Sukhoi S-54 Trainer
In 1961, the L-29 was selected in a competition (mostly, due to political considerations) for the future trainer for the Warsaw Pact countries, having one-upped the Soviet Yak-30 and Polish Iskra. Since then, Czech-made trainers had made up the mainstay of the air force academies in many countries. In 1974, the L-29 was ousted by the more-advanced L-39 powered by the Soviet-built AI-25TL turbofan. By the time the Soviet Union and the Warsaw Pact dissolved, the Soviet Air Force had had about a thousand L-39 in its inventory. They constituted the backbone of the trainer fleets operated by the military flight schools. In the early 1990s, the Czech Republic ceased to supply new aircraft and spares. The in-service trainers were growing old, with their service life nearing expiry due to their being used heavily.
In addition, given the en-masse conversion to the fourth-generation Su-27 and MiG-29 fighters with radically novel characteristics and given the even more capable fifth-generation fighter's development underway, the L-39 was unable to provide adequate training to advanced fighters' pilots.
These considerations prompted the Soviet Air Force in the early 1990s to launch the development of a new tactical flight crew trainer. The need for replacing the L-39 with a brand-new trainer was voiced by the Soviet Air Force's commander-in-chief, Air Marshal Yefimov, on 20 April 1990. In summer 1990, the first official document was issued. It was the resolution by the State Military Industrial Commission, dated 25 June 1990 and tasking the Mikoyan design bureau with developing the future trainer.
To reduce technical risk and obtain the best aircraft, the military called for a trainer aircraft competition among major Soviet aircraft developers. In January 1991, specifications requirements for a trainer for future tactical aircraft pilots were sent to MiG, Sukhoi, Yakovlev and Myasishchev. On 25 November 1991, Air Force CINC Col.-Gen. Pyotr Deynekin ordered a commission set up to review the conceptual designs submitted by the four bidders. The outcome of the tender was to be known on 15 January 1992.
Sukhoi submitted the conceptual design of the S-54 aircraft - a single-engine derivative of the Su-27 fighter. It was to be powered by a single NPO Motor's R-195FS engine that was to be developed as an afterburning version of the production R-195 turbojet powering the Su-25 attack aircraft and producing supersonic speed of Mach 1.55. Unlike other contenders, the S-54 was intended for basic and advanced training. Sukhoi suggested the very concept of training on the 'common' aircraft be reconsidered. In the opinion of Sukhoi's design team, a combination of requirements for the initial, basic and advanced training capabilities in a single aircraft could be achieved at the expense of either safety or training quality.
The aerodynamic design of the S-54 was based on the Su-27, to make the trainers flight performance close to that of production combat aircraft such as the Su-27 and the MiG-29. Unstable aerodynamics improved its maneuverability and decreased its structural weight. The designers considered alternate single-engined and twin-engined trainer configurations. Preference was given to the single-engined design. The proposed S-54 had a conventional aerodynamic arrangement with a twin-fin vertical stabilizer and a low-set horizontal stabilizer attached to the tail booms. Dorsal fins were the same as those seen on the Su-27. High-lift devices on the thin, low-aspect-ratio wing include rotary leading edge flaps and trailing edge flaps. The fuselage and wing are integrated like those of the Su-27. The original design, incorporating rectangular, ventral air intakes had horizontal flow control panels. A boundary layer air bleed wedge was placed between the air intake and the lower fuselage. Newer S-54 designs have a bifurcated intake design.
The first design study, shown publicly not long afterwards, was upgraded and improved during 1992. A new version, with airframe enlarged by approximately 25 per cent, was revealed at 1996 Farnborough Air Show. However, by June 1997, Sukhoi had prepared yet another configuration for the S-54 more closely resembling a scaled-down, single-seat Su-27 equipped with Phazotron Sokol-X radar. This would indicate a change of emphasis to a combat role with secondary advanced training capabilities. No further promotion appears to have taken place in the two following years.
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