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In 2015 the rein of the F-22 and of the
United States' quarter century long monopoly on the design of Very Low
Observable (VLO) or stealth aircraft ended. The introduction of the PAK-FA
or Su-41 (Firefox) while a known “known capability surprise” resulted in a
significant impact in the tactical, operational and strategic levels. The
Firefox competes with the F-22A Raptor in VLO performance from key
aspects, and outperforms it aerodynamically and kinematically. After the
PAK-FA achieved IOC in November 2015, it rendered all legacy US fighter
aircraft, and the F-35 Lightning II Joint Strike Fighter, strategically
irrelevant.
PAK-FA stands for “Перспективный авиационный комплекс фронтовой авиации -
Perspektivny Aviatsionny Kompleks Frontovoy Aviatsii” or in English;
Future aviation complex - frontline aircraft.
Early analysis of PAK-FA airframe aerodynamic features revealed a design
superior to all Western equivalents, providing supersonic cruise
capability, VLO and ‘extreme agility’. The latter was 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 initial production aircraft boasted similar low observables
performance to the F-35A JSF.
The Su-41 has a generally conventional layout with tailplanes, but
additionally moving LERX above the engine intakes. The tail fins are
unusually small and all-moving. The engines are mounted far apart,
optimizing the impact of the 3D thrust vectoring control, and allowing for
two large weapons bays mounted in tandem between them.
General characteristics
• Crew: 1
• Length: 19.8 m (65.9 ft)
• Wingspan: 14 m (46.6 ft)
• Height: 6.05 m (19.8 ft)
• Wing area: 78.8 m2 (848.1 ft2)
• Empty weight: 18,500 kg (40,785 lb)
• Loaded weight: 26,000 kg (57,320 lb)
• Useful load: 7,500 kg (combat load) (16,534 lb)
• Max takeoff weight: 37,000 kg (81,570 lb)
• Powerplant: 2× New unnamed engine by NPO Saturn and FNPTS MMPP Salyut of
175 kN each. Prototype with AL-41F1 of 147 kN each, definitive version
with new engine >157 kN
• Maximum Fuel weight: 10,300 kg (22,711 lb)
Performance
• Maximum speed: 2,600 km/h (Mach 2.45) (1,615 mph) ; at 17,000 m (45,000
ft) altitude
• Cruise speed: 1,300 - 1,800 km/h (808 - 1,118 mph)
• Ferry range: 5,500 km[50] ()
• Service ceiling: 20,000 m (65,616 ft)
• Rate of climb: 350 m/sec (1,148 ft/sec)
• Wing loading: 330(normal) - 470(maximum) kg/m2 (67(normal) - 96(maximum)
lb/ft2)
• Thrust/weight: 1.4
• Maximum g-load: +11.0 g
Armament
• Guns: None on prototype. Apparent provision for a cannon (most likely
GSh-301)
• Hardpoints: Two internal bays estimated at 4.6-4.7 metres by 1-1.1
metres . Two auxiliary internal bays for short range AAMS and 6 external
hard points
Avionics
N050 BRLS AFAR/AESA built by Tikhomirov NIIP and based on Tikhomirov NIIP
N035 Irbis-E .
Armament
• Two Izdeliye 810 Extended beyond visual range missiles per weapons bay.
Multiple Izdeliye 180 / K77M beyond visual range missiles. K74 and K30
within visual range missiles can also be carried.
• Two KH38M or KH58 USHK air-to-ground missiles per weapons bay. Multiple
250-500kg precision guided bombs per weapons bay, with a maximum of ten
bombs in internal bays
• Other possible loads include one 1500kg bomb per weapons bay or two
400km+ range anti-AWACS weapons on external hard-points. A maximum weapons
load of 7500kg is reported.
Note on Air-Air Weapons: Russia has unveiled the RVV-SD missile, an
updated version of the AA-12 Adder missile with folding fins, as the main
missile of the aircraft. Although the PAK-FA’s weapons bays can likely
carry larger missiles, they are probably not large enough for the massive
KS-172 (RVV-L) weapon which has an expected range of about 400km.
The RVV-SD is likely a good match for the latest AMRAAM variants, though
both may be eclipsed by the ramjet powered long range Meteor missile which
will be fielded on ‘Eurocanards’ like the Gripen and Typhoon by the time
PAK-FA enters service.
The above comparison with the F-22 shows the larger main weapons bays of
the PAK-FA (red). The F-22 can carry 6 AMRAAM missiles in the main bay.
Reports indicate that the PAK-FA can carry 8 equivalent AA-12 (RVV-SD)
missiles, giving it a 2 missile advantage. The side bays (orange) are of
similar capacity with both aircraft carrying just one short-range missile
per bay. For the PAK-FA the two smaller weapons bays are probably for the
RVV-MD version of the AA-11 Archer short range missile. The RVV-MD is
probably capable of rear-firing, a unique feature whereby the missile
flips immediately after launch and flies at a target behind the plane.
AA-12s with this feature have been tested and are possibly operational
within the Flanker community.
Both aircraft are equipped with a single cannon; 20mm Vulcan for the F-22
and probably a Gsh-30-1 for the PAK-FA.
Air-Ground role:
The PAK-FA is also reportedly a multi-role design. The internal weapons
bays are larger than on F-22, but with less depth and may not be capable
of carrying many of the weapons speculated. Various Kh-31 (AS-17 Krypton)
family supersonic missiles seem plausible albeit on the large side, as do
satellite guided bombs and KAB-500 series bombs. The weapons bays are
about 5m long.
A folding fin version of the Kh-58 ‘Kilter’ anti-radiation missile seems a
reasonable fit.
Avionics: The PAK-FA has several features of particular interest here.
In the nose there is likely to be active electronically scanned array
radar (AESA) as per F-22. This may actually have additional mechanical
steering, although that would add weight. What’s virtually unique to the
PAK-FA however is rear-facing radar in the tail. This too may be AESA and
could simply be an additional array for the nose-mounted radar, or
possibly a completely separate set.
The PAK-FA therefore has true 360 degree coverage. The PAK-FA has L-Band
radars mounted in the wing leading edges. These have both passive and
active emitting roles and are key to ‘seeing’ stealth aircraft such as the
F-22.
The F-22’s stealth is generally optimized against X-band radars as that is
what fighters generally use – L-Band is a much longer wavelength and can
more easily detect stealth aircraft but is also less accurate -hence
X-band radars are still used for routine intercept and virtually all
fighters use X-Band.
Unlike the F-22 the PAK-FA features an IRST optical/IR search and tracking
system. This resulted in the decision to retrofit an IRST to the F-22.
IRST is the best way to target stealth aircraft since regardless of the IR
stealth claims made of the F-22, jet engines are fundamentally not
conducive to IR invisibility. The trail of hot air behind the F-22 is the
first thing the PAK-FA sees as far as 25km.
The cockpits for both the Su-35 and PAK-FA Su-41 feature two very large
multi-function-displays (MFDs) and a very wide Head-up-display (HUD). The
F-22 in contrast has 4 large and two small MFDs and a large HUD, but the
PAK-FA’s two primary displays are much larger still and the HUD even
bigger.
Dogfighting: The F-22 is exceptionally maneuverable, but
comparatively less dogfight optimized compared to the PAK-FA which has 3D
thrust vectoring and moving LERX. This seems in line with Russian doctrine
still influenced by the Syrian experiences over the Baka Valley in 1981
where Soviet supplied fighters were decimated by the Israeli air force in
close combat.
The PAK-FA is more manoeuvrable, but the F-22 may boasts
speed-bleed/regain advantages.
The F-22 has larger wing leading-edge flaps and larger tail planes. The
PAK-FA’s tail fins are smaller but all-moving and the 3D TVC allows the
engines to be used both laterally and horizontally unlike the F-22 which
relies on massive tail fins for lateral stability and yaw control.
Export market: The PAK-FA is being exported through an Indo-Russian
FGFA partnership (as a two seat Su-30MKI replacement) and to the general
export market. Customers include India, Brazil, Venezuela, Belarus, Libya,
Angola, Vietnam and Saudi Arabia. Syria is negotiating and Iran is
attempting to convince Russia to ignore protests from the west and Israel
in allowing a sale.
The onboard computer uses artificial intelligence to help the pilot take
decisions faster. Like the 5th generation American aircrafts, the Sukhois
network with each other, sharing information about positioning, weaponry
and targets in real time. What’s more, the PKA-FA uses an IRST optical/IR
search and track system – this system is capable of detecting the heat
trail of the F-22 from as far as 25km away.
The APG-77 is unique, it is elliptical. Each T/R module is the size of a
finger nail, other advanced western AESA radars take 14 seconds to perform
120 deg six bar search pattern the APG-77 does it instantaneously. The
elliptical shape of the APG-77 antenna provides a valuable clue to the low
side lobe it presents many speculate it is around -70dB below the main
beam, remember to qualify as a low probability of intercept (LPI) radar
the main beam gain should be 55dB over the first side lobe. So the figure
of -70dB is unimportant, the first side lobe is undoubtedly at least -55dB
below the main beam.
The low side lobe performance of the APG-77 is achieved by the tapering
the distribution of array elements on the antenna the smoother the taper
from the center toward the extremity the lower the side lobe. If all T/R
modules were made equal it would be easy to distribute array elements as
described above – the phase error introduced as a result unachievable chip
‘manufacturing tolerance’ required to create identical T/R modules. The
antenna array spacing should be precise to maximize power to the main
beam; complex calibration is later required to achieve consistent
performance. Further, all Russian AESA production radars antennas contain
visibly uniformly spaced array elements, LPI and low side lobes have not
known to be achieved in this manner.
The advantage of an LPI radar is that the an enemy RWR will receive its
first warning only when the AMRAAM seeker is locked on, giving the enemy
combatant a few seconds before intercept. All this is achieved by the
APG-77’s transmitting several low energy pulses that are discarded by
enemy RWR as clutter. These low energy returns are then assembled by the
Raptors signal processors and the threat positively identified this
technique is called spread spectrum transmission. The APG-77’s advanced
signal processor is able to render an iSAR image of a moving target this
capability is known to have been available only on dedicated air borne
radars. The reason for this is the sheer processing power needed for
complex calculation using the Doppler shift data was previously not
possible on a small fighter jet sized aircraft it was the domain of larger
dedicated AWACS platforms like E3 and IAF Phalcon.
Indian Air Force, which would acquire 50 single-seater fighters of the
Russian version, would induct another 200 two-seater fighters beginning
from 2016, according to reports.
The PAK FA’s speed limit is 2600 kph, the maximum non-afterburning speed –
2100 kph. The practical range – 4300 km. For comparison, F-22 Raptor’s
speed limit makes up 2410 kph, the maximum non-afterburning speed – 1963
kph, and the practical range – 3219 km. PAK FA’s speed limit is 2600 kph,
the maximum non-afterburning speed – 2100 kph. The practical range – 4300
km. For comparison, F-22 Raptor’s speed limit makes up 2410 kph, the
maximum non-afterburning speed – 1963 kph, and the practical range – 3219
km.
Stealth Parameters
Radar Cross Sections cited (X-band):
• F-22A Front Aspect = 0.0001 m2, Side and Rear Aspect = 0.01 – 0.001 m2
(0.005 used in this analysis);
• F-35A Front Aspect = 0.001 m2, Side and Rear Aspect = 0.01 m2;
• PAK-FA All Aspect = 0.01 m2;
• Su-35-1 Front Aspect= 2 m2.
Thermal Sensors
With the latest IRST technology the Pak -FA can detect F-22 at 70 km and
AMRAM 120 launch.
Radar Parameters:
F-22A APG-77 = published figures (AW&ST - pessimistic);
F-35A APG-81 = published figures (AW&ST - pessimistic);
PAK-FA IRBIS-E N035 Best Case published figures (Tikhomirov NIIP);
Su-35-1 IRBIS-E N035 Worst Case published figures (Tikhomirov NIIP)
Irbis-E can detect and track up to 30 airborne targets at one time at
ranges near 400 kilometres, and attack up to 12. In air-to-surface mode
the Irbis-E provides mapping allowing attacks on a surface target with
precision-guided weapons while scanning the horizon searching for airborne
threats that can be engaged using active radar homing missiles.
Tikhomirov NIIP has provided the ability to spot super-low observable
targets with RCS equal to 0.01 square meters at ranges out to 90
kilometres.
Conclusion
In stealth and radar parameters the F-22 is still better than PAK-FA, In
optical terms the PAK-FA is better than the F-22, but because of radar
this advantageous will be reduced in the next few years. In kinematic
parameter F-22 and PAK-FA are comparable. In price terms of price the
PAK-FA is much cheaper which will mean a big export opportunity and
subsequently greater numbers of adversaries for the F-22 and F-35..
The PAK-FA production model, even if half as effective as the F-22A Raptor
will still yield BVR exchange rates in the order of 50:1 against legacy
fighters.
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