Here's What You Need to Remember: While the awesome-looking Berkut never evolved into a production fighter, it still played a useful role testing new technologies.

In 1996, the March/April issue of Russian military periodical Air Fleet Bulletin published an innocuous-seeming photo of a meeting between Russian military chiefs and aviation industry counterparts. Sitting on the table before them were two model airplanes. One was an advanced variant of the by-then well-known Flanker multi-role fighter.

The other was a strange black jet with forward swept wings—that is, the wings seemed to be swept the “wrong way.”

Whether the image amounted to an accidental leak or an intentional plant, it set off a firestorm of excited speculation in Western and Russian press forecasting a new cutting-edge jet that could outperform the F-22 Raptor stealth fighter, the production model of which made its first flight the same year.

In fact, the model represented an advanced tech demonstrator—the Sukhoi Su-47 Berkut (“Golden Eagle”).

Early in the 1980s, as the Soviet Union introduced the fourth-generation Su-27 and MiG-29 jets to oppose the American F-15 and F-16, it thought ahead to developing a fifth-generation fighter to defeat the U.S.’s Advanced Tactical Fighter program which would eventually spawn the F-22 Raptor.

Mikoyan i Gurevich worked on the MiG 1.44, which arrived nine years late after the fall of the Soviet Union only to be canceled. Concurrently, the Soviet Navy sought a new fighter with good low-speed handling characteristics to fly off the steam-catapult equipped supercarrier Ulyanovsk, laid down in Ukraine in 1988.

Manufacturer Sukhoi chose to explore the concept of Forward Swept Wings (FSW) which in theory would enable greatly increase maneuverability, particularly at low speeds and high angles of attack, improved spin resistance, shorten take off distances, and enable greater range by decreasing air resistance. At the end of World War II, the Red Army had captured prototypes of a Nazi Ju-287 jet bomber under construction incorporating forward-swept wings.

However, forward-swept wings had not been widely adopted because they required extremely sturdy wings to withstand the aero-elastic twisting pressure exerted upon the wing roots. The added weight of the reinforcements canceled out the benefits of a forward-swept configuration.

Both U.S. and Russian engineers sought to get around this problem by using new composite-fiber materials to build lighter but sturdier wings. Grumman built two forward-swept X-29 technology demonstrators to test out the concept, which may have spurred Sukhoi’s own interest in the scheme.

The Sukhoi design, which at various times was called the S-22, the Su-27KM, the S-37 and eventually the Su-47, also featured moveable canards, a second set of small wings next to the cockpit which further enhance maneuverability and lift. Together, the forward-swept wings, canards, and horizontal tail-stabilizers gave it a “tri-plane” configuration. In addition to these new elements, the S-37 retained a fuselage and twin-tail configuration from the Su-27 Flanker, though with unequal-length tail booms extending behind carrying rearward-facing radar and a breaker-chute.

Two D-30F-11 turbojet engines—similar to those on the powerful MiG-31 Foxhound interceptor—provided propulsion, though eventually a more advanced AL-41F thrust-vectoring turbofans were planned to take their place. Like the F-16, the S-37 was so responsive it relied on a fly-by-wire system to automatically correct its aerodynamically unstable characteristics.

The aircraft’s good low-speed handling certainly made it attractive as a carrier-based fighter. But with the fall of the Soviet Union in 1991, both the Ulyanovsk and the Navy’s demand for the new carrier-fighter were scrapped. The Sukhoi project was far enough along, however, that the manufacturer was able to privately fund the completion of one demonstrator model.

Western publications particularly attributed stealth characteristics to the jet. The Berkut may have incorporated radar-absorbent coatings and materials, and Sukhoi planned for it to feature an internal weapons baby which could accommodate four long-range R-77 air-to-air missiles (then still under development), in addition to four external short-range R-73 missiles. However, Sukhoi would later admit the Su-47 had not been conceived foremost as stealth jet.

Instead, the Su-47’s design emphasized extreme dogfighting agility. The demonstrator jet made its first flight on September 25, 1997, piloted by Igor Kozintsev—and two years later performed at a Moscow airshow. The S-37 made return appearances in 2001, 2003 and 2005, where it displayed its extraordinary maneuverability—as you can see in this recording.

The Golden Eagle was able to achieve extreme angles of attack, or the ability to pitch the aircraft’s nose beyond its current vector. The S-37 could achieve an AoA of 120 degrees, pitching its nose “away” from its trajectory even as it continued to coast forward on its remaining momentum.

But this agility masked the fact that, like Boeing’s X-29, even the composite-fiber wings were excessively stressed when performing high-speed maneuvers. Worse, the resulting stress cracks necessitated replacement of the entire composite component rather than spot-repairs. Combined with the weight weapons would have added to the 18-ton jet, the Su-47 would have likely been constrained to limited G-loads to avoid over-stressing its wings and proven extremely expensive to maintain.

Moreover, while it demonstrated amazing instant turning performance, it was poor at sustained turns as it bled off speed quickly. Though claimed to be Mach 2-capable, the fastest speed Berkut flight speed reported was Mach 1.65.

In the end, the Su-47 was never more than a privately-developed tech demonstrator—one that ended up demonstrating that forward-swept wings were an idea whose time had not yet come. Instead, Russian fighters like the Su-35S multi-role fighter and Su-57 stealth jet rely upon thrust-vector control turbofans, which can tilt exhaust nozzles, to achieve super-maneuverability.

In fact, the Berkut ended up pioneering several technologies which eventually found their way into the Su-57, which amounts to a more dedicated effort to develop a true stealth fighter, a capability which takes precedence in fifth-generation aircraft design over maneuverability.

Experience from the Su-47 also informed Sukhoi’s development of the forward-swept-wing KB SAT SR-10 trainer, an agile and nifty-looking subsonic jet that would have proven highly spin-resistant. However, the privately-funded SR-10 too has failed to secure government orders.

While the awesome-looking Berkut never evolved into a production fighter, it still played a useful role testing new technologies—and coincidentally, revealed how external observers could be quick to attribute extraordinary capabilities based on a few images of an awesome-looking jet.

Sébastien Roblin holds a master’s degree in conflict resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States. He currently writes on security and military history for War Is Boring.

This article first appeared earlier in 2019. It is being republished due to reader interest.

Image: Flickr