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

http://www.ausairpower.net/APA-2010-01.html

First prototype of the PAK-FA during an early test flight, January 2010 (Sukhoi image).

Abstract

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.

Introduction
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.

Early rendering of the PAK-FA design (NPO Saturn).

The evolution and development history of the PAK-FA, historically, has not been well documented in open sources, largely due to the high levels of secrecy surrounding this program since its inception. What is known from open sources largely amounts to a collation of various intentional and incidental Russian disclosures, and increasingly, disclosures by India, who have a 25% share in the development of the design.

Study of the aircraft's design features, and earlier Sukhoi demonstrators, indicate that much careful thought has been invested into this design and its progressive development over a period of two decades.

When the Soviets deployed the Su-27S Flanker B during the early 1980s, investment into a replacement was initiated. This resulted in the reasonably well known 1990s MiG I.44 MFI (Mnogo-Funktsionniy Istrebitel' or Multi-Role Fighter), which was a multirole fighter modelled on the aerodynamics of the three “Eurocanard” designs, but much larger and intended to be powered by the Al-41F supersonic cruise engine.

The MFI was built to supercruise, and to provide very high agility, but no investment was made into signature reduction, making it fundamentally uncompetitive against the early 1990s US Air Force Advanced Tactical Fighter (ATF) YF-22 and YF-23 demonstrators.

The lack of a future for an expensive high signature fighter, and the MiG organisations de facto bankruptcy due to the export market success of the larger Sukhoi Flanker, saw the MFI relegated to a demonstration program. The important product of the MFI program was the Al-41F supercruising engine, modelled on the United States' Pratt & Whitney F119 series, which powers the F-22A. The Al-41F is the basis of the high temperature core components used in the supercruise capable 117S series engine, which now powers the production Su-35S Flanker and PAK-FA prototypes.

During this period Sukhoi developed the unusual S.32/S.37 forward swept wing demonstrator, intended to combine supersonic performance with super-manoeuvrability. This design demonstrated the use of large LEX, over large quarter circular inlets. Like the MFI, this design was not stealthy and was used to prove basic technologies and design rules.

A more successful demonstrator built during this period was the Su-37 “Super Flanker”, derived from the earlier Su-27M/Su-35 Flanker E. The Su-37 was intended to extend the T-10 Flanker design to the limit, especially in avionic systems and manoeuvre performance. It introduced the first axi-symmetric 3D (three dimensional) Thrust Vector Control (TVC) nozzles, manually controlled, and later integrated with the Digital Flight Control System (DFCS); the first quadruplex DFCS in a Russian fighter; composite structural components; a modern glass cockpit and force sensitive sidestick controller; digital core avionics; the N-011M BARS hybrid Electronically Steered Array (ESA) radar; and, a compact ESA tail warning radar.

The combination of aerodynamic design refined through progressive evolutionary development, DFCS, twin 3D vectoring thrust supercruising engines interoperating in and on an advanced kinematic design airframe, extended the Flanker design squarely into the category of “extreme agility” - which can be defined as the harmonised and complementary balance of extreme manoeuvrability and extreme controllability.

The Su-37 Super Flanker demonstration effort extended the viability of the basic T-10 Flanker design by almost two decades, and yielded basic technology used in the design of the Su-30MKI/MKM Flanker H and, as seen in the latter part of 2008, the Su-35S, often labelled the “4++ Generation Flanker”. It also provided experience which was critical to the development of the replacement for the T-10 Flanker series.

The PAK-FA properly qualifies as a 21st century project, as formal tendering for the program was launched during the 2000 - 2001 period by the Russian MoD. Russian sources claim that Sukhoi, MiG and Yakovlev were invited to bid proposals. Initial thinking was to develop a fighter larger than the MiG-29 Fulcrum, but smaller than the Su-27 Flanker, with greater range/persistence to the Flanker, low observable capability, extreme agility, supersonic cruise capability, and near STOL short field capabilities. Sukhoi won the tender in 2002 with its T-50/I-21 proposal, with MiG and Yakovlev engaged as subcontractors in the development. Russian sources state that Sukhoi's ability to fund much of the development effort from company export revenue profits was a major factor in the decision.

The initial design of the PAK-FA was finished in 2004, amid public controversies about lower than intended maximum speed, and greater than intended empty weight. Full Russian MoD funding was not provided until 2005 - 20064.

The prototype flown on the 29th January, 2010, is intended to prove aircraft aerodynamics, structure, and compatibility of the VLO shaping with aerodynamic and structural constraints. It is claimed to be fitted with the 117S Al-31F engine variant, common to the Su-35S, as the intended new engine has yet to complete development and enter production. The latter is expected to be a variant or derivative of the Al-41F design. The existing prototype probably lacks a complete version of its final avionic suite, most likely employing large parts of the new and fully digital Su-35S avionic suite as a basis for evolving the design of the final avionics fit, as has been the case on the development of previous Flanker variants.

The first “public” flight lasted 47 minutes and was intended to test handling, engine behaviour, landing gear operation, and basic systems functions2.

The PAK-FA was designed with a stated requirement of being able to operate from short, unprepared runways in support of expeditionary operations. With the exception of an observable deployed arrestor hook, the PAK-FA design incorporates all of the key design characteristics that are required in aircraft built to operate from Russian Navy ski-jump equipped aircraft carriers. It is not known whether the extant structural design includes the necessary provisions for arrestor hook loads.

Equipped with 3D TVC and large LEX control surfaces, power approach speeds in the order of 100 knots, sink rates somewhat less than 20 ft/sec and quite flat aircraft approach attitudes can be expected from this design, as can commensurately low arrestor hook and related carrier landing loads. Such performance, when combined with the extensive field of view provided by the fighter/strike/attack canopy configuration, and a functional arrestor hook system, likely integrated into the rear ventral internal weapon bay, would make the PAK-FA an eminently suitable aircraft for maritime operations.

India was engaged early in the PAK-FA development effort, but Russian sources suggest that negotiations on the work share between HAL and Sukhoi/KnAAPO were protracted. Open sources suggest that India is responsible for 25% of the development of the PAK-FA, primarily in software and systems integration, areas where India has recent experience via the Su-30MKI program. India is to also contribute in composite materials, with claims the PAK-FA structure is, by total aircraft weight, rather than just the airframe structural weight, some 25% titanium alloys, and 20% composites. Indian sources suggest that both single and dual seat variants will be built for India.

Tactical, Operational and Strategic Impact of the PAK-FA
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.

The PAK-FA represents an excellent example of the kind of “capability surprise” studied in the late 2009 Defense Science Board report. While the failure to account for the imminent arrival of this design in United States TACAIR force structure planning qualifies the PAK-FA as a “known capability surprise”, the important advances in PAK-FA aerodynamic, kinematic and low observables design also qualify it as a “surprising capability surprise”.

Technical analysis of the PAK-FA, in the following sections of this paper, shows that its aerodynamic performance and agility will exceed that of all United States built combat aircraft currently in service or planned, with the exception of the yet to be defined “sixth generation fighter”, which at best is 15 - 20 years away from Initial Operational Capability (IOC). 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 analyses 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.

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.

Parametric and tactical analysis performed by Air Power Australia in 2008 - 2009 on the likely impact of a mature production PAK-FA deployed against United States' fighter types has been completely validated, given the configuration of the PAK-FA prototype.

“How stealthy does the PAK-FA need to be to defeat US legacy fighters? A radar cross section of only -20 dBSM would deny early Beyond Visual Range (BVR) missile shots using the AIM-120C/D AMRAAM to all current and planned US fighters. Doing any better, like -30 dBSM or -40 dBSM, simply increases the level of difficulty in prosecuting long range missile attacks.”

“The consequence of this is that missile combat will be compressed into shorter distances and shorter timelines, putting a premium on the stealth, supersonic persistence and close combat agility of US fighters. A larger portion of engagements will be at visual range, and most BVR engagements will end up taking place inside 30 nautical miles.”5

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 PAK-FA can thus be expected to produce greater lopsided air combat exchange rates to those achieved by the F-22A Raptor when flown against legacy “teen series” fighters in exercises since 2004. Even if the PAK-FA design were only to attain half of the effectiveness of the F-22A Raptor, it will still yield BVR exchange rates of the order of 50:1 against legacy fighters.

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.

No less interesting is the impact at a tactical level when the PAK-FA is flown against the F-22A Raptor.

“Fights between the F-22A and the PAK-FA will be close, high, fast and lethal. The F-22A may get ‘first look’ with the APG-77, the Advanced Infra Red Search and Track (AIRST) sensor having been deleted to save money, but the PAK-FA may get ‘first look’ using its advanced infrared sensor. Then, the engagement becomes a supersonic equivalent of the Battle of Britain or air combat over North Korea. The outcome will be difficult to predict as it will depend a lot on the combat skills of the pilots and the capabilities of the missiles for end-game kills. There is no guarantee that the F-22 will prevail every time.”6

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 United States' Office of the Secretary for Defence (OSD) has since late 2008 promoted the use of the F-35 Joint Strike Fighter as a substitute for the F-22A Raptor, employing this rationale as a justification to Congress for the premature termination of F-22 production. Therefore, the survivability and lethality of the F-35 Joint Strike Fighter when pitted against a mature PAK-FA has become the critical measure of the operational and strategic value of planned United States TACAIR capabilities.

Parametric and tactical analysis performed by Air Power Australia in 2008 - 2009 on likely engagement outcomes between the PAK-FA and F-35 Joint Strike Fighter are also validated by technical analysis of the PAK-FA prototype design.

“The F-35 Joint Strike Fighter struggles to survive against the conventional Su-35BM Flanker, with only its -30 dBSM class front sector stealth keeping it alive in some BVR combat situations. Against even a -20 dBSM class PAK-FA, the F-35 falls within the survivability black hole, into which US legacy fighters such as the F-16C/E, F-15C/E and F/A-18A-F have already fallen.”5

“The fate of the F-35 Lightning II would be far worse in an air combat environment challenged by the PAK-FA. If the Mach 1.5 PAK-FA is using its infrared sensor as the primary sensor and observes radio frequency emission control (EMCON), then the first detection by the F-35’s APG-81 radar could be at ~20 nautical miles or less with a missile launched by the PAK-FA’s infrared sensors already inbound from 60 to 70 nautical miles away. The PAK-FA could easily break to a direction outside the F-35’s AIM-120 engagement zone.”6

“The sustained turning performance of the F-35A Lightning II was recently disclosed as 4.95 G at Mach 0.8 and 15,000 ft. A 1969 F-4E Phantom II could sustain 5.5 Gs at 0.8 Mach with 40 percent internal fuel at 20,000 feet. The F-35 is also much slower than the 1960s F-4E or F-105D. So the F-35A’s aerodynamic performance is ‘retrograde’ when compared with 1960s legacy fighters. The consequence of such inferior JSF performance is that its DAS might detect an incoming missile, but the aircraft lacks the turn-rate to out-fly it. As the F-35 also lacks the performance to engage or escape, repeated ‘freebie’ shots from the PAK-FA could inflict high losses. Expect the exchange rate to be of the order of 4:1 in favour of the PAK-FA, possibly much higher.”6

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.

Once the PAK-FA is deployed within a theatre of operations, especially if it is supported robustly by counter-VLO capable ISR systems, the United States will no longer have the capability to rapidly impose air superiority, or possibly even achieve air superiority. This will not only deny the United States access to an opponent's defended airspace, it also presents the prospect of United States forces being unable to reliably defend in-theatre basing and lines of resupply. Should this occur, in-theatre basing and surface assets become exposed to air attack by aircraft armed with a wide range of accurate and highly lethal Precision Guided Munitions, with the potential for very high loss of life and equipment deployed in-theatre.

Conventional thinking in the planning of air campaigns, empirically observable from the Blitzkrieg campaigns of the 1940s through to the recent United States led air campaigns since 1991, places a heavy emphasis on the defeat of opposing airfields by aerial attack, to deny an opponent the opportunity to contest airspace. To achieve this effect, an attacker needs the capability to repeatedly penetrate defended airspace to shut down airfields, keep them shut down, and inflict attrition upon opposing aircraft on the ground.

The execution of this campaign strategy by United States forces, and Allies, is now becoming problematic due to the development and proliferation of advanced anti-access capabilities such as counter-VLO capable ISR systems, and advanced high mobility Surface Air Missile systems, such as the S-300PMU2 Favorit / SA-20B, S-400 Triumf / SA-21 and planned S-500 series. This strongly limits United States options, as only the B-2A Spirit and F-22A Raptor can penetrate such defences with acceptably low loss rates.

The deployment of a mature PAK-FA into such an environment very significantly increases risks to United States forces, as the aircraft can credibly challenge the F-22A Raptor in air combat. While the intended survivable strike/ISR aircraft defined in the most recent Quadrennial Defense Review document may, eventually, provide a credible capability to penetrate advanced anti-access capabilities, and thus attack opposing airfields, it will need to be defended against the PAK-FA, and airfields deploying this aircraft will also need to be defended against PAK-FA aircraft tasked with counter-air strike missions.

In terms of technological strategy, the PAK-FA thus effectively defeats the force structure model planned for United States TACAIR capabilities, as defined by OSD policy statements, and as reiterated in the recently released Quadrennial Defense Review document.

Should the United States continue along the force structure path for TACAIR mapped out by OSD policy definition of the last three years, it will be denied access to any operational theatre into which credible numbers of the PAK-FA are deployed by an opponent. In turn, the United States will be deterred from the use of conventional forces in such a scenario. The consequence of this, in turn, is that significant pressure will be placed upon a future President to threaten the use of, or operationally use, tactical nuclear weapons7.

A not dissimilar situation would arise in the scenario where the Su-35S is deployed, in tactically significant numbers, or in concert with the PAK-FA. Jointly and severally, these scenarios have deeper geostrategic and political implications which are beyond the scope of this paper.

If the United States does not effect some fundamental changes to its force structure plan, it will lose the strategic option of employing non-nuclear military capabilities in theatres where the PAK-FA and/or significant numbers of the Su-35S are deployed.

The only practical low risk option available to the United States is to deploy over this decade large numbers of advanced fighter aircraft which are competitive against the PAK-FA in air combat, both BVR and WVR.

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.

In basic grand strategy terms, the arrival of the PAK-FA leaves the United States with only one viable option if it intends to remain viable in the global air power game - build enough F-22 Raptors to replace most of the US legacy fighter fleet, and terminate the F-35 Joint Strike Fighter as soon as possible, as the F-35 will no longer be a usable combat aircraft for roles other than Counter Insurgency (COIN), though more cost effective and more appropriate solutions already exist for this role.

In strategic and techno-strategic terms, the PAK-FA is the most prominent “game changer” in the fighter domain since the T-10/Su-27S Flanker B entered operational service during the mid 1980s. 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.

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And so on at source above.

IZAKOVIC