Sukhoi Su-57

In 1979, the Soviet Union outlined a need for a next-generation aircraft intended to enter service in the 1990s. The project was designated the I-90 (Russian: Истребитель, Istrebitel, "Fighter") and required the fighter to have substantial ground attack capabilities and would eventually replace the MiG-29s and Su-27s in frontline tactical aviation service. The subsequent programme designed to meet these requirements, the MFI (Russian: МФИ, Russian: Многофункциональный фронтовой истребитель, Mnogofunksionalni Frontovoy Istrebitel, "Multifunctional Frontline Fighter"), resulted in Mikoyan's selection to develop the MiG 1.44.[21] Though not a participant in the MFI, Sukhoi started its own programme in 1983 to develop technologies for a next-generation fighter aircraft, resulting in the S-37, later designated Su-47. Due to a lack of funds after the collapse of the Soviet Union, the MiG 1.44 programme was repeatedly delayed and the first flight of the prototype did not occur until 2000, nine years behind schedule.[21] The MiG 1.44 was subsequently cancelled and a new programme for a next-generation fighter, PAK FA, was initiated. The programme requirements reflected the capabilities of Western fighter aircraft, such as the Eurofighter Typhoon and F-22 Raptor. In 2002, Sukhoi was selected over Mikoyan as the winner of the PAK FA competition and would lead the design of the new aircraft; Mikoyan continued to develop its proposal as the LMFS (Russian: ЛМФС, Russian: Легкий многофункциональный фронтальный самолёт, Liogkiy Mnogofunktsionalniy Frontovoi Samolyet, "Light Multifunctional Frontline Fighter") which was designed to be smaller and more affordable.[22][23]

To reduce the PAK FA's developmental risk and spread out associated costs, as well as to bridge the gap between it and older previous generation fighters, some of its technology and features, such as propulsion and avionics, were implemented in the Sukhoi Su-35S fighter, an advanced variant of the Su-27.[24][25] The Novosibirsk Aircraft Production Association (NAPO) is manufacturing the new multi-role fighter at Komsomol'sk-on-Amur along with Komsomolsk-on-Amur Aircraft Production Association (KnAAPO), and final assembly is to take place at Komsomol'sk-on-Amur.[26][27] Following a competition held in 2003, the Tekhnokompleks Scientific and Production Center, Ramenskoye Instrument Building Design Bureau, the Tikhomirov Scientific Research Institute of Instrument Design (NIIP), the Ural Optical and Mechanical Plant (UOMZ) in Yekaterinburg, the Polet firm in Nizhny Novgorod and the Central Scientific Research Radio Engineering Institute in Moscow were selected for the development of the PAK-FA's avionics suite. NPO Saturn is the lead contractor for the interim engines; Saturn and MMPP Salyut will compete for the definitive second stage engines.[28] In 2004, the fighter's conceptual design was completed and approved by Russia's Defense Ministry, with Alexander Davidenko selected as the Chief designer.[1] Funding of the programme began in 2005.[29]

On 8 August 2007, Russian Air Force Commander-in-Chief (CinC) Alexander Zelin was quoted by Russian news agencies that the programme's development stage was complete and construction of the first aircraft for flight testing would begin.[30][31] Three flyable prototypes were planned to be built by 2009.[29] In 2009, the aircraft's design was officially approved.[22]

Sukhoi T-50 in flight with landing gear deployed, 2010

In 2007, Russia and India agreed to jointly develop the Fifth Generation Fighter Aircraft Programme (FGFA) for India.[32][33] In September 2010, it was reported that India and Russia had agreed on a preliminary design contract where each country was to invest $6 billion; development of the FGFA fighter was expected to take 8–10 years.[34] The agreement on the preliminary design was to be signed in December 2010.[35] India planned on acquiring a modified version for its FGFA programme. It originally planned on buying 166 single-seat and 48 two-seat fighters,[36] but later changed it to 214 single-seat fighters,[37] and later decreased its purchasing size to 144 fighters by 2012.[38][39] In early 2018, India pulled out of the FGFA project, which it believed did not meet its requirements for stealth, combat avionics, radars and sensors by that time.[40] This news lead some observers to question the future of the whole Su-57 project.[41]

The Russian Air Force was expected to procure more than 150 fighters for PAK FA with the first fighter to be delivered in 2016.[42][43] In 2011, the Russian Defence Ministry planned on purchasing the first 10 evaluation aircraft after 2012 and then 60 production standard aircraft after 2016.[44] In December 2014, the Russian Air Force planned to receive 55 fighters by 2020.[45] Russian Deputy Minister of Defence Yury Borisov stated in 2015 that the Air Force would slow production, reduce its initial order to 12 fighters, and retain large fleets of fourth-generation fighters due to the nation's economy.[46][47][48]

Russian Air Force Commander-in-Chief Viktor Bondarev stated that the fighter planned to enter serial production in 2017, after all trials would be completed.[49] In 2017, Deputy Minister Yury Borisov stated that the Su-57 would most likely enter service in 2018, due to implementation of more advanced engines, and further testing. He also stated that it would be part of the new 2018-2027 state armament programme. Actual number of aircraft to be delivered is yet unknown.[50]

On 30 June 2018, it was reported that an order for 12 aircraft was agreed,[51][52][53] with deliveries to the ranks of the Russian Armed Forces starting in 2019. The first aircraft will join fighter regiments at the Lipetsk Air Center.[54] At the same time, the Deputy Prime Minister for Defence and Space Industry Yury Borisov stated that "Today, the Su-35 is one of the world's best fighters, so there is no reason for us to speed up work on mass production of the fifth-generation fighter."[55] Borisov's statement caused confusion among observers. Some interpreted the fifth generation fighter he referenced as the FGFA, the exported variant of the Su-57, while others interpreted it to be directly alluding to the Su-57 itself. This also led to predictions and concerns about the project's future: some have interpreted it as reiteration that the Su-57 program would continue as previously planned, others interpreted it as the Su-57 program would not be mass-produced, and some believe it to be an implicit announcement of the project's cancellation.[53][56][57] The slowing of procurement could be because of the current slow growth of the Russian economy, while the future patches' procurement are for an unknown future; the Russian military could be waiting for the more powerful Saturn izdeliye 30 engine to be ready for serial production.[58]

On 22 August 2018, during the International Military-Technical Forum «ARMY-2018», the Russian Defence Ministry and the JSC Sukhoi signed the first contract for delivery of two serial Su-57 fighters. The deliveries of the first two such aircraft are scheduled for 2019 and 2020, respectively.[59]

Russian Defence Ministry planned to conclude a second contract for 13 more aircraft in 2020.[60] However, on 15 May 2019, Russian President Vladimir Putin announced that 76 aircraft will be purchased and delivered to the Air Force by 2028. This came after the price of the Su-57 and equipment was reduced by 20%.[61] The contract for the 76 aircraft was formally signed on 27 June 2019 at the International Military-Technical Forum «ARMY-2019».[62][63] The same month, General Director of Tactical Missiles Corporation (KRTV) Boris Obnosov reported, a contract for serial production of ammunition for Su-57 fighters was signed, and is being inducted.[64]

JSC Sukhoi has started the serial production of the aircraft in late July 2019.[5]

T-50 at the MAKS 2011 air show

The prototype's maiden flight was repeatedly postponed from early 2007 after encountering unspecified technical problems. In August 2009, Alexander Zelin acknowledged that problems with the engine and in technical research remained unsolved.[65] On 28 February 2009, Mikhail Pogosyan announced that the air-frame was almost finished and that the first prototype should be ready by August 2009.[66] On 20 August 2009, Pogosyan said that the first flight would be by year's end. Konstantin Makiyenko, deputy head of the Moscow-based Centre for Analysis of Strategies and Technologies said that "even with delays", the aircraft would likely make its first flight by January or February, adding that it would take five to ten years for commercial production.[67]

Flight testing was further delayed when Deputy Prime Minister Sergei Ivanov announced in December 2009 that the first trials would begin in 2010.[68] The first taxi test was successfully completed on 24 December 2009.[69][70] Flight testing began with T-50-1, the first prototype aircraft, on 29 January 2010.[71] Piloted by Hero of the Russian Federation Sergey Bogdan, the aircraft's 47-minute maiden flight took place at KnAAPO's Dzemgi Airport in the Russian Far East.[72][73] The second prototype, T-50-2, was originally planned to fly in late 2010, but this was pushed back to March 2011.[74] The first two prototypes lacked radar and weapon control systems. On 14 March 2011, the fighter achieved supersonic flight at a test range near Komsomolsk-on-Amur.[75] The T-50 was displayed publicly for the first time at the 2011 MAKS Airshow.[76][77]

T-50 climbing after takeoff, 2011

The third and fourth prototypes first flew in November 2011 and December 2012, respectively, and lack the pitot tube found on earlier aircraft.[78] By the end of 2013, five prototypes were flown, with the fifth prototype having its first flight on 27 October 2013; with this flight the programme has amassed more than 450 flights.[79] The first aircraft for state test trials was delivered on 21 February 2014.[80]

Testing would reveal that the initial prototypes did not have adequate fatigue life, with early cracks forming in the fuselage. The five initial prototypes required additional structural reinforcements in order to continue flight tests. The aircraft subsequently underwent a structural redesign, with increased composite material usage, reinforced airframe to meet full life cycle requirements, elongated tail "sting", and slightly greater wingspan; the sixth flyable prototype was the first of the redesigned "second stage" aircraft, with the five prior prototypes considered "first stage" vehicles.[81][82][83]

A total of ten flying and three non-flying prototypes were built for flight tests and initial combat trials.[84] Five flying and two non-flying prototypes comprise the "first stage" aircraft design, with the two non-flying prototypes testing static flight loads and avionics integration. The first two flying prototypes tested flight characteristics, while the second two prototypes conducted airborne tests of avionics systems, including the radar and electronic warfare suite.[85][86][87][82][88] The second prototype has since been used to test the second stage izdeliye 30 engine. The fifth prototype was severely damaged by an in-flight fire, and the remains were combined with parts cannibalized from the sixth prototype in order to return the aircraft to flight status.[89] Starting with the sixth flying aircraft, five more of the structurally redesigned "second stage" aircraft were built, as well as one non-flying prototype to test flight loads on the new structure. The last two prototypes were test articles of production aircraft.[90] Issues and accidents during the testing resulted in repeated delays to the programme, with the first production aircraft originally planned for delivery in 2015; this has been delayed multiple times, and the date is now expected to be in 2020.[91]

Prototype T-50 flying upside down

T-50 aerodynamic condensation at MAKS-2015

The Su-57 is intended to be a fifth-generation multirole fighter aircraft and the first operational stealth aircraft for the Russian Air Force. 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.[17][27][103]

The aircraft has a blended wing body fuselage[104] 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 behaviour, including a quick stall recovery if the thrust vectoring system fails.[105] 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.[106][107][108] The Su-57 has a climb rate ranging from 330 m/s (1,100 ft/s) to 361 m/s (1,180 ft/s).[109][110] 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.[111] 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.[N 2] 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.[104][106][112] Extendable refueling probe is available to further increase its range.[113] 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.[114]

On 27 April, 2020, it was reported by the Izvestia that the Su-57 hydraulic systems were planned to be replaced with electromechanical drives (actuators), improving the aircraft's combat survivability, stealth characteristics, maneuverability and reducing the maintenance complexity. According to the report, the first flight of a modernized Su-57 was scheduled for the middle of 2022, with the trials of the "electric" fighter version to take at least two years.[115][116]

The Su-57 is planned to be the first operational aircraft in Russian Air Force service to use stealth technology. 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.[117] Weapons are carried internally in weapons bays within the airframe and antennas are recessed from the surface of the skin to preserve the aircraft's stealthy shape. 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. The fuselage of the aircraft is coated with RAM to absorb radar emissions and reduce the reflection back to the source.[118][119][120]

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.[121] 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.[122] 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.[104][123] However, during MAKS 2019 the craftsmanship of the fuselage was actually finer than expected and looked smooth despite the rivets.[124]

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.[125] Sukhoi's patent for the Su-57's stealth features cites an average RCS of approximately 0.1 to 1 m²,[119] compared to the Su-27's of approximately 10 to 15 m².[126][127] 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.[128][129]

AL-41F1 engine compressor stall at MAKS-2011

Pre-production T-50 and initial production batches of the Su-57 will use interim engines, a pair of NPO Saturn izdeliye 117,[N 3] or AL-41F1, augmented turbofans.[130] The engine is a highly improved and uprated variant of the AL-31 that powers the Su-27 family of aircraft and produces 93.1 kN (21,000 lbf) of dry thrust, 147.1 kN (33,067 lbf) of thrust in afterburner, and has a dry weight of approximately 1,600 kg (3,530 lb). The engines have full authority digital engine control (FADEC) and are integrated into the flight control system to facilitate maneuverability and handling.[104] The AL-41F1 is closely related to the Saturn izdeliye 117S engine, or AL-41F1S, used by the Su-35S, with the latter's separate engine control system being the key difference.[131][132]

The AL-41F1 engines incorporate thrust vectoring (TVC) nozzles whose rotational axes are each canted at an angle, similar to the nozzle arrangement of the Su-35S. This configuration allows the aircraft to produce thrust vectoring moments about all three rotational axes, pitch, yaw and roll. Thrust vectoring nozzles themselves operate in only one plane; the canting allows the aircraft to produce both roll and yaw by vectoring each engine nozzle differently. The engine inlet incorporates variable intake ramps for increased supersonic efficiency and retractable mesh screens to prevent foreign object debris being ingested that would cause engine damage.[104] The AL-41F1 is to also incorporate infrared and RCS reduction measures.[133][134] In 2014, the Indian Air Force openly expressed concerns over the reliability and performance of the AL-41F1; during the 2011 Moscow Air Show, a T-50 suffered a compressor stall that forced the aircraft to abort takeoff.[135]

Production fighters from mid-2020s onward will be equipped with a more powerful engine known as the izdeliye 30.[N 3] Compared to the AL-41F1, the new powerplant will have increased thrust, lower costs, better fuel efficiency, and fewer moving parts; the engine also has glass-fibre plastic IGVs to reduce the aircraft's radar signature. Those features, along with subsequently improved reliability and lower maintenance costs will improve the aircraft performance and reliability.[136][131][137] The izdeliye 30 is designed to be 30% lower specific weight than its AL-41F1 predecessor. The new engine is estimated to produce approximately 107 kN (24,054 lbf) of dry thrust and 176 kN (39,556 lbf) in afterburner.[138] Full scale development began in 2011 and the engine's compressor began bench testing in December 2014.[138] The first test engines were completed in 2016. The new powerplant is designed to be a drop-in replacement for the AL-41F1 with minimal changes to the airframe.[139]

On 5 December 2017, the second Su-57 prototype (T-50-2, bort no. 052), fitted with the izdeliye 30 engine, first took off from the Gromov Flight Research Institute. The 17–minute test flight was carried out by Sergei Bogdan, Sukhoi chief test pilot.[140] The izdeliye 30 engine was installed on the port-side engine position while the AL-41F1 remained on the starboard side. The izdeliye 30 features a new nozzle with serrated flaps compared to conventional ones on the AL-41F1 nozzle.[92] On 8 February 2018, Russian Deputy Minister of Defence Yury Borisov said that the new engine's performance was "...difficult to judge, because all we have had is this one flight. Everything seems normal, but... many flights are to be performed. As a rule, such trials take 2-3 years".[141] By 6 December 2019, Rostec has conducted 16 flights of the Izdeliye 30 engine to check its characteristics in various flight modes, specifically, the operation of the vectoring jet nozzle and the oil system at negative overloads.[142]

The T-50 prototype has two tandem main internal weapon bays each approximately 4.6 m (15.1 ft) long and 1.0 m (3.3 ft) wide and two small triangular-section weapon bays that protrude under the fuselage near the wing root.[125][143] Internal carriage of weapons preserves the aircraft's stealth and significantly reduces aerodynamic drag, thus preserving kinematic performance compared to performance with external stores. The Su-57's high cruising speed is expected to substantially increase weapon effectiveness compared to its predecessors.[125] Vympel is developing two ejection launchers for the main bays: the UVKU-50L for missiles weighing up to 300 kg (660 lb) and the UVKU-50U for ordnance weighing up to 700 kg (1,500 lb).[144][145]

For air-to-air combat, the Su-57 is expected to carry four beyond-visual-range missiles in its two main weapons bays and two short-range missiles in the wing root weapons bays.[143][146] The primary medium-range missile is the active radar-homing K-77M (izdeliye 180), an upgraded R-77 variant with AESA seeker and conventional rear fins.[147] The short-range missile is the infrared-homing ("heat seeking") K-74M2 (izdeliye 760), an upgraded R-74 variant with reduced cross-section for internal carriage.[145][148] A clean-sheet design short-range missile designated K-MD (izdeliye 300) is being developed to eventually replace the K-74M2.[144] For longer ranged applications, four large izdeliye 810 beyond-visual-range missiles can be carried, with two in each main weapons bay.[143] Reportedly, the fighter will also be able to carry the long–range hypersonic R-37M missile.[149]

The main bays can also accommodate air-to-ground missiles such as the Kh-38M, as well as multiple 250 kg (550 lb) KAB-250 or 500 kg (1,100 lb) KAB-500 precision guided bombs.[143] The aircraft is also expected to carry further developed and modified variants of Kh-35UE (AS-20 "Kayak") anti-ship missile and Kh-58UShK (AS-11 "Kilter") anti-radiation missile.[150] For missions that do not require stealth, the Su-57 can carry stores on its six external hardpoints. BrahMos Aerospace chief A. Sivathanu Pillai stated that there was a possibility of the installation of BrahMos supersonic cruise missile on the Su-57 FGFA derivative.[151] New hypersonic missile with characteristics similar to the Kh-47M2 Kinzhal ALBM is also being developed for the Su-57. The missile is to have intra-body accommodation and smaller dimensions to allow it to be carried inside the Su-57's main central weapon bays.[152] A new missile appeared to be a derivative of R-77, was displayed during Vympel's 70th anniversary on 18 November 2019. The new missile's length was approximately just 2/3 of R-77's 12 feet length, and thought to be designed to fit inside the triangular wing root bays under the Su-57's wings.[153]

The aircraft has an internally mounted 9A1-4071K (GSh-30-1) 30 mm autocannon near the right LEVCON root.[20][154] The cannon is the lightest in 30mm class with 50 kg weight, and could fire up to 1,800 rounds per minute. The cannon can fire blast-fragmentation, incendiary and armor-piercing tracer rounds and is effective against even lightly armored ground, sea and aerial target up to 800 m for aerial target and 1,800 m for ground target. The cannon is equipped with autonomous water cooling system, where water inside the barrel jacket is vaporized during operation.[155][156][157]

The Su-57 has a glass cockpit with two 38 cm (15 in) main multi-functional LCD displays similar to the arrangement of the Su-35S. Positioned around the cockpit are three smaller control panel displays. The cockpit has a wide-angle (30° by 22°) head-up display (HUD). Primary controls are the joystick and a pair of throttles.[158][159] The aircraft uses a two-piece canopy, with the aft section sliding forward and locking into place. The canopy is treated with special coatings to increase the aircraft's stealth.[160]

The Su-57 employs the NPP Zvezda K-36D-5 ejection seat and the SOZhE-50 life support system, which comprises the anti-g and oxygen generating system. The 30 kg (66 lb) oxygen generating system will provide the pilot with unlimited oxygen supply.[161][162] The life support system will enable pilots to perform 9-g maneuvers for up to 30 seconds at a time, and the new VKK-17 partial pressure suit will allow safe ejection at altitudes of up to 23,000 m (75,000 ft).[163] In November 2018, the system is said to be at the final stage of test -the stage of state flight tests- and the test pilots are already flying in this equipment.[164] The pilot gear also consisted of a digital helmet which connected to on-board photo and video cameras to improve pilot's situational awareness. It also features pupil's movement detection system to allow automatic targeting unlike previous Soviet fighters.[165] There also a survival kit consisting a pan, antenna, signal mirror, 16 cubes of sugar, first aid kit, two match boxes, a signal pistol with charges, 1.5-liter bottle of water, machete knife, radio beacon, and portable radio. The pilot could use the survival kit's container as a boat or water-proof sleeping bag if necessary.[165]

The main avionics systems are the Sh-121 (Russian: Ш-121) multifunctional integrated radio electronic system (MIRES) and the 101KS "Atoll" (Russian: 101КС "Атолл") electro-optical system.[166]

The Sh-121 consists of the N036 Byelka radar system and L402 Himalayas electronic countermeasures system. Developed by Tikhomirov NIIP Institute, the N036 consists of the main nose-mounted N036-1-01 X band active electronically scanned array (AESA) radar, or active phased array radar (Russian: Активная фазированная антенная решётка, Aktivnaya Fazirovannaya Antennaya Reshotka, Russian: АФАР, AFAR) in Russian nomenclature, with 1,552 T/R modules and two side-looking N036B-1-01 X-band AESA radars with 358 T/R modules embedded in the cheeks of the forward fuselage for increased angular coverage.[117] Moreover, the side-looking radar could enable the Su-57 to employ extreme beaming tactic (fighter turns 90 degrees away / perpendicular to an enemy's pulse doppler radar array, so that the enemy's radar would not detect / misinterpret it as a non-moving object) while still able to guide its own missile.[167] The suite also has two N036L-1-01 L band transceivers on the wing's leading edge extensions that are not only used to handle the N036Sh Pokosnik (Reaper) friend-or-foe identification system but also for electronic warfare purposes. Computer processing of the X- and L-band signals by the N036UVS computer and processor enable the system's information to be significantly enhanced.[106][168]

In 2012, ground tests of the N036 radar began on the third T-50 prototype aircraft.[169] The L402 Himalayas electronic countermeasures (ECM) suite made by the Kaluga Research Radio Engineering Institute uses both its own arrays and that of the N036 radar system. One of its arrays is mounted in the dorsal sting between the two engines.[131] The system was mounted on the aircraft in 2014.[170] Radio telephone communication and encrypted data exchange among various aircraft and also command centers (ground and sea-based and airborne) will be provided by the S-111 system, developed by Polyot. The system will be based on a modular concept and could be installed not only on the Su-57, but also on various aircraft, helicopter, and drones.[171] "Its effective range of operation is up to 1,500 kilometres (930 mi)" a spokesman said. "The system's reliability is guaranteed by the multiple redundancy of the main functions and cutting edge technical solutions, as well as a wide range of radio channels."[172]

The UOMZ' 101KS "Atoll" electro-optical system consisted of:

• The 101KS-V infra-red search and track turret mounted on the starboard side in front of the cockpit. This sensor can detect, identify, and track multiple airborne targets simultaneously.[117]
• The 101KS-O Directional Infrared Counter Measures system has sensors housed in turrets mounted on the dorsal spine and forward fuselage under the cockpit and uses modulated laser-based countermeasures to confuse or destroy heat-seeking missiles' tracking mechanism.[173] Judging from its position, the system is allegedly intended not only as a self-protection against MANPADS but also air-to-air missile. In this regard, the Su-57 could be something of a pioneer, while similar DIRCM capabilities haven't been ported over to the latest generations of high-flying western fighter aircraft.[167][174][175]
• The 101KS-U ultraviolet missile approach warning sensors (MAWS) are used against infra-red homing missiles. MAWS, using ultraviolet technology, can operate under all weather conditions and will not be affected by solar clutter. It provides good directional information of the incoming missile for good decoy dispensing decision making, maneuvering and to cue the DIRCM system into action.[173]
• The 101KS-P, a high-resolution thermal imager, provides low-altitude piloting and landing in night conditions.[176] It is installed in front of the short-range missile compartments and is not used for targeting purposes, but for efficient low altitude flight and night landing operations.[173]
• The optional 101KS-N is an external navigation and targeting pod.[177][173] It will have similar function to the AN/AAQ28 Litening and AN/AAQ33 Sniper advanced targeting pods of the US military and will be mounted under the air intake.[178][179]

In 2014, Concern Radio-Electronic Technologies (KRET) announced it had created an upgraded BINS-SP2M strapdown inertial navigation system, developed by its two enterprises, Moscow Institute of Electromechanics and Automatics (MIEA) and Ramensky Instrument Engineering Plant (RPZ). Built on the basis of laser gyros and quartz accelerometers, it autonomously processes navigation and flight information, determines position and motion parameters in the absence of satellite navigation, and can integrate with GLONASS. It is guaranteed to last at least 10,000 hours, and can be used universally, not only in airborne, but also in marine and terrestrial equipment.[180] In 2016, KRET announced it is developing a multifunctional video processing system called "Okhotnik" (Hunter) to increase the Su-57's target detection range as well as to improve automatic detection and tracking of targets.[181][182]

In April 2017, UAC announced that a new next-generation integrated avionics suite has started flight-testing.[183] According to Dmitry Gribov, a chief designer of the new complex, the new avionics suite—called the ИМА БК, the Russian acronym for Интегрированная модульная авионика боевого комплекса (integrated modular avionics combat systems)—will replace a system designed in 2004 called Багет (Baguette) used on the Su-35.[183][184] The still-in-development system has more than 4 million lines of code. The IMA BK makes use of indigenous Russian multi-core microprocessors and a new indigenous real-time operating system called "BagrOS-4000".[185][186] The new avionic suite also makes use of fiber-optic channels with a throughput of more than 8 Gbit/s, which is up from 100 Mbit/sec for traditional copper wires.[184][187] The new IMA BK integrated avionics suite is designed to automatically detect, identify, and track the most dangerous targets and offer the pilot the best solution to engage an enemy. The new system will take control of almost all of the key sensors of the aircraft—radar, navigation and communication that in previous aircraft were controlled by separate computers—then simultaneously performs the role of an electronic pilot, electronic navigator and electronic flight engineer.[188]

A monitoring system mimicking a living organism's nervous system will allow real-time assessment of the aircraft's condition and predict the remaining 'life' of the composite parts of the aircraft by combining optical fibers, with sensitivity to mechanical influences, with the aircraft's network system. The information about the aircraft's condition will be transmitted via laser beam through the optical fiber woven into the structure.[189] It will decrease the aircraft's maintenance costs and allow parts to be repaired preemptively, thus improving flight safety.[190][191]

• 
  NIIP N036-1-01 X-band AESA radar
• 
  N036L-1-01 L-band AESA radar
• 
  N036B-1-01 X-band AESA radar
• 
  101KS-V infra-red search and track
• 
  101KS-O DIRCM turret
• 
  101KS-N Targeting pods and 101KS-U ultraviolet warning sensors and N036UVS computer and processor
• 
  101KS-P low-level flight/nighttime landing assistance device, to be installed in front of the wingroot weapon bay

Viktor Pryadka said that the Su-57 is capable to fly on its own and able to withstand up to 15G in UAV mode.[192] On 16 May 2020, it was reported by RIA that one of the Su-57 prototypes had been tested in an "unmanned mode", with the pilot acting as an observer of the plane's actions.[193]

According to the latest Russian military doctrine which considers the Russian Armed Forces as defensive forces meant to protect the country and its allies while maintaining a strategic deterrence capability, this fighter follows a different design philosophy when compared to western fifth generation fighter[179]. With its forward-optimized stealth and infrared sensor,[167] the aircraft could be considered as a counter-stealth fighter meant to get as close as possible to adversary stealth jets before engaging them,[179] diminishing the enemy's stealth advantage and forcing them to a close quarter dogfight, where it has the theoretical advantage due to its 3-D thrust vectoring and supermaneuverability.[194]

According to Bill Sweetman, the Su-57's high operational speed and altitude combined with its standoff weaponry[195] could be hinting at its role as a "sort of airborne sniper", designed to fly fast and high to engage enemy support aircraft.[196] This claim is supported by Russia's intentions to adapt the new R-37M (Izdeliye 810) air-to-air missile with range of more than 300 km to the Su-57's armament, giving it a role similar to the MiG-31BM interceptors.[197] Newly designed anti-ship weapons could also enable the Su-57 to perform as a maritime strike aircraft.[198][199]

The 929th State Flight Test Centre (GLITS) received its first T-50 prototype for further testing and state trials in March 2014, and Russian Air Force Commander-in-Chief Lieutenant General Viktor Bondarev said that deliveries of initial production T-50 fighter were expected to begin in 2016.[43][200][201] External weapon trials started in May 2014.[202] In the event, the 2016 date for production was missed.

On 8 February 2018, then Deputy Minister of Defence Yury Borisov said that the first stage of state trials had been concluded and that the combat trials were on schedule. During the interview, he also reported that the contract for an initial batch of 12 aircraft was to be signed in 2018.[141] First two serial units were ordered in August 2018, with term of delivery by 2020.[59] State trials are to be complete in 2019.[203]

On 27 September 2019, Russian MoD released a video showcasing the first flight of Okhotnik alongside Su-57. Reportedly the UAV operated autonomously and flew for more than 30 minutes interacting with the Su-57 to test extending the fighter's radar and target designation range for use of long-range air-launched weapons from the outside of enemy air defenses.[204]

On 24 March 2020, the Russian MoD released a video with the first demonstration of the fighter firing an air-to-air missile. The Su-57 in the video fires what appears to be a short-range R-74/K-74 missile series.[205]

According to the Executive Director of Rostec Corporation, Oleg Yevtushenko, Su-57 have been flight tested several thousand times. The flight tests experience, as well as the results of the investigation of the first serial airplane crash, are "used by the aircraft developers".[206]

On 21 February 2018, two Su-57s performed first international flight as they were spotted landing at the Russian Khmeimim air base in Syria. The aircraft were deployed along with four Sukhoi Su-35 fighters, four Sukhoi Su-25s, and one Beriev A-50 AEW&C aircraft.[207][208] Three days later two more Su-57s were reported to have arrived in Syria.[209] The deployment was criticised by some experts as overly risky, especially after reports of drone attacks at Khmeimim air base.[210][211] Military correspondent of Komsomolskaya Pravda Viktor Baranets was cited as saying that according to his information the Su-57s have "excellently" carried out their mission in Eastern Ghouta.[212] On 1 March 2018, the Russian Defence Minister Sergey Shoygu confirmed that the two Su-57s indeed spent two days in Syria and successfully completed a trials program, including combat trials during which parameters of weapons work were monitored.[213][214] On 25 May 2018, the Russian Defence Ministry disclosed that during the February 2018 deployment to Syria, a Su-57 fired a cruise missile in combat, likely a Kh-59MK2.[215] On 18 November 2018, the Russian Defence Ministry posted an extended video of the fighters' flights, and announced that Su-57 performed 10 flights during its deployment to Syria.[216][217] However, the video did not specify when the test flights took place.[218]

On 18 December 2019, Chief of the Russian General Staff, Valery Gerasimov said that Russian Defense Ministry has once again tested Su-57 in Syria, and all tasks have been successfully fulfilled.[219]

In May 2018, Turkish media Yeni Safak stated that Turkey might evaluate Su-57 purchase if the US cancels F-35 deliveries due to Turkey's S-400 purchase.[220][221] However, internal source stated that the possibility of Su-57 purchase was based on expert's opinion and do not reflect the official position of Ankara.[222] While on 30 June 2018, Turkey received its first F-35 in a ceremony at Lockheed Martin's facilities in Texas,[223] the US ultimately expelled Turkey from the F-35 fighter programme after the first S-400 delivery in July 2019.[224]

In May 2019, CEO of Rostec Sergey Chemezov said that Russia was ready to cooperate with Turkey on the export and local production of the Su-57.[225] On 30 August 2019, President Erdogan confirmed Turkey and Russia are negotiating possible Su-57 fighter deliveries after he personally inspected the aircraft at the 2019 MAKS air show in Moscow.[226] On 14 September 2019, a Sukhoi Su-57 fighter reportedly took part in the 2019 Technofest festival held in Istanbul.[227]

On 27 December 2019, Algeria has reportedly signed a contract for 14 aircraft as part of large military deal that also includes purchase of Su-34 and Su-35 fighters. The decision was reportedly taken in summer 2019, when Algerian delegation personally inspected the Su-57 at the 2019 MAKS air show.[228] However, neither Russian nor Algerian governments ever confirmed that such deal exists.

During the 2019 Dubai Air Show in the UAE, Sergey Chemezov, in charge of Rostec, talked about the possibility of "localization" of portions of the Su-57 supply chain within other countries that decide to buy those jets, including '...United Arab Emirates, India or Turkey...', depends on the capabilities of the defense industrial base of the customer in question.[229]

The completed joint Indian/Russian versions of the single-seat or two-seat FGFA will differ from the current T-50 flying prototypes in 43 ways with improvements to stealth, supercruise, sensors, networking, and combat avionics.[230]

In March 2010, Sukhoi director Mikhail Pogosyan projected a market for 1,000 fighter aircraft over the next four decades, which will be produced in a joint venture with India, 200 each for Russia and India and 600 for other countries.[231] He has also said that the Indian contribution would be in the form of joint work under the current agreement rather than as a joint venture.[232] In June 2010, the Indian Air Force planned to receive 50 of the single-seat "Russian version" before receiving the two-seat FGFA.[233] Then in an October 2012 interview the Chief of Air Staff of India, NAK Browne, said that the IAF will purchase 144 of the single-seat FGFA. To reduce development costs and timelines, the IAF plans to begin induction of the FGFA in 2020.[38]

In April 2018, it was reported that India is withdrawing from the program. India has become increasingly disappointed with the project's progress after years of negotiations, delays, and struggles with Russia. India is also not satisfied with the capabilities of Su-57, the basis of the FGFA with one of the main issues being the Su-57's insufficient stealth design.[234][235][236]

On 9 July 2019, during a meeting with IAF representatives, Russia offered India to resume its participation in Su-57 program. Deputy Director of Russia's Federal Service for Military and Technical Cooperation Vladimir Drozhzhov told that "Russia is open to that... We are ready and are proposing this program to our Indian partners".[237] IAF Air Chief Marshall Birender Singh Dhanoa during an interview with Russian Ministry of Defense's official newspaper Krasnaya Zvezda (Red Star), stated that while Su-57 is currently not being considered for the IAF, but the combat aircraft can be evaluated once it joins active service with the Russian Air Force.[238][239]

Alexei Fedorov has said that any decision on applying fifth-generation technologies to produce a smaller fighter (comparable to the F-35) must wait until after the heavy fighter, based on the T-50, is completed.[240]

A naval version of the Su-57 was proposed for the Project 23000E or Shtorm supercarrier. Models of the aircraft carrier project are showing Su-57 on board, with folding wings and stabilators. The Su-57 should be able to use the takeoff ramp as well as the Electromagnetic Aircraft Launch System.[241][242]

The aircraft is used as a testbed for integration with UAVs as well as various subsystems (including weapon, control and navigation systems) being developed for Russia's future sixth-generation combat system, both in manned and unmanned version.[243][244][245][246] In January 2019, it was reported the third flyable Su-57 prototype (bort. no 053) is being used for interaction with the Sukhoi S-70 Okhotnik UCAV, and testing of its avionics systems.[247]

Sukhoi states that the main export advantage of the PAK FA is its lower cost than current US fifth generation jet fighters.[248] Russia was reported to be offering the PAK FA for South Korea's next generation jet fighter.[249] South Korea's defence procurement agency confirmed that the Sukhoi PAK FA was a candidate for the Republic of Korea Air Force's next-generation fighter (F-X Phase 3) aircraft;[250] however, Sukhoi did not submit a bid by the January 2012 deadline.[251]

The PAK FA was slated to be introduced for export in 2022[39] with the introduction of the Sukhoi/HAL FGFA, the primary export version,[252] for the Indian Air Force.[253] Ruslan Pukhov, director of the Centre for Analysis of Strategies and Technologies, has projected that Vietnam will be the second export customer for the fighter.[254] In 2012, Russian Defence Minister Anatoly Serdyukov said that Russia and India would jointly build the export version of the T-50 starting in 2020.[255] Mikhail Pogosyan, the head of United Aircraft Corporation, said in 2013 that the Russian PAK FA and the Sukhoi/HAL FGFA will use "identical onboard systems and avionics".[256]

In 2013, Russia offered Brazil participation and joint production in a next-generation fighter based on the T-50.[257][258]

On 28 March 2019, an export version dubbed Su-57E was first promoted to international customers during the 2019 Langkawi International Maritime and Aerospace Exhibition.[259] The aircraft was officially unveiled at the 2019 MAKS International Aviation and Space Salon.[260] Su-57E was first publicly displayed in August 2019 at the 2019 MAKS International Aviation and Space Salon held in Moscow.[260]