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
it as a “surprising capability
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
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
“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
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
the effectiveness of the F-22A Raptor, it will still yield BVR exchange
the order of 50:1 against legacy fighters.
arrival of the PAK-FA therefore irrevocably enforces
the end of the operational usefulness of the teen series (F-15 / F-16 /
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.
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
“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
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
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.
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
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
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.
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
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
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
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
fleet, and terminate the F-35 Joint Strike Fighter as soon as possible,
as the F-35 will
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.
and techno-strategic terms, the PAK-FA is the most
in the fighter domain since the T-10/Su-27S Flanker B entered
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.
The first high quality in
flight image of the prototype to be released by Sukhoi/KnAAPO. Closer
inspection of the details in this image, particularly the absence of
surface mounted INSTM on the fully articulated fin control surfaces
suggests this image is from a different flight and might even be an
in-flight image of another prototype airframe (Sukhoi).
The PAK-FA was quickly dubbed
by Western observers as the “Raptor-ski” or “F-22-ski”. This
label is reasonable in terms of the niche the aircraft
is intended to occupy, as it is intended to directly challenge
the F-22A Raptor, but this label is quite inaccurate in terms of the
configuration of the aircraft and its detailed design.
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. A powerful approach evident in the
development of the Flanker family of aircraft has been, firstly, to
plan long term, then to spread developmental risks across the
series of planned new aircraft types and variants as well as parallel
design/development activities. The benefits of such an approach are
The best illustration of how much more effective Russian systems
development philosophy is, 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.
objective is to produce a design on-time and on-cost without unpleasant
surprises, there is much to be said for the Russian approach to systems
Russian sources indicate that the prototypes will be fitted with a
derivative of the existing Su-35S avionic suite to reduce risk and
cost. It is likely that this strategy of risk reduction by the use of
existing production hardware will apply to other key internal
components. The use of the 117S series engine common to the
Su-35S in PAK-FA prototypes is a prime example.
Another example is the basic layout or configuration of the PAK-FA
airframe design, which is demonstrably based on the T-10 Flanker
series, with a large centre fuselage carapace, a pair of long
serpentine engine inlet ducts, with inlets beneath a large LEX, the
engines mounted in blast resistant tubes, which also provide the means
for reacting empennage control surface and TVC loads, and a blended
forward fuselage raised above the engine centrelines, not unlike the
Flanker and F-14 series. The forward and centre fuselage design is
therefore closer to the Flanker and YF-23 than the F-22A. The wing
planform is closest to F-22, reflecting design aims in VLO shaping and
supersonic cruise performance.
Where the PAK-FA departs most strongly from the earlier Flanker, the
F-22 and the YF-23
is in the aft fuselage design, and the moving LEX or Povorotnaya Chast' Naplyva (PChN)
design, intended to provide extreme manoeuvrability and controllability
and, thus, extreme agility - an attribute
in the F-22 and YF-23, but
extant in some later Flanker variants, demonstrators and prototype
To provide extreme agility, Sukhoi's design team employed all-moving
stabilators and canted tail fins, a nodding movable LEX design, and 3D
axi-symmetric engine nozzles. The wide spacing of the fully articulated
fins and engine nozzles provides a much larger moment arm for both
aerodynamic and TVC roll and yaw inputs, than observed with previous
designs. While the tail surfaces do not impair observables, the use of
axi-symmetric 3D nozzles does, no differently than the fixed
axisymmetric nozzle of the F-35 Joint Strike Fighter.
The latter raises some very interesting questions about key design
trade-offs, as yet not explained by Sukhoi. The existing design
configuration suggests that extreme manoeuvrability was rated to be
important than all-aspect stealth was, suggesting in turn that the
aircraft was not intended for use as a deep penetrator in the manner of
the F-22 and YF-23. Given the low priority given in Western nations to
the maintenance of deep overlapping SAM belt air defences, the
susceptibility to aft quarter SAM shots inherent in limited all aspect
stealth performance may not have been assessed as a risk worth serious
investment in defeating.
Conversely, the current design may be an
expedient development shortcut, with a more refined aft quarter VLO
design to appear with the final production engine. The quality of the
front quarter VLO design demonstrates that Sukhoi are capable of
producing an aft quarter VLO shaping design no worse than the F-22A or
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
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.
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
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
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. This emulates the strategy pursued by
American designers in the F-22, and claimed but not properly
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.
|Preliminary PAK-FA Performance
to 1.6M >36kft, ISA), though analysis
suggests a likely higher top end point of ~1.9M.
|Sources: Sukhoi via Russian media,
preliminary APA analysis
1 - supersonic flight duration not specified
2 - ceiling constraints not specified
Above PAK-FA prototype, below production
F-22A Raptor. and Dem/Val YF-23A. These images expose both similarities
differences in the three designs (Sukhoi, US Air Force).
inlet and lower fuselage area (Sukhoi).
The low observable design
shaping employed in the PAK-FA prototype shows an excellent grasp of
the design rules employed by American designers in the development of
the F-22A and YF-23 Advanced Tactical Fighter. This reflects an
observation made to one the authors by a senior American design
engineer some years ago “we always end up doing the really hard work
learning how to build these things, making it easy for the Russians to
follow with their designs”.
The likely exploitation of F-22A and YF-23 Advanced Tactical Fighter
low observable shaping design rules was predicted through analysis as
most likely during the past decade, and subsequently published in
March 2009. Sukhoi's prototype shaping validated that analytical
As observed previously, the Russian approach to development follows an
“evolutionary” design philosophy, in which risks are retired early in
the development phase of a new aircraft type or variant. Where
possible, the retirement of risks is achieved in earlier programs, as
demonstrated repeatedly in the development of the T-10 Flanker series
prototypes displayed in January, 2010, are clearly intended to validate
the compatibility of the overall observables shaping with the
aerodynamic and structural design needs and clearly so, as the
expensive detail RCS flare spot treatments we are accustomed to seeing
on US prototypes are absent. The rationale for this is simple - why
expend valuable but scarce development resources if aerodynamic /
testing shows that
major changes are required to shaping of important design elements? For
Western contractors, where the imperative is to extract the maximum of
development funding from the customer, and make early cancellation of a
program difficult, the highest risk approach will nearly always
be sought by senior management. An excellent case study of the latter
is the extremely high level of “concurrency risk”, reported by the
General Accounting Office, in the F-35 Joint Strike Fighter program.
The risk minimisation oriented development strategy explains the
absence of serrations on the ventral inlet blow-in doors, and the
absence of a serrated nozzle on the interim engine design. Design
features which are intended to be permanent, such as the ventral weapon
bay doors, aerial refuelling probe doors, and large access panels, all
employ edge alignment or serrations no differently than the B-2A,
F-22A and YF-23 demonstrator.
It is important to note that
VLO shaping design is the single most critical aspect of VLO design
with contemporary basic technology. This is because once the shaping is
fixed in the design, the cost of implementing changes is prohibitive
downstream, impacting structural design, aerodynamic behaviour and
internal packaging of systems. If VLO shaping is done poorly, early in
the development cycle, with the F-35 lower and aft fuselages being the
representative case study, no reasonable downstream investment in
additional absorbent materials and structures can overcome the
resulting signature problems, and may introduce additional problems
with weight, cost and strength/stiffness of skin panels.
By aiming for the best possible VLO shaping in the PAK-FA design from
the very outset, Sukhoi's designers have demonstrated that they
understand this aspect of VLO design very well. This strategy also
opens up the prospect of progressive improvements in VLO performance as
the design matures, and better VLO materials technology becomes
The prototypes show the extensive use of what appears to be
conventional riveting, and conventional construction. If genuine VLO
capability is intended, extensive robotic surface coating
treatment or appliqué laminate technology will be required, with both
techniques requiring a
highly conductive substrate layer to suppress the surface impedance
discontinuities resulting from the construction technique used.
As observed in other areas of the Russian industrial base, coating and
surface treatment technologies are well understood, and world class
capabilities are available.
The forward fuselage is closest in general configuration to the YF-23,
especially in the chining, cockpit placement, and hump aft of the
cockpit canopy, although the blending of the upper forward fuselage
into the upper carapace is more gradual. There are important
differences from the YF-23. The chine curvature design rule is purely
convex, like the chine design on the F-22A. The nose height is greater,
to accommodate an AESA with a much larger aperture than that intended
for the YF-23 or F-22A. If flare spots are properly controlled by the
application of materials and serrated edge treatments around the
canopy, and a good bandpass radome design using a frequency selective
laminate is employed, the shaping related RCS contribution of the
forward fuselage in
the S/X/Ku-bands will be similar to that observed with the F-22A, YF-23
The Electro-Optical System (OLS) turret employed on the prototype is
the Su-35S OLS, and is incompatible with a VLO design, as it is a
broadband spherical reflector. We can expect to
see a faceted VLO fairing similar to that designed for the cancelled
F-22A AIRST (Advanced IRST [Image
The conventional pitot-static probes currently mounted around and
forward of the cockpit are like the OLS turret, incompatible with a VLO
design, and we can also expect to see these replaced with VLO design
ports in a production PAK-FA configuration.
The edge aligned movable LEX are readily treated with leading edge
absorbers and will not present a major RCS flare spot. The treatment of
the movable join will present the principal challenge in this portion
of the design. The obtuse angle in the join between the LEX and forward
fuselage is characteristic of good design and is very similar to the
used in the F-22.
The lower fuselage of the
prototype displays interesting incongruities. There is an abrupt
transition between the carefully sculpted faceting of the inlet
nacelles, and the smoothly curved aft engine nacelles and conventional
aft fuselage. The faceting strategy is similar to the F-22 design
rules, with singly or doubly curved transitions between planes (C.
The edge aligned trapezoidal main engine inlets are similar in
configuration to the F-22, but with important differences. The inlet
aspect ratio is different, and the corners are truncated in a manner
similar to the YF-23. If properly treated with leading edge inserts and
inlet tunnel absorbent materials, the inlet design should yield similar
RCS to its US counterparts.
The placement of the engine centrelines well above the inlet centroids,
in the manner of the YF-23, results in an inlet tunnel S-bend in the
vertical plane. Sukhoi have not disclosed whether an inlet blocker will
be employed. Public disclosures on Su-35S inlet treatments claimed a
~15 dB reduction in X-band RCS compared to the untreated inlet tunnels
on the Su-27SK. The use of an S-bend in the PAK-FA would permit an
increase in the number of surface bounces further increasing
attenuation and reducing RCS.
In the S/X/Ku-bands the basic shaping of the forward fuselage will
permit the attainment of genuine VLO performance with the
application of mature RAS and RAM, where the centre and aft fuselage do
not introduce larger RCS contributions from the forward aspect.
Above: PAK-FA upper
forward fuselage showing shaping details; below: YF-23A (Sukhoi, US Air
The wing design from a planform perspective is closest to the F-22A,
and the upper fuselage similar to the YF-23, permitting the achievement
of similar RCS performance to these US types, from respective aspects.
Where the PAK-FA falls well short of the F-22A and YF-23 is the shaping
design of the lower fuselage and side fuselage, where the general
configuration, wing/fuselage join angles, and inlet/engine nacelle join
angles introduce similar intractable specular return problems as
observed with the F-35 Joint Strike Fighter design. These are inherent
in the current
shaping design and cannot be significantly improved by materials
application. Like the F-35 Joint Strike Fighter, the PAK-FA prototype
produce a large specular return in any manoeuvre where the lower
fuselage is exposed to a threat emitter, and this problem will be
prominent from the Ku-band down to the L-band.
This problem is exacerbated by the inboard ventral wing root fairings,
claimed by some Russian sources to be pods for the concealed carriage
of folding fin close combat AAMs, such as the RVV-MD/R-74 series. While
these fairings do not introduce large RCS contributions from fore or
aft aspects, they will adversely contribute to beam aspect RCS,
especially for threats well below the plane of flight of the aircraft.
The shaping remedy for the beam aspect signature problem lies in more
obtuse join angles, which would require considerable effort in
resculpting the fuselage/wing join from the main undercarriage bays to
the tail, and narrowing the usable width of the lower fuselage tunnel
between the nacelles. The latter is problematic. An alternative may be
the use of thick RAM treatments, in effect replacing the skins of the
of the inner forward lower fuselage tunnel with RAM panels, with some
penalty as a result, which would not be significant relative to
overall aircraft weight, given the small area to be treated.
The tailboom shaping is reminiscent of the F-22 and F-35 designs, and
will not yield significant RCS contributions from the front or aft
aspects. In the lower hemisphere, it will suffer penalties due to the
insufficiently obtuse join angles between the wings and stabilators,
and outer engine nacelles. The
upper fuselage fairings which house the all moving vertical tail
are well shaped, and the join angles are well chosen. The outward cant
of the empennage fins is similar to United States designs, and like the
YF-23 tail surfaces, these are fully articulated with the VLO benefit
of removing surface impedance discontinuities at the join of a
conventional rudder control surface.
The axi-symmetric 3D TVC nozzles present the same RCS problems
observed with the fixed
the F-35 JSF [analysis/imagery]
shroud treatments and tailpipe blockers
as used with the F-35 JSF will not overcome the inherent limitations of
this canonical shaping design. Observed from the aft hemisphere in the
through Ku-bands, the PAK-FA prototype configuration will produce to an
order of magnitude an equally poor RCS as the F-35 Joint Strike Fighter10
The centre fuselage beavertail follows a similar chine design rule as
the forward fuselage does, and will not present a significant RCS
contribution from behind.
If production PAK-FA aircraft employ the same lower and aft fuselage
design as the prototype does, they will be susceptible to aft
hemisphere and beam aspect threats at depressed angles, operating from
the L-band through to the Ku-band, in a manner no different to the F-35
Joint Strike Fighter.
It is worth observing that the unconventional flight control
capabilities of the PAK-FA do open up some possibilities, in that they
permit manoeuvres such as flat turns, or even turns where the bank
angle is opposite to a conventional banking turn. Such manoeuvres
permit the PAK-FA to execute, without difficulty or high energy bleed,
turns away from beam
aspect threats without significant exposure of the problematic lower
fuselage, unlike the conventional F-35 JSF which becomes unavoidably
susceptible to detection, tracking and missile shots in such
geometries. As the PAK-FA
will provide a similar supersonic cruise capability to the F-22, its
window of vulnerability is very much shorter when attempting to evade a
tail aspect threat, and it has a credible capability to defeat missile
Whether the current aft fuselage design of the PAK-FA is an artefact of
the use of off-the-shelf Su-35S engines, or a permanent long term
feature of the design, is unclear.
The general configuration of the PAK-FA aft fuselage is as compatible
the style of 2D VLO shaped TVC nozzles used in the F-22A, and
integrated with the F119-PW-100 engines, as it is compatible in
principle with the superb non-thrust vector aft fuselage design used in
the YF-23. The latter remains the benchmark for wideband aft sector VLO
Producing a 3D TVC nozzle design which has similar VLO shaping
performance as the F-22A 2D TVC nozzle design is not a trivial task -
there is no obvious simple solution to this problem. If the Russians
solved it, it would be a major advance in VLO nozzle design.
Until Sukhoi disclose their intentions in this area, such as deployable
LO shrouds for cruising flight, or provide imagery
of the production PAK-FA aft fuselage design, this will remain an
From an RCS engineering perspective, the shaping design of the PAK-FA
is an excellent first attempt by the Russians to produce a high quality
VLO design. The forward fuselage and engine inlet area shaping design
is highly competitive against more recent US designs, and with mature
high quality RAS and RAM application, have genuine VLO potential. The
upper fuselage, wing and tail surface shaping and planform alignment
are also competitive against US designs.
The problematic lower and aft fuselage designs, if retained in
production aircraft, will deny the PAK-FA the kind of deep penetration
capability sought in the design of the F-22A and YF-23.
The only cited RCS performance data was a recent claim by Sukhoi that
the PAK-AF will have 1/40 of the RCS of the Su-35S. Unfortunately this
was not qualified by threat operating band, aspect, or whether the
Su-35S was clean or laden with external stores. The RCS of the Su-35S,
head-on in the X-band, has not been disclosed, but given the extensive
RAM treatments applied could be as low as 0.5 - 2 m2
clean aircraft with no stores. If the latter were true, then the PAK-FA
X-band head-on RCS would be of the order of -13 to -19 dBSM. Such
performance would be consistent with the shaping design, but not with
the application of mature RAM and RAS to same.
Analysis of tactical options, as published in March 2009, assumed a
forward sector X-band RCS of about -20 dBSM, which fits the outer
envelope of the Sukhoi disclosure almost exactly5,6
The Russians have claimed that the design has engine infrared signature
reduction measures, but these have not been detailed. The conventional
axi-symmetric nozzle design is generally ineffective, from an infrared
signature perspective, as the nozzle shrouds are exposed radiators, and
the cylindrical exhaust aperture radiates into a conical volume behind
The use of 3D TVC nozzles with high angle rates, which are fully
integrated in the DFCS, would present opportunities to minimise RCS
contributions resulting from aerodynamic control surface movements, by
employing where possible TVC controls for primary pitch, roll and yaw
control when performing stealthy penetration. Given that this flight
regime entails flight in cruise configuration, and gentle turning
manoeuvres to minimise bank angles, observably large deflection control
would be unusual and thus very infrequent. As a result the pitch, roll
and yaw rates produced by the TVC system alone would be sufficient for
most control inputs in the stealthy penetration regime of flight.
Above: PAK-FA upper aft
fuselage / tail showing shaping details; below: YF-23A, F-22A Raptor
(Sukhoi, US Air
Examination of the
displayed PAK-FA prototypes show that this design is a
continuation of the
highly evolved pedigree of Flanker aerodynamic design. However, as
and predicted from the most recent Flanker variant, the Su-35S, and the
done during the deep modernisation program that resulted in this
have evidently taken the next step by providing the PAK-FA with
static stability in the directional axis.
Open source materials
such as high
resolution imagery and video camera footage show there are a number of
about the aerodynamic design of the PAK-FA that are different to, but
enhancements on the tried and proven aerodynamics of the Flanker family
- 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
wing, truncated and blended with the leading edges of the horizontal
- 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
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
- 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
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”
- 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
- 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
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.
The results of detailed
observations and analyses of
the material now in the public domain combined with knowledge of the
development of aerodynamic techniques
by Sukhoi over more than two decades, demonstrates that Sukhoi and its
supporting team of engineers and scientists have achieved mastery of
agility throughout the whole air combat continuum. Since the
design is already accredited with the title of “extreme agility”, the
aerodynamic and kinematic capabilities of the PAK-FA will likely
coining of the term “extreme plus agility”
to do them
The introduction of relaxed static directional
stability in the PAK-FA design, alone, will ensure that the PAK-FA has
manoeuvrability and controllability capabilities and, thus, the agility
Western fighter design can provide.
There is only one Western
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
Structural, Systems and Propulsion Design
Vitaliy V. Kuzmin).
Examinations of the PAK-FA prototypes show clearly that the
structural, airframe systems and propulsion aspects of the PAK-FA
follow the now quite predictable, well managed and low risk
developmental paths established by Sukhoi in the T-10 Flanker
family of aircraft designs.
Over the last three decades, this approach has seen technological
advancements, extensions and enhancements grounded solidly in those
employed in previous designs, prototype programs and the resulting
fighter/strike/attack/interceptor aircraft systems that were placed
into operational service with Russian military forces as well as
exported around the world.
The structural enhancements and advancements to be seen in the PAK-FA
design include further use of light weight, high strength metal
alloys, such as Ti, Al, and AlBe alloys, and the greater use of
composite technologies and the associated materials, both of which
provide a stiffer, stronger airframe with an even further reduction in
the air vehicle's relative structural weight than that achieved
in the Su-35S design revealed in the latter part of 2008.
There can be no doubt from the basic airframe shaping that the internal
airframe structural details are derived from and were proven in the
Su-35S and its preceding Su-35BM deep modernisation Program.
The same applies for the airframe systems, including the hydraulic,
electrical, pneudraulic and fueldraulic power systems; fuel
distribution and engine feed systems; environmental control systems
(ECS), OBOGS, auxiliary power; and, all important thermal management
The large internal fuel capacity of ~25,000 lbs and the significant
amount of high pressure air available from the oversize main engine
inlets will ensure the PAK-FA will have none of the problems and
challenges confronting earlier US fighter designs, and known to have
become a critical and severely limiting design issue in the JSF
The existing PAK-FA prototype effort is clearly focussed on minimising
risk during the initial process of proving the aerodynamic, airframe
and systems design. Russian open sources have stated that the
prototypes are powered by the existing production Al-31F 117S, often
labelled for marketing reasons as the Al-41F1A, variant
19,400/32,000 lbf (8,800/14,500 kp) engine, employed in the
Su-35S. While this engine
lacks the performance
rating of the earlier developmental Al-41F series and its likely
it is capable of supercruise and thus permits significant flight test
and flight control system development to be performed without the high
risks characteristic of the concurrent use of a developmental
The cited TVC capability of the 117S engine is ±15° in the vertical
plane, and ±8° in the horizontal plane, with deflection angle rates of
now up to 60 °/sec, putting them in the same onset rate category as
fighter-type aerodynamic flight control surfaces. The engine employs a
larger diameter fan, at 932 mm vs.
the 905 mm fan in the earlier Al-31FP TVC engine. Key hot end
components in the core were redesigned to employ the cooling system
technology developed in the 1990s Al-41F, permitting much higher TIT
ratings and a commensurately reduced thrust lapse rate with altitude,
in turn permitting supercruise operation.
Harmonisation of the digital flight control laws with the precision 3D
TVC nozzle system requires a robust and reliable 3D TVC nozzle equipped
Uncertainties remain in terms of the capabilities and design of the
intended powerplant for Full Rate
Production aircraft. Saturn have been developing a new engine for the
PAK-FA since 2006, labelled as the “Fifth Generation Fighter Engine”.
Clearly this will employ technology from the existing 39,600 lbf class
Al-41F, developed initially for the MFI8
workshare breakdown for the developmental fifth generation engine;
below: intended applications for same. The Russian language legend
shows a common core [Basic Gas Generator] exploited for a range
of other applications, including maritime surface combatant
powerplants, and fixed power station or gasline pumping
applications (NPO Saturn).
Public comments by Russian parliamentary scientific advisor Konstantin
Makienko, in a
recent media interview, indicate that the Russians envisage the PAK-FA
project in terms of a 40 - 50 year operational life cycle, reflecting
historical experience with the T-10, which entered development during
the early 1970s4
Against such timescales, it is a certainty that production PAK-FA
aircraft will see two or three generations of powerplant fitted to the
design, which further explains the employment of the large, seemingly
oversize propulsion system intakes. Clearly, the Sukhoi penchant for
alternate intakes in Flanker designs continues with the PAK-FA design.
Production PAK-FA aircraft will therefore at some stage acquire a high
variable bypass supercruising engine with a variable cycle core and
augmenter, as the diverse needs of long range/persistence and
supercruise dictate this design approach. When the US dropped the
variable cycle YF-120 from the ATF program during the early 1990s, it
was for fear of development risks impacting deployment timelines,
leaving the production F-22A Raptor with a much more basic F119-PW-100
The 117S powerplant (©
Vitaliy V. Kuzmin).
Avionics and Radar Design
Russian statements on the
core avionic suite intended for the PAK-FA have not been particularly
to date, but indicate the design will be in many parts an evolution of
the Su-35S avionic design. Given that the avionic suite for the Su-35S
is an entirely new and fully digital design, in basic technology terms
it will differ little from the technology in current United States
designs. The expectation that the PAK-FA might be combat ineffective if
equipped with a derivative of the Su-35S Flanker avionic suite is
illogical and clearly optimistic, as the Su-35S digital avionic system
design is credible by any measure.
A minimal adaptation would retain all core components of the Su-35S
avionic design, but replace all conventional apertures with VLO
equivalents, and alter waveforms to provide LPI operating modes.
Sukhoi will face some interesting design challenges in developing the
PAK-FA avionic suite. These will lie in
the same areas which have bedevilled US designers in all recent VLO
aircraft development projects, specifically in the provision of
high capacity avionic
cooling, which does not produce infrared hotspots, and in the design of
wideband, yet very low RCS radio-frequency apertures for both passive
and active sensors, and aircraft datalink/network terminal
VLO aperture design has been a source of ongoing difficulties in
structural mode RCS and impedance mismatches against the aperture can
result in prominent RCS flare spots, which can be disastrous in a
design. Even a small RCS contribution can be problematic, given the
number of apertures required to support especially wideband all aspect
An unknown at this point in time is the extent to which Russian
designers will have exploited wreckage from the F-117A Nighthawk, lost
in the 1999 OAF campaign over Serbia. The remains of this aircraft
would be a valuable source of detail components, especially VLO
VLO rated instrumentation ports and probes, and proven albeit older VLO
Russian parliamentary scientific advisor Konstantin Makienko, in a
recent media interview, noted that the PAK-FA avionic suite would be
used as the basis for technology insertion upgrades on the Su-35S. He
also observed that “Not just an active radar but an entire
multifunctional integrated radio electronic system that contains five
integrated arrays is being developed for PAK FA”4
The latter is interesting, as the beavertail has a radome compatible
with an aft looking X-band AESA, an option available for a number
of later Flanker variants. Statements have also emerged that cheek
X-band AESA apertures, to supplement the forward AESA, were planned,
analogous to the cheek AESAs planned for the F-22A. This however does
not account for five AESA apertures.
If some RCS degradation in the L-band is tolerated, then L-band AESAs [analysis/imagery
] could be installed in
leading edges of the LEX or wings, using a frequency selective bandpass
This however does not add up to five apertures, unless the paired
L-band AESAs are counted as a single aperture, a possibility since both
are operated as a single phase steered array14
As noted in the discussion of observables, the prototypes are likely to
be equipped with a derivative of the Su-35S OLS.
Su-30MKM aircraft supplied to
Malaysia have been fitted with a multiple aperture optical MAWS. A
similar MAWS design for a VLO airframe will confront analogous problems
to radio-frequency apertures, likely resulting in similar flush window
designs as used with the F-35 Distributed Aperture System (DAS).
Until representative late PAK-FA prototypes are seen, with the full
avionic suite fitted, uncertainties will remain in properly assessing
the capabilities of the active and passive sensor suites, threat
warning systems, active countermeasures fit, and expendables options.
The lengthy intended service life of the PAK-FA and rapid evolution of
avionics technology over coming decades indicates that this design is
likely to see two or three generations of avionic suite installed over
the aircraft's life cycle.
There have been no prominent
disclosures on the PAK-FA cockpit design. It is likely that a
the ergonomically well fashioned Su-35S glass cockpit would be used -
this design employs a pair of large AMLCD panels to emulate the
arrangement in the F-35, but with more robust fault tolerance, greater
simplicity in design, yet similar ease in operation.
claim that the new OKB
control set is likely to be used in the PAK-FA, but no formal
disclosures by manufacturers have been made to date.
Like the Su-35S, the PAK-FA will employ a dual mode Glonass/GPS
receiver and Kalman filter based inertial navigation suite, with an RLG.
As with the Su-35S, the PAK-FA will carry datalinks for bi-directional
data transfers. There have been no disclosures at this time on the
datalink terminals or waveforms intended.
controls which Russian sources claim to be the most likely design
employed in the PAK-FA cockpit (Aviaavtomatika).
In the integration of network
terminals, Russian industry will
confront much the same issues the US Air Force has had to resolve in
defining and developing Low Probability of Intercept (LPI) datalink
modulations compatible with stealthy operations. The Russians will be
acutely aware of the design issues, given their previous effort in
terminal emissions for passive targeting of SAMs.
A number of Russian sources
have commented on the use of “data fusion” in the PAK-FA avionic
design, a technique which is used currently in the F-22A and intended
for the F-35.
Enhanced stills from a Russian
television broadcast reporting the Tikhomirov NIIP PAK-FA AESA design.
Static display images of the antenna have a dielectric impedance
matching screen installed, which obscures the actual TR module
apertures (Vesti - Moskva via Youtube).
The Tikhomirov NIIP X-band AESA
for the PAK-FA is better understood than the core avionic suite, due to
extensive disclosure by Tikhomirov NIIP at MAKS 2009.
The antenna aperture is very similar in size, if not identical, to the
aperture of the N-011M Irbis E used in the Su-35S. The design is
intended for fixed low signature
tilted installation, rather than gimballed installation, and auxiliary
arrays are planned for. The design is also claimed to have been
with an existing BARS/Irbis radar for testing and design validation
Public statements made in
Russia through 2009 claim 1,500 TR module elements.
Counting exposed radiating elements on video stills of the antenna
indicates an estimated 1,524 TR channels, with a tolerance of several
percent. This is within 5% of the 2008 analytical model for a Flanker
NIIP have publicly cited
detection range performance of 350 to 400 km
(190 to 215 NMI), which assuming a Russian industry standard 2.5m2
target, is also consistent with the 2008 model for an AESA radar using
rated TR modules, which in turn is the power rating for the modules
used in the Zhuk AE prototypes. This puts the nett peak power at ~15
kiloWatts, slightly below the Irbis E, but even a very modest 25%
increase in TR
module output rating would overcome this.
There are distinct differences between the AESA displayed by NIIP for
Vesti, which has less depth and uses circular radiators, and the
examples displayed at MAKS 2009 and depicted on brochures, which are
constructed using TR module sticks and are several inches deeper.
To drive down the cost of this AESA, the best strategy
available to the Russians is the export of AESA upgrades to the global
community of Flanker users over the coming decade, emulating the US
approach with this technology, and driving up the volume of TR modules
built. Tikhomirov NIIP brochures state that the
existing AESA would be the basis of AESA upgrade designs for the
A design problem that Tikhomirov NIIP will have to grapple with is that
of LPI waveforms for the AESA, as these are critical to covert stealthy
combat operations. This will require that the AESA employ wideband feed
networks, a wideband digital waveform generator, and generous provision
of computing power for signal and data processing. LPI techniques have
not been discussed to any extent in unclassified Russian literature,
but are well covered in United States academic publications, and the
available to the Russian industry to develop and implement LPI
In conclusion, 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. 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. The
absence of public disclosures on the avionic suite does not indicate
the absence of advanced avionic subsystems, for which Russian industry
has all of the basic technology, but rather an intentional and
demonstrated policy of non-disclosure until the greatest competitive
advantage can be extracted in the market.
The primary BVR weapon to be carried by
early production variants of
the PAK-FA is the KTRV RVV-SD, an extended range evolution of the R-77
/ AA-12 Adder similar to the AIM-120D. Note the laser proximity fuse
supplanting the radiofrequency fuse (© 2009 Vitaliy V. Kuzmin).
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
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
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 primary close combat weapon to be carried by early production variants
of the PAK-FA is the KTRV RVV-MD, an extended range evolution of the
R-73/74 / AA-11 Archer with a jam resistant two colour scanning seeker
and a laser proximity fuse. Note the wideband ZnS or ZnSe IR window
replacing the narrowband MgF2 design used in earlier
Kh-38 mockup on display. Note the folding
fins for internal carriage ( ©
Kilter anti-radiation missile. Note the significantly revised radome
and cruciform reduced span folding wing design of this recent variant
(© 2009 Vitaliy V. Kuzmin).