Russia's PAK FA (Perspektivnnyi Aviatsionnyi Kompleks Frontovoi Aviatsyi : Prospective Aviation Complex for Frontal Aviation) - A Comprehensive study.
 Development programme
Successor programme to original quest for fifth-generation fighter, for which MiG 1.42 and Sukhoi S-37/Su-47 Berkut demonstrators were built. Development began in 1998 to meet Russian Air Forces TTZ (tactical technical assessment) of the same year. Sukhoi-led co-operative project launched May 2001; initially termed LFS (legkiy frontovoy samolet : Light Frontline Aircraft), although competition also known as LFI (legkiy frontovoy istrebitel : Light Frontline Fighter). Air Forces' project name is PAKFA (perspektivnnyi aviatsionnyi kompleks frontovoi aviatsyi : Prospective Aviation Complex for Frontal Aviation). In January 2006, Air Forces' C-in-C quoted designation I-21 for PAKFA; company designation is T-50.
Examining committee established 10 January 2002 to assess competing bids from RSK 'MiG' and AVPK Sukhoi, each of which nominated Yakovlev as associate. On 26 April 2002, Russian Federation Ministry of Industry, Science and Technology declared Sukhoi as lead developer of new aircraft, to be assisted by RSK 'MiG' and Yakovlev as subcontractors. Chief designer Aleksandr Davidenko. In May 2002, development agreement signed by AVPK Sukhoi, Sukhoi OKB, State Research Institute of Aviation Systems (Gos-NIIAS), Central Aero- and Hydrodynamic Institute (TsAGI), Research Institute of Aero Engine Technology and Production (TsIAM), Central Research Institute of Material (VIAM), National Institute of Aviation Technologies (NIAT), Lyulka/Saturn engine bureau, Ramenskoye Instrument Design Bureau (RPKB), Aviapribor holding company, Aviakosmitcheskoye Oborudvanyye and Vympel and Strela weapon companies. Several manufacturing plants expected to join at later stage. Participation of KnAAPO production plant was agreed in June 2002. Timetable for PAKFA initially was draft design by end of 2002; first flight in 2006; production from 2010. Official funding equivalent to USD1.5 billion promised for R & D, but this considered inadequate, representing some 20% of needs, excluding production investment. In January 2006, Air Forces revealed that target max level speed had been reduced from Mach 2.15 to 2.0 to assist design. Manufacture at Komsomolsk by KnAAPO; forward fuselage subcontracted to NAPO; all drawings had been despatched to Komsomolsk by mid-2007. By early 2006, schedule had slipped to first flight in 2009 and, according to Air Forces' deputy C-in-C, first delivery in "2015 to 2016". Sukhoi had spent USD100 million on PAKFA by mid-2005. In August 2007, Russian Air Forces' C-in-C spoke of "second stage" PAKFA which was to have flown in 2012 with production engine rated at some 157 kN (35,275 lb st). In 2010, IOC was predicted in 2015, following trials of pre-production batch at Lipetsk operational test centre, beginning 2013. 
The FGFA variant for India
In January 2003, India discussed terms of invitation by Russia to join PAKFA design team. Potential Indian involvement continued, including agreement of November 2007 and joint development contract signed by HAL and Komsomolsk plant on 22 December 2008, reportedly for two-seat version, for which India to provide cockpit display navigation systems, self-defence measures and on-board computer. Media reports suggest India to have 25% programme share and interested in 250 aircraft, of which 200 would be two-seat, based on proposed T-50UB Russian trainer. First T-50 displayed to Indian delegation at Zhukovsky on 31 August 2010; draft joint development contract signed in India by Russian President in December 2010; this appears to cover advanced version to fly in prototype form five years thereafter; this to be known as FGFA (Fifth Generation Fighter Aircraft). By late 2013, FGFA at least two years late, with USD295 million, "18-month" preliminary design contract of December 2010 still incomplete and intended USD11 billion R&D phase still not begun. Delivery to India of three FGFA prototypes also affected, these originally due to start flight tests in 2014, 2017 and 2019. Reported on 2 April 2015 that India had suspended FGFA, although completion of detailed design by partners had only been reported in January 2015. By July 2015, said to be prepared to re-start programme and build 126 aircraft; in following month, was reported to be considering direct purchase of 54 T-50s as replacement, even though FGFA design featured two crew. India resumed negotiations in Moscow during December 2015, seeking 100 FGFAs; each partner expected to invest USD4 billion over the next seven years, including USD1 billion each in the first year and the rest evenly over next six. Total development cost USD10 billion, of which unfunded USD2 billion to be recouped from exports. Long-delayed signature to launch joint project due in "second half of 2017" according to May 2017 media report quoting undisclosed Indian MoD source. By May 2017, India had spent USD300 million on FGFA preliminary design and had been advised of USD6.7 billion cost of completion of four prototypes; thereafter, USD135 million for each of 127 production aircraft, deliverable from 2027-28. 
Prototype Phase
Five (originally stated to be four) flying prototypes; further, non-flying, but taxiiable, prototype; and two static test airframes. This increased to six flyable aircraft. Prototype (T-50-1) began taxiing trials at Komsomolsk on 21 January 2010 and first flew on 29 January in unpainted state. PAKFA's external shape remained secret until maiden flight, although artist's impression issued some years earlier by engine-maker, Saturn proved to be most accurate among a sea of speculative drawings. Prototype received grey and white camouflage and board number '51' immediately after maiden sortie; second flight 5 February and third on 13 February. Prototype powered by 117M (AL-41F1 family) engines, although this version only began flight testing (in port position on Su-35 '710') on 21 January 2010. Some systems tested in advance of first flight on Su-35 '708'. Type's 100th sortie flown 3 November 2011. Total 450 sorties by four prototypes up to October 2013 first flight of fifth. State Tests by 929th Test Centre at Akhtubinsk began on 21 February 2014 with transfer of initial aircraft (T-50-2) from Zhukovsky. By late 2016, T-50-8 flying with newly-developed Integrated Modular Avionics of Combat Systems (IMA BK; Integrirovannoy Modulnoy Avioniki Boevykh Kompleksov ). First flight of definitive power plant had slipped to late 2017 or early 2018, and production deliveries to 2020. The Phase II aircraft were the first to have composite cowlings over the engines along with other many external changes like the extra long stinger and the stealthy "air bleed" doors on the sides of the intake.However, probably the most important changes happened on the inside. T-50's has suffered with some serious structural issues so their internal frame had to be heavily reworked and significantly beefed up. "Phase 2" increases the share of composites (and the composites themselves are a further development) and has important structural upgrades. Note also the composites cowlings, until now all the prototypes had metal ones although that was always a temporary measure. Other changes include possible the installation of the N036B-1-01 cheek array as given by the radiation hazard warning on the side. The 101KS-O and KS-U on the underside of the forward fuselage underneath the cockpit. 
Current Airframes
T-50-KNSKompleksnyi Naturnyi Stend (integrated, full-scale testbed), non-flying, but fully complete with engines, KSU-50 flight control-, electric-and fuel systems. Performed first taxiing run at Komsomolsk on 23 December 2009, including deployment of braking parachutes. Transferred by An-124 to Zhukovsky test centre, Moscow region, on 8 April 2010 to support T-50-1flight trials.
T-50-0Static test airframe. Completed at Komsomolsk on 29 October 2009. T-50-1First flying prototype; maiden sortie 29 January 2010. Noseprobe. Side number '51'. Dismantled and airlifted by An-124 to Zhukovsky test centre, Moscow region, on 8 April 2010; reassembled and reflown on 29 April (seventh sortie). First Mach 1 flight was announced on 15 March 2011, having taken place few days previously. Retrofitted with sharply pointed tailcone by mid-2011, this temporary installation of anti-spin parachute. 274 hours/227 sorties by 1 February 2016. T-50-2Second prototype. Noseprobe. Side number '52'. First flight 3 March 2011. Airfreighted to Zhukovsky (An-124) 3 April 2011. Re-flown August 2011. To Akhtubinsk 21 February 2014. 244 hours/251 sorties by 1 February 2016. T-50-3Third flying prototype; first with mission system (including radar) installed. Side number '53'. First flight 22 November 2011. Airfreighted to Zhukovsky on 28 December 2011; fitted with AESA radar; re-flown 21 June 2012. On 8 August 2012, Sukhoi belatedly confirmed that it had begun flight tests of T-50-3 "with a unique [Tikhomirov] on-board active phased array radar system. [Early] ground- and flight tests of the radar air-to-air and air-to-surface test modes ... showed a stable and effective performance comparable with the most advanced existing radar systems. ... The optical channels tests have begun." 340 hours/175 sorties by 1 February 2016. T-50-4Fourth flying prototype. First flight 12 December 2012. Side number '054'. Arrived Zhukovsky 17 January 2013. 225 hours/152 sorties by 1 February 2016. T-50-5Fifth flying prototype. First flight 27 October 2013; side number '055'; transferred to Zhukovsky 20 November 2013. Seriously damaged at Zhukovsky on 10 June 2014, apparently as consequence of starboard engine fire immediately after landing. Had then flown 29 hours/18 sorties. T-50-6Manufacture abandoned and components transferred to repair of T-50-5. T-50-5RRebuild of fire-damaged T-50-5; expedited by cannibalisation of T-50-6. First flight 16 October 2015. Re-delivered to Zhukovsky 6 December 2015. 19 hours/12 sorties by 1 February 2016 T-50-6-1Intended as static test airframe. Instead became T-50-7. T-50-7Static test airframe. T-50-6-2Sixth flying prototype; originally due 2014; first flight 27 April 2016; side number '056'. To Zhukovsky in An-124. Second flight 19 May 2016. T-50-8Seventh flying prototype. First flight 17 November 2016. First for military trials. Side number '058'. T-50-9 First flight 24 April 2017; side number '509'. Improved landing gear. Delivered Zhukovsky 11-12 May 2017. Airframe
The aerodynamic configuration of the PAKFA maintains a vague reference to the Su-27 as regards the fuselage and the location of the engines, which are installed in widely separated nacelles forming a tunnel with the flat bottom of the fuselage. The general planform is a tailed delta, similar to the F-22, with the all-moving horizontal tailplanes close-coupled and on the same plane to the wing without any gap. The twin vertical surfaces, canted outward by perhaps 25°. are also all-moving. The Leading edge sweepback is approximately 47° on LERX, outer wing and stabilators; with trailing edge sweepforward approx 10° on outer wings and stabilators. The Fin sweepback approx 45°.
This solution has bean used rarely in recent times, in particular the ill-fated Northrop YF-23 had a pair of allmoving butterfly tailplanes. The all-moving verticals however had been fairly used in supersonic designs dating back to the late 1950s or 60s, in particular the SR-71 which used a pair of all-moving verticals canted inward to reduce the induced roll moment when the surfaces were rotated, and most of the hJorth American design of the period - the RA-5C VIGILANTE, its contemporary YF-107 and the unique XB-70 - as well as the British BAC TSR 2 used a similar solution. In the PAK FA design, their reason arguably consists in enabling the smallest possible vertical surfaces for the sake of reduced radar signature and supercruise drag. While at the same time also maintaining (in combination with the 3D TVC nozzles) excellent manoeuvrability. The underfuselage tunnel between the engine nacelles contributes significantly to the overall aerodynamic lift generation, just as in the Su-27 and MiG-29 as well as in the F-14 - arguably the real originator of the "centreplane lift" concept. This lift is added to that provided by the large wing and should enable excellent manoeuvrability even at high altitude - a potential advantage of the F-22 and now the PAK FA over all their rivals. The widely separated engines also offer much better survivability in the event of battle damage or accidental fire/explosion. 
The fuselage sides have marked "chines", again like the F-22 and its unfortunate competitor, the YF-23. This shaping can be assumed both to contribute toward reducing radar reflectivity and to develop, at high angles of attack, favourable lift-enhancing vortexes flowing above the inner wing upper surface just above the engine nacelles. The wing has dropping leading edges providing for a variable camber airfoil and separate flaps and ailerons, these latter contributing towards enhanced TO/landing performance (this should anyway be very good, given the huge lift generated by the aircraft configuration as a whole). The inner part of the wing leading edges is stepped longitudinally with a much longer chord which blends forming, in part, the engine nacelles' upper "tips" and then merging into the fuselage to enhance the lift generating characteristics of the overall aircraft configuration, somewhat akin to a lifting body. Possibly for this reason, but also to ease a smooth airflow into the engines at very high angle of attack, the upper intake projecting false "lips" appear to be hinged parallel to the sweep real intake lips, thus providing a variable camber like the wing leading edge. In this way, the upper surface of the air intake contributes to overall lift generation. It is also possible that the movements of these peculiar elements, when linked to the full authority digital flight control system, could contribute in some way to the aircraft's longitudinal control, acting like a third control surface (in line Viiith the Sukhoi tradition as exemplified in the three-surfaces Su-30MKI).
It seem however clear that the "lips" cannot move as fully independent control surfaces, due to their primary role in ensuring a correct airflow to the engines. The possible rationale behind the fuselage "chines" and wing strakes could be to generate two vortexes over each wing upper surface, thus enhancing lift {via more diffused vortex lift} at high AoA- In particular, the two inner vortexes (those generated by the fuselage "chines") would energise the airflow over the inner wing upper surlace blending with the fuselage above the engine nacelles. The two outer vortexes (those generated from the wing strakes outboard the intakes lips) would transfer their kinematic energy to the upper outer panel wing airflow. Furthermore, given the expected path of such latter vortexes, they would also interact with the upper airflow over the all-moving horizontal tailplanes - thus replicating the superior longitudinal control provided in the Su-27 by its peculiarly located slab tailplanes. The fuselage has the already mentioned flat bottom and a straight tapered upper part ending in a flat and somewhat smaller "sting" between the engine exhausts. The installation of a braking parachute in a bay in the upper part of the sting makes room for the rational introduction in the extreme tailcone of a wide-scanning ECM antenna or perhaps a rear hemisphere surveillance/tracking radar (experiments were carried out a few years ago on a modified Su-34). The second prototype, which was used for taxi trials on 23 January appears to have a different tail cone, for unclear reasons. The rear fuselage beavertail appears wider than in the Su-27/-30 albeit with a similar layout, and should offer more freedom of movement to the multi-axis thrust vectoring control (TVC) exhaust nozzles which will most certainly be fitted to the engines of the T-50. This configuration with the widely exposed round engine exhaust nozzles is however detrimental in terms of rear-emisphere IR and radar signature. The PAK FA is claimed by Sukhoi to offer "unprecedented small signatures in the radar, optical and infrared range", and this is certainly true as regards Russian combat aircraft and quite possibly all existing non-American designs. At the same time, it is evident that the PAK FA has been designed with a close attention to stealth characteristics, but is not intended to be uncompromising stealth aircraft like the F-22 Raptor. When certain design features detrimental to low observability were deemed to be all-important, these were adopted nonetheless. It would be extremely interesting to watch the eventual results of this approach in terms of maintainability and operational availability, particularly in the light of the in-service experience so far with the F-22, An element which maintain some similarity to the Su-27 family is the landing gear. All the members retract forward, easing the emergency extension which in this way can be accomplished simply by gravity and air pressure. The main tyres, again like the previous Sukhoi design, when retracted lays flat in bays partially above the air intakes and partially inside the thick wing root fairing born out from the air intake upper part and as a continuation of the sweep surface linking the fuselage side to the outer wing, running above the upper air intake lip. Unconfirmed reports suggest 70% of airframe (by weight) is titanium alloy. Composites account for 25%, being employed in fins, radome, tailcone, slats, engine air intake lips, inspection doors and lower centre fuselage (except weapon bay doors). 
Most stealth aircraft have serpentine, RAM-lined inlet ducts that curve to block any line of sight to the engine face. However, aerodynamic considerations set a limit on how tightly the duct can turn, so serpentine ducts can be awkwardly long. Subsonic aircraft with non-afterburning engines can have curved exhaust ducts, at a price in cooling, complexity and weight,
The T-50's inlets are a compromise design. They are serpentine but the curvature is insufficient to obscure the entire engine face (as on the F-22, F-35 and Eurofighter Typhoon), so they also feature a radial blocker similar in principal to that used on the BoeingF/A-18E/F Super Hornet. Unlike the F-22 inlets, however, they feature a variable throat section and spill doors on the inboard, outboard and lower surfaces of the ducts. The result is a complex multiple-shock pattern at supersonic speed, which the Russians consider essential for efficient operation at Mach 2. The inlets also feature clamshell-like mesh screens and diverter slots to keep foreign objects out of the engine, as used on the Su-27 family. 
SIGNATURE MANAGEMENT
Although the PAK FA is often cited as being Russia's first stealth fighter, no reliable information has been published on the aircraft's radar cross section. As on the Lockheed Martin F/A-22 and other US stealth aircraft, the leading and trailing edges of the PAK FA use planform alignment, while the leading and trailing edges of the weapon bay doors incorporate sawtooth edges, as do some skin panels. Head-on photographs of the prototypes show that although the air inlets are of serpentine form, they do not obscure all of the compressor faces of the engines. Production aircraft are expected to use inlets that incorporate radar blockers able to hide the engine from all forward angles. While the front part of the aircraft embodies signature-reduction measures, the rear section is broadly similar in configuration to that of the Su-27/30/35 "Flanker" series. This raises the possibility that low-observable technology has been used only to reduce the frontal-aspect RCS, and that the beam and rear-aspect RCS may be more like those of an earlier-generation fighter, A frontal RCS one-fortieth that of the Sukhoi Su-27 has been reported. One estimate of the Su-27 RCS is 10-15 square meters, raising the possibility that the frontal RCS of the T-50 is in the order of 0.25-0.4 square meters. Several reports in the Russian press have cited an RCS of around 0.5 m. Futher RCS reduction is mitigated by the use of RAM, however these levels of RCS are orders of magnitude above that reported for US stealth aircraft, which makes industry analysts weigh in on the the PAK FA a "reduced observable" aircraft. Patent Figures According to the patent paperwork, taken together, all of the stealthy measures offer significant improvements over legacy fighter designs. The papers claim that the radar cross-section (RCS) of an Su-27 was in the order of 10-15 m 2 , with the intention being to reduce the size of the RCS in the T-50 to an "average figure of 0.1-1 m 2 ". In common with other low observable aircraft designs, this reduction is achieved throught the use of radar-absorbing and radar-shielding materials and coatings, panel shaping (especially around the air intakes) and in the design of the junctions between moving elements, such as flaps and hatches. 
In particular, the patent spells out the benefits of internal weapons carriage, 'S'-shaped engine air ducts, (which were considered but are actually not implemented in the production PAK FA), and the use of radar blockers. It adds that the inlet guide vanes of the engines' compressors generate "a significant portion [up to 60%] of the radar cross-section of the airframe-powerplant system in the forward hemisphere" and that this is reduced by using radar-blocking devices and radar-absorbing coatings in the walls of the air ducts.
The shape of the airframe reduces the number of directions that radar signals are reflected in with the angles of sweep of the wings and the tail plane's leading and trailing edges, the edges of the air intakes and hatch covers being reduced and deflected from the aircraft's axis. Viewing the aircraft from the flank, the fuselage sides, lateral edges of the air intakes and vertical empennage are all deflected at the same angle. Some openings and slots on the airframe's surface - such as the boundary-layer bleeds on the sides of the air intakes and the openings on the upper fuselage immediately aft of the cockpit - are covered with a thick grid, featuring a mesh of less than one quarter of the wavelength of a search radar, which reduces the reflections from these uneven surfaces. Gaps between the airframe elements are filled with conducting sealants, while the glazing of the cockpit canopy is metallized with Indium Tin Oxide or Carbon based RAM. The surfaces of the PAK FA's own five radar arrays are also angled off from the vertical plane, helping to 'deflect' enemy radar signals. The covers of the radar arrays are selective, letting through their own signals, but blocking other frequencies. Additionally, the array compartments are edged with radar-absorbing 'curtains' to reduce possible leaks of these amplified signals. Antennas are recessed from the surface of the skin to reduce protuberances (the vertical empennage serves as a communications antenna), while the turret of the aircraft's nose-mounted infrared search-and-track (IRST) sight is rotated backwards into a cruise position, exposing its rear hemisphere, which is covered with a radar-absorbing coating. The release of this list of patents follows the July 2013 release of documentation covering the configuration of the fighter's integrated avionics suite. 
Low Observable Canopy
Russia's Technology Scientific & Production Enterprise has developed a radar-insulating composite coating for the cockpit of the Sukhoi T-50 PAK-FA fighter aircraft. The Obninsk-based organisation describes the coating as "unique", but it exploits similar technology to the coating used on the canopy of the Lockheed Martin F-22 Raptor. The coating is transparent for the crew and protects them against solar radiation, but is principally designed to minimise reflections from air defence radars and prevent snooping on cockpit instruments and displays. It also protects cabin plastics from deterioration caused by infrared and ultraviolet radiation. It comprises several layers of metal - including gold, indium and tin - chosen after several years of spectral analysis, with no layer exceeding 20 nm in thickness. The whole film coating is specified as 90 nm and the enterprise claims that this is sufficient to reduce the radiation of cabin equipment by 250 times. The coating is sprayed over a traditional fighter canopy using a magnetron device, in a vacuum autoclave to ensure regular coating over the curvature of the screen..  Byelka Radar Complex
The Sh-121 is an active electronically scanned array (AESA)-integrated fire-control radar (FCR), incorporating multiple apertures to provide for multiwaveband (X- and L-band) and wide FoV capabilities. The N036 X-band AESA forward array incorporates a development of the Gallium Arsenide (GaAs) MMIC (Monolithic Microwave Integrated Circuit) technology utilised in Phazotron's Zhuk-AE. However, while the configuration of transmit/receive modules in the Zhuk-AE antenna is blocks of four (reported to enable more efficient cooling), images of the NIIP AESA show a different multiple configuration across the aperture. Two strips of the aerial were shown during MAKS 2007; one of them contained 12 modules and the other, 16 modules. At the time, the only characteristic of the antenna to be revealed was the +/-60° look angle.
Developed by Russia's V. Tikhomirov Scientific-Research Institute of Instrument Design (Tikhomirov-NIIP) and designated Sh-l21, it is based on a forward-facing N036-01-1 in nose, two lateral arrays designated N036B-01 mounted on either side of the forward fuselage, and N036L-01 located in the inboard section of the leading-edge slats. The N036-01-1 and N036B-01 operate in X-band, while the N036L-01 operates in L-band. The associated computer system is designated N036UVS. Using these antennas, the Sh-121 radar will be able to provide the pilot with an air picture that includes coverage of both sides of the aircraft as well as the front sector. Information will be presented via cockpit and helmet-mounted displays. The complete system will be used for detecting and tracking air and ground targets, the targeting of weapons and navigation. It will also incorporate jamming functions. The wing-mounted L-band AESA was the first to be publicly displayed, followed by the X-band forward-looking AESA in 2009, and the side-looking array in 2013.
By the time that all three were shown simultaneously in 2015, the arrays had been further refined by the use of more advanced technology in order to reduce their size and weight and to improve the performance. Flight trials using T-50 prototypes started in 2012. The forward-looking radar was first flown on the third prototype in April of that year, and intensive flight tests were conducted that summer to explore the basic air-to-air and air-tosurface modes. By the time of the MAKS 2015 air show, the third and fourth flying prototypes were fitted with the radar, and were flying at Akhtubinsk state flight testing center. The third had already logged around 120 test sorties with its forward-looking AESA radar activated.
In an interview with Take-Off magazine, Tikhomirov-NIIP Director General Yuri Bely stated that the radar on the fourth aircraft was of higher performance than that on the third, and further improvements were expected with the radar earmarked for the fifth flying prototype. The fifth flying prototype started its trials in Komsomolsk-onAmur following a repair. Initial reliability problems with the T/R modules had required some module replacements during the assembly and test stage, he stated, but said that more recent modules had displayed what he described as "a radical increase in reliability." These problems had been due to delays in the modernization of production facilities at Istok, where the modules were manufactured. T-50-6-2 will be the first prototype to carry the full set of AESA arrays - the forward-looking and side-looking Xband antennas, as well as wing-mounted L-band antennas. In an interview with the Russian newspaper Izvestia, Anatoly Sinani, chief designer at Tikhomirov-NIIP, said that the PAK FA's radar has "about 1,500" transmit/receive (T/R) modules and a total field of view of more than 200 degrees. Unofficial T/R module counts based on hardware shown at various MAKS exhibitions suggest that the main array has around 1,500 modules, while the side arrays have up to 400 each. According to a 2015 article in the UK aviation magazine Air Enthusiast by aviation writer Piotr Butowski, the main array has 1,552 T/R modules and is tilted upwards by around 15 degrees. The sidelooking array shown at MAKS 2015 was tilted downwards by about 15 degrees, he reported. It had 358 modules, plus space for 40 more. 
L-band array located in the leading edge of the wing and the two lowest strips of the frontal X-band AESA antenna
No detailed information had been published of the radar's operating modes. But the wing- mounted arrays are reported to be used for both the N036Sh Pokosnik (Reaper) identification friend-or-foe (IFF) and for the detection of ground and aerial targets. In perspective The Irbis radar carried by the Su-35 uses a passive electronically-scanned array. It is currently Russia's longer-range fighter radar, with a maximum range of 350 km against targets of 3 square meters radar cross section.
The primary use of the L-band is against LO aircraft which are optimized against X-band and but have lower degraded performance L-band radar. Of course. the lower the frequency the higher the wavelength the poorer the accuracy of distance and angular measurements, and thus even apart from excessive volume, weight, power and cooling requirements a fighter aircraft could not possibly rely on a main L-band system alone. However, the presence of the additional L-band antennas will provide an important early warning function against at least some low-observable targets, and it may also enable a "miniAWACS" role. It is additionally conceivable that these antennas could also be used for the detection and disruption of sensors and digital communications systems operating in L-band when passive. The L-band AESA is also expected to be a functional part of Polyot S-lll-N long range directional transmit and receive data link which is hardened by encryption against SIGINT platforms. The capability is augmented by higher efficiency in a heavy jamming environment . Furthermore, the L-band is expected to be operated in an active electronic attack against communication data links and SATCOM receivers on aircraft although it risks giving its position against ESM platforms snooping on jamming signals. Russian design teams have had to cope with the relatively poor level of technology in areas such as MMIC fabrication and component packaging. The T/R modules available for these fighter radars are larger than those created by Western manufacturers, so the module counts of the resulting antennas are lower than their Western equivalents. This could degrade sidelobe performance. The PAK FA radar reportedly does not currently match the performance of the Irbis, but Tikhomirov-NIIP has predicted that given new technologies, new materials and new electronic components, this performance gap can be narrowed. NIIP have publicly cited detection range performance of 350 to 400 km (190 to 215 NMI), which assuming a Russian industry standard 2.5m2 target, is also consistent with the 2008 model for an AESA radar using ~10W rated TR modules, which in turn is the power rating for the modules used in the Zhuk AE prototypes. This puts the nett peak power at ~15 kiloWatts, slightly below the Irbis E, but even a very modest 25% increase in TR module output rating would overcome this. Electronic Warfare SUITE
The Sh-121 radar is supplemented by an extensive array of electro-optical sensors. Manufactured by the Urals Optical and Mechanical Plant (UOMZ), the 101KS Atoll electro-optical system consists of a 101KS-V infrared search and track (IRST) located ahead of windscreen, a 101KS-U ultraviolet missile approach warning system, a 101KS-0 laser-based directed infrared countermeasures (DIRCM) system mounted on top the fuselage aft of the cockpit, a 101KS-P wide-angle instrumental flight augmentor for the pilot to aid low-altitude flight which is bi-spectral (IR & UV) with night/all weather capability and an optional 101KS-N IRST targeting pod that can be used to acquire, identify and track ground targets
The 101KS-V is has a new-generation Optical Locator System (OLS) developed by NIIPP, capable of detecting a non-afterburning MiG-29 at 45 km in a rear hemisphere engagement and at 15 km head-on. Afterburning targets can be detected at up to 90 km under ideal conditions. The OLS can identify aerial targets at around ten kilometres and generate estimates of target range at separations up to 15 km. Using QWIP (Quantum Well Imaging Photodetector) technology, the 101KS-V operates in multiple bandwiths and has better infrared image resolution by picking up heat by surface friction or discernible "hot spots" of other aircraft.
In 2014, Concern Radio-Electronic Technologies (KRET) announced that deliveries of hardware for the aircraft's new L402 Himalayas EW system had begun. Developed by KNIRTI in Kaluga, the system is being manufactured by the Radioplant Signal in Stavropol. (Both organizations are KRET subsidiaries.) The L402 uses its own dedicated antenna arrays (located at several locations on the aircraft, including the dorsal sting between the two engines) and those of the N036 radar system. The presence of radiation-warning symbols on the wing's moveable leading edge extensions (LEVCONS) suggests that they incorporate antennas that form part of the IFF or EW systems. The L402 Himalaya integrated with the UV-MAWS and DIRCM are capable of autonomous function against threats in the management of ECM stores and providing pilots with a significant increase in situational awareness by reducing workload in a high threat environment. The system can also be manually assisted by the pilot's judgement of the situation. The semi-autonomous, autonomous function in dealing with threats is a capable feature of fifth generation aircraft as seen on the F-22's EW RF IAR and the F-35's AN/ASQ-239 system. 
Integrated Avionics
The PAK FA's cockpit is reported to be fitted with two 38-cm (15-in.) multifunctional LCD displays, supplemented by three smaller LCD panels, plus a wide-angle (30 degrees by 22 degrees) head-up display (HUD). The pilot's ZSh-10 helmet incorporates a NSTsIV helmet-mounted sight developed by Geofizika-NV. According to a report by Russia's Zvezda TV channel, the helmet will be able to sense the movements of the pilot's eyes, and use this data for automatic targeting. A Polyot S-lll-N datalink will provide secure communication with friendly aircraft operating in the general area general area, and with airborne and ground-based command and control systems. The avionics architecture is highly automated to reduce pilot workload while maintaining mission capability thus earning the title "Virtual Co-Pilot" as seen on other 5th Generation aircraft such as the F-22, F-35. This includes controlling the CMDS as well as assisting in the stores management of the aircraft. The system can also maintains a check on the sub-system health and runs multiple computations integrating the multi-spectral information provided by the various sensor array and providing it to the pilot. This allows offensive and defensive actions to be committed effectively without pilot being subjected to information overload and disorientation from "Helmet-Fire". According to KRET, the aircraft's communication systems can be used in a "protected mode" in which data will be exchanged only in selected directions. The navigation system of the T-50 is based on the BINS-SP2M laser gyroscope based inertial navigation system complemented by GLONASS SATNAV link. The earlier BINS-SP1 was selected for the planned Tu-160M2 new-build variant of Tupolev "Blackjack" strategic bomber, while the BINS-SP2 is used on the Su-35S.  POWERPLANT
The engines are fed by two-dimensional raked air intakes with the upper lip generating an oblique shock wave favourable to dynamic pressure recovery in the supersonic regime, which for the PAK FA could approach Mach 2.3-2.5 although it has been reduced to a standard target of Mach 2. While in appearance of fixed geometry, it has a variable-position upper ramp, to generate multiple oblique shocks is part of the system for a further better dynamic pressure recovery in the high supersonic speed regime.
The tight shape of the engine nacelles and the position of the ventral 'Venetian blind" auxiliary intakes seem to suggest that the PAK FA does not feature a serpentine air duct to the engine compressors, as typically adopted for low-RCS aircraft, it is possible that the Sukhoi designers have preferred to limit the compressors strong radar reflection by inserting a grill in front of them, while optimizing the air intakes for higher max. speed and supercruise performance.. The engines are mounted with a slight forward convergence (some 3°). This, in twin engine aircraft with conventional exhaust nozzles, would typically reduce thrust asymmetry in the event of an engine flame-out - although with the drawback of reduced controllability. Given however the installation of TVC nozzles, the choice of converging axis built into the nacelles could be the outcome of an aerodynamic local airflow optimization due to interaction of all the aircraft elements. The Prototypes have two turbofans by Saturn, reportedly Type 117M (AL-41F1A) of 147 kN (33,070 lb st) with afterburning. Definitive power plant yet to be determined, and early production T-50s may employ Type 117 engines. One possibility, previously mooted, was new 157 kN (35,275 lb st) engine from Salyut, variously known as Iz 127 or Iz 217. However, by late 2012, Lyulka Scientific- and Technical Centre, within NPO Saturn, was planning first bench run in 2014 of new Type 30 engine for T-50, this to have both specific weight and life-cycle cost 30% lower than AL-41F1. Max thrust 107 kN (24,050 lb st) dry and 176 kN (39,565 lb st) in full afterburner. Saturn stated in 2012 that first Type 30 could be ready in mid-2015, coincident with first T-50 deliveries. By 2016, flight testing of Type 30 in a T-50 was planned for late 2017/early 2018. 
Izdeliye 30 engines
The engine’s characteristics have been refined through a sharp improvement in the operating cycle parameters, efficiency of units and introduction of advanced technologies and materials in the first place. It features higher thrust and a sizeable reduction in specific fuel consumption in virtually all operating modes, i.e. not only in the cruising range mode, but in the acceleration and afterburning modes as well - the modes the aircraft is normally flown in. This implies a life cycle cost reduction, The Engine also includes FADEC which comes with autonomous health monitoring to increase the engine MTBF as well as increase mission turnaround speed. The PAK FA izdeliye 30 engines expected to complete state trials in 2020. The first of the izdeliye 30 engines are expected to be integrated on the aircraft in the last quarter of 2017. Following which further development and validations tests will be carried our through 2018-19. Currently, the izdeliye 30 engine is mounted on a flying laboratory and has a target date of November 6, 2017 to complete performance check flights. However, the schedule is said to have slipped past the date due to delays in the development and implementation of the Automatic Engine Control System 
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