In the mid 1990s, Russia had a problem. It was a pretty important one, too, for both pilots and the grunts on the ground. It was a problem they needed to solve very quickly.
Earlier that decade, a United States F-15 Eagle had easily shot down the MiG-29 "Fulcrum," supposedly the pinnacle of Soviet fighter technology, in combat over Iraq. Worse, the F-22 Raptor was headed into service, and as it did so, it dominated the once-dominant Eagle. Russia needed to play catch-up.
That was where Sukhoi came in. Sukhoi had designed the Su-27/30/33 Flanker family of aircraft, which did reasonably well over Eritrea, fighting the MiG-29 Fulcrum. As such, Sukhoi began to work on both an upgraded Flanker (later known as the Su-35) and on fifth-generation projects to counter the F-22 Raptor. According to MilitaryFactory.com, Sukhoi's prototype was the S-32 Berkut. The plane first flew in 1997, and was later called the Su-37.
The X-29 technology demonstrator aircraft. (NASA Photo by Larry Sammons)
The Berkut looked like an ordinary Flanker, but the big difference was in the wings. The Russians went with forward-swept wings to improve the design's agility at low speed, not to mention improved takeoff and landing performance. The big problem is that that the wings can snap if the force goes the wrong way. Russia got around that by using composites that were flexible enough to handle stresses.
This wasn't the first time someone modified a design for forward-swept wings. Northrop used the F-5E Tiger II as the basis for the X-29, a forward-swept wing test-bed that flew in the 1980s. Nazi Germany had a forward-swept wing bomber, the Junkers Ju 287, but only one prototype was completed.
By the mid-2000s, it was obvious that the Su-37 would not be a combat airframe, and suffered the same fate as the X-29. The Russians re-designated it the Su-47, flew a number of test flights, then retired the four prototypes. Learn more about this strange experiment in the video below: