As Moscow ‘flexes the muscles’ with Su-57 jets, see Russia’s original stealth aircraft that inspired the Felon

During the Cold War, the Soviet Union attempted to build a number of weapons in hopes of gaining an advantage over Western military industry. However, many of these weapon platforms never reached the production stage.

One such military equipment was the Su-47 “Berkut” fighter aircraft. Only one aircraft was produced, widely described as a predecessor to the 5th generation Russian Su-57 (Felon) stealth fighter.

In 1996, a photo of a meeting between Russian military officials and aviation industry peers appeared in the March/April issue of the Air Fleet Bulletin. This photograph aroused considerable interest for another reason: two fighter jets were placed on the table.

One was a more advanced version of the Flanker multirole fighter, which was already well known at the time. The other was an unusual black jet with forward-swept wings, that is, wings swept in the wrong direction.

Sukhoi Su-47 (Wikipedia)

At the time, this second fighter aircraft attracted much attention from Western defense experts. While it’s unclear whether the image was leaked accidentally or deliberately, it sparked a flurry of speculation in the Western and Russian press.

The reason for all the excitement was that the F-22 production model made its first flight the same year, and this advanced new jet was soon seen as eclipsing the F-22 Raptor stealth fighter. This new model of fighter aircraft was a Sukhoi Su-47 Berkut (“Golden Eagle”), a high-tech prototype.

Unconventional design

During the Cold War, the USSR and the United States developed a good number of weapons to counter each other. To confront the American Advanced Tactical Fighter program, which gave birth to the F-22 Raptor, the Soviet Union planned a fifth-generation fighter.

At the same time, the Soviet Navy was looking for a new fighter with good low-speed handling characteristics to fly from the Ulyanovsk, a super carrier with steam-powered catapults, which was abandoned in Ukraine in 1988.

The Su-47 development project was initially conceived in the 1980s. Sukhoi decided to research the possibility of Forward Swept Wings (FSW).

Theoretically, this concept allows for greater maneuverability, especially at low speeds and high angles of attack, better spin resistance, shorter launch distances, and increased range by reducing air resistance.

Su-47
Su-47 (file photo)

The Western press speculated that Russia was developing a stealth aircraft. Sukhoi proposed that the Berkut have an internal weapons bay that could accept four long-range R-77 air-to-air missiles (then still in development), as well as four external short-range R-73 missiles. However, Sukhoi later admitted that the Su-47 was not designed to be stealthy.

According to Airforce Technology, the Su-47 possessed a high lift-to-drag ratio, 9g capacity, improved stall resistance, and increased stability at high angles of attack, despite its slower speed than the Su-57.

The fighter, which was known by several designations such as the S-22, Su-27KM, S-37 and finally the Su-47 at various stages, also had adjustable canards, the second set of small wings adjacent to the cockpit to improve maneuverability and lift.

The plane was equipped with the two D-30F-11 turbojet engines, identical to those of the powerful MiG-31 Foxhound interceptor. However, more advanced AL-41F thrust-vectoring turbofans were intended to eventually replace them. The S-37, like the F-16, was so nimble that it relied on fly-by-wire technology to automatically rectify its aerodynamically unstable characteristics.

Su-47
Su-47 next to a Sukhoi Su-35UB at the MAKS-2003 airshow. (Wikimedia Commons)

The aircraft’s excellent low-speed maneuverability made it a strong contender for a carrier-based fighter. The Ulyanovsk and the Navy’s requirement for a replacement aircraft carrier were both canceled after the collapse of the Soviet Union in 1991. The manufacturer, on the other hand, funded this project single-handedly for develop a demonstrator model.

What went wrong?

Forward-swept wings have major drawbacks, however. The flight dynamics of aircraft with forward swept wings are extremely unstable. The wings themselves are subjected to high stresses, especially at high speed. The wings must bend without breaking due to the high stress loads. This is quite a difficult task for engineers.

The Su-47 would have limited G loads as the weight of the weapons would have added 18 tons to the aircraft. And it would have proven incredibly expensive to maintain.

Su-47
Artist’s rendering of the Su-47.

Also, while it had incredible fast cornering performance, it struggled to maintain speed in extended corners.

While the fighter’s projected speed was Mach 2, the fastest speed reported by Berkut was Mach 1.65. A single Su-47 appeared at air shows from time to time, raising concerns that the manufacturer is not too confident in the product.

Nevertheless, Berkut was responsible for the development of various technologies that helped make the Su-57 “Felon”.

The American X-29

The United States also considered using forward-swept wings. The Defense Advanced Research Projects Agency has even built a technology demonstrator that resembles the Su-47. Called the X-29, the plane is billed as the most aerodynamically unstable aircraft ever created, according to DARPA.

The technology used in the development of the X-29, like those employed in the Su-47, pushed the limits of what was feasible.

X-29 Forward Swept Wing Technology Demonstration |  Nasa
X-29 Forward Swept Wing Technology Demonstration | Nasa

Some of the technology from the X-29 was then used in the development of future platforms. According to a DARPA statement, “advanced composite materials are now widely used in military and commercial aircraft.”

Although the Berkut and X-29 were never produced for operational deployment, they acted as an important test bed for new technologies.

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