Tuesday, August 25, 2009

Stealthy Sukhois

Stealthy Sukhois: "

Talking about stealth in relation to the Sukhoi Su-27 and its extended family, including the new Su-35S, tends to cause people to fall over in fits of mirth. Like Chandler's Moose Malloy, the basic airplane looks about as inconspicuous as a tarantula on a slice of angel food.

But just about six years ago, in late 2003, Defense IQ managed to persuade a team from the Institute of Theoretical and Applied Electromagnetics (ITAE), part of the Russian Academy of Sciences, to present at a conference on stealth in London. I was a presenter - I don't recall any other journalists being present. It sounded as if the paper was going to be some kind of theoretical snorefest and I didn't expect much from it.

I was wrong. 

The ITAE researchers produced a highly detailed paper showing how the institute had developed radar cross-section (RCS) prediction software, test facilities for measuring the RCS of real aircraft, and a variety of RCS-reduction materials, all with the Su-27 family as the main application. One illustration showed an RCS test on Bort (fuselage number) 708, one of the Su-27M prototypes that were precursors to the Su-35S:


blog post photo


The invaluable Flateric has recently posted my full account here, together with some artwork from the paper. (Ignore the comments from the f-16.net F-35 fans, who have a hard time with words of more than two syllables.) 

According to the paper, the ITAE researchers had found materials that solved the dominant problem in the Sukhoi design:  straight-through inlets to the compressor face, with no line-of-sight blockage. Rather than placing an absorber-treated blocker in front of the engine, as on the Super Hornet, ITAE developed a radar absorbent material (RAM) that could be applied to the first-stage compressor blades. The rest of the RAM suite included a metallic treated canopy and sprayed-on RAM coatings on the missiles. 

ITAE had also experimented with a plasma screen in front of the radar antenna. Details were few - it was possible that it was contained in some kind of dielectric plastic envelope - but it could be switched on and off in tens of microseconds, so that it could be turned off when the radar needed to operate and turned on at other times. Along with RCS-reduction treatments for the exhaust, it seemed less mature than the rest of the technology. 

One year later, the same presenter appeared at IQPCs conference. I asked him if any production aircraft had been modified, and he responded that 'about 100' Sukhois had received RCS-reduction mods. 

Of course, this by no means will render a Sukhoi invisible - and similar measures have been implemented on many aircraft, including F-16s (Have Glass I and II), the Super Hornet and new European fighters. But when you consider that the most recent versions carry a very serious jamming suite, the complexion of the issue changes.

Jamming and RCS reduction are highly synergistic. The 'burn-through' range - the point at which none of my jamming works because the jammer power is less than the scatter from the target - goes down much more quickly with lower RCS than the detection range.

Yes, there are 'home-on-jam' technologies that can be applied to missiles - but if the missiles computer has to match its wits with the agility of the jammer, its a more dicey proposition. New jammers with solid state directional transmitters and digital RF memory (DRFM), which allows you to parrot the incoming signal back in a nanosecond, can give anyone a hard time. 


(Via Ares.)

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