While the collapse of the Soviet Empire in 1991 stymied many-a-program in Russia, the Sukhoi concern proceeded with their Su-37/47 "Berkut" ("Golden Eagle") technology demonstrator. The aircraft borrowed much from the other Sukhoi product - the Su-27 "Flanker" - with the exception of its main wing assemblies which were cranked forward in an attempt to research agility at subsonic speeds, post-stall maneuverability, use of strong-yet-lightweight composites and advanced fly-by-wire systems in a modern-day, turbofan-powered airframe. Four working prototypes were eventually completed though no formal adoption was made by the Russian Air Force, leaving the Su-47 to the pages of aviation history. However, the data collected from the various Berkut test flights were used in development of the Su-35 (an advanced Su-27 model line) as well as Russia's first 5th Generation Fighter - the PAK-FA "T-50" - this development intended to compete with the American Lockheed F-22 "Raptor".
The use of forward-swept wing assemblies offers some inherent advantages to conventional, rear-swept appendages seen in nearly all jet-powered aircraft today. With such a configuration, the aircraft is capable of excellent maneuverability at subsonic speeds, reduced take-off and landing rolls, a reduced radar signature and increased control during high angles of attack. The primary detriment of the configuration remains the stress loads placed upon each wing, forcing them to twist and bend in an unnatural fashion, which can lead to midair disasters in the right circumstances. In the Su-37/47 design, the wings are purposely constructed of twisting/bending composites to alleviate such stresses.
During World War 2, German engineers were able to successfully launch the jet-powered Junkers Ju 287 as a multi-engined bomber. This design was powered by 4 x Junkers Jumo 004 turbojets with two paired engines slung under each wing. The wings themselves were high-mounted and cranked forward along the fuselage sides. One working prototype was eventually completed and followed by two unfinished airframes before the end of the war. The examples were captured by advancing Soviet forces during the last weeks of the war and appropriately dissected by Soviet engineers. The concept of a forward-swept wing fighter was also entertained by the Americans during the Cold War years, embodied through the Grumman X-29 technology demonstrator. This aircraft first flew on December 14th, 1984 and utilized the fuselage of the Northrop F-5A "Freedom Fighter", two of which were converted into X-29 prototype form. Like the Berkut, the X-29 program reached its project end and was never adopted by the US military.
The Berkut herself was born during the waning years of the Soviet Empire when, in 1983, the Soviet Air Force began funding the forward-swept wing program with Sukhoi. The product was originally born as the S-32 before graduating to become the Su-37 and, finally, the Su-47. The program was first leaked in 1996 and understood by the West to be the acting prototype for a Russian 5th Generation Fighter - perhaps intended to match with the American F-22 which was also in development at the time. First flight of the S-32 was recorded on September 25th, 1997 and its first public display was noted at Zhukovsky in August of 1999. The aircraft achieved supersonic flight in August of 2000 and by this time it was understood that the S-32/Su-37 design was, in fact, only a true technology demonstrator and not a direct prototype to something forthcoming. The Su-37 was redesignated to Su-47 in 2002.
However, the fall of the Soviet Empire jeopardized development of the S-32/37/47 for the reborn Russian Ministry of Defense lacked the funding required to keep many programs afloat. Sukhoi continued the Berkut as a private venture, helped along by its many Su-27 sales, in the hopes the Berkut could further internal knowledge of forward-swept flight for possible integration into a future Sukhoi fighter design. The aircraft continued to progress, though at a much slower pace, and testing eventually proved the design sound. The forward-swept nature of the wings allowed for the expected improvement in agility at low speeds with enhanced maneuverability. The demonstrator netted a maximum speed of Mach 1.6 during testing.
Outwardly, and beyond the obviously forward-swept wings, the Su-37/47 remained a largely conventional aircraft design. The cockpit (taken from the Su-27) was set at the front of the fuselage and aft of a short nose cone assembly. The engines were paired at the rear in a side-by-side arrangement, set between the twin, outward-canted vertical tail fins. While the inlets of the aircraft were fixed, air scoops were embedded into the leading edge of each wing to provide additional airflow to the engines during low-speed flight. Ahead of the main wings were small forward canards to increase controllability and lift. Aft of the main wings were shallow horizontal planes. The undercarriage was fully retractable and of a tricycle arrangement, borrowed from the Su-27K model to expedite development.
The Su-32/37/47 demonstrator was outfitted with 2 x Aviadvigatel D-30F6 turbofan engines capable of afterburn (the same as fitted to the Mikoyan MiG-31 "Foxhound" interceptor). Output was listed at 18,700lbs under "dry" thrust with 32,000lbs of thrust generated through afterburning (raw fuel pumped into the exhaust for limited bursts of thrust). Advanced demonstrators were to field 2 x Lyulka brand AL-37FU/FP turbofans with thrust-vectoring. The Berkut achieved a maximum speed of 1,066 miles per hour with a cruising speed of 870 miles per hour. Range was listed at 2,050 miles with a service ceiling of 59,000 feet and rate-of-climb of 46,200 feet-per-minute.
In comparison, the Su-27SK model (and export-minded single-seater) yielded a maximum speed of 1,550 miles per hour with a rnage out to 2,070 miles. Its service ceiling was 62,500 feet with a rate-of-climb nearing 54,000 feet per minute.
Intended from the beginning as a technology demonstrator, the Su-37/47 was not officially armed. Had it reached the formal adoption stage, it may have included an internal 30mm cannon as well as various underwing and underfuselage hardpoints for the carrying of guided/unguided, powered/unpowered munitions similar in scope to the rest of the Flanker family.
As it stands, the Su-47 existed only through the four aforementioned prototypes and it is believed that all active development on the series have been stopped.