PAK-FA Cockpit, Avionics and Radar Design
Tikhomirov NIIP AESA on display at MAKS 2009 (© 2009, Miroslav Gyűrösi).
Russian statements on the core avionic suite intended for the PAK-FA have not been particularly revealing 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 transceivers.
VLO aperture design has been a source of ongoing difficulties in design, as structural mode RCS and impedance mismatches against the aperture can result in prominent RCS flare spots, which can be disastrous in a VLO design. Even a small RCS contribution can be problematic, given the number of apertures required to support especially wideband all aspect ESM/RFS sensors.
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 rated antennas, VLO rated instrumentation ports and probes, and proven albeit older VLO materials technology.
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”
.
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 [
] could be installed in the leading edges of the LEX or wings, using a frequency selective bandpass radome. 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 array
.
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 derivative of the ergonomically well fashioned Su-35S glass cockpit would be used - this design employs a pair of large AMLCD panels to emulate the projector based arrangement in the F-35, but with more robust fault tolerance, greater simplicity in design, yet similar ease in operation.
Russian sources claim that the new OKB Aviaavtomatika HOTAS 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.
OKB Aviaavtomatika HOTAS 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 exploiting datalink 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 design 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 cheek arrays are planned for. The design is also claimed to have been integrated with an existing BARS/Irbis radar for testing and design validation purposes.
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 AESA
.
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 ~10W 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 Su-27/30/35 Flankers.
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 technology is available to the Russian industry to develop and implement LPI equipment.
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.
Su-35S Electro-Optical System turret fitted to PAK-FA prototype (© 2009 Vitaliy V. Kuzmin).
Su-35S cockpit (Sukhoi brochure).
أخواني هل هذا المحرك والردار للباك فا أم للسوخوي 35 ؟؟؟؟؟؟
مع خااااااااالص تحيااااااااااااتي أخواني الأعزاء .,.,.,.,.
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