Su-57 and Su-75
The Sukhoi Su-57 (Russian: Сухой Су-57; unconfirmed NATO reporting name: Felon) is a stealth, single-seat, twin-engine multirole fifth-generation jet fighter being developed since 2002 for air superiority and attack operations. The Su-57 is planned to be the first aircraft in Russian military service to use stealth technology. Its maiden flight took place on 29 January 2010 and the first production aircraft delivered in 2020.Although most information is classified, sources within the Sukhoi company and Defence Ministry have openly stated that the aircraft is to be stealthy, supermaneuverable, have supercruise capability, incorporate substantial amounts of composite materials, and possess advanced avionics such as active phased-array radar and sensor fusion with the prior generation fighter aircraft as well as ground and naval defenses. The Su-57 is intended to succeed the MiG-29 and Su-27 in the Russian Air Force. An advanced clean-sheet design engine, currently designated the IZ-30, currently in final stages of development and expected to be available after mid-2020s. The aircraft is expected to have a service life of up to 35 years. The aircraft has a blended wing body fuselage and incorporates all-moving horizontal and vertical stabilizers; the vertical stabilizers toe inwards to serve as the aircraft’s airbrake. The aircraft incorporates thrust vectoring and has adjustable leading–edge vortex controllers (LEVCONs) designed to control vortices generated by the leading edge root extensions, and can provide trim and improve high angle of attack behavior, including a quick stall recovery if the thrust vectoring system fails. The advanced flight control system and thrust vectoring nozzles make the aircraft departure-resistant and highly maneuverable in both pitch and yaw, enabling the aircraft to perform very high angles of attack maneuvers such as the Pugachev’s Cobra and the bell maneuver, along with doing flat rotations with little altitude loss. The Su-57 has a climb rate ranging from 330 m/s (1,100 ft/s) to 361 m/s (1,180 ft/s). The aircraft makes extensive use of composites, with the material comprising 25% of the structural weight and almost 70% of the outer surface. Weapons are housed in two tandem main weapons bays between the engine nacelles and smaller bulged, triangular-section bays near the wing root. Internal weapons carriage eliminates drag from external stores and enables higher performance compared to external carriage, as well as enhancing stealth. The Su-57’s aerodynamics and engines enable it to achieve Mach 2 and fly supersonic without afterburners, or supercruise, a significant kinematic advantage over prior generations of aircraft. Combined with a high fuel load, the fighter has a supersonic range of over 1,500 km (930 mi), more than twice that of the Su-27. Extendable refueling probe is available to further increase its range. In the Su-57’s design, Sukhoi addressed what it considered to be the F-22’s limitations, such as its inability to use thrust vectoring to induce roll and yaw moments and a lack of space for weapons bays between the engines, and complications for stall recovery if thrust vectoring fails.
Similar to other stealth fighters such as the F-22, the airframe incorporates planform edge alignment to reduce its radar cross-section (RCS); the leading and trailing edges of the wings and control surfaces and the serrated edges of skin panels are carefully angled to reduce the number of directions the radar waves can be reflected. The infrared search-and-track sensor housing is turned backwards when not in use and its rear is treated with radar-absorbent material (RAM) to reduce its radar return. To mask the significant RCS contribution of the engine face, the walls of the inlet ducts are coated with RAM and the partial serpentine ducts obscure most of the engines’ fan and inlet guide-vanes (IGV); the remaining exposed engine face is masked by a radar blocker similar in principle to that used on the F/A-18E/F. According to Sukhoi’s radar blocker patent, the slanted blocker grid is placed in front of the IGV at a distance of 0.7—1.2 times the diameter of the duct, giving the Su-57 RCS similar to a F-35. The fuselage of the aircraft is coated with RAM to absorb radar emissions and reduce the reflection back to the source. Due to the extensive use of polymeric carbon plastics composites, the aircraft has four times fewer parts compared to the Su-27, weighs less and is easier to mass-produce. The aircraft canopy is made of composite material and 70-90 nm thick metal oxide layers with enhanced radar wave absorbing to minimize the radar return of the cockpit by 30% and protect the pilot from the impact of ultraviolet and thermal radiation. The Su-57’s design emphasizes frontal stealth, with RCS-reducing features most apparent in the forward hemisphere; the shaping of the aft fuselage, the seams between parts, and rivets are much less optimized for radar stealth compared to the F-22. However, during MAKS 2019 the craftsmanship of the fuselage was actually finer than expected and looked smooth despite the rivets. The combined effect of airframe shape and RAM of the production aircraft is estimated to have reduced the aircraft’s RCS to a value thirty times smaller than that of the Su-27. Sukhoi’s patent for the Su-57’s stealth features cites an average RCS of approximately 0.1 to 1 m2,compared to the Su-27’s of approximately 10 to 15 m2. Like other stealth fighters, the Su-57’s low observability measures are chiefly effective against high-frequency (between 3 and 30 GHz) radars, usually found on other aircraft. The effects of Rayleigh scattering and resonance mean that low-frequency radars, employed by weather radars and early-warning radars are more likely to detect the Su-57 due to its size. Such radars are also large, susceptible to clutter and are less precise which makes them not able to produce targeting data.
The Su-75 Checkmate is Sukhoi export friendly 5th generation fighter its designed to be even lower cost then the Su-57 and features many of the same systems, the Su-75 and Su-57 represent Russian air doctrine shift to a high/low fighter design which was first proven in the US with the F-15/F-16 which the Russia have adopted, the Su-75 is a single seat, single engine fighter that uses many of the technologies as the Su-57 but with less expensive materials the Su-75 is design for export customers that can’t operate the more complex twin engine Su-57, the Su-75 features internal bays for air-to-air and air-to-ground missiles.
The Su-75 has the same avionics and IRST systems as the Su-57, and two large MFD displays. The Su-75 has four internal bays and six external hardpoints making it able to carry up to 7000 kg of weapons both guided and unguided munitions. The main sensors are the AESA radar and IRST system which gives the Su-75 the ability to fire radar-guided missiles and IR-guided missiles.
Developer Commentary
The Su-75 and Su-57 represent Russian best stealth aircraft designs, each compromising in some areas rear aspect stealth and infrared, but having enough general stealth to avoid radars and other 5th gen fighters. The Su-57 is faster and can fly higher its radar is more powerful than the Su-75, while the Su-75 is a better dogfighter and has more agile maneuverability. Both fighters share the same sensors and weapons systems with the Su-75 having slightly fewer hardpoints and inferior avionics. They can be used quite effectively with the right doctrine.