- The Su-47 Berkut at the 2019 MAKS airshow. | Photo: Krassotkin

Flightline: 206 - Sukhoi Su-47 Berkut (NATO: Firkin)

Intended to be a next-generation heavy fighter, the forward-swept wing Su-47 wound up being a technology demonstrator.

History and development

As with the United States, the Soviet Union made it a priority to acquire research and technology (along with the researchers and technologists themselves) from Nazi Germany as WW2 came to a close. One of the aircraft captured by the Red Army was the Junkers Ju 287, with which Germany was researching forward-swept wings. As with the more-commonly used aft swept or delta wings, forward-swept wings allow an aircraft to fly faster, while FSW also improve maneuverability at speed as well as improving the stall characteristics of an airplane. As both the Soviet Central Aerohydrodynamic Institute (TsAGI) and the various German researchers found, however, FSW also exhibit a number of drawbacks, including a tendency for the wings to flex so much that they would twist off.

By the late 1970s, technology had advanced to the point that new materials such as carbon fiber composites would allow a forward-swept wing aircraft to be built. In 1983 the Soviet Air Force ordered a prototype from the Sukhoi OKB as the S-32 (later redesignated S-37, redesignated again in 2002 as the Su-47) Беркут (Berkut, "Golden Eagle"). To reduce construction time as well as to cut costs, the forward fuselage, vertical fins and landing gear of the Su-27 were used, to which a new wing, canards and horizontal fins were added. The structure of the wing and the composite skins were specially engineered and fabricated with the aeroelastic 'twisting' forces in mind, reducing the chances of the wings failing in flight. The Berkut has two tailbooms of unequal length, with the longer right-side unit containing a breaking parachute, while the left boom houses a rear-facing radar. The advanced design of the S-32 led to a long development period, which was exacerbated by the collapse of the Soviet Union and subsequent budget shortfalls.

Specifications

Orthograph of the Su-47. | Illustration: Dr Dan Saranga

Orthograph of the Su-47. | Illustration: Dr Dan Saranga

The S-37 is 22.6 meters long, with a wingspan of 16.7 meters and a height of 6.4 meters, making it comparable to the Su-27 or Su-35 (NATO: Flanker). Empty, the S-37 weighs 16,375kg, while max-TO weight is 35,000kg. Two Soloviev D-30F6 afterburning turbofans (rated at 93.1kN each) are fitted with 2-dimensional thrust vectoring nozzles, and propel the S-37 to a maximum speed of Mach 1.6. The service ceiling is 18,000 meters, and the aircraft has a rate of climb of 233 meters per second. At normal operating weight, the Berkut has a thrust-to-weight ratio of 1.21, which drops to 0.92 at MTOW. The aircraft's structure is stressed to +9g. Weapons were not fitted, but an internal cannon was planned, and an internal bay would have accommodated then current or possible future air-to-air missiles.

Testing

The S-37 Berkut in flight. | Photo: Sukhoi OKB

The S-37 Berkut in flight. | Photo: Sukhoi OKB

The Berkut program survived the collapse of the Soviet Union in 1991, and the prototype was rolled out in 1997, with the maiden flight taking place on 25 September. The following flight test program proved that the FSW design was viable, delivering higher lift-to-drag ratio, better agility in dogfight situations, higher range at subsonic speed and improved stall resistance and anti-spin characteristics. The S-37 also proved it had improved stability at high angles of attack, a lower minimum flight speed and a shorter take-off and landing distance than a conventional design. A later upgrade of the S-37 would have added thrust vectoring (with PFU engine modification) of ±20° at 30°/second in both pitch and yaw directions. No radar was fitted, but the design allowed for the addition of an advanced active electronically scanned array (AESA) radar. The S-37 was in unofficial competition with the MiG 1.44 to be the next fighter aircraft of Russia, but the post-USSR economic and political climate saw both programs terminated. Sukhoi continued flying the Berkut, redesignated the Su-47 in 2002 to both distinguish it from the Su-37 (NATO: Flanker-F) and to denote it as a possible production aircraft rather than an experimental design. The Su-47 was given the NATO code name Firkin.

Sukhoi Su-35UB combat trainer and Su-47 experimental fighter flying together at MAKS-2003 airshow. | Photo: Yevgeny Pashnin

Sukhoi Su-35UB combat trainer and Su-47 experimental fighter flying together at MAKS-2003 airshow. | Photo: Yevgeny Pashnin

As technology trends shifted more to low-observable "stealth" designs, work on the Su-47 slowed even further, with flights tapering off in the mid-2000s. The Su-47 was demonstrated at the 2005 MAKS show, but was placed into storage afterwards and was not seen again until MAKS 2019, when the plane was towed into the static display area without ceremony. Although the forward-swept wings of the Su-47 appear to be a dead end (for now), the Berkut did advance the state of the art for digital fly-by-wire systems and advanced composite construction, both of which are incorporated into the Su-57 (Felon) and Su-75 "Checkmate" 5th generation designs.

The Su-47 leads a pair of Su-27-based designs at the 2005 MAKS show. | Photo: Sergey Krivchikov

The Su-47 leads a pair of Su-27-based designs at the 2005 MAKS show. | Photo: Sergey Krivchikov

The Su-47 being towed to the static display area at the 2019 MAKS show. | Photo: Tom Demerly/TheAviationist

The Su-47 being towed to the static display area at the 2019 MAKS show. | Photo: Tom Demerly/TheAviationist

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Comments (4)

  • I had a model of one years ago. It looked futuristic.

      13 hours ago
  • If:

    “The following flight test program proved that the FSW design was viable, delivering higher lift-to-drag ratio, better agility in dogfight situations, higher range at subsonic speed and improved stall resistance and anti-spin characteristics. The S-37 also proved it had improved stability at high angles of attack, a lower minimum flight speed and a shorter take-off and landing distance than a conventional design.”

    Then:

    Why aren’t ALL Fighters built with FSW’s? Maybe Musk will jumpstart the technology with a Forward Swept ElectricTruck?

      5 days ago
    • Fabbing forward-swept wings is still expensive and difficult, so the benefits are still outweighed by the vices, and FSW doesn't lend itself to stealth, so when requirements shifted the technology languished.

        5 days ago
  • That’s look brutish but cool

      6 days ago
4