The Su-47 Berkut ( NATO codename: "Firkin" ) is a Russian technology demonstrator for an extreme maneuverable air-superiority fighter, based on the Su-27 Flanker. However it has a very low top speed of only Mach 1.6. The resulsts of the Su-47 testing are now used for the PAK-FA fifth generation Multirole Fighter Aircraft, the Su-47 prevailed itself against the MiG 1.44.
Development of the Su-47 begun in the 1970s, the project was called I-90 and flowed into the test projects S-37 by Sukhoi and MiG 1.44 by Mikoyan-Gurevich. From the S-37 the forward-swept wing demonstrator Su-47 resulted.
The advantages of forward swepted wings are the better agility, higher angles of attack, because of more buoyancy and a lower stall speed than on most of the other aircraft.
The first flight of the S-37 was on 25th September 1997, the S-37 is often incorrectly called Su-37 or S-47. At this time it was equipped with the Solovjev D-30F-6 engines from the Mikoyan MiG-31, but it should be later equipped with better engines. Those engines had thrust vectoring. The intakes of the Su-47, which are notably large, are supplemented by the additional intakes on the fuselage. On the tail the Berkut is equipped with an additional radar and a tailhook.
Although Sukhoi had financial problems, testing was continued. In the year 2001 it was officially named Su-47. The results of the Su-47 tesing are now used on the Sukhoi T-50 PAK-FA .