By now, as many as four prototypes of the advanced aircraft are used under the PAK FA test programme, of which two are flying prototypes. The so-called ‘zero’ static test prototype (T50-0) has been undergoing endurance tests at a dedicated facility of Sukhoi in Moscow since summer 2009. The T50-KNS integrated full-scale testbed is used for ground trials of onboard systems, including the fuel and hydraulic systems, powerplant, control system, etc. In 2009, it was moved to KnAAPO’s airfield where it performed its first taxiing and high-speed runs. Then, it was airlifted on 8 April last year by an An-124 transport to Zhukovsky along with the first flying prototype and has carried on with the ground tests at Sukhoi’s flight test and debugging facility in the Moscow Region.

The first flying prototype, T50-1, has been undergoing the flight tests in Zhukovsky since 29 April 2010, having logged six acceptance test sorties in Komsomolsk-on-Amur from 29 January to 26 March 2010. It had had about 40 flights under its belt by late autumn 2010, including several demonstration sorties when it was shown to Prime Minister Vladimir Putin on 17 June 2010 and an Indian delegation on 31 August 2010.

Sukhoi’s March news release reads: “36 flights have been performed on the first flying prototype in support of the flight test programme” and “the preliminary ground and flight test programme has been completed in full”. Early in February this year, the T50-1 resumed flight tests after it had undergone a planned improvement programme that had begun last autumn. This done, its check flight took place on 10 February.

The first flying prototype of the T-50 plane first broke the sonic barrier in the Moscow Region on a test flight on 9 March, with Test Pilot Sergey Bogdan, Sukhoi’s project pilot under the PAK FA programme, at the controls. The T-50 started flying at supersonic speed owing to the prototype’s operating envelope expansion based on the results produced by the preliminary test phase, during which its stability, controllability and other characteristics were evaluated against the backdrop of the gradually dwindling g-load, speed and altitude limits inherent in the phase of the initial flight tests characteristic for any newly-developed aircraft. The way the aircraft behaved at supersonic speed was pronounced satisfactory, which allows another expansion of the maximal authorised flight speed and altitude range.

Meanwhile, the acceptance tests of the second PAK FA flying prototype were wrapped up in Komsomolsk-on-Amur in early March. Overall, Sergey Bogdan had flown four missions from 3 to 5 March, after which the aircraft was sent to be painted and prepared for the transfer to Sukhoi’s flight test and debugging facility in Zhukovsky. An Antonov An-124 heavylifter hauled the T50-2 from Komsomolsk-on-Amur to the Moscow Region on 3 April. Once brought to Zhukovsky and subjected to relevant assembly, debugging and checkouts, the second flying prototype joined the PAK FA flight test programme alongside the T50-1.

Several Sukhoi test pilots fly the PAK FA prototypes now. Project pilot Sergey Bogdan recently awarded with a title of the Hero of Russia has flown most of the sorties. However, other Sukhoi test pilots have been prepared for the PAK FA’s trials due to the increasing scope of work under the programme, for instance, Roman Kondratyev and Yuri Vaschuk conducted their first flights on the T50-1 last September. Roman Kondratyev has been taking an active part in the continued tests of the first PAK FA prototype in Zhukovsky. Other pilots are gearing up for the test programme too.

The third flying prototype is sitting in KnAAPO’s assembly shop and components of the fourth one are being manufactured. Thus, “we will have generated the core that will ensure a positive preliminary report”, said Mikhail Pogosyan, Sukhoi Director General and UAC president. The third PAK FA flying prototype is supposed to be equipped with a prototype active electronically scanned array (AESA) radar that Tikhomirov-NIIP has been developing. The developer has made and conducted numerous tests of three AESA radars, with the third of them earmarked for fitting the PAK FA prototype.

At the same time, the third and fourth aircraft will be furnished with a number of other avionics systems, which tests are not supposed to be carried out by the first and second prototypes. “We will use two more aircraft for the tests in 2012, as we planned”, Mikhail Pogosyan said during the Bangalore air show in February. Probably, he meant the fifth and sixth flying prototypes to be equipped with the complete avionics and weapons suites.

As is known, Vladimir Putin set the task of having the early PAK FAs of the low-rate initial production (LRIP) batch delivered to the Russian Air Force centre in Lipetsk in 2013 for their operation evaluation and launching deliveries of production-standard fighters to RusAF combat units in 2015. As the then Deputy Defence Minister and armed forces armament chief Vladimir Popovkin told the media during the PAK FA’s unveiling in Zhukovsky in June 2010, the draft governmental armament programme designed to cover throughout 2020 stipulated acquisition of “more than 50 fifth-generation fighters” from 2016.

PAK FA flying prototype is slated for the public unveiling during the MAKS 2011 international air show in August this year.