Sukhoi Su-27 T-10

The programme was the Soviet answer to the American F-X competition, which in 1969 produced the F-15 Eagle. The Soviet General Staff issued a requirement for a Perspektivnyy Frontovoy Istrebitel (PFI, "advanced frontline fighter") with very ambitious goals: long range, good short-field performance from austere runways, excellent agility, Mach 2+ speed and heavy armament. When it became clear that a single aircraft could not meet all of this in the numbers needed, the requirement was split into a lightweight fighter (LPFI), which became the MiG-29, and a heavy fighter (TPFI), assigned to the Sukhoi bureau. Sukhoi had already carried out preliminary studies on the subject in 1967, and in early 1971 the formal decision was taken to start work on the aircraft, known internally as "izdeliye T-10". In 1972 two scientific-technical councils eliminated the Yak-45 and Yak-47 proposals and endorsed the split into two fighters sharing as much equipment as possible.

The aerodynamics of the T-10 were largely worked out by TsAGI together with the design bureau and the Siberian institute SibNIA. The team adopted the so-called "integral layout", in which fuselage and wing form a single lifting body, with longitudinal instability in subsonic flight and a fly-by-wire pitch channel with no mechanical linkage between the stick and the stabilator. The two engines sat in separate nacelles under the lifting body, and the "tunnel" between them acted as an extra lifting surface and shielded stores from radar. The prototype wing had a curved (ogival) leading edge without leading-edge flaps and large root extensions; the two fins were mounted on top of the engine nacelles.

The first aircraft, T-10-1, powered by two Lyulka AL-21F-3 turbojets, took off on 20 May 1977 flown by test pilot Vladimir Ilyushin, Hero of the Soviet Union. It was used to assess general airworthiness, stability and handling; according to the Russian source it made 38 test flights that led to a set of modifications, including anti-flutter rods on the wingtips and fins. No weapons system was fitted. The aerodynamic layout had already been judged unsatisfactory during construction, and the maiden flight confirmed it: the pilot found directional stability problems at high speed with the closely spaced fins.

T-10-2 first flew on 16 May 1978. On 7 July 1978, during a flight to check the gains of the longitudinal control system, it entered a pitch oscillation, exceeded its g limit and broke up in flight; the pilot, Yevgeny Solovyov, Hero of the Soviet Union, was killed. Western intelligence had spotted the aircraft on satellite imagery at the Flight Research Institute (LII) airfield at Ramenskoye, Zhukovsky, first calling them "Ram-K" and later assigning the NATO reporting name Flanker-A.

The second batch, T-10-3 and T-10-4, was built at the Komsomolsk-on-Amur plant (KnAAPO) from 1978. These were the first to receive the intended engine, the Lyulka AL-31 turbofan, still with the accessories mounted underneath, which meant redesigned nacelles. T-10-3, devoted to powerplant testing, flew on 23 August 1979 after delays caused by engine trouble; in 1982 and 1983 it was used for land-based ski-jump (STOBAR) trials for naval aviation. T-10-4 additionally carried the experimental Mech radar for avionics and weapons tests. Trials with this aircraft and with the later T-10-10 revealed serious shortcomings in the radar.

By 1979 three aircraft were under test and a pre-production batch was launched at Komsomolsk: five AL-21-powered aircraft known as "Su-27 type T-10-5" (T-10-5, T-10-6, T-10-9, T-10-10 and T-10-11), intended for equipment and weapons development. The first of them, serial number 02-02, was ready in June 1980; T-10-6 was destroyed in October 1980 by a ground fire caused by a leaking fuel line, while T-10-10 and T-10-11 carried out radar, weapons-control and targeting tests. Altogether, counting the prototypes assembled at Sukhoi's experimental plant, nine flying examples of the original configuration plus one static-test airframe had been built by 1982.

The downward trend in performance had already shown up in 1976 in SibNIA wind-tunnel tests: without high-performance computers, the theoretical work on aeroelasticity and flutter could not be fully applied. On top of that, the avionics suppliers failed to keep within their weight and volume allocations, which pushed the centre of gravity forward; the AL-31 burned more fuel than specified; and the radar did not work properly. When reliable data on the F-15 arrived, it was clear that the T-10 did not meet the requirement and was markedly inferior to its rival. The bureau faced a dilemma: put the aircraft into production as it was, or rebuild it from scratch. It chose the latter, and work moved to the new T-10S configuration, with far closer cooperation with SibNIA and a careful look at contemporary Western aircraft.

T-10-1 completed its trials in November 1983 and was donated to the Soviet Air Force Museum in late 1985. Although the production aircraft bore only a superficial resemblance to it, the T-10 fixed the principles that would define the whole family: the integral layout, static instability with fly-by-wire control, and engines in isolated nacelles beneath the lifting body.