Maybe because of T-50 study results made by Carlo Kopp few years ago:
Assessing the Sukhoi PAK-FA
Sukhoi/KnAAPO T-50/I-21/Article 701 PAK-FA
Перспективный Авиационный Комплекс Фронтовой Авиации
Air Power Australia Analysis 2010-01
15th February 2010
by Dr Carlo Kopp, SMAIAA, MIEEE, PEng,
Peter Goon, BE (Mech), FTE (USNTPS)
© 2010, Carlo Kopp, Peter Goon
First prototype of the PAK-FA during an early test flight, January 2010 (Sukhoi image).
The public exposure of the Sukhoi/KnAAPO T-50/I-21/Article 701 PAK-FA or Перспективный Авиационный Комплекс Фронтовой Авиации following the 29th January, 2010, test flight has provided sufficient high resolution imagery, video camera footage, and incidental disclosures to perform an initial technical, techno-strategic, and strategic assessment of this new high performance low observable multirole fighter design.
The observed prototype design employs an interim supercruising and thrust vectoring engine, common to the production Su-35S Flanker. The configuration is intended to validate aerodynamic and systems performance, and is clearly not intended for full validation of low observables performance. A new 35 - 40 klbf class 3D TVC supercruising engine for the PAK-FA is currently being developed by NPO Saturn.
Analysis of PAK-FA prototype airframe shaping shows a design which has forward fuselage, inlet, upper fuselage, wing and tail surface airframe Very Low Observable (VLO/stealth) shaping which is highly competitive against the US F-22A Raptor and YF-23 ATF designs. Aft and centre lower fuselage, and aft fuselage and nozzle shaping is inferior to the F-22A Raptor and YF-23 ATF designs, sharing the same deficiencies as the F-35 Joint Strike Fighter. This may be an artefact of the use of the interim engines, and uncertainty about aft and beam sector observables performance will remain until later prototypes with the production engine and aft/lower fuselage shaping are available.
Analysis of PAK-FA prototype airframe aerodynamic features shows a design which is superior to all Western equivalents, providing ‘extreme agility’, superior to that of the Su-35S, through much of the flight envelope. This is accomplished by the combined use of 3D thrust vector control of the engine nozzles, all moving tail surfaces, and refined aerodynamic design with relaxed directional static stability and careful mass distribution to control inertial effects. The PAK-FA is fitted with unusually robust high sink rate undercarriage, intended for STOL operations.
Disclosures indicate that the avionic suite and systems fit will be derived from the Su-35S design, with the important difference in the use of an very high power-aperture product X-band multimode primary AESA radar. Five AESA apertures are intended for production PAK-FA aircraft. The highly integrated avionic suite is intended to provide similar data fusion and networking capabilities to the F-22A Raptor.
The available evidence demonstrates at this time that a mature production PAK-FA design has the potential to compete with the F-22A Raptor in VLO performance from key aspects, and will outperform the F-22A Raptor aerodynamically and kinematically. Therefore, from a technological strategy perspective, the PAK-FA renders all legacy US fighter aircraft, and the F-35 Lightning II Joint Strike Fighter, strategically irrelevant and non-viable after the PAK-FA achieves IOC in 2015.
Detailed strategic analysis indicates that the only viable strategic survival strategy now remaining for the United States is to terminate the Joint Strike Fighter program immediately, redirect freed funding to further develop the F-22 Raptor, and employ variants of the F-22 aircraft as the primary fighter aircraft for all United States and Allied TACAIR needs.
If the United States does not fundamentally change its planning for the future of tactical air power, the advantage held for decades will be soon lost and American air power will become an artefact of history.
PAK-FA Development History
Tactical, Operational and Strategic Impact of the PAK-FA
PAK-FA Design Philosophy
PAK-FA Low Observable Design
PAK-FA Aerodynamic Design
PAK-FA Structural, Systems and Propulsion Design
PAK-FA Cockpit, Avionics and Radar Design
PAK-FA Weapons Capabilities
Annex A PAK-FA Prototypes
Annex B PAK-FA Multimedia
The emergence of the Russian Sukhoi PAK-FA marks the end of the United States' quarter century long monopoly on the design of Very Low Observable (VLO) or stealth aircraft1.
The capabilities of the PAK-FA make a clear statement defining the Russian view of Within-Visual-Range (WVR) and Beyond-Visual-Range (BVR) air combat, which diverges fundamentally from contemporary Western thinking. The Russian paradigm is clearly centred on the idea that BVR and WVR combat are much alike, insofar as during the engagement endgame the fighter under attack is within tracking range of the weapon fire control system and where possible the weapon or fire control element should be defeated kinematically. The principal observed difference between WVR and BVR combat in the Russian model, is that the latter relies more heavily on long range sensors and their ability to defeat low observability measures, or active countermeasures.
Designed to compete against the F-22 in traditional Beyond Visual Range (BVR) and Within Visual Range (WVR) air combat, the PAK-FA shares all of the key fifth generation attributes until now unique to the F-22 - stealth, supersonic cruise, thrust vectoring, highly integrated avionics and a powerful suite of active and passive sensors. While the PAK-FA firmly qualifies as a fifth generation design, it has two further attributes absent in the extant F-22 design. The first is extreme agility, resulting from advanced aerodynamic design, exceptional thrust/weight ratio performance and three dimensional thrust vectoring integrated with an advanced digital flight control system. The second attribute is exceptional combat persistence, the result of a 25,000 lb internal fuel load. The internal and external weapon payload are likely to be somewhat larger, though comparable to those of the F-22A.
Russia intends to operate at least two hundred PAK-FAs, India two hundred and fifty of the Indian Fifth Generation Fighter Aircraft (FGFA) variant, with global PAK-FA exports likely to add at least 500 more tails to the production tally. The stated intent is to supply the PAK-FA as a replacement for existing T-10 Flanker series fighter aircraft.
Initial analysis of PAK-FA imagery and public disclosures by the Russian government and Sukhoi bureau indicate that a production PAK-FA will yield greater aerodynamic and kinematic performance to the current F-22A design, and similar low observables performance to the F-35A JSF2.
While the basic shaping observed on this first prototype of the PAK-FA will deny it the critical all-aspect stealth performance of the F-22 in BVR air combat and deep penetration, its extreme manoeuvrability/controllability design features, which result in extreme agility, give it the potential to become the most lethal and survivable fighter ever built for air combat engagements3.
It is important to consider that the publicly displayed PAK-FA prototype does not represent a production configuration of the aircraft, which is to employ a new engine design, and extensive VLO treatments which are not required on a prototype. A number of observers have attempted to draw conclusions about production PAK-FA VLO performance based on the absence of such treatments, the result of which have been a series of unrealistically optimistic commentaries.
PAK-FA Low Rate Initial Production is planned for 2013, and Full Rate Production for 2015, with initial deliveries of the Indian dual seat variant planned for 2017.
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Maybe because of T-50 study results made by Carlo Kopp few years ago: