The Antonov An-74 (NATO codename 'Coaler') was the military version of the An-72 STOL transport. In some quarters of the V-VS, the An-74's upper surface blowing concept was overly ambitious for a frontline service aircraft. To hedge its bets, Antonov OKB developed the less risky An-78 (NATO codename 'Coattail').
The An-78 combined the fuselage and tail surfaces of the An-72/An-74 with a new unswept wing (in effect, An-12 outer panels attached to a reduced-span centre section). In place of the An-72/An-74's Lotarev D-36 turbofans, the An-78 was powered by twin Ivchenko AI-20D turboprops (in cowlings from the Antonov An-32 'Cline').
The An-78 design was prompted in part by the Indian Air Force cancelling its proposed An-32 purchase in 1980. [1] However, the An-78 'Coattail' did enter Soviet service in small numbers, serving alongside V-VS Antonov An-26 and An-32 transports but always overshadowed by the more dramatic performance of the 'risky' Antonov An-74 'Coaler'. In the end, the entire V-VS An-78M fleet was transferred to Aeroflot (as An-78As) for use on civilian cargo routes.
(Top) Early-production Antonov An-78M 'Coattail' transport in V-VS service markings.
Another lesser-known Antonov An-74 development was the Antonov An-174 intended for export. In place of twin Lotarev D-36s, the An-174 featured four smaller Avco Lycoming ALF 502 turbofans mounted over the wings. This combination turned the An-174 into a STOL tactical transport equivalent to the Western BAe 146 airliner. The An-178 was widely demonstrated but found no export customers -- partly due to the higher cost of its US engines, partly to a Western boycott of Soviet products after the 1980 invasion of Afghanistan. [2]
(Bottom) The sole prototype Antonov An-174 'Coalface'. This aircraft would later fly in support of the Soviet Antarctic Expedition (SovAE).
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[1] The Indian AF reversed its decision again and accepted the An-32 in 1981. The back-up An-78-I concept was not required.
[2] As the updated Antonov An-274, this concept would later be revived as a potential rival to the proposed Ilyushin Il-112. In the event, neither tactical transport type was built.
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