India and Russia are all set to develop a new generation fighter plane which is known as PAK-FA, a fifth generation aircraft based on T-50 prototype model that can challenge even most advanced fighters in the world, perhaps, performing better in some segments than the F-22 Raptor.
Russia and India are jointly developing two versions of the combat aircraft - a two-seater version to meet the requirements of India’s air superiority policy of Indian Air Force, and a single-seat version for the Russian Air Force.
While India’s HAL is giving technological support to the project in many new areas, Sukhoi has constructed three prototypes at the Komsomolsk-on-Amur Aviation Production Association (KNAAPO) in Russia’s Far East.
However, India is expected to supply composite-material parts of the airframe, avionics and software packages for the aircraft.
Sukhoi Design Bureau has built a basic fifth-generation fighter- the PAK-FA (Perspektivnyi Aviatsionnyi Kompleks Frontovoi Aviatsy). A prototype has already made its first flight in January 2010 and design task has been completed in 2013.
The fighter, is expected to feature super maneuverability, super cruise, sensor fusion and stealth with an internal weapon bay. However, exact range and speed of the jet will depend on the engines that finally power it.
The Russians say the Raptor was primarily designed to evade ground radar. The PAK-FA will be able to detect a Raptor first and then engage it using its superior maneuverability.
The T-50 is also designed to have extreme maneuverability at both supersonic and subsonic speeds. It is thought that the T-50 could outperform both the F-35 and the F-22 in this regard. Likewise, the T-50 can maintain a super cruising speed of approximately Mach 1.8, matching the F-22 and surpassing the F-35.
In terms of overall stealth, however, the T-50 is surpassed by both the F-35 and the F-22. The T-50’s radar-cross section (RCS) is an average of 0.1-1 m 2. In comparison, the RCS of the F-22 is 0.01 - 0.001 m2 from the side and behind, while the F-35’s is 0.01 m2. A lower RCS indicates that the plane is more difficult to detect on radar.
In the broadest of terms, the PAK-FA is a fusion of ideas and design features seen in late model Flanker variants and demonstrators, but incorporating specific stealth shaping features employed previously in the Northrop/MDC YF-23 ATF demonstrator, and the production LM F-22 Raptor. The PAK-FA is clearly a unique Russian design and is neither a copy of the F-22 or the YF-23.
No less importantly, the PAK-FA is by Western standards a low risk design, following the Russian philosophy of evolutionary design, rather than the “Big Bang” approach currently favoured in the West, of trying to start from scratch with most or every key portion of the design.
It is important to note that the Russian approach to development more than often differs from the Western approach, particularly that of the United States industry, with a much stronger Russian focus on risk management and risk minimisation.
The best illustration of how much more effective Russian systems development philosophy is, that the development of the PAK-FA, with a projected budget in the order of US$10 Billion, was launched officially in 2002.
Concurrently with the launch of the F-35 Joint Strike Fighter program, yet the latter has experienced repeated delays in schedule, repeated problems with basic technology, and remains heavily laden with accumulated design risks as well as inordinately high and growing costs.
Modern avionics
The aircraft is expected to feature a variant of the Tikhomirov NIIP AESA radar first displayed at MAKS 2009. At the event, Anatoly Sinany, Tikhomirov’s chief designer, explained that T-50’s radar antenna will have 1,500 T/R modules, produced by Iztok company from Fryazino, near Moscow.
The aircarft has five radars: 3 X-band AESA, one in the nose and two on the sides, and 2 L-band in the leading edge root (LEX) extension of the wings.
The current version of the Tikhomirov AESA is able to simultaneously track 20-30 targets.
The Russians say, unlike the Raptor, which is designed to evade ground radar, the T-50 is honed for detecting the Raptor earlier and then engaging it in close combat.
The sensor fusion suite is being developed by Ramenskoye Design Bureau around a six-processor computer and includes visualization tools and flight instrument system.
The T-50 will be able to exchange real-time data within the air group and with ground command posts.
The initial batch of the fighter will be powered by NPO Saturn Item 117S engines, derived from the supplier’s AL-31F series.
The Item 117S, which produces 14.5 tons thrust in full after-burning and comes with a new full-authority digital engine control unit, is fitted on the SU-35 and uses key components of the AL-41F supercruising core.
The SU-35 is the first non-US fighter with substantial sustained supersonic cruise capability, so even initial models of PA-FA should support good supercruise giving it a good advantage in initial engagement.
A new engine, Saturn AL-41F, will be incorporated with later production examples. It is expected to offer about 17.5 tons of thrust in full afterburning mode and somewhere in the range of 12 tons in dry mode, allowing the aircraft to comfortably super-cruise at around Mach 1.5.
Features
According Ilya Fedorov, Saturn CEO and head of the PAK FA engine program, the T-50 flew with completely new powerplants. Compared to the 117S, the new powerplant has increased thrust and a digital control system adapted to T-50’s performance.
The following LO features are evident in the first prototype:
• Aerodynamic fuselage and wing shaping
• Reduced area all moving fins canted to reduce radar reflections
• Use of composite materials, advanced aerodynamic techniques and
• Measures to reduce the aircraft’s engine signature,
• Internal weapons bay. The aircraft features two weapons bay in the under fuselage area between the engines. In addition, it is beleived to have two smaller housings for short-range weapons on the inboard section of the wings.
• Air intake ducts are not curved to shield engine compressors as in the Raptor; instead ducts are blocked using composite material. Similarly, the nozzles are blocked to shield turbine blades. The extent of shielding is variable. It is minimized when engine power requirements are high. The blocking concept is illustrated in the video below.
The supersonic cruise capability, integrated sensor suite, respectable VLO performance, extreme agility and exceptional persistence of a mature production PAK-FA will produce a significant impact in the post 2015 period, at the tactical, operational and strategic levels. In turn, this will also produce a political impact.
Technical analysis of the PAK-FA also shows that the aircraft’s VLO shaping permits the existing prototype configuration to achieve similar VLO performance to the F-35 Joint Strike Fighter, and with lower and aft fuselage VLO shaping design improvements, potentially competitive VLO performance against the F-22A Raptor.
At the tactical level this will produce a large impact in Beyond Visual Range and Within Visual Range air combat.
An important qualification is that most recent analysis of relative air combat capabilities performed in the United States assume that BVR combat will arise much more frequently than WVR combat.
The basis of this assumption is that opposing air combat capabilities are easily detected and tracked by ISR systems, permitting United States fighter aircraft to choose the time, place and type of engagements to an advantage.
This assumption collapses if the opposing fighter has significant VLO capability, as a mature PAK-FA will.
The result is that attacking PAK-FAs will have to be engaged at much closer ranges than existing non-stealthy threats, as they enter predictable geometries, when attacking high value targets such as AWACS/AEW&C platforms, tankers, or defended surface assets.
Kill capability
Another important qualification is that the extreme agility of the PAK-FA design will significantly degrade the kill probability of all United States Air to Air Missiles, (AAM) especially though the AIM-120 AMRAAM, which will be challenged to sustain the necessary manoeuvres to defeat the PAK-FA.
Like the F-22A Raptor, the PAK-FA will provide a significant capability for the kinematic defeat of inbound missile shots.
In Beyond Visual Range combat, the combination of supersonic cruise and competitive VLO performance will allow the PAK-FA to emulate the tactics developed for the F-22A Raptor.
The arrival of the PAK-FA therefore irrevocably enforces the end of the operational usefulness of the teen series (F-15 / F-16 / F/A-18) generation of fighter aircraft, marked by the advent of the Su-35S, in the traditional fighter roles of air superiority, air defence and tactical strike in contested airspace.
These aircraft will retain operational utility only in permissive environments, where neither the Su-35S nor the PAK-FA is deployed or is able to be deployed.
The tactical impact of a mature production PAK-FA is therefore a loss of the overwhelming advantage provided until now by the F-22A Raptor.
Flown against the PAK-FA, a decisive outcome can only be guaranteed by numerical superiority of the F-22A force in theatre.
The arrival of the PAK-FA therefore also irrevocably enforces the end of the operational usefulness of the F-35 Lightning II Joint Strike Fighter, defined around a 1990s technology threat spectrum, in the traditional fighter roles of air superiority, air defence and tactical strike in contested airspace.
The F-35 will, not unlike legacy fighters, retain operational utility only in permissive environments, where neither the Su-35S nor the PAK-FA is deployed or is able to be deployed.
The operational impact of indecisive combat loss exchange rates between a mature production PAK-FA and the F-22A Raptor, and very high F-35 Joint Strike Fighter loss rates against a mature production PAK-FA have major implications at an operational level, and consequently, at a strategic and political level.
The proposed “sixth generation fighter” is not a viable contender in this time frame. The F-35 Lightning II Joint Strike Fighter is not competitive and cannot be made to be competitive due to basic design limitations in aerodynamic and VLO shaping performance.
The only aircraft built by the United States which can survive in airspace contested by the PAK-FA is the F-22 Raptor, and given the time frame of interest, it is the only design which can be adapted to defeat the PAK-FA.
With the current PAK-FA configuration, which may well differ from a production configuration, stealth appears to be used primarily to deny an aerial opponent an early BVR firing opportunity, permitting the PAK-FA to close to a distance where its superior energy performance, extreme agility and large internal missile payload permit it to dominate the close combat engagement.
The combination of aerodynamic design features for extreme agility, high thrust/weight performance supersonic cruise engines to provide supersonic persistence, and the large combat persistence provided by a large internal fuel load and large weapons loads, make the PAK-FA the best fit to the Boyd energy manoeuvrability model yet to be developed.
Extreme agility
The extreme agility of the PAK-FA design, when employed harmoniously with the other 5th generation design features, opens up a range of new tactical options, not feasible with established or currently planned Western fighter designs.
Consider a conventional BVR tail chase engagement geometry against an operational PAK-FA derivative air dominance fighter.
A conventional fighter with legacy teen series class aerodynamic design and performance, an example being the F-35A Joint Strike Fighter, is positioned behind the PAK-FA, at a range of ~50 nm, with its X-band multimode radar locked and tracking, assuming that the PAK-FA aircraft retains the high signature aft fuselage and nozzle design.
The use of extreme agility design features would permit the PAK-FA derivative to perform reversal manoeuvres faster than conventional fighter designs, causing the pursuing fighter to lose radar lock as the PAK-FA presents its VLO class nose aspect to the pursuing fighter.
Within seconds the PAK-FA can establish a weapons lock, as the weapon system will have established the position and identity of the pursuing fighter during the immediately preceding tailchase.
The pilot of the initially pursuing fighter will then be presented with a salvo of mixed seeker equipped BVR missiles closing at high speed on a reciprocal heading.
The full tactical potential of extreme agility, especially in BVR engagements, remains to be explored at this time, as most studies to date have been strongly focussed on the close combat advantages arising from this flight regime.
Multiple Russian sources state that the PAK-FA will carry eight Air-to-Air Missiles in internal bays, with the option of another eight externally carried weapons in “permissive” threat environments.
Modern design
This emulates the strategy pursued by American designers in the F-22, and claimed but not properly implemented with the F-35 designs.
The PAK-FA has an unusually robust undercarriage design, more typical for carrier based naval fighters than land based fighters.
This is consistent with the intended STOL capability to operate from short field FOBs, or MOBs with damaged runways, but also fulfils the intent to deploy a navalised carrier variant in the future.
The latter was the subject of some discussion during the public debate in Russia, at the time the PAK-FA program was launched, but not a feature of the more recent debate. The configuration of the existing design would require that the tailhook be carried in the aft centreline weapons bay.
Based on analysis of the features and history of the PAK-FA design observed to date, an apt summary of this aircraft would be a High Speed/High Agility Interceptor/Air Dominance Fighter/Persistent Strike/ISR Platform, built for operation from short unprepared FOBs, and readily adapted for aircraft carrier operations.
What is abundantly clear from the basic design of the PAK-FA, is that this aircraft is the only design globally, which will be credibly capable of competing with the F-22 Raptor in air combat.
It is also a much better fit to the stated, but very poorly implemented in the F-35, intent for a multi-service multirole fighter.
Examination of the publicly displayed PAK-FA prototypes shows that this design is a continuation of the highly evolved pedigree of Flanker aerodynamic design.
However, as observed in and predicted from the most recent Flanker variant, the SU-35S, and the work done during the deep modernization program that resulted in this design, Sukhoi have evidently taken the next step by providing the PAK-FA with relaxed static stability in the directional axis.
Open source materials such as high resolution imagery and video camera footage show there are a number of features about the aerodynamic design of the PAK-FA that are different to, but clearly enhancements on the tried and proven aerodynamics of the Flanker family of aircraft, including:
• Fully articulated, reduced aspect ratio dorsal fins that are canted outwards. These provide large control power and control authority while minimising drag and side area with the additional LO benefit of the latter.
• Articulated LEX sections /control surfaces above and immediately forward of the quite large intakes of the propulsion system.
• Main wing leading edge sweep angle of ~46.5° to which the leading edges of the LEX sections and the horizontal stabilisers are edge aligned, with the latter closely nested with the wing trailing edge flaperons.
• Large wing area, estimated to be ~840 square feet.
• Large leading edge flaps, around 90% span of each of the outboard sections of the main wing.
• Large trailing edge flaperons spanning about 60% of each of the outboard sections of the main wing, truncated and blended with the leading edges of the horizontal stabilators.
• Large aileron control surfaces of ~30% span of the outboard sections of the main wing.
• Prodigious wing/fuselage blending with primary area ruling achieved through shaping of the upper and lower portions of the engine nacelles.
• Classic later generation Flanker Boundary Layer Control (BLC) systems in and around the intakes, extending aft along the engine lower nacelles.
• The propulsion system intakes are quite large and clearly intended to accommodate thrust growth, possibly the use of ‘ejector nozzle technology’ for increased thrust augmentation (akin to the J58 engine of the SR-71 and more recent DARPA Vulcan program), and overall thermal management, as well as providing additional air for exhaust plume shrouding, the latter for infrared signature control.
• Alternate intakes for the propulsion system, as seen on earlier Flankers.
The introduction of relaxed static directional stability in the PAK- FA design, alone, will ensure that the PAK-FA has the manoeuvrability and controllability capabilities and, thus, the agility that no Western fighter design can provide.
There is only one Western fighter design configuration that, with some upgrades and modification, will be able to approach the PAK-FA in manoeuvrability and controllability capabilities; specifically, the F-22A Raptor.
The aerodynamic design of all other US air vehicles precludes such modifications, this including the F-35 Joint Strike Fighter.
Sukhoi and its team of subcontractors will have to deal with a range of design challenges, mostly related to observables, no different to those which the United States industry has had to master during the B-2 and F-22 programs.
Challenges
This is well understood by the Sukhoi designers, as is evident from the careful thought invested into risk management across the whole PAK-FA design. Yet there are problem between India and Russia over the course of PAK-FA development.
Even as New Delhi and Moscow finalize a $6 billion deal to co- develop an FGFA with capabilities tailor-made for India, the IAF has alleged the Russians would be unable to meet their promises about its performance.
The IAF’s three top objections to the FGFA are that the Russians are reluctant to share critical design information with India.
On the top of it, the fighter’s current AL-41F1 engines are inadequate being mere upgrades of the Sukhoi-30MKI’s AL-31 engines and it is too expensive.
In October 2012, then IAF boss, Air Chief Marshal NAK Browne, announced the IAF would buy only 144 FGFAs instead of the 214 that were originally planned. Having cut the numbers, the IAF is now questioning the very benefit of co-developing the FGFA with Russia.
The MoD and HAL have countered the IAF’s objections to the FGFA. Russian officials have clarified that the current prototype’s engine, the AL-41F1, is a temporary solution to let the flight-test program continue.
A new engine being developed in Russia will eventually power both the FGFA and PAK-FA.
