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|Sukhoi Su-47 Berkut (Golden Eagle)|
|First flight||25 September 1997|
|Status||Development ceased|
|Primary user||Russian Air Force|
|Number built||4 flight testing prototypes|
The Sukhoi Su-47 Berkut (Russian: Су-47 Беркут—Golden Eagle) (NATO reporting name Firkin), also designated S-32 and S-37 (not to be confused with the twin-engined delta canard design offered by Sukhoi in the early 1990s under the designation Su-37) during initial development, was an experimental supersonic jet fighter developed by Sukhoi Aviation Corporation. A distinguishing feature of the aircraft was its forward-swept wing that gave the aircraft excellent agility and maneuverability. While serial production of the type never materialized, the sole aircraft produced served as a technology demonstrator prototype for a number of advanced technologies later used in the 4.5 generation fighter SU-35BM and current fifth-generation jet fighter prototype Sukhoi PAK FA T-50.
Originally known as the S-37, Sukhoi redesignated its advanced test aircraft as the Su-47 in 2002. Officially nicknamed Berkut (Golden Eagle), the Su-47 was originally built as Russia's principal testbed for composite materials and sophisticated fly-by-wire control systems.
TsAGI has long been aware of the advantages of forward-swept wings, with research including the development of the Tsibin LL and study of the captured Junkers Ju 287 in the 1940s. Rearward-swept wings yield a higher maximum lift coefficient, reduced bending moments, and delayed stall when compared to more traditional wing shapes. At high angles of attack, the wing tips remain unstalled allowing the aircraft to retain aileron control. Conversely, forward sweep geometrically creates increased angle of incidence of the outer wing sections when the wing bends under load. The wings experiences higher bending moments, leading to a tendency for the wings to fail structurally at lower speeds than for a straight or aft-swept wing. The increased bending moment is countered by designing the wings to twist downward (opposite the angle of incidence) as they bend upward.
The project was launched in 1983 on order from the Soviet Air Force. But when the USSR dissolved, funding was frozen and development continued only through funding by Sukhoi. Like its US counterpart, the Grumman X-29, the Su-47 was primarily a technology demonstrator for future Russian fighters.
The Su-47 is of similar dimensions to previous large Sukhoi fighters, such as the Su-35. To reduce development costs, the Su-47 borrowed the forward fuselage, vertical tails, and landing gear of the Su-27 family. Nonetheless, the aircraft includes reduced radar signature features, an internal weapons bay, and space set aside for an advanced radar. Though similar in overall concept to the Grumman X-29 research aircraft of the 1980s, the Su-47 is larger and far closer to an actual combat aircraft than the US design.
To solve the problem of wing-twisting, the Su-47 makes use of composite materials carefully tailored to resist twisting while still allowing the wing to bend for improved aerodynamic behavior.
Like its immediate predecessor, the Su-37, the Su-47 is of tandem-triple layout, with canards ahead of wings and tailplanes. Interestingly, the Su-47 has two tailbooms of unequal length outboard of the exhaust nozzles. The shorter boom, on the left-hand side, houses rear-facing radar, while the longer boom houses a brake parachute.
The Su-47 has extremely high agility at subsonic speeds, enabling the aircraft to alter its angle of attack and its flight path very quickly while retaining maneuverability in supersonic flight. The Su-47 has a maximum speed of Mach 1.6 at high altitudes and a 9g capability.
The Su-47 aircraft has very high levels of maneuverability with maintained stability and controllability at extreme angles of attack. Maximum turn rates are important in close combat and also at medium and long range, when the mission may involve engaging consecutive targets in different sectors of the airspace.
The swept-forward wing, compared to a swept-back wing of the same area, provides a number of advantages:
- higher lift-to-drag ratio
- better agility in dogfight situations
- higher range at subsonic speed
- improved stall resistance and anti-spin characteristics
- improved stability at high angles of attack
- a lower minimum flight speed
- a shorter take-off and landing distance
The forward-swept midwing gives the Su-47 its unconventional appearance. A substantial part of the lift generated by the forward-swept wing occurs at the inner portion of the wingspan. This inboard lift is not restricted by wingtip stall and the lift-induced wingtip vortex generation is thus reduced. The ailerons—the wing's control surfaces—remain effective at the highest angles of attack, and controllability of the aircraft is retained even in the event of airflow separating from the remainder of the wings' surface.
A downside of such a forward-swept wing design is that it geometrically produces wing twisting as it bends under load, resulting in greater stress on the wing than for a similar straight or aft-swept wing. This requires the wing be designed to twist as it bends—opposite to the geometric twisting. This is done by the use of composites wing skins laid-up to twist. Despite this, the plane was initially limited to Mach 1.6. Recent engineering modifications have raised this limit, but the new limit has not been specified.
The thrust vectoring (with PFU engine modification) of ±20° at 30°/second in pitch and yaw will greatly support the agility gained by other aspects of the design.
The cockpit's design has focused on maintaining a high degree of comfort for the pilot and also on the pilot being able to control the aircraft in extremely high g-load maneuvers. The aircraft is equipped with a new ejection seat and life support system.
Data from World Aircraft & Systems Directory
- Crew: 1
- Length: 22.6 m (74 ft 2 in)
- Wingspan: 15.16 m to 16.7 m (49 ft 9 in to 54 ft 9 in)
- Height: 6.3 m (20 ft 8 in)
- Wing area: 61.87 m² (666 ft²)
- Empty weight: 16,375 kg (36,100 lbs)
- Loaded weight: 25,000 kg (55,115 lb)
- Max. takeoff weight: 35,000 kg (77,162 lbs)
- Powerplant: 2 × Lyulka AL-37FU (planned), prototypes used 2 Aviadvigatel D-30F6 afterburning, thrust-vectoring (in PFU modification) turbofans
- Dry thrust: 83.4 kN (18,700 lbf) each
- Thrust with afterburner: 142.2 kN (32,000 lbf) each
- Thrust vectoring: ±20° at 30° per second in pitch and yaw
- Maximum speed: Mach 1.65 (Achieved in test flights) (1,717 km/h, 1,066 mph)
- Cruise speed: 
- Range: 3,300 km (2,050 mi)
- Service ceiling: 18,000 m (59,050 ft)
- Rate of climb: 233 m/s (46,200 ft/min)
- Wing loading: 360 kg/m² (79.4 lb/ft²)
- Thrust/weight: 1.16 (loaded) / 1.77 (empty)
The Su-47 is an unarmed technology demonstrator. If further developed into a fighter the armament could include the following weapons:
- Guns: 1 × 30 mm GSh-30-1
- Missiles: up to 14 hardpoints (2 wingtip, 6-8 underwing, 4-6 conformal under the fuselage)
- Related development
- Aircraft of comparable role, configuration and era
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