joe81
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The public exposure of the Sukhoi PAK-FA 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 aircraft.
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.
PAK-FA Development History
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.
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.
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.
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.
PAK-FA Aerodynamic Design
Examination of the publicly displayed PAK-FA prototypes show 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 modernisation 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.
-Nominal engine thrust lines are canted outwards about 2° to 3° off the longitudinal centreline, with the engines spaced symmetrically around BL 00, at around 10 feet centre to centre spacing at the nozzle exit planes. This configuration reduces the risk of the rapid onset of large yaw rates at large thrust settings due to single engine in-flight shutdowns, while, when combined with the increased ~60°/sec angular TVC rates observed in the Su-35S design, enhancing the ability of the TVC system to augment/replace aerodynamic flight control inputs, while aiding in the provision of 'apparent static directional stability' through dynamic control to replace the normally 'natural inherent static directional stability' that has been relaxed.
-There has clearly been a concerted effort to establish harmony and complementarities between the inertial properties in each of the aircraft axes, as well as the physical sizing of the control surfaces for each axes. This work has its roots in earlier T-10 Flanker series designs, most recently, the Su-35S.
As seen on the Su-35S, there is no separate, dedicated speed brake control surface, this function being subsumed by differential deployment of control surfaces.
-With the undercarriage fully deployed, the primary Nose Landing Gear (NLG) doors are closed with small ancillary doors providing the opening through which the NLG oleo and related dual wheel and steering assembly protrude, thus removing the directionally destabilising effect of the primary doors in the powered approach (PA) configuration.
-When deployed, the sizeable Main Landing Gear (MLG) doors are aligned to the longitudinal plane of the aircraft and likely contribute to the static directional stability of the aircraft in the PA configuration.
Observations from the video footage of the first "public" flight include:
-The relatively high speed taxi to the hold short line showed very little vertical motion or forward/aft interaction of the undercarriage oleos/tires spring/damper system which suggested the aircraft was likely at a relatively light, mid-fuel/mid centre of gravity (CoG) configuration.
-The aircraft flew away from the runway during the take off with no perceptible pitch control input, evidenced by no leading edge displacement of the horizontal stabilisers and no deflection of the TVC nozzles in pitch being observed. This is akin to the F-22A Raptor wherein take off trim and lift off speed are all that are required for the aircraft to unstick off the runway. This contrasts strongly with the F-35 series of designs, where a conventional take off requires an elevator input in the order of 30° LE down to initiate the unstick /rotation process.
-Very little leading edge flap deployment, most likely employing the minimal take off trim setting, appeared to be required and no significant deployment of the trailing edge flaps was evident.
During the ground roll, engine nozzles were in the trail position and no vectored input in either the longitudinal or lateral axes was evident.
-Take off roll to un-stick was estimated at somewhat less than 1,500 feet, taking some 12 seconds from brake release to rotation speed (Vr).
-Rotation and initial climb out appeared smooth, stable and well controlled with increasing rate of climb, with the causally increasing climb angle and climb attitude evident and monotonically climbing within 2 seconds after lift off.
-Little coverage of the up and away part of this flight was released into the public domain, though there are multiple reports that the undercarriage was cycled when airborne and some time was allocated for mild side slip and flat turn manoeuvres, along with lateral control excursions to around 45° from wings level flight.
-The landing was uneventful with what appeared to be minimum leading and trailing edge flap settings and little, if any, employment of TVC and/or the LEX control surfaces. The pilot held the nose wheel off the runway for approximately 4 seconds after the MLG contacted the runway, with the nose wheel run on to the tarmac coinciding with deployment of the two arrestor drag parachutes. These chutes were released some 10 seconds later, signalling the end of the 14 second ground roll portion of the landing iteration. Overall, the distance of this portion of the landing was estimated at somewhat less than 1,300 feet.
PAK-FA Weapons Capabilities
Very little has been disclosed to date on the intended weapons suite for the PAK-FA. The internal bays are claimed to fit eight AAMs. The limited width of the centre fuselage bays indicates that most likely these would each fit three staggered RVV-SD rounds, this being the latest variant of the R-77 / AA-12 Adder and a direct equivalent to the US AIM-120 AMRAAM series. To date only the active radar seeker equipped RVV-SD variant has been displayed, the intended heatseeking and anti-radiation variants have yet to be seen in mockup form or marketing literature.
While a new WVR AAM has been planned, it is likely that a derivative of the RVV-MD / R-74 Archer series will be used with early PAK-FA variants.
For very close air combat, a 30 mm gun mounted in the starboard forward fuselage will be employed - the type has not been disclosed to date but it is likely to be a variant of the GSh-30 series carried by the Su-35S Flanker.
With eight stations cited for external stores, and the diversity of guided bombs, ASMs and cruise missiles available for the Su-30MK/Su-35S Flanker series, there is no shortage of alternatives for external carriage by the PAK-FA7.
Internal weapons for strike roles are a much more interesting consideration, due to the limited volume of the internal bays. Recent designs known to have folding surfaces for internal carriage include the new KTRV Kh-38 and Kh-58UShKE Kilter.
It is likely, but yet to be confirmed, that KTRV are developing an analogue to the GBU-39/B Small Diameter Bomb.
Given the well established and managed aerodynamics of this area of the Flanker designs, weapon clearances from the internal bays across the whole of the PAK-FA's operational envelope should be achieved with little, if any, difficulties, and without the need for employment of exotic and heavy techniques such as aero-acoustic local flow control and shaping or similar.
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 aircraft.
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.
PAK-FA Development History
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.
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.
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.
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.
PAK-FA Aerodynamic Design
Examination of the publicly displayed PAK-FA prototypes show 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 modernisation 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.
-Nominal engine thrust lines are canted outwards about 2° to 3° off the longitudinal centreline, with the engines spaced symmetrically around BL 00, at around 10 feet centre to centre spacing at the nozzle exit planes. This configuration reduces the risk of the rapid onset of large yaw rates at large thrust settings due to single engine in-flight shutdowns, while, when combined with the increased ~60°/sec angular TVC rates observed in the Su-35S design, enhancing the ability of the TVC system to augment/replace aerodynamic flight control inputs, while aiding in the provision of 'apparent static directional stability' through dynamic control to replace the normally 'natural inherent static directional stability' that has been relaxed.
-There has clearly been a concerted effort to establish harmony and complementarities between the inertial properties in each of the aircraft axes, as well as the physical sizing of the control surfaces for each axes. This work has its roots in earlier T-10 Flanker series designs, most recently, the Su-35S.
As seen on the Su-35S, there is no separate, dedicated speed brake control surface, this function being subsumed by differential deployment of control surfaces.
-With the undercarriage fully deployed, the primary Nose Landing Gear (NLG) doors are closed with small ancillary doors providing the opening through which the NLG oleo and related dual wheel and steering assembly protrude, thus removing the directionally destabilising effect of the primary doors in the powered approach (PA) configuration.
-When deployed, the sizeable Main Landing Gear (MLG) doors are aligned to the longitudinal plane of the aircraft and likely contribute to the static directional stability of the aircraft in the PA configuration.
Observations from the video footage of the first "public" flight include:
-The relatively high speed taxi to the hold short line showed very little vertical motion or forward/aft interaction of the undercarriage oleos/tires spring/damper system which suggested the aircraft was likely at a relatively light, mid-fuel/mid centre of gravity (CoG) configuration.
-The aircraft flew away from the runway during the take off with no perceptible pitch control input, evidenced by no leading edge displacement of the horizontal stabilisers and no deflection of the TVC nozzles in pitch being observed. This is akin to the F-22A Raptor wherein take off trim and lift off speed are all that are required for the aircraft to unstick off the runway. This contrasts strongly with the F-35 series of designs, where a conventional take off requires an elevator input in the order of 30° LE down to initiate the unstick /rotation process.
-Very little leading edge flap deployment, most likely employing the minimal take off trim setting, appeared to be required and no significant deployment of the trailing edge flaps was evident.
During the ground roll, engine nozzles were in the trail position and no vectored input in either the longitudinal or lateral axes was evident.
-Take off roll to un-stick was estimated at somewhat less than 1,500 feet, taking some 12 seconds from brake release to rotation speed (Vr).
-Rotation and initial climb out appeared smooth, stable and well controlled with increasing rate of climb, with the causally increasing climb angle and climb attitude evident and monotonically climbing within 2 seconds after lift off.
-Little coverage of the up and away part of this flight was released into the public domain, though there are multiple reports that the undercarriage was cycled when airborne and some time was allocated for mild side slip and flat turn manoeuvres, along with lateral control excursions to around 45° from wings level flight.
-The landing was uneventful with what appeared to be minimum leading and trailing edge flap settings and little, if any, employment of TVC and/or the LEX control surfaces. The pilot held the nose wheel off the runway for approximately 4 seconds after the MLG contacted the runway, with the nose wheel run on to the tarmac coinciding with deployment of the two arrestor drag parachutes. These chutes were released some 10 seconds later, signalling the end of the 14 second ground roll portion of the landing iteration. Overall, the distance of this portion of the landing was estimated at somewhat less than 1,300 feet.
PAK-FA Weapons Capabilities
Very little has been disclosed to date on the intended weapons suite for the PAK-FA. The internal bays are claimed to fit eight AAMs. The limited width of the centre fuselage bays indicates that most likely these would each fit three staggered RVV-SD rounds, this being the latest variant of the R-77 / AA-12 Adder and a direct equivalent to the US AIM-120 AMRAAM series. To date only the active radar seeker equipped RVV-SD variant has been displayed, the intended heatseeking and anti-radiation variants have yet to be seen in mockup form or marketing literature.
While a new WVR AAM has been planned, it is likely that a derivative of the RVV-MD / R-74 Archer series will be used with early PAK-FA variants.
For very close air combat, a 30 mm gun mounted in the starboard forward fuselage will be employed - the type has not been disclosed to date but it is likely to be a variant of the GSh-30 series carried by the Su-35S Flanker.
With eight stations cited for external stores, and the diversity of guided bombs, ASMs and cruise missiles available for the Su-30MK/Su-35S Flanker series, there is no shortage of alternatives for external carriage by the PAK-FA7.
Internal weapons for strike roles are a much more interesting consideration, due to the limited volume of the internal bays. Recent designs known to have folding surfaces for internal carriage include the new KTRV Kh-38 and Kh-58UShKE Kilter.
It is likely, but yet to be confirmed, that KTRV are developing an analogue to the GBU-39/B Small Diameter Bomb.
Given the well established and managed aerodynamics of this area of the Flanker designs, weapon clearances from the internal bays across the whole of the PAK-FA's operational envelope should be achieved with little, if any, difficulties, and without the need for employment of exotic and heavy techniques such as aero-acoustic local flow control and shaping or similar.
