The Sukhoi S-37 ‘Berkut’ ( Golden Eagle )

The Sukhoi S-37 is one of two prototypes, the second being the MIG 1.44, built to fulfil the perceived requirement for a '5th generation' multifunction tactical fighter ( MFI – Mnogofunktsyonalniy Frontovoy Istrebitel ). Although conceived back in the mid '80s a combination of factors, not the least of which being a critical shortage of development budget, resulted in a delay in first flight to 1997. Some 50+ flights had been made by the end of 1999 but as yet little is known regarding detailed specification or performance.
Unlike the western nations, and the USA in particular, the emphasis on fighter design in the former Soviet Union has moved increasingly in the direction of super manoeuvrability at the relatively low speed end of the performance spectrum. Top end speed and stealth characteristics have become secondary considerations. The S-37 is (or was) the ultimate expression of this philosophy. The airframe design has been described as a triple tandem wing with the canards, forward-swept wing and independent tail linked by elongated fuselage stakes. The twin fins are mounted just outboard of the engines and are angled slightly outwards. As with most current fighter designs the aircraft is inherently unstable and relies on complex flight computers to ensure stability and provide for the maximum degree of manoeuvrability under high g load. The initial design is also believed to have incorporated 3D thrust vectoring nozzles on the twin engines, but these have yet to be installed and may also have suffered budget problems. The engine intakes are simple fixed geometry quarter-circle designs mounted below the fuselage strakes and are clearly optimised for sub-sonic efficiency. The aircraft is designed to supercruise without afterburner. Auxiliary intakes are located on the top of the fuselage. The single seat cockpit is fitted with an ejector seat reclined at 30o, to aid G-tolerance, and it has been suggested that work was in hand to enable this recline angle to vary through the flight envelope. View from the cockpit should be excellent in all quarters with no significant obstruction to downward view on either side, the strakes are located mainly behind the pilot, or ahead over the short slightly drooped nose radome. The relatively high position of the cockpit in relation to the roll axis may, as in the F-22, limit rate of roll due to unacceptable lateral acceleration on the pilot. The weapon load is held in internal bays and there are no hardpoints on the wings. The aircraft is finished in radar absorbent material to give a measure of stealth capability but as the aircraft is optimised for close quarter 'dog fights' rather the ‘beyond visible range’ encounters this is not a prime feature of the design. It appears that the philosophy is to use agility to evade a BVR attack and to gain superiority in the following close quarters engagement.
Only basic specification data has been released with further information the result of extrapolation or speculation from western sources. The design was originally presented in model form as the S-32 in 1996 and appeared to incorporate a layout more reminiscent of the X-29 but with a degree of stealth characteristics, such as inward angled twin fins. By the time of the first flight on 25th October 1997 the aircraft had been renamed, for unknown reasons, as the S-37, a designation previously assigned to delta wing project from the early ‘90s.
Russian sources deny that the S-37 is only a technology test vehicle but it is difficult to escape that conclusion. The use of forward-swept wings is technically extremely challenging and has only become a viable proposition in recent years with the advent of high performance and lightweight composite materials. Although various experimental aircraft have been fitted with such a wing, most notably the X-29, performance data is still limited and it is unlikely that there is sufficient data available across the whole flight envelope to enable construction of a true fighter prototype without the requirement for the intermediate step of a technology proof vehicle. Both the European EF2000 and American F-22 were developed via this route, albeit for slightly different reasons. Similar arguments apply to the stated intention of installing thrust vectoring capability. Both 2D and 3D vectoring nozzles have been installed experimentally on US and Russian aircraft but the technology is still to be matured.
The potential rival to the Sukhoi S-37, The MIG 1.44, is, by comparison, relatively conventional in layout. This aircraft combines an apparently simple delta wing with large canards and double fin tail. The twin engines are fed by a single square section variable geometry intake optimised for supersonic speeds. It resembles, superficially, a scaled up, twin finned, EF2000 Typhoon. The question that arises is why Sukhoi have elected for the complexity of a forward-swept wing. In comparison with a rear-swept wing of similar area forward sweep has the known benefits of slightly lower subsonic induced drag, lower speed and more predictable stall, and more responsive pitch characteristics. The downside is the need for greater rigidity, and hence higher weight, to resist flexure, and poorer supersonic performance. These aerodynamic and agility benefits can be further enhanced through synergies with close-coupled canards and tailplanes. Overall the benefits have not until now been seen to be sufficiently compelling to overcome the structure complexity that were imposed and airframe designers have only rarely proposed such a layout. It remains to be seen whether the performance of the S-37 will show the decision to be justified.
Perhaps a more serious question hanging over both the Sukhoi and MIG aircraft is whether there is indeed a need for a 5th generation fighter to the MFI specifications. The Sukhoi S-27/S-35 family in service today probably stands as the most flexible and capable fighter airframe design of the 20th century. The performance of the basic aircraft coupled with it's proven ability to incorporate major structural, aerodynamic and mission changes without compromise to capability has not been achieved by a single design since the Spitfires and Mustangs of the 2nd World War. There is clear potential for a long and successful life for these aircraft and it is hard to see how the S-37 or MIG 1.44, both similar in size and power to the S-27/S-35, represent sufficient advance to justify development.

Following the long delayed first flight of the MIG 1.44 in February 2000 it has been confirmed that the aircraft will not go into production but will be used to gather data to aid in future fighter designs.

Specifications ( speculative data in italics )

Length 74.1 ft

Span 54.8 ft

TO weight (normal) 52910 lb

TO weight (max) 77160 lb

Engines 2 x AL-31F rated at 18,700 lb dry, 32,000 lb with afterburner (approx)

Max Speed 1,080 – 1,188 kts

Cruise Speed 810 – 918 kts

Subsonic range >2484 miles

Ceiling 61,680 ft

Climb 45,275 ft/min

# References

The Mikoyan MFI vs. the Sukhoi S-37 Piotr Butowski Combat Aircraft Jan 2000

Of the many Web sites with information on the S-37 the following are recommended:

http://aeroweb.lucia.it/~agretch/RAFAQ/six5th_5.html Good background information

http://members.xoom.com/_XMCM/082499/aviation/nws001/s37biblio.htm excellent links

http://members.xoom.com/_XMCM/082499/aviation/nws001/afm023.htm

www.geocities.com/CapeCanaveral/9735/suclass.htm

Data on the X-29 forward swept wing research can be found at:

http://trc.dfrc.nasa.gov/PAO/PAIS/HTML/x29/X-29.html

A paper ( H-1913.pdf) with detailed flight data can be downloaded in Acrobat format from:

www.searchpdf.adobe.com/proxies/0/98/43/2.html