BERKUT S37

Description

The next piece of information about the S-32 appeared simultaneously in Russian newspapers Kommersant-Daily and Nezavisimaya Gazeta (October 24, 1997), shortly followed by an Associated Press article. The article in Kommersant-Daily was accompanied by a photo of the S-32 fighter, which was referred to as S-37 "Berkut" (or "Golden Eagle"). The change of name from S-32 to S-37 caused a short-lived confusion whether the "Berkut" is the same S-37 fighter project officially confirmed by Sukhoi in 1991 which later came to a stall due to the lack of funding (its cancellation was never officially confirmed). The original, 1991 S-37 project was a smaller aircraft with a delta wing design and a single AL-41F engine. This apparently was not the case with the 1997 S-37 "Berkut": the new aircraft is significantly larger, it is equipped with two engines, and employs a forward-swept wing design. Thus, the "Berkut", apparently, took the place of the original S-37.

Perhaps one of the most interesting and confusing technical issue about the new Russian fighter is its engines. The Kommersant-Daily mentioned that the combined thrust of S-37's engines is 25 tons, or lb., no make of engine, however, was mentioned. The thrust of lb. is consistent with the two AL-31F engines commonly used on Russian Su-27 fighters. This, however, raised very interesting questions: why the significantly more powerful D-30F6 engines were used during the initial flight tests when there were AL-37FU engines available and why the engine thrust mentioned by the Kommersant-Daily is consistent only with the older AL-31F engines?

The available information suggests that the basic dimensions and weight of the S-37 "Berkut" are similar to those of Su-37 (see table below). While the main advantage of the forward-swept wing design is the improved maneuverability at subsonic speeds and high angles of attack its primary drawbacks are the reduced lift and handling problems at supersonic speeds. A natural way to counter such problems is by using more powerful engines and an advanced thrust-vectoring controls. There is little doubt that the S-37 would require more powerful engines than the AL-31Fs for stable performance. This conclusion is fully supported by the fact that the initial flight tests were conducted with the powerful D-30F6 engines, though there is no knowledge of any thrust-vectoring version of these engines. Considering all these arguments and facts an interesting possibility arises.

The 1991 S-37 project was designed with very powerful AL-41F engines in mind. There is a strong possibility that a thrust-vectoring version of this engine exists. The AL-41F would be able to satisfy the power requirements of the S-37, as well as to explain why MiG-31's D-30F6 engines were used for initial test flights (this was suggested to me by Yevgeniy Chizhikov from rec.aviation.military).