How the Golden Eagle’s wings were clipped: The story of the Su-47 Berkut

At the Russian International Space and Aviation Show (MAKS) 1999 the veil of secrecy was lifted on a new advanced fighter prototype. This sleek black jet was characterized by forward swept wings flanked by canard foreplanes.

Such an unusual configuration was already a hot topic amongst western defence experts and the aviation press. Speculation had been rife since the Russian military periodical Air Fleet Bulletin published a photo featuring a model of the same aircraft in 1996. All available evidence pointed to this plane, the S-37 Berkut (Golden Eagle) later known as the Su-47 was the Russian’s answer to the F-22 Raptor, the production model having first flown that same year.

Despite evidence of the prototype undergoing test flights, nothing was said about a production model entering service. On August 11, 2014, Commander-in-chief of the Russian Air Forces, Colonel General Viktor Bondarev claimed that Russia was still continuing the research and development of Su-47 or similar forward-swept wing fighters.

Sukhoi Su-47 on static display at MAKS 2019.

Fast Forward to 2019. The Su-47 once again graced the spectators at the MAKS air show. In front of fascinated spectators the black jet demonstrated feats of extreme agility.

The F-22 at this point had been in service with the US Air Force since 2007. However Western analysts and the manufacturers confirmed that the Su-47 was not destined for series production, only functioning as a technology demonstrator.

So why didn’t the golden eagle enter service like the F-22? Available evidence suggested the Su-47 was a supermanoeuvrable stealth fighter capable of speeds exceeding Mach 2. These claims whilst fascinating overlooked the sobering economic and practical truths of the project.

Rewind back to the end of the Cold War. In response to the emergence of the MiG-29 and Su-27 by the soviets to counter the F-15 and F-16 fighters, the Americans realised a fifth generation fighter was needed to secure air dominance. The Air Tactical Fighter program was given the go ahead, which would culminate in the F-22 Raptor.

F-22 Raptor. In the absence of reliable information, analysts believed the Su-47 was a fifth generation fighter design to rival the american stealth fighter. (USAF)

Back in the Soviet Union, similar developments were taking place. The soviets knew they needed an equivalent quantum leap in fighter design to stay in the air superiority arms race. Mikoyan Guerevich instigated development of the MiG-1.44, a delta winged heavy fighter. Sukhoi on the other hand pursued a different layout, utilising reverse wing sweep. This was the Su-47 Berkut.

A MiG-1.44 prototype. Another testbed for the Russian fifth generation fighter program, production was cancelled due to spiralling unit costs. It first flew on February 29 2000.

Initial hopes were placed on the Forward Swept Wing design leading a fighter which could outperform the Raptor and other western aircraft. But the aforementioned claims of it’s performance identified more with the fever dreams of aircraft designers and popular culture, rather than actual reality.

Lets go back to the claim of supermanoeuvrability. Theoretically Forward Swept Wings provide a host of advantages for air to air combat. Inherent aerodynamic instability allowed greater turning performance at higher angles of attack. In a stall condition a reverse wing sweep also permits more control for recovery. This is because on a conventional wing air travels to the rearmost point, in this case the wingtips. On a Forward Swept Wing the air instead goes to the wing root, allowing full control despite loss of lift. A pilot can additionally point the nose higher before stalling.

Another potential advantage is that the air properties change less approaching supersonic speed. Encroaching on the sound barrier at transonic speeds, turbulent air builds up in front of a wing, reducing control. Forward Swept Wings can delay this buildup, enduring little reduction in control.

Initial testing of the Su-47 demonstrated such strengths of the configuration. However the physical strength of the wings posed a difficult problem.

Analysis of the wing structure revealed the layout exerted far greater twisting forces on the wing surface and roots. Similar problems were encountered by the Americans when they underwent similar testing with the Grumman X-29. Reinforcing the wing structure would add excessive weight, and so lightweight composite materials were tested.

The Grumman X-29 was a cooperative effort by the USAF and NASA to test Forward Swept Wings in conjunction with composite materials and advanced Fly By Wire (FBW) controls. It was first flown in 1984.

Unfortunately, over the course of the Su-47 program, the composite wings also proved to be fragile under the stress of high G forces. Eventual cracks could only be rectified by complete replacement of the wings. Such implications for high maintenance were considered an unattractive prospect for a frontline fighter aircraft.

In addition, sustained turning at high speeds was ill-advised in the Su-47 bled off speed and energy rapidly.

What about the other claims of speed and stealth capability? Initial reports of speeds beyond Mach 2 were overstated, as the fastest speed achieved by the Berkut was only Mach 1.65. Furthermore the black paint was a misnomer. Sukhoi never intended for the Su-47 to utilise stealth.

So while the golden eagle could fly, turning it into a reliable and capable fighter was a different story. And that is before financial constraints are considered.

Advanced aircraft concepts are often cut short due to prohibiting costs. To an extent the Su-47 was a victim of this, as was the MiG-1.44. Towards the 2000s the defence budget shrank exponentially, and funding for procurement was scarce. The fall of the Soviet Union and ensuing economic reforms made it difficult for the Russian Air Force to justify investing in a relatively unproven design requiring heavy maintenance every other flight.

Meanwhile other technology demonstrators also showed the effectiveness of alternative design concepts. The Sukhoi Su-37 also exhibited high agility utilising thrust vectoring, without the pitfalls suffered by its Forward Swept Wing cousin. In fact the Su-37 could pull a maximum of 10Gs whilst the Su-47 only achieved 9Gs. The modern Russian fifth generation fighter, the Su-57 uses thrust vectoring and technology incorporated design traits from both Sukhoi demonstrators, but is arguably more suited for multiple mission modes with dedicated stealth capability.

The Su-37 unlike the Berkut was developed from the Su-27 Flanker airframe. It was designed to test the concept of thrust vectoring to bolster turning ability in combat. Much like it’s cousin the Su-37 was never destined for series production, but the technology was incorporated in the Su-35S fighter, pictured below.
Sukhoi Su-35S Flanker E

The Su-47 Berkut’s configuration, whilst aesthetically imposing, is optimised for close range combat. The Su-57 will replace derivatives of the Su-27 and MiG-29, exemplifying that the costs of such advanced combat aircraft demand a platform with versatility in mind. Close range dogfights whilst not a thing of the past, are just one aspect of a multitude of roles the Su-57 will be required to perform in air defence duties.

Sukhoi Su-57.

Sebastien Roblin of the National Interest has argued that although the Golden Eagle never went into production, the Su-47 provided valuable lessons and flight data that the Russians used to develop a true fifth generation fighter. The legacy of the golden eagle also speaks to a weakness of external observers attributing extraordinary capabilities based on a few images and lacking detailed information.

The Su-47 was a machine too fantastic, specialised and flawed to be considered for service in an unfavourable climate.

Sources:

S. Roblin, Why Russia’s Super-Maneuverable Su-47 ‘Golden Eagle’ Fighter Jet Failed, The National Interest, (29 July 2019), https://nationalinterest.org/blog/buzz/why-russia%E2%80%99s-super-maneuverable-su-47-%E2%80%98golden-eagle%E2%80%99-fighter-jet-failed-54497 Accessed 10/05/20.

T. Demerley, MAKS 2019 Surprise Appearance: The Mysterious Sukhoi Su-47 Berkut Re-emerges, The Aviationist, (August 27 2019), https://theaviationist.com/2019/08/27/maks-2019-surprise-appearance-the-mysterious-sukhoi-su-47-berkut-re-emerges/ Accessed 09/05/20.

C. Grant, A Century of Triumph: The History of Aviation, (New York, 2002).

‘A New Approach to Technology Security in a Globalized World’ in S. Bryen (eds.) Technology Security and National Power: Winners and Losers, (New York, 2017).

T. Buttler, Y. Gordon, Soviet Secret Projects: Fighters Since 1945, (Oxford, 2005).

Y. Gordon, D. Komissarov, OKB Sukhoi: A History of the Design Bureau and its Aircraft, (Surrey, 2010).

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