Yakovlev Yak-42M

The Yak-42M was the Yakovlev design bureau's attempt to give the Yak-42 a second generation without abandoning the layout that had entered Aeroflot scheduled service in 1980. Forecast International's programme timetable places the start of Yak-42M development in 1987; the Spanish Wikipedia account instead treats 1987 as the year the new version was expected to enter service. Either way, it never left the design office: no example was built and, as a Russian industry review puts it, the project was never fully brought to the stage of certification testing.

What set the Yak-42M apart was the scale of the change. Western and Spanish-language sources describe a stretched fuselage — the Spanish Wikipedia specifies a 45 dm plug in the tail section, taking capacity from 156 to 168 passengers — together with more fuel capacity and a maximum take-off weight of 66,000 kg. The wing was not modified but replaced: Forecast International speaks of an entirely new wing, and the Russian review gives the figure that explains why. The production Yak-42 wing has an aspect ratio of 7.6; on the Yak-42M, with its greater span, the designers reached 10.5, a far more slender wing for an airliner of this class.

The trijet layout stayed. Instead of the Lotarev D-36 turbofans of the series aircraft, the Yak-42M was to use three Progress D-436M engines rated at 7500 kgf (about 73.5 kN) each — more powerful engines than those of the basic aircraft, as Forecast International notes. That source also describes a different installation for the centre engine, mounted in the manner of the DC-10 and combined with a cruciform tail. On the standard Yak-42 the centre engine is fed through a curved intake duct about 7 m long running inside the rear fuselage, one of the most complex parts of the airframe.

The systems were to be just as new. Forecast International lists a digital fly-by-wire flight control system and a flight deck equipped with CRT displays. The Russian Wikipedia adds the TsPNK-42M digital flight and navigation complex, intended to allow automatic landings in ICAO Category IIIa weather minima.

The sources do not describe exactly the same aircraft. The Russian Wikipedia presents the Yak-42M as a modernised Yak-42D with three D-436M engines and the new avionics, without mentioning a stretch, and the Russian industry review dates it to the late 1990s, whereas Forecast International and the Spanish Wikipedia place it in the late 1980s and early 1990s. They agree on the three D-436M engines and on the fact that the aircraft was never series-produced.

The project was reworked repeatedly. According to the Spanish Wikipedia, by 1991 several of its iterations used Aviadvigatel PS-90 engines. The preliminary design approved on 20 December 1992, which foresaw a deep modernisation of the Yak-42, still carried the name "Yak-42M with two PS-90A12 engines" before it was redesignated Yak-242, and Forecast International records 1993 as the year the Yak-42M effort was abandoned and replaced by the Yak-242: an aircraft generally similar in configuration, but with two engines instead of three. The work accumulated along that line was later drawn on by the Yakovlev bureau for the MC-21 programme, which is why the English Wikipedia describes the design as having evolved, through the Yak-242, into the Irkut MC-21.