S-37 «Berkut»
prototype

History of project

DESIGN FEATURES. The S-37 features the very unstable triplane aerodynamic configuration, which is a novelty for an aircraft of the class.
    The forward-swept mid-wing has a rather high aspect ratio. The wing panels blend smoothly into the leading edge root extensions (LERX) featuring a high leading-edge sweep angle. The wing panels are outfitted with deflec-table slats, flaps and ailerons. The leading edge root extensions act as the base for all-moving trapezoidal-planform canards.
    The all-moving horizontal stabilizers has a rather small area and corniculate planform. With such a configuration, the inner stabilizer portions act as elevators in support of the wing-to-airframe blending area.
    The design of the two vertical tails is similar to that of the Su-27 but has a smaller relative area. The outwardly canted tails are fixed to the center wing section.
    The fuselage has an oval cross-section. To enhance the fighter's anti-spin characteristics, the fore section of the radome is made flat and features edges on the sides. The lower fuselage in front of the air intakes has the reversed trape-zoid cross-section that, coupled with the LERXes above the intakes, ensures stable operation of the engines at any angle of attack. The LERXes furnish the airframe's upper nose section with an aerodynamic lifting shape blending smoothly with the wing roots. Auxiliary dorsal inlets open when the airflow pressure is insufficient or nonexistent.
    The airframe is made mostly of aluminum and titanium alloys. Its design relies on large panels, new materials and technologies. The share of composites account for 13 per cent of the fighter's weight.
    In developing the S-37, the Sukhoi Design Bureau came up with a new technology of double-curvature panel manufacture and ensured the panels' accurate joining. The use of large panels as the fuselage skin ensured extraordinary smoothness of the fuselage while minimizing the number of fasteners.
    The fighter features a new-generation crew life-support and ejection system. The ejection seat is declined back at 30 degrees, which reduces the impact of high Gs on the pilot.
    The realised concept of the variable-geometry adaptive ejection seat shall allow the dogfight-ing with g-loading much higher than that of any existing fighter. This will ensure the maximization of the fighter's maneuverability advantages.
    To fly the S-37, a side-mounted low-travel control stick and tensometric throttle controls are provided. Test pilot Igor Votintsev mentioned the cockpit's high degree of comfort and the aircraft's being easier on the pilot as compared with other agile fighters as far as g-loads are concerned.
    To save on time and money, some S-37's components (canopy, landing gear, vertical tails, some avionics systems) were inherited from the production Su-27.
THE POWER PLANT. The prototype is supplied with two turbofan D-30F6 (2x15.600 kgf) arranged in a tail part of a fuselage. Further the reequipment of an airplane by engines is supposed AL-41F with a control system of thrust vector. Fixed-geometry air intakes, the form of which section is close to sector of a circle, are arranged under wing inflows. The air passages have the S-figurative shape, that provides shielding blades of turbofan compressors. On the upper surface of a fuselage two doors serving for an additional air scooping at manoeuvring and on take-off and landing modes are arranged.
ON-BOARD EQUIPMENT AND AVIONICS. On an airplane the S-37 are established the iterated remote control system by flight which is capable to decide of a problem of spin recovery and a piloting by means of the lateral handle, developed by the experts MNPK «Avionics» and used, also, on a fighter Su-37 (generation 4+). The activities on creation for «Berkut» of «side» of the fifth generation are conducted.
ARMAMENT. On a prototype airplane the arms is absent. The production fighter created on base «Berkut», should bear a part of controlled means of a defeat on internal suspension points. The capability of the installation and underwings of units of the external suspension is stipulated. In left wings inflow the built-in gun such as GSh-301 (30mm) is established.

References and Credits:

1. Aviatsia i Kosmonavtika №8. 1999
2. «Aerospace Herald» 1-2, 3'99, 4'2000