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S-37 Berkut (Golden Eagle)


Remember the Cold War, when disclosure of a new Soviet aircraft would be met in the West with warnings of the threat it posed? Contrast that with the recent revelation of Russia's Sukhoi S-37 Berkut (Golden Eagle)--seen more with curiosity than caution by aircraft experts. But make no mistake, the aerodynamics, materials, and components in this prototype are pushing Russian technology such that an after-the-turn-of-the-century competitor to the U.S. Lockheed Martin F-22 Raptor might well be on the world arms market. The Berkut first flew late last September. Sukhoi says the design has maneuverability and stealth to rival the F-22 and can be refined into a production airplane. Berkut is clearly based on its operational Su-27 family roughly equivalent in function to the US F-15 Eagle. The most striking feature is its forward swept wing (FSW). This "inverted arrow," as the Russians term it, smoothes the nose-to-tail cross-sectional area distribution, cutting transonic (Mach 1) drag. Air-flow along the wing is toward the fuselage, rather than the tip, eliminating tip stalling, thus the roll-controlling ailerons on the wing trailing edge are more effective in high angle-of-attack fighter maneuvering. Russian aircraft expert Bill Sweetman of International Defence Review also points out the center of pressure is closer to the fuselage, reducing the wing bending moment. For the same of bending, a longer wing can be used, again lowering drag.

Only a composite wing can be used, and the Russians say the wing on S-37 is 90% composite. This tailors the wing. It twists leading-edge down as it bends upward under lift. If it simply bent upward, as with a metal wing, the angle of attack closer to the tip becomes greater, raising lift and bending the wing further. Structural failure can take place. The FSW was demonstrated on the Grumman X-29 in the mid-eighties and, notes Sweetman, on a Sukhoi demonstrator in 1982.

Queen of the slipstream. Also obvious is the "tandem triplane:" the FSW; a forward maneuver-trigger canard; and a small-area horizontal tail. Lift from the canard and tail lift can balance the airplane in pitch, maximizing overall aircraft lift. The fly-by-wire electronic flight controls "dither" the canard for stability and displace it for maneuvers. The canard also affects air-flow over the wings and tail.

Future developments are said to include digitally-controlled hydraulically-powered vectorable nozzles to aid maneuvers and trim the aircraft. Current vectored thrust Su-27 derivatives have demonstrated eye-catching low-speed aerobatics such as summersaults and "cobra-strike" moves, but these may be of limited use in combat because at low speed an airplane is a sitting duck. S-37 maneuvering limits are likely around that for current fighters, 9 g. Anything greater `needs a superhuman to fly it' says aerospace consultant lay Miller.

Stealth features center on application of radar absorbing materials to the air-frame, curved inlet ducts to prevent radar from "seeing" the flat engine faces, and internal or faired-over conformal carriage of weapons to reduce radar reflection. Miller, who has visited Sukhoi facilities says, Russian workmanship and manufacturing tolerances are not fine enough to produce the tight radar-stifling "fit and finish," found on high-stealth US aircraft.

Russian reports say the S-37 cockpit is equipped with LCD multi-function displays. "They are ten years behind the West in displays and electronic controls," notes Miller, "and I would expect the guts of their avionics are based on Western technology," using microchip technology but without integrated digital data-bus architecture. Noting the Russian hallmark of high-thrust engines, he adds, "What they can't do with finesse, they do with power, making up for weight. It pays off: propulsion growth is linear but systems shrink exponentially. resulting in great thrust-to-weight."

So when is it likely that flocks of Golden Eagles will be seen in the skies? Not soon, according to Sweetman and Miller. Neither sees an operational airplane for up to a decade, and then only if some export customer bankrolls development. The threat to the West, says Miller, may be in setting up the S-37 as a "straw man" in order for Western air forces to obtain scarce funding for weapons to counter it.

RELATED ARTICLE: Berkut by the (provisional) numbers

Length 74 ft
Wingspan 54 ft
Height 21 ft
Speed Mach 2
Current max. thrust 2 x 34,200 lb
Empty weight 52,900 lb
Max. takeoff weight 75,000 lb
Service ceiling 60,000 ft

further links on

bulletSukhoi analyses S-37 flight test results
(source: Jane's Defence Weekly, 09/30/1998, Issue: PSA-2192; EUROPE Section)
bulletSukhoi's S-37: years away from production
(source: International Defense Review, 01/01/1998, 1998; Vol. 21, Issue: 21; INTERNATIONAL DEFENSE)
bulletRussian aspirations airborne with Sukhoi's Golden Eagle
(source: Jane's Intelligence Review , 02/01/1998, 1998; Issue: PSA- 2049; EUROPE Section)
bulletRussians offer radical stealth device for export
(source: Jane's Defence Weekly, 03/17/1999 , Vol. 031, Issue: 011; HEADLINES Section)
bulletHas Mikoyan's MFI fallen too far behind?
(source: Jane's Intelligence Review, 02/01/1999, Vol. 011, Issue: 002; RUSSIA Section)
bulletClearing skies
(source: Jane's Defense Weekly, 04-29-98, 1998; Issue: PSA-2084; Wednesday, April 29, 1998; BRIEFING Section)
bulletA new Russia, a new military instrument
(source: Military Technology, 03/01/1998, ISSN: 0722-3226; Vol. 22 No. 3; p. 30)
bulletRussia's Golden Eagle challenges U.S. Raptor
(source: Design News, 02/02/1998, Volume 53 Number 3 Pg. 46)
(using information from Jane's Intelligence Review, 02/01/1998, 1998; Issue: PSA- 2049; EUROPE Section)
bulletThe strange case of the Royal Eagle
(article from WAPJ, Fall 1998, by Piotr Butowski )
bulletFlight Tests of 5th Generation Fighter Continue at Zhukovsky
(source: Itar-Tass 08-OCT-97)
bulletReport: new Russian stealth fighter mired in controversy
(source: Associated Press, 10/24/97 16:28)
bulletFlight of the Golden Eagle (in Russian)
(source: Aviatsiya i Kosmonavtika, Jan. 1998)
bulletRussia begun testing fifth generation fighters (in Russian)
(source: Independent Military Review, #41, 1997)
bulletA fighter is always a fighter (in Russian)
(source: Aviapanorama, Feb. 1998)
bulletDuel: High-Flying Intrigues (in Russian)
(source: Profile, 01-25-99, n. 2, 124)
bullet"Really" TV-Center show (in Russian)
(source: TV-Center, "Really" show, 01-13-99)
bulletUnstable fighter designs (in Russian)
(source: KompuTerra, No. 223, Sept. 1998)
bulletS-37 testbed evaluates new fighter concepts
(source: Aviation Week & Space Technology, Nov 10, 1997 v147 n19 p46(2))
bulletSukhoi schedules S-32 maiden flight
(source: Aviation Week and Space Technology (New York) v147 n9 Sep 1 1997 p 36 ISSN: 0005-2175)
bulletRussia's Sukhoi S-32 completes first flights
(source: Defense Daily, Oct 10, 1997 v197 n8 p5(1))
bulletSukhoi fifth-generation fighter flies
(source: Flight international, Volume 152, Number 4595, pp. 4, 1997)
bulletFifth-generation Sukhoi makes its maiden flight
(source: Jane's defence weekly, Volume 28, Number 15, pp. 11, 1997)
bulletRadical Sukhoi design to fly this year
(source: Jane's defence weekly, Volume 27, Number 1, pp. 3, 1997)
bulletSukhoi continues with S-32 work
(source: Flight international, Volume 150, Number 4553, pp. 18, 1996)
bulletFlight Tests Of 5Th Generation Fighter Continue At Zhukovsky
(source: ITAR-TASS, 10/08/1997 02:12 PM)
bulletSukhoi Design Bureau Tests Fifth Generation Fighter
(source: ITAR-TASS, 10/07/1997 03:30 PM)
bulletSukhoi's Black Bird (S-37)
(source: Air Forces Monthly, 09-1999, p.64)
bulletRussia's Advanced Warplanes, Part II
(source: Combat Aircraft, January 2000, pp. 456-460)

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