Sukhoi Su-57 T-50

T-50 is the designation of the prototypes and pre-production aircraft of the PAK FA programme, assembled at the KnAAZ plant in Komsomolsk-on-Amur before the fighter became the Su-57. Its maiden flight was repeatedly postponed from early 2007 because of unspecified technical problems. In August 2009 Alexander Zelin acknowledged that the engine and technical research issues remained unsolved; that same year Mikhail Pogosyan announced first that the airframe was almost finished and the first prototype would be ready by August, then in August that the flight would come by the end of the year. After Sergei Ivanov announced in December 2009 that trials would begin in 2010, the first taxi test was completed on 24 December 2009. To reduce risk, several subsystems were first tested on other aircraft: one Su-27M flew the AL-41F1 engine and another the KSU-50 flight control system. After a high-speed taxi run on 21 January 2010, T-50-1 (bort number 051) flew on 29 January 2010 with Sukhoi test pilot Sergei Bogdan at the controls: a 47-minute flight from KnAAPO's Dzemgi Airport in the Russian Far East. The prototypes and the first production aircraft were powered by two first-stage AL-41F1 (izdeliye 117) engines.

According to the list in the Russian Wikipedia, the development batch comprised thirteen airframes. Three never flew: T-50-0, for static ground tests; T-50-KNS, a full-scale integrated ground test rig; and T-50-7, a "second stage" static test airframe. The English Wikipedia specifies that they tested static flight loads for each of the two structures and avionics integration. The ten flying aircraft were T-50-1 (051); T-50-2 (052), first flown on 3 March 2011; T-50-3 (053), on 22 November 2011; T-50-4 (054), on 12 December 2012; T-50-5 (055), on 27 October 2013; T-50-6 (056), the first second-stage prototype, on 27 April 2016; T-50-8 (058), on 17 November 2016; T-50-9 (509), on 24 April 2017; T-50-11 (511), which completed the batch, on 6 August 2017; and T-50-10 (510), on 23 December 2017. The initial plan had called for up to six prototypes before series production. The first two flying aircraft had no mission systems and tested flight characteristics and basic mechanical systems; radar and electronic warfare testing began with the third, each later aircraft carrying slightly different avionics, and the final pre-production aircraft had full mission systems. T-50-3 began trials with the N036 active array radar on 24 July 2012.

Testing consisted of preliminary trials (PI) run by Sukhoi at the Gromov Flight Research Institute (LII) at Zhukovsky and two stages of joint state trials (GSI) run by the Ministry of Defence at the 929th State Flight Test Centre at Akhtubinsk. On 14 March 2011, after 40 flights, the T-50 went supersonic for the first time over a range near Komsomolsk-on-Amur. That summer the first two prototypes were shown at MAKS-2011, and their airframes cracked despite a restrictive 5 g limit, forcing more than a year on the ground for structural reinforcement. On 21 August 2011, at the show itself, T-50-2 aborted its take-off after a visible flash and deployed its braking parachute: the Russian Wikipedia blames a failure of the engine automation, the English one an AL-41F1 compressor stall. By the end of October 2013 the programme had flown more than 450 sorties with five aircraft, and that year KnAAZ began building a small batch for weapons trials.

Inadequate fatigue life forced a structural redesign: more composite material, an airframe reinforced for the full life cycle, an elongated tail sting and a slightly greater wingspan. The sixth flying prototype was the first of this "second stage"; the five earlier "first stage" aircraft needed reinforcement to keep flying. The redesign curbed weight growth, but normal take-off weight still rose to about 26.7 tonnes.

In February 2014 the first phase of preliminary trials (PI-1) ended and the Akhtubinsk centre received its first T-50 for state trials. On 10 June 2014 T-50-5 caught fire at Zhukovsky. Accounts differ: according to the Russian Wikipedia, smoke appeared over the right intake on landing and a local fire was quickly put out; Bogdan escaped unhurt, the aircraft was repaired, returned to Zhukovsky on 7 December 2015 and flew as T-50-5R on 16 October 2015. The English Wikipedia describes an in-flight fire, a write-off and an incomplete airframe finished with its parts. The second preliminary phase (PI-2) ran from 2014 to 2019 with reinforced first-stage aircraft, while GSI-1 was halted until 2016 to wait for the new airframes. External weapons trials began in May 2014 and internal trials in March 2016; the final stage of testing opened on 18 September 2015. GSI-1 ended on 8 February 2018 and was formally signed in May; after more than 3,500 flights GSI-2 was due in 2019 but slipped to 2020, partly because the first production aircraft was lost in December 2019. Problems and accidents pushed the first production delivery from 2015 to 2020.

The prototypes also served other purposes. In 2010 one was shown at Ramenskoye airfield, Zhukovsky, to representatives of India's Ministry of Defence, Air Force and HAL during negotiations on the joint fighter. On 21 February 2018 two aircraft landed at Khmeimim air base in Syria and two more followed days later; the English Wikipedia identifies them as prototypes. Sergey Shoygu stated on 1 March 2018 that they had completed a two-day trials programme including combat trials, and on 25 May 2018 the Defence Ministry disclosed the firing of a cruise missile, likely a Kh-59MK2. T-50-2 first flew the izdeliye 30 engine on 5 December 2017, and the third prototype was configured in 2018 for teaming trials with the Sukhoi S-70 Okhotnik drone, a video of which the ministry released on 27 September 2019. On 3 November 2024 T-50-4 "054 Blue" landed at the Zhuhai Airshow, the type's first appearance abroad, alongside T-50-7 "057 Blue", brought disassembled in an An-124; The Aviationist noted non-flush gaps, screws and rivets and the missing N101KS electro-optical suite on 054. At the 2025 Dubai Airshow T-50-9 flew with a single wide-area cockpit display reflecting the configuration Russia is offering as the Su-57E.