US warns Egypt over Russian Su-35 fighter jets deal

Military aircraft - Post cold war aircraft, including for example B-2, Gripen, F-18E/F Super Hornet, Rafale, and Typhoon.
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marsavian

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Unread post16 Apr 2019, 15:10

swiss wrote:
marsavian wrote:That is not the RCS plot of the Su-35 but a theoretical example of what RCS reduction on a Su-27 would look like.


Yes you are right. But this is what the Su-35 is. A Su-27 with ram coating at the airframe and canopy. Or do you now any other version of the Su-27 in service with ram?
The study is from 2003. A view years bevor the first flight of the Su-35.


Also Ram on the engine fan/ducts and reduced antenna size ultimately led to an order of magnitude difference between Su-27 and Su-35 i.e. ~2 vs ~20 sq m.

https://www.fighter-planes.com/stealth2.htm

Russian stealth researchers have developed materials and techniques that can reduce the head-on radar cross-section (RCS) of a Sukhoi Su-35 fighter by an order of magnitude, halving the range at which hostile radars can detect it. The research group - working with Sukhoi, but based at the Institute for Theoretical and Applied Electromagnetics (ITAE) at the Russian Academy of Sciences in Moscow - has performed more than 100 hours of testing on a reduced-RCS Su-35 and has also experimented with the use of plasmas - ionized gases - to reduce RCS.

US and European aircraft manufacturers have used specially developed materials to reduce the RCS of basically non-stealthy aircraft for many years. Notable examples include the Have Glass and Have Glass II modifications to the F-16. However, Russian work in this area was undisclosed until ITAE researchers presented a paper to a conference on stealth in London in late October 2003, which was organized by the International Quality and Productivity Centre.

According to the ITAE presentation, Russian researchers have developed mathematical tools that can calculate scattering from complex configurations, such as an Su-35 carrying a full external missile load, by breaking them down into small facets and adding the effects of edge waves and surface currents. The antennas are modelled separately and then are added to the entire RCS picture.

"A problem of huge size" is how the researchers describe the Su-35 inlet, with a straight duct that provides direct visibility to the entire face of the engine compressor. The basic solution has been to apply ferro-magnetic radar absorbent material (RAM) to the compressor face and to the inlet duct walls, but this involves challenges. The researchers note: the material cannot be allowed to constrict airflow or impede the operation of anti-icing systems and must withstand high-speed airflows and temperatures up to 200°C. The ITAE team has developed and tested coating materials that meet these standards. A layer of RAM between 0.7mm and 1.4mm thick is applied to the ducts and a 0.5mm coating is applied to the front stages of the low-pressure compressor, using a robotic spray system. The result is a 10-15dB reduction in the RCS contribution from the inlets.

The modified Su-35 also has a treated cockpit canopy which reflects radar waves, concealing the high RCS contribution from metal components in the cockpit. ITAE has developed a plasma-deposition process to deposit alternating layers of metallic and polymer materials, creating a coating that blocks radio-frequency waves, is resistant to cracking and crazing and does not trap solar heat in the cockpit. The plasma-coating process is then carried out robotically in a 22 m3 vacuum chamber.

ITAE and its partners have also developed plasma-type technology for applying ceramic coatings to the exhaust and afterburner. The conference video also showed the use of hand-held sprays to apply RAM to R-27 air-to-air missiles.


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swiss

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Unread post16 Apr 2019, 17:14

marsavian wrote:Also Ram on the engine fan/ducts and reduced antenna size ultimately led to an order of magnitude difference between Su-27 and Su-35 i.e. ~2 vs ~20 sq m.



Well the Russian researchers can tell a lot on a conference. :wink: The study is from the same year and say 50 % lower RCS. And has the same RCS Reduces as they claim at the conference.

Which is much more realistic. Boeing and Dassault claims also 1 order of magnitude lower RCS for the Super hornet ( compare to the F/A-18) and Rafale( compare to the Mirage 2000). And they did a lot more than to spray some ram coating on the airframe. New air intakes, Radarblockers, S-ducts, serrated patterns on the trailing edges of the wings and canards. Use of composite materials. The Su-35 has nothing of this RCS reducing features compare to the Su-27/30.The Engines blades of the Su-35 are still fully visible. Which increase the frontal RCS a lot.

BTW if the Su-35 has a RCS of 2 m2 that would be nearly same level than the Su-57. Which has a RCS of 0.1-1 m2. :wink:
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marsavian

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Unread post16 Apr 2019, 17:27

One is a theoretical study on which you are eyeballing and averaging the end result of very thick dashed lines, the other is actual detailed work on the airframe giving precise numbers. That Su-57 number is also for the frontal shape alone before RAM. RAM can reduce your RCS by order(s) of magnitude if you are prepared to take the weight hit.

A layer of RAM between 0.7mm and 1.4mm thick is applied to the ducts and a 0.5mm coating is applied to the front stages of the low-pressure compressor, using a robotic spray system. The result is a 10-15dB reduction in the RCS contribution from the inlets.
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Unread post16 Apr 2019, 17:54

marsavian wrote:One is a theoretical study on which you are eyeballing and averaging the end result of very thick dashed lines, the other is actual detailed work on the airframe giving precise numbers.


Well that's your opinion. You can see at the diagram 1 is bit more then 20m2. 2 its nearly 10m2. And this was posted years ago in this forum. So its not only my opinion. :wink:

viewtopic.php?f=55&t=16457&start=450

viewtopic.php?f=55&t=16457&start=435

marsavian wrote:That Su-57 number is also for the frontal shape alone before RAM. RAM can reduce your RCS by order(s) of magnitude if you are prepared to take the weight hit.


Who said that?

And as far as i know, shape is the most imported factor for stealth.

And you really believe sukhoi can do the same RCS reduction ( 1 order of magnitude) like Boeing and Dassault only with ram coating. And full visible engines blades. Boeing who developed F-22 btw.
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Unread post16 Apr 2019, 20:20

swiss wrote:Who said that?


http://www.scielo.br/pdf/jatm/v8n1/1984 ... 1-0040.pdf

And you really believe sukhoi can do the same RCS reduction ( 1 order of magnitude) like Boeing and Dassault only with ram coating.


You can get an order of magnitude RCS reduction with any RAM as long as you are prepared to take the weight hit i.e. F-117's RAM overcoat cost it 2000lb of weight. The Russians have already said they got 10-15 dBsm less from the standard inlets which is your order of magnitude reduction. Shape gets you lower RCS without a weight penalty which is why it's the first order design point for stealth aircraft but RAM can get you there too, why do you think F-22/F-35 RAM maintenance is so crucial for their day to day running, it's the RAM that smooths out the big spikes at some angles leading to a more uniform RCS reduction beyond the basic LO shape.
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Unread post16 Apr 2019, 23:07

marsavian wrote:
swiss wrote:Who said that?


http://www.scielo.br/pdf/jatm/v8n1/1984 ... 1-0040.pdf


And where in this study its mentioned that the prototypes of the Su-57 have an RCS of 0.5 m2 without ram coating. And if, from where should they know that?

BTW the patens about the stealth features from the Su-57 from sukhoi says the opposite.

https://web.archive.org/web/20141023114 ... -published

with the intention being to reduce the size of the RCS in the T-50 to an "average figure of 0.1-1 m 2 ".

In common with other low observable aircraft designs, this reduction is achieved throught the use of radar-absorbing and radar-shielding materials and coatings, panel shaping (especially around the air intakes) and in the design of the junctions between moving elements, such as flaps and hatches.


You see here also what an effort they did, to reduce the RCS of under 1m2.

marsavian wrote:You can get an order of magnitude RCS reduction with any RAM as long as you are prepared to take the weight hit i.e. F-117's RAM overcoat cost it 2000lb of weight. The Russians have already said they got 10-15 dBsm less from the standard inlets which is your order of magnitude reduction. Shape gets you lower RCS without a weight penalty which is why it's the first order design point for stealth aircraft but RAM can get you there too, why do you think F-22/F-35 RAM maintenance is so crucial for their day to day running, it's the RAM that smooths out the big spikes at some angles leading to a more uniform RCS reduction beyond the basic LO shape.


Well you give the answer for you self. 2000lb of weight increase. So that would mean the Su-35 must be clearly heavier then the Su-30. which is not the case. According this study ( 4 last page) To reduce RCS about -10dbsm vs 8-12 Ghz (frequency where a fighter Radar operates) you need a layer of 9,5mm .

https://web.archive.org/web/20140221205 ... h_Part.pdf

And you think the Russian can do this with a coating thickness of roughly 1mm or even lower. Thy are over 2 decades behind the U.S. in stealth technology. In even this would be true. The visible engine blades would ruin your RCS reduction in the frontal hemisphere. Why do you think latest 4 gen like EF, SH or Rafale have hidden engine faces? If the russian ubercoating is so good, the could spray it on there airframes and the -10-15dbsm reduction is done. No S-duct, no inlet changes, no composite materials and no serrated patterns. Or the the USAF could used it on there F-15 to reduce the RCS from 20 to 1 m2.

Its an open secret, that the russian are very optimistic, with the capability of there military products.
Last edited by swiss on 17 Apr 2019, 09:46, edited 1 time in total.
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Unread post17 Apr 2019, 03:29

As we all know spinning turbofan blades are like a bright beacon of light in regards to radar returns. I dont care what kind of RAM you got, you see those big fellas spinning- youre a glowing target.
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Unread post17 Apr 2019, 13:40

I believe there was some RCS reduction done on the SU-35, just not as much as the Russians would have us believe. I also think they're continuing to do that on the SU-57. The problem is that they started with a super-maneuverable airplane, then attempted to bolt stealth onto it.

Whereas the F-22 and F-35 started with stealth as a given, its most important attribute. The fact that both are super-maneuverable is a testament to the engineers working on them.

Had the Russians done the same, the PAK FA would have taken a lot longer IMO. They knew going that route would result in delays, if not outright never getting there. So they engineered what they understood, what their fighters are best known for. I think on balance, they've done OK.

Problem being that 2nd best in air combat = Dead. There's no silver medal...
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