reached the production stage.

For many years the Mi-8 was used for testing new main rotor blades. These included reinforced all-metal blades with spars and ribs of various designs; mixed-construction blades with a glass fibre-plated steel spar and glass fibre ribs; blades with honeycomb, Styrofoam or Nomex-filled pockets; and others.

Under the conditions of planned economy it was not easy to bridge the gap between an experimental design which had proved its high efficiency, and its production model. The governing bodies of the Soviet aircraft industry were always reluctant to undertake changes in the well-established production routine. Far from all successful designs of various devices or assemblies could be introduced into series production.

In the course of more than 30 years of operational service of the Mi-8, the Mil OKB designers together with their colleagues from Kazan and Ulan-Ude and specialists from the Izotov EDB succeeded in significantly improving its design and extending the life of its aggregates. The assigned life of the Mi-8T current versions exceeds 20,000 hours. In 1980 the Mi-8 became the first Soviet helicopter to receive a type certificate in accordance with the US FAR-29 regulations when operating in Japan. In the 1970s and 1980s Mi-8s were equipped with vibration dampers installed above the main rotor hub, a Doppler speed and drift indicator and a radar. The pendulum-type system for the carriage of the slung cargoes was replaced by a cable sling system capable of handling the slung loads weighing 3 tonnes. Combat survivability was enhanced, armor protection introduced and heavier armament fitted; various items of equipment were upgraded several times. A version developed to meet an order from the Polish Air Force provided accommodation for 37 troops in the cargo cabin.

Development and improvement of various aggregates of the Mi-8 were conducted not only by specialists in the home country; the same task was tackled by foreign operators. In particular, the Egyptian Air Force installed dust filters developed by the British company APME (Aircraft Porous Media Equipment) on the air intakes of its Mi-8Ts and the Finnish Air Force equipped its Mi-8s with navigation radars. In the second half of the 1980s the Mil EDB conducted a comprehensive research programme designed to improve the helicopter's aerodynamics: the external strap-on tanks were deleted, new clamshell cargo doors were installed, fairings were fitted to the swashplate and the exhausts etc

Powerplant upgrades played a crucial role in enhancing the Mi-8's performance. Shortly after the helicopter entered production improved TV2-117A engines were introduced. From 1973 onwards, helicopters intended for delivery to countries in southern areas were fitted with specially modified engines optimized for operation in 'hot-and-high' conditions. At the end of the 1970s an uprated version, designated TV2-117F was developed; it had a 1,700-shp emergency rating. This engine powered the Mi-8PA variant which was successfully certificated in Japan in 1980. In the 1980s production Mi-8 helicopters received the longer-life TV2-117AG turboshaft with graphite seals in the compressor bearings. This version was designated Mi-8AT. This version was the basis for the development of different modifications, mainly civil ones. Mi-8AT helicopters powered by the cheap TV2-117AG engines are in widespread operational service in non-mountainous areas with moderate ambient air temperatures.

In 1987 the Mil EDB developed the experimental Mi-8TG version powered by TV2-117TG engines; this was the world's first helicopter adapted for operation on liquid methane. To increase the reliability of power plant operation, dust filters of various types were developed. Of these, the so-called 'mushroom' type was selected in 1979 for series production and operational service. However, the most notable chapter in the history of the Mi-8's development was the helicopter's modernization to accept the new and more powerful TV3-117MT engine.



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Page last modified: 09-07-2011 13:18:58 ZULU