10 July 2010

Tupolev's Own Tristar Design

Amongst the Russian aircraft design bureaus (called OKBs), it's common practice to reuse designations for aircraft projects that have been previously used for aircraft that never made it past the design stage. The Tupolev Tu-204 twin jetliner, for example, is the third design to use the Tu-204 designation. Work on the first Tu-204 project began in 1973, at which time OKB Tupolev was studying the concept of a family of related aircraft designs that shared common features, powerplants and systems. At the time the Tu-134 and Tu-154 were the main domestic jetliners in the Aeroflot fleet as well as in the Soviet client states. The first Tu-204 project was for a short-haul transport carrying up to 180 passengers with two Kuznetsov NK-8 low-bypass turbofan engines (the same powerplant used on the Tu-154) mounted under a T-tail on the aft fuselage. In keeping with Tupolev's ideas for a family of related airliners, this first Tu-204 design would have shared many features of the Tu-134.

By the mid-1970s, though, the design bureau's work and moved towards a medium range airliner with comparable performance to the Airbus A300, the Lockheed L-1011 Tristar, and the McDonnell Douglas DC-10. The expected growth in air travel made a larger-capacity aircraft a more attractive proposition and efforts were made for this new, second Tu-204 project to embody many of the same cabin comforts of the Western wide-bodies. Work began in 1975 on this newer and larger Tu-204 project.

The second Tu-204 project would have had a large fuselage on par with that of the DC-10 and Tristar and underfuselage cargo holds that could accommodate LD-1 and LD-3 containers. A 28-degree sweptback wing with a supercritical airfoil combined with an extensive array of high-lift devices offered good field performance and efficient cruising speeds. A significant amount of time was spent on determining the ideal number of engines, location of the engines, and the type of engines to be used. Again returning to the idea of a family of airliners, Tupolev's designers created to variants of the Tu-204- a twin-engined version and a three-engined version. Both designs used the Soloviev D-30 turbofan (also used on the Il-76 airlifter). The trijet version had a longer fuselage and had its third engine mounted in the end of the aft fuselage and fed by a curved S-duct with its intake ahead of the vertical fin. For all intents and purposes, it strongly resembled the Lockheed Tristar.

Interestingly enough, in 1974 British charter operator Court Line flew one of its Tristars to Moscow along with cadre of Rolls-Royce engineers for a series of demonstrations for Aeroflot that took place over three days. While debatable about how serious Aeroflot's interest in the Tristar was, Aeroflot's engineers were given full access to the aircraft for close examination. This would have been just a year before the launch of the second Tu-204 project.

In the late 1970s the Soviet Council of Ministers issued a directive for a more comfortable and technologically-advanced jetliner that had efficiency as its key selling point. It had to be on par with what was seen as the most advanced jetliner of the day, the Boeing 757/767 series that were under development in the late 1970s (the 767's first flight was in 1981, the 757's was in 1982). As a result, in 1979, the Tu-204 family were redesigned with the more advanced Soloviev D-90 turbofan. Work on the two versions was done in parallel, but Tupolev's designers were steadily starting to favor the twin-engined design as the D-90 was showing promise and growth potential as a powerplant. By 1981 disputes emerged between differing design viewpoints at OKB Tupolev. One group felt that the twin-engined design was just as safe as the three-engined version and that design work should focus on a wide-body twin. Another group wanted to pursue the three-engined design for safety reasons and that the power of three engines offered more growth potential. And a third group emerged that favored a twin-engined design, but felt that the only way to match the 757/767's fuel economy was to use a narrow-body design.

In 1986 the third group won out the internal battle over the Tu-204's design. After a shuffling of design and engineering heads on the project, the Soviet Council of Ministers gave its approval for the Tu-204 to be a twin-jet narrow-body design that strongly resembled the Boeing 757 in layout. That marked the third use of the Tu-204 designation and that is the aircraft that made its first flight on 2 January 1989.

Source: OKB Tupolev: A History of the Design Bureau and Its Aircraft by Yefim Gordon and Vladimir Rigmant. Midland Publishing/Ian Allan, 2006, p267-273.

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