The Sukhoi PAK FA  is a fifth-generation jet fighter being developed by Sukhoi OKB for the Russian Air Force.The current prototype is Sukhoi's T-50. The PAK FA when fully developed is intended to replace the MiG-29 Fulcrum and Su-27 Flanker in the Russian inventory and serve as the basis of the Sukhoi/HAL FGFA project being developed with India. A fifth generation jet fighter, it is designed to directly compete with Lockheed Martin's F-22 Raptor and F-35 Lightning II. The T-50 performed its first flight January 29, 2010. Its second flight was on February 6 and its third on February 12. As of June 17th, it has made 16 flights in total.The Russian Defense Ministry will purchase the first ten aircraft after 2012 and then 60 after 2016. The first batch of fighters will be delivered without the "Fifth generation" engines.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.The PAK-FA is expected to have a service life of about 30-35 years

  Although most of information about the PAK FA is classified, it is believed from interviews with people in the Russian Air Force and Defense Ministry that it will be stealthy, have the ability to supercruise, be outfitted with the next generation of air-to-air, air-to-surface, and air-to-ship missiles, incorporate a fix-mounted AESA radar with a 1,500-element array and have an "artificial intellect".Sukhoi says that the new radar will reduce pilot load and that the aircraft will have a new data link to share information between aircraft.Composites are used extensively on the T-50 and comprise 25% of its weight and almost 70% of the outer surface. It is estimated that titanium alloy content of the fuselage is 75%. Further reductions in structural weight, drag and radar signature are achieved by the use of three-dimensional thrust vectoring engines. Sukhoi's concern for minimizing RCS (and drag) is also shown by the provision of two tandem main weapons bays in the centre fuselage, between the engine nacelles. Each is estimated to be between 4.9-5.1m long. The main bays are augmented by bulged, triangular-section bays at the wing root.The Moskovsky Komsomolets reported that the T-50 has been designed to be more maneuverable than the F-22 Raptor at the cost of making it less stealthy than the F-22.
The PAK-FA SH121 radar complex includes three X-Band AESA radars located on the front and sides of the aircraft. These will be accompanied by L-Band radars on the wing leading edges. L-Band radars are proven to have increased effectiveness against VLO targets which are optimized only against X-Band frequencies, but their longer wavelengths reduce their resolution.The PAK-FA will feature an IRST optical/IR search and tracking system.Sukhoi recently demonstrated cockpit mock-ups, which may relate to both Su-35 or PAK-FA, suggest two very large MFDs and a very wide HUD.Hindustan Aeronautics Limited will reportedly provide the navigation system and the mission computer.
The PAK FA was expected to use a pair of Saturn 117S engines on its first flights. The 117S (AL-41F1A) is a major upgrade of the AL-31F based on the AL-41F intended to power the Su-35BM, producing 142 kN (32,000 lb) of thrust in afterburner and 86.3 kN (19,400 lb) dry. In fact, PAK FA already used a completely new engine in its first flight, as stated by NPO Saturn. The engine is not based on the Saturn 117S. The engine generates a larger thrust and has a complex automation system, to facilitate flight modes such as maneuverability. Exact specifications of the new engine are still secret. Each engine can independently vector its thrust upwards, downward or side to side. Vectoring one engine up with the other one down can produce a twisting force. Therefore the PAK FA will be the first fifth generation fighter with full 3-D thrust vectoring along all three aircraft axes: pitch, yaw and roll.

The first flight video shows that PAK-FA has no conventional rudders, its vertical tails are fully movable.This special tail fin design is mechanically similar to V-tails used by the Northrop YF-23 in 1990s, but is supplemented by dedicated horizontal stabilators (as on the F-22). The T-50 has wing leading-edge devices above the jet engine intakes that have been called a challenge for signature control.

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