The Sukhoi Su-57 `Felon’ was originally conceived in an effort to compete against Lockheed Martin’s F-22 and F-35. Initially known as the PAK-FA, its development has progressed at a relatively slow pace – but has it matured as a force to be reckoned with?
The Su-57 is also known as the PAK-FA (Perspektivnyi Aviatsionnyi Kompleks Frontovoi Aviatsii – Future Air Complex of Tactical Aviation). It incorporates a significant level of cutting-edge technology including stealthy characteristics, aerodynamics, powerplant design, system integration and weapons. Most of the aircraft’s features are highly classified and there are more questions than answers when it comes to its true operational capabilities and performance. It is difficult to evaluate just how successful Sukhoi’s world-class designers have been in solving serious challenges posed by an all-new high-performance stealthfighter design, combining extremely high agility and maneuverability with supersonic cruise (supercruise), advanced sensors, sensor fusion and robust multi-role mission capabilities. This fighter has been conceived to meet a complex VKS requirement that includes the ability to undertake deep penetration missions to knock out well-defended, high-value targets, and command the air in high-threat scenarios.
Evaluating the stealth
Sukhoi designers claim that the Su-57’s radar cross-section (RCS) is about 30 times smaller than that of a `Flanker’. Its fuselage is distinctively angular and flattened for RCS reduction, and there is extensive use of radar-absorbing coatings plus enclosed weapons bays.
Sukhoi designers aligned the leading edges of the wings, tailplanes and forward leading-edge extensions to make them parallel to each other. This all points to a reasonably stealthy forward hemisphere that offers tactical advantages in head-on air-to-air and air-to-surface engagements. However, there is little evidence of RCS reduction measures in the rear hemisphere, with well-exposed engine nozzles. In fact, this approach is likely attributed to the Russian concept for low observable design – there’s little inclination to trade overall performance with RCS reduction. Instead, Sukhoi has tended to rely on the use of an advanced multi-spectral sensor suite. This approach was conceived to afford better detection capability to counter the potential advantage of other low-observable (LO) platforms such as the F-22.
It is also noteworthy that the Su-57’s engines aren’t obscured by S-shaped inlet ducts. The existing curvature appears insufficient to completely mask the engine compressors from incoming radar energy. However, the masking could be achieved by adding radar blockers in the inlets, but this aspect of the Su-57’s design still remains highly classified.
Super maneuverability
The Su-57 can perform `Flanker’ type post-stall maneuvers, indicating a high level of agility for close-in fighting. Its blended-body aerodynamic configuration features a lift-generating body, fuselage extensions for improving aerodynamic performance at high angles of attack and wings liberally endowed with high-lift devices. There are no fewer than 12 flight-control surfaces, grouped in six symmetrical pairs, augmented by moving engine nozzles for thrust vectoring control. The six pairs of aerodynamic surfaces include all-moving horizontal stabilizers, all-moving vertical tails, ailerons, wing leading-edge flaps, flaperons and wing moving leading-edge extensions.
The nozzles of the widely separated engines can be deflected in two planes, thereby providing effective 3D thrust vectoring, with resultant control forces in pitch, roll and yaw axes – a design solution borrowed from the Su-30SM and Su-35 where the symmetric nozzle deflection is used for pitch control, while asymmetric deflection creates roll and yaw control forces. The 3D thrust-vectoring technology is considered to be a useful feature for retaining accurate control at slow speeds, when aerodynamic control surfaces are rendered ineffective.
According to Sergey Bogdan, flight performance is more or less similar to that of the Su-35. He reports a notable difference in supersonic acceleration – where he claims the Su-57 has no equal. Bogdan has said that the Su-57’s acceleration is `raw and wild’. In addition, he noted that the new fighter features good controlled spin characteristics, with rapid revolutions and a swift recovery.
Supercruising capability
The ability to cruise in dry power and supersonic speed (supercruise) is considered vital in modern fighter design and this is achieved in the Su-57 via two principal design features. For the `Felon’ it’s a combination of low drag for a high lift-to-drag ratio in supersonic cruise, combined with a high thrust-to- weight ratio. The Su-57’s wide engine installation accommodates rather large and deep weapons bays, affording a `clean’ configuration in all mission modes, with increased-thrust engines and a lightweight airframe using composite materials. The aircraft can optionally carry external stores if required.
The Su-57, in its initial configuration, is powered by a pair of AL-41F-1 afterburning turbofans – an evolution of the AL-31 series of engines powering the Su-27/30 family, developed by NPO Saturn-Lyul’ka and designated as the so-called `Phase 1′ powerplant. Its design is based on the izdeliye 117S engine of the Su-35, with a dry rating of 20,938lb (93kN) thrust while the full afterburner rating is 33,060lb (147kN) thrust.
The definitive Su-57 engine, dubbed izdeliye 30, began flight-testing in December 2017 on the T-50-2 prototype. This is the so-called `Phase 2 engine’, with full-authority digital control, expected to be rated at about 24,220lb (107kN) dry and 37,468lb (166.77kN) at full afterburner. The new engine – expected to be installed on production-standard Su-57s by 2022 at the earliest – is lighter, more powerful and includes a reduced number of components. In addition, the Su-57 uses variable-area intakes for optimum performance in both supersonic and subsonic regimes of flight, hitting Mach 2.0 and above.
Sensor fusion
The Su-57 features the brand new NIIP Tikhomirov N036 Byelka modular multi- band radar system, also known as Sh121. This integrates three principal modules – one being the nose-mounted X-band active electronic scanning array (AESA) radar. This is augmented by a second module, also working in the X-band, which employs a pair of side-looking antennas just aft of the nose antenna, designed to expand the system’s angular coverage in azimuth. The third element is a pair of L-band phased-array antennas built into the wing leading-edge extensions, intended to endow the Su-57 with enhanced detection performance against stealth aircraft, as well as for identification friend or foe (IFF) purposes.
Stealth technologies fielded in Western fighters are mostly tailored to counter airborne and ground-based radars operating in the X-band; as a consequence, LO characteristics are deemed less effective when pitted against L-band airborne radars. This could be also regarded as an attempt to compensate for the Su-57’s apparently higher RCS compared with that of the F-22 and F-35, which would facilitate extended-range detection of these fighters.
The infrared search-and-track (IRST) sensor suite is integrated with the Su-57’s weapons control system, and it includes the 101KS-V targeting system installed in the nose as well as 101KS-U ultraviolet missile approach warning sensors under the nose and built into the rear fuselage, along with an 101KS-O electro-optical jammer. A navigation/targeting pod, dubbed 101KS-N, can also be carried in uncontested strike missions when stealth performance is not required.
The Su-57 also features the L402 Gimalay integrated electronic warfare (EW) system, but no specific information has been released yet about its components and real operational capabilities.
Weapons for all occasions
The Su-57 features centerline weapons bays capable of housing up to four K-77M medium-range active radar-guided missiles (also known as the RVV-SD) for beyond-visual-range engagements, while two short-range K-74M2s (RVV-SD) are accommodated in side bays in the underwing fairings. In 2018, it was further revealed that the `Felon’ can also use the K-37M (RVV-BD) long-range air-to-air missile, capable of engaging targets at up to 110nm (200km) distance in head- on attacks. The tandem internal bays between the engines can also house large- size air-to-surface and anti-ship missiles as well as large guided bombs.
When stealth is not required, the Su-57 can carry missiles and bombs on at least four underwing pylons plus two more under the engine trunks. In these missions the aircraft is advertised as being capable of delivering heavy warloads of up to 11,000lb (5,000kg). In March and April 2016, the T-50-2 prototype was spotted involved in aerodynamic flight trials carrying six distinctly old-fashioned OFAB-250-270 freefall fragmentation/ high-explosive `dumb’ bombs.
It also features the proven 30mm GSh- 30-1 single-barrel cannon as used on the Su-27/35 and MiG-29, albeit in a vastly improved version dubbed the 9-A1-4071K. It is installed starboard, with the barrel protruding adjacent to the cockpit, and is provided with 150 rounds.
The air-to-surface precision-guided arsenal includes the newly developed Kh-38 modular missile that uses a variety of guidance packages, plus the Kh-58UShK long-range anti-radar missile optimized for internal carriage (with maximum range of 132nm [245km]) and two new versions of the Mach-3 Kh-31 missile. The Kh-31AD, intended for use against ships, is outfitted with an active radar seeker and has a maximum range of 86nm (160km), while the Kh-31PD is designed for knocking out radars, with a passive radar seeker and maximum range quoted as 135nm (250km). The Kh-35U is another anti-ship missile touted for the Su-57, with range of up to 140nm (260km).
There is also a range of guided bombs with laser, TV and satellite guidance systems set to be incorporated into the Su- 57, such as the 550lb (250kg) KAB-250 and the 3,306lb (1,500kg) KAB-1500. In 2019, the Tactical Missiles Corporation showed to the public two brand new guided bomb types with satellite/INS guidance packages, which can be carried by the Su-57. The first of these is the K08BE, weighing 1,113lb (504kg) and the second one is the K029BE, weighing 3,361lb (1,525kg). Boris Obnosov, director general at the Tactical Missiles Corporation, hinted in August 2018 that his company could start developing new-generation guided bombs weighing 220lb (100kg) and possibly 110lb (50kg) for the `Felon’.
The Su-57 is also set to use new- generation, special-purpose unguided bombs such as the 1,100lb (500kg) OFZAB-350 (outfitted with a high-explosive/fragmentation/incendiary warhead) and the ODAB-500PMV with a thermobaric warhead.
Deployment to Syria Defence
Minister Sergey Shoygu has spoken about missile launches in the context of Russian operations in Syria but refrained from explicitly saying that combat condition launches took place in Syria. Low-quality footage presented by Shoygu featured a red missile, which is peculiar for an experimental version undergoing range tests and therefore arouses doubt.
Two Su-57s were deployed to Syria for a couple of days in February, 2018, a fact only publicised by the Russian Ministry of Defence in November, when it released video footage showing two aircraft taking off and landing at Hmeimim Air Base . Both aircraft’s tactical numbers were painted over, but their camouflage schemes indicated the aircraft to be side numbers 509 and 511 (T-50-9 and T-50-11) Commentary on the video stated: “The aircraft’s technical characteristics intellectual data management and indication system, activity of all on board systems, including the weapons, were checked in real conditions in higher temperatures, complex terrain and other factors. The Su-57 crews performed more than ten flights in Syria.”
Both Su-57s flew without corner reflectors which enabled any surveillance system operating in the skies over Syria to discover the aircraft’s radar signature.
Hunter Wingman
Associated with the Su-57 is the S-70 Okhotnik (hunter) unmanned combat air vehicle which is being developed specifically for joint operations with the Su-57 as a wingman. In one of the few known official documents in which the Okhotnik is mentioned, it is categorised as a “sixth-generation unmanned air vehicle.”
According to an unconfirmed report an S-70 Okhotnik air vehicle prototype was built at the company’s Novosibirsk aircraft plant and performed the maiden flight at Akhtubinsk on August 3, 2019.
The Sukhoi S-70 Okhotnik is a large drone in all-wing configuration and produced using elements of the Su-57. It is fitted with a single engine, most likely an AL-41F-1.
Okhotnik carries weapons in two internal weapon bays, which are likely to be the same size as those of the Su-57 so that al weapons under development specifically for the fighter will fit the Okhotnik.
Components of the Okhotnik testing programme is being carried out with T-50-3, the third Su-57 prototype. It is feasible that T-50-3 is being used to evaluate autonomous navigation, automatic take-off and landing, and other systems developed for Okhotnik T-50-3 is fitted with new antennas that appear to be like those fitted on the Okhotnik. Furthermore, T-50-3’s current aircraft’s colour scheme features the Okhotnik’s silhouette.
