Sukhoi Su-57 / T-50 / PAK FA - flight testing and development Part II [2012-current]

[Evgeniy]

Actually, it all makes sense: first tests of the modernized, second stage or call it what we want Su-57 in 2022, finish of the tests by 2024, and possibly they can be performed on a production unit as you say.

Well, that's exactly what I mean.

 

[flanker]

No word either on by far the biggest stealth problem on the Su-57, the lack of edge alignment and serrations on panel joints.

What? Where do you see lack of edge alignment on T-50? Su-57 is coated by thicc RAM and panels that are to be accessed a lot are serrated. Is it perfect solution? Probably not, but it probably gets 99,9% there with far less complexity and cost.

EDIT; In other news, it is probably nothing, but in case it isnt nothing... Zvezda's 1/48 Su-57 with weapon bays and three ejectors...

 

[AGS-1787]

Why don't we wait to see what the new prototype looks like before calling it crappy? it is really pointless to eye-meter the stealth of a prototype. Let's not forget the Russians are building this thing to satisfy their needs and not the Western airforces. Honestly, do you imagine an f-22 type operating in Russia? Left outside during the cold winter and then taxing in runways full of grass, rocks, ice, and then have some young kids work on it? I don't see it happening or staying pristine. Maybe they deem it stealthy enough to be practically useful without breaking the bank, especially since they don't spend the same amount of money other countries do. I also think this is their new "su-27" and they hope to evolve to new "su-30, 35, 34s" levels.

 

[Trident]

What? Where do you see lack of edge alignment on T-50? Su-57 is coated by thicc RAM and panels that are to be accessed a lot are serrated. Is it perfect solution? Probably not, but it probably gets 99,9% there with far less complexity and cost.

The joints marked on the following photos are gaps between separate panels (as opposed to rows of fasteners within the bounds of an individual panel) and as such should be aligned/serrated. As you say, they ARE coated with RAM on the most recent prototypes, but the F-22, F-35 and J-20 use both alignment and RAM for such seams.







[Two things to note on the final image: 1) it shows something that the Su-57 does do remarkably well, especially compared to the J-20 - its top surface is largely comprised of a small number of HUGE panels, with correspondingly few edges. 2) this is the first airframe, from mid-fuselage aft the final prototypes differ significantly, but I couldn't find a decent photo - as far as I can tell from the stage II static test specimen, alignment did not get any better though.]

EDIT; In other news, it is probably nothing, but in case it isnt nothing... Zvezda's 1/48 Su-57 with weapon bays and three ejectors...

Would be good news!

 

[stealthflanker]

No word either on by far the biggest stealth problem on the Su-57, the lack of edge alignment and serrations on panel joints.

EDIT; In other news, it is probably nothing, but in case it isnt nothing... Zvezda's 1/48 Su-57 with weapon bays and three ejectors...

Paralay must be happy XD

 

[Samoderzhets]

What? Where do you see lack of edge alignment on T-50? Su-57 is coated by thicc RAM and panels that are to be accessed a lot are serrated. Is it perfect solution? Probably not, but it probably gets 99,9% there with far less complexity and cost.

The joints marked on the following photos are gaps between separate panels (as opposed to rows of fasteners within the bounds of an individual panel) and as such should be aligned/serrated. As you say, they ARE coated with RAM on the most recent prototypes, but the F-22, F-35 and J-20 use both alignment and RAM for such seams.

In Sukhoi's patent about radar signature management solutions on PAK FA the solution they offer for this exact problem is the use of conductive sealants on these gaps. The conductive sealant allows the electromagnetic wave to pass the gap without causing scattering behavior.

The relevant part:

Использование токопроводящих герметиков позволяет обеспечить электрическую проводимость между отдельными конструктивно-технологическими элементами планера, что, в свою очередь, позволяет исключить составляющую в ЭПР самолета «неоднородностей» (типа щель, стык) за счет того, что при отсутствии электрических неоднородностей отсутствует рассеяние поверхностных ЭМ волн.

https://findpatent.ru/patent/250/2502643.html
© , 2012-2020

And a google translation of it:

The use of conductive sealants makes it possible to ensure electrical conductivity between individual structural and technological elements of the airframe, which, in turn, eliminates the component in the RCS of the aircraft of "inhomogeneities" (such as a gap, a joint) due to the fact that in the absence of electrical inhomogeneities there is no scattering of surface EM waves

 

[GARGEAN]

Naah, what patents? It is not copying western approach - means it is inferior.

 

[Ronny]

In Sukhoi's patent about radar signature management solutions on PAK FA the solution they offer for this exact problem is the use of conductive sealants on these gaps. The conductive sealant allows the electromagnetic wave to pass the gap without causing scattering behavior.

The relevant part:

Использование токопроводящих герметиков позволяет обеспечить электрическую проводимость между отдельными конструктивно-технологическими элементами планера, что, в свою очередь, позволяет исключить составляющую в ЭПР самолета «неоднородностей» (типа щель, стык) за счет того, что при отсутствии электрических неоднородностей отсутствует рассеяние поверхностных ЭМ волн.

https://findpatent.ru/patent/250/2502643.html
© , 2012-2020

And a google translation of it:

The use of conductive sealants makes it possible to ensure electrical conductivity between individual structural and technological elements of the airframe, which, in turn, eliminates the component in the RCS of the aircraft of "inhomogeneities" (such as a gap, a joint) due to the fact that in the absence of electrical inhomogeneities there is no scattering of surface EM waves

Isn't conductive tape at the gap a feature of all stealth aircraft?

 

[LMFS]

In Sukhoi's patent about radar signature management solutions on PAK FA the solution they offer for this exact problem is the use of conductive sealants on these gaps. The conductive sealant allows the electromagnetic wave to pass the gap without causing scattering behavior.

Excellent find, I was mentioning exactly this option in Trident's "Su-52" thread as was also apparently explored by Northrop in the past. What would be the point for Sukhoi to serrate the edges of doors that cannot be sealed on the ground and leave other covers (pretty much all of the plane's seams according to him) scattering freely? I understand the sealants are not external but form a layer between the fuselage and the covers, since I have not seen tape covering those gaps, does anybody know better? In fact the solution seems more elegant than the Western one...

BTW, re. the IRST issue also in discussion where I proposed its aperture to be transparent to RF instead of a spherical reflector as it is widely claimed: we know it has RAM on the backside, but why would they employ RAM inside if the glazing was reflecting RF? This is elementary...

Such basic thoughts as those two above are normally not even considered when criticising the plane, we instead talk about "reducing" Su-57's RCS, when we have no idea how big or small it is to start with...

 

[Cannonfodder43]

In Sukhoi's patent about radar signature management solutions on PAK FA the solution they offer for this exact problem is the use of conductive sealants on these gaps. The conductive sealant allows the electromagnetic wave to pass the gap without causing scattering behavior.

Excellent find, I was mentioning exactly this option in Trident's "Su-52" thread as was also apparently explored by Northrop in the past. What would be the point for Sukhoi to serrate the edges of doors that cannot be sealed on the ground and leave other covers (pretty much all of the plane's seams according to him) scattering freely? I understand the sealants are not external but form a layer between the fuselage and the covers, since I have not seen tape covering those gaps, does anybody know better? In fact the solution seems more elegant than the Western one...

BTW, re. the IRST issue also in discussion where I proposed its aperture to be transparent to RF instead of a spherical reflector as it is widely claimed: we know it has RAM on the backside, but why would they employ RAM inside if the glazing was reflecting RF? This is elementary...

Such basic thoughts as those two above are normally not even considered when criticising the plane, we instead talk about "reducing" Su-57's RCS, when we have no idea how big or small it is to start with...

I find myself quite surprised that I never heard of this solution to the non serrated panel gaps. Might be quite a simple solution and explain Sukhoi's choice in this matter. I don't think it may be enough though.

Such basic thoughts as those two above are normally not even considered when criticising the plane, we instead talk about "reducing" Su-57's RCS, when we have no idea how big or small it is to start with...

Much of mine and I am assuming others on this site's familiarity with VLO design principles comes from observations of Western stealth aircraft and how they implement such features, combined with open literature on the subject. Principles like a near fanatical adherence to edge alignment + RAM are very easy to see and understand, which when combined with relatively open sources regarding its success informs us of such VLO design philosophy.

So naturally we apply the same scrutiny to the Su-57 and are puzzled by what we see. The seeming incongruent choices regarding finer edge alignment of the panels, lower aft engine nacelles and additional serrations puzzles us when one also see's the work put into reducing the RCS by said principles. As seen from the front aspect and elsewhere.

From my own informed observations and from reading of what sources I can like Air Power Australia (their analysis is literally the only comprehensive one I could find on it) and C.MANO database, I generally agree that its RCS is actually not that bad. No matter what people misconstrue from the "Average 1 sq-meter RCS) that people take out of context instead of looking at the facts.

However only the Russians know for sure and they are tight lipped on this. So we are left with educated guesses and only with the knowledge that there is so much we don't know. And what we do know and learn can't really be verified satisfactorily. The Russians may very well have solutions to these "problems" that we don't know or don't believe in. They are not dumb after all.

That said the Indian's put their FGFA on hold and insufficient stealth was one of the stated reasons. So maybe Western criticisms may have some merit but we have no idea how stealthy of an aircraft India wants. And heavens knows if a partial or full Trident optimization of the Su-57 would bring it up to Western or let alone Indian Standards. (IMO it would though)

 

[Trident]

Isn't conductive tape at the gap a feature of all stealth aircraft?

Exactly - even on aircraft which are not nominally full VLO designs:



Conductive sealants are NOT a substitute for alignment/serration (even on the only semi-LO Super Hornet shown above, a large fraction of the relevant gaps is aligned).

 

[TR1]

That said the Indian's put their FGFA on hold and insufficient stealth was one of the stated reasons. So maybe Western criticisms may have some merit but we have no idea how stealthy of an aircraft India wants. And heavens knows if a partial or full Trident optimization of the Su-57 would bring it up to Western or let alone Indian Standards. (IMO it would though)

India never had access to the program to such a level where they could asses its RCS or levels of stealth.

Stealth inadequacy was just part of a litany of reasons made up by Indian media, when the reality is- they couldn't afford it last decade, and the bird would not have been ready back then for purchase in any case. They did not have the means to add to its development either.

Just look at their drawn out Rafale purchase.

 

[LMFS]

@Cannonfodder43 :

I generally find very reasonable what you say and agree with it, though there are a couple of issues I think deserve comment:

I don't think it may be enough though.

How much it is enough? You know, this is a very complex issue that depends not in some boutique values but in some specific detection ranges under certain conditions, aspects, frequencies, illumination power and what not. It is not some schoolyard discussion about if US' way is VLO and Russia's is not.

So naturally we apply the same scrutiny to the Su-57 and are puzzled by what we see. The seeming incongruent choices regarding finer edge alignment of the panels, lower aft engine nacelles and additional serrations puzzles us when one also see's the work put into reducing the RCS by said principles. As seen from the front aspect and elsewhere.

Sure, and I think that being sceptical is perfectly legitimate, I am myself puzzled about the round section of the nacelles too, but being categorical is IMHO out of place, we do not know the real performances of the design solutions taken and compromises incurred by US or Russia. Maybe one solution is better in X band but the other is better overall over a broader band, or a specific approach was taken like using a certain material that provides destructive interference at a certain wavelength at a given critical spot. There are simply too many complexities involved to know from the outside.

That said the Indian's put their FGFA on hold and insufficient stealth was one of the stated reasons.

Was that ever stated officially or were "sources" quoted?

Conductive sealants are NOT a substitute for alignment/serration (even on the only semi-LO Super Hornet shown above, a large fraction of the relevant gaps is aligned).

Same question as above, what is the difference in global RCS values at what frequencies and aspects? How do they impair the plane's tactical performance in the designated conditions? Do we at least have a technically supported dB estimation of the difference they make?

 

[Firefinder]

Same question as above, what is the difference in global RCS values at what frequencies and aspects? How do they impair the plane's tactical performance in the designated conditions? Do we at least have a technically supported dB estimation of the difference they make?

The second line of questioning is one that is often forgotten about.

How maintainable is edge alignment/serrations verses Sealants?

Cause even with thd uder update user friendly RAM tech on the F35 it is STILL basically a DEPOT LEVEL job to redo and the like. And is still a PITA to maintain and work around.

Most western countries do expect to be able to rotate out the F35 for such repairs and the like with an European Base one planning on bring built in a few years.

If the sealants are easier to maintain/do restealthing at lower levels I can see Russia choosing those out of pragmatism.

IE they know they can make a SU57 that can out stealth the Raptor but dont cause they know they cant maintain it to that level. So they dont bother, they just make the plane STEALTH ENOUGH to be deadly and add advantance countermeasures to cover the rest.

 

[Acatomic]

Whenever I see talk about stealth I always remember this post from 12 years ago, especially the part at the end . Some of you may remember him:

RSM55

The PAK-FA Saga Episode VI

Goodbye Raptor :( Hello PAK-FA :)...

www.key.aero

My final words in this thread

Dear all,
since the beginning of this Saga, I have tried to post only reliable, unbiased and truthful information about the programme of the "5th gen. fighter", PAK FA, T-50, whatever it might be called and is called by the "community" and the gullible media and "experts". Obviously, because of the aforementioned ethical prerequisites, I haven't posted that much.
For the time being, I am relatively proud to say that none of my "supputations", suppositions and information that I have provided has proven untrue. Indeed, it seems that Zelin himself confirms (for example) the all-aspect sensor fusion I have talked about more than a year ago.
I have also written here that the "PAK FA" or whatever will be "more like the YF-23 than the F-22". I have also stated that those who expect some kind of flying sauski or Firefox will be disappointed, as the RuAF requirements for the PAK FA differ from USAF requirements for the Raptor. I have also pointed out that the main breakthrough, and the main challenge, of the PAK FA programme will not be new aerodynamics, amazing stealth or incredible overall characteristics, but simply total sensor fusion and the implementation of brand new weapon systems and a very potent sensor/RWR/ECM suite.

Why do I point that out again?
Because this post is going to be my last post on this thread until the subject matter will publicly fly.
Why that?
I am sick and tired of reading speculations and trying to temperate them.
I am sick and tired of seeing artists renderings, some good, some less, being naively discussed as if the honorable person who devised them on his or her PC between 2am and a bottle of Moskovskaya (or Château Rotschild 1956 for that matter, I don't care) had the Sukhoi blueprints next to the keyboard.
And on top of it, I am very, very tired of all the nationalist, pro-Russian, anti-Russian, pseudo-pro-anti-Russian redneck whatever ramblings that seem to enthuse the hon. members of this board much more than thinking about the next word they will use in order to describe their honorable feelings.

My last input:
Russian mass-media are not autocracy-driven, or democratic, or free, or unfree - they are just (for defense matter) mostly lame and incompetent.
Zelin has talked about 3 "5th gen. programmes".
He meant: PAK FA, PAK DA, future land-attack UCAV. No it's not the Skat.
He did not mention any "august 2009" deadline. The journalists made that up.

The said programme is doing well and progressing fast.
The airframes are all but ready.
Integration will be a big challenge, but I'm confident.
And again, "the first flight will not be the first"

Now.
If I wouldn't be so upset about what I read and if I would claim some recognition and respect, I would certainly humbly ask the moderators to close the thread till next summer at least because it's getting nowhere.
But as I'm certainly not - please go on and speculate further and further - the sky's the limit.
Till you see the real thing you all dream about, sometime next year, and then start an infinite number of threads like "PAK FA (it will be Su-.. ... by the time) vs F-22", "PAK FA is a hoax" or "PAK FA is not really stealthy (for flamers)".

All in all, God bless you all, let 2009 be better than the pundits say it will be and clear skies ahead.

It's nice that he talked about Okhotnik before that was even a thing.

 

[Trident]

Well, there's a lot of room between "the Su-57 is not stealthy" and "it doesn't quite match the RCS of other 5th generation designs".

There indeed are people who implicitly refuse to believe it is stealthy at all, by taking the average RCS value of 0.5m² (which I'm still uncertain if it can even be traced back to a reputable source to begin with) out of context and comparing it to the frontal values of other aircraft. That's patently nonsense, as this would make it worse than some 4.5 generation fighters like Rafale, Gripen and the Super Hornet which are claimed to achieve 0.1m² when clean. With the Su-57, for all its faults, having internal weapons bays and much better shaping for LO than these fighters, that is clearly not a tenable position.

 

[Cannonfodder43]

That said the Indian's put their FGFA on hold and insufficient stealth was one of the stated reasons. So maybe Western criticisms may have some merit but we have no idea how stealthy of an aircraft India wants. And heavens knows if a partial or full Trident optimization of the Su-57 would bring it up to Western or let alone Indian Standards. (IMO it would though)

India never had access to the program to such a level where they could asses its RCS or levels of stealth.

Stealth inadequacy was just part of a litany of reasons made up by Indian media, when the reality is- they couldn't afford it last decade, and the bird would not have been ready back then for purchase in any case. They did not have the means to add to its development either.

Just look at their drawn out Rafale purchase.

Indian procurement is something of a soap drama, such delays and cancellations are not unexpected. Hell for me they are a source of entertainment.

That said I am curious as to the level of Indian involvement in the program. I have not been able to find any hard sources that tell how much real access they had other than other news articles detailing their list of reasons for dropping out. or just official announcements of budgeting and tech sharing and the like. Of which again list no sources themselves.

 

[Cannonfodder43]

@LMFS thank for being so considerate in your response. If this cordiality is the level of typical interactions here than I am in the right place.

How much it is enough? You know, this is a very complex issue that depends not in some boutique values but in some specific detection ranges under certain conditions, aspects, frequencies, illumination power and what not. It is not some schoolyard discussion about if US' way is VLO and Russia's is not.

In regards to it not or being enough, my opinions remain "semi-informed" as I would say. The obsessive level of American effort in reducing RCS with such measures remains my baseline so I remain sort of skeptical of the Russian method. I am however quite open to change in this area for its ever apparent that they know more than me. And the Russian aims and goals n this area are complex and informed by the very factors you mention. I don't think its as bad as many think but it does leave me scratching my head while I look for more. There is simply too much I don't know.

Sure, and I think that being sceptical is perfectly legitimate, I am myself puzzled about the round section of the nacelles too, but being categorical is IMHO out of place, we do not know the real performances of the design solutions taken and compromises incurred by US or Russia. Maybe one solution is better in X band but the other is better overall over a broader band, or a specific approach was taken like using a certain material that provides destructive interference at a certain wavelength at a given critical spot. There are simply too many complexities involved to know from the outside.

In regards to the round nacelles and solutions I don't think I tried to be categorical on that topic, my apologies for being unclear in that. Again it relates to my points stated above. I am only going on what I know while keeping in mind that I don't have all the details at hand to understand the Russian design. Its just that the two different approaches of RCS reduction, Edge Alignment a la American philosophy and Russian materials and conductive paneling seals produce something that looks unusual to my American eyes. When one looks at the J-20 one is only left with questions that need answers.

Was that ever stated officially or were "sources" quoted?

Its only what I could find in reporting. And the reporting itself never names the sources other than the vague descriptions of origin. I would like to know more of the Indian involvement in the FGFA and its true extent.

 

[haavarla]

Why don't we wait to see what the new prototype looks like before calling it crappy? it is really pointless to eye-meter the stealth of a prototype. Let's not forget the Russians are building this thing to satisfy their needs and not the Western airforces. Honestly, do you imagine an f-22 type operating in Russia? Left outside during the cold winter and then taxing in runways full of grass, rocks, ice, and then have some young kids work on it? I don't see it happening or staying pristine. Maybe they deem it stealthy enough to be practically useful without breaking the bank, especially since they don't spend the same amount of money other countries do. I also think this is their new "su-27" and they hope to evolve to new "su-30, 35, 34s" levels.

There are talks that Su-57 will indeed be sheltered from harsh climate conditions within Russia. What kind of shelters remains to be seen.
Do we even know where the first Su-57 Air Regiment will get stood up? Dzemgi, same as first Su-35S?

 

[Edi213009]

Whenever I see talk about stealth I always remember this post from 12 years ago, especially the part at the end . Some of you may remember him:

RSM55

The PAK-FA Saga Episode VI

Goodbye Raptor :( Hello PAK-FA :)...

www.key.aero

My final words in this thread

Dear all,
since the beginning of this Saga, I have tried to post only reliable, unbiased and truthful information about the programme of the "5th gen. fighter", PAK FA, T-50, whatever it might be called and is called by the "community" and the gullible media and "experts". Obviously, because of the aforementioned ethical prerequisites, I haven't posted that much.
For the time being, I am relatively proud to say that none of my "supputations", suppositions and information that I have provided has proven untrue. Indeed, it seems that Zelin himself confirms (for example) the all-aspect sensor fusion I have talked about more than a year ago.
I have also written here that the "PAK FA" or whatever will be "more like the YF-23 than the F-22". I have also stated that those who expect some kind of flying sauski or Firefox will be disappointed, as the RuAF requirements for the PAK FA differ from USAF requirements for the Raptor. I have also pointed out that the main breakthrough, and the main challenge, of the PAK FA programme will not be new aerodynamics, amazing stealth or incredible overall characteristics, but simply total sensor fusion and the implementation of brand new weapon systems and a very potent sensor/RWR/ECM suite.

Why do I point that out again?
Because this post is going to be my last post on this thread until the subject matter will publicly fly.
Why that?
I am sick and tired of reading speculations and trying to temperate them.
I am sick and tired of seeing artists renderings, some good, some less, being naively discussed as if the honorable person who devised them on his or her PC between 2am and a bottle of Moskovskaya (or Château Rotschild 1956 for that matter, I don't care) had the Sukhoi blueprints next to the keyboard.
And on top of it, I am very, very tired of all the nationalist, pro-Russian, anti-Russian, pseudo-pro-anti-Russian redneck whatever ramblings that seem to enthuse the hon. members of this board much more than thinking about the next word they will use in order to describe their honorable feelings.

My last input:
Russian mass-media are not autocracy-driven, or democratic, or free, or unfree - they are just (for defense matter) mostly lame and incompetent.
Zelin has talked about 3 "5th gen. programmes".
He meant: PAK FA, PAK DA, future land-attack UCAV. No it's not the Skat.
He did not mention any "august 2009" deadline. The journalists made that up.

The said programme is doing well and progressing fast.
The airframes are all but ready.
Integration will be a big challenge, but I'm confident.
And again, "the first flight will not be the first"

Now.
If I wouldn't be so upset about what I read and if I would claim some recognition and respect, I would certainly humbly ask the moderators to close the thread till next summer at least because it's getting nowhere.
But as I'm certainly not - please go on and speculate further and further - the sky's the limit.
Till you see the real thing you all dream about, sometime next year, and then start an infinite number of threads like "PAK FA (it will be Su-.. ... by the time) vs F-22", "PAK FA is a hoax" or "PAK FA is not really stealthy (for flamers)".

All in all, God bless you all, let 2009 be better than the pundits say it will be and clear skies ahead.

It's nice that he talked about Okhotnik before that was even a thing.

I miss him, he was a mine of reliable information.He got big time pissed there....what was both boring and amusing is when he would call Bs to Garry B.
Garry B is now a moderator at russiadefence, i simply ignore his posts,he is still ridiculous

 

[overscan (PaulMM)]

All the evidence points to a basic airframe configuration optimised for low RCS from the front only, with lesser regard for other angles.

The existing Su-57 airframes don't show the attention to detail needed for a truly low (VLO) RCS. We have no idea what the requirement was however - presumably it meets the requirements in the area.

 

[TomcatViP]

Let's not forget that this airframe can "crab" efficiently, widening somewhat the frontal aspect effect to a larger cone.

 

[flanker]

All the evidence points to a basic airframe configuration optimised for low RCS from the front only, with lesser regard for other angles.

The existing Su-57 airframes don't show the attention to detail needed for a truly low (VLO) RCS. We have no idea what the requirement was however - presumably it meets the requirements in the area.

Considering the detailed changes between Phase 1 and Phase 2 frames (note the main weaponbay doors for instance) they have good understanding of the details and where they are worth it. According to the now chief engineer of the project, T-50 exceeded the stealth requirements. And someone who has worked on the stealth of F-22 and F-35 claimed T-50 is "metal marble class". Personally i dont think T-50 is as stealthy as F-22 - but i think it is stealthier than what most people give it credit for being.

 

[litzj]

Three YouTube video which can show some details of Su-57.
(It seems like video documentary from Russia)
Not much informative, but enjoyable Eye-candy.
Part_1
Part_2
Part_3

 

[LMFS]

Considering the detailed changes between Phase 1 and Phase 2 frames (note the main weaponbay doors for instance) they have good understanding of the details and where they are worth it. According to the now chief engineer of the project, T-50 exceeded the stealth requirements. And someone who has worked on the stealth of F-22 and F-35 claimed T-50 is "metal marble class". Personally i dont think T-50 is as stealthy as F-22 - but i think it is stealthier than what most people give it credit for being.

The real issue IMO is that narrow band stealth has already been defeated, so what is the point of going for impossibly low RCS values in X band, with fundamental effects on other aspects of the plane's performance, when you are being detected and even tracked otherwise? What does (hypothetically since no one here has measured either plane's RCS) gain a F-22 or F-35 from seeing the Su-57 say 5 km before the Sukhoi detects them, if they have been already glowing for hours on the screens of OTH and low frequency radars?

The existing Su-57 airframes don't show the attention to detail needed for a truly low (VLO) RCS.

I don't know how you discern that, but in any case we have not seen any serial Su-57 so let's wait a bit, probably in a few days we will have the answer.

 

[overscan (PaulMM)]

The real issue IMO is that narrow band stealth has already been defeated, so what is the point of going for impossibly low RCS values in X band, with fundamental effects on other aspects of the plane's performance, when you are being detected and even tracked otherwise? What does (hypothetically since no one here has measured either plane's RCS) gain a F-22 or F-35 from seeing the Su-57 say 5 km before the Sukhoi detects them, if they have been already glowing for hours on the screens of OTH and low frequency radars?

OTH and low frequency radars are difficult to fit in aircraft and near impossible to fit in missile seekers, I'd say. Finding something isn't the same as shooting it down.

you make an assumption that F-22 and F-35 are only stealthy in X band. The only stealth aircraft with serious optimisation for a specific band was F-117. From B-2 onward, it's been more balanced.

Secondly, low frequency radars are imprecise, and historically good only for early warning. OTH are similar - good for knowing the Russian bombers are on their way, not so good at telling you precisely where. Modern processing can improve things but I think the jury is still out on real world examples.

In your specific example, say the Su-57 is 0.01 sq m RCS and the F-22 is 0.001 sq m RCS. This will translate to a 44% reduction in detection range for the Su-57 compared to the F-22 given identical radars. A lower RCS means ECM is potentially more effective, and also will likely affect missile seekers more. There may even be a floor value below which the seeker cannot ever lock on. In this case, you are down to IR missiles only.

So, even if the Su-57 pilot knows roughly where the F-22 is from early warning radars, the F-22 pilot will have the advantage of knowing exactly where the Su-57 earlier.

Lastly, "narrow band stealth has been defeated" when all aircraft, SAMs, ground radars in service are able routinely to track and shoot down stealth aircraft. I think we are very far from that world. Even if Russia develops such a radar and SAM and aircraft and AAM today, until every threat nation buys them, then stealth still has value.

 

[Acatomic]

Eighter way, i'd see this as a future concept. For now, Okhotnik would have to work properly with a Ground Controller, and then move on to a Air assets, like AWACS. To have a singel crew jet controlling this thing seems too early.

I don't think this is just a future concept but an actual requirement set by RuAF for Okhotnik project. You have proof in 053 airframe and the fact that only one month after the first flight, Okhotnik was already doing MUM-T with Su-57 (055 airframe). Due to autonomous nature there is no need for control by pilot.

 

[Acatomic]

@overscan (PaulMM)

LMFS was talking about ground based OTH radar.

Fun fact: proper IADS also includes fighter aircraft

 

[overscan (PaulMM)]

I am aware, I am just saying if you rely on low frequency radar you won't be shoehorning them into AAM or SAM seekers. In which case, you'll be shooting with IR missiles or guns.

 

[LMFS]

you make an assumption that F-22 and F-35 are only stealthy in X band. The only stealth aircraft with serious optimisation for a specific band was F-117. From B-2 onward, it's been more balanced.

They are visible in lower frequency radars, that is all is needed to know. Of course they show useful reductions on L band and even below, but that is simply not enough today.

Secondly, low frequency radars are imprecise, and historically good only for early warning. OTH are similar - good for knowing the Russian bombers are on their way, not so good at telling you precisely where. Modern processing can improve things but I think the jury is still out on real world examples.

Historically is the right word. Radars today use complex adaptive digital processing that make useless all that is known from historical performance of analog radars. Nor even talking about interferometric radars like the ones being developed in China to increase the precision at low frequencies. On the other hand, no cm-precise guidance is needed when missiles have seekers themselves.

In your specific example, say the Su-57 is 0.01 sq m RCS and the F-22 is 0.001 sq m RCS. This will translate to a 44% reduction in detection range for the Su-57 compared to the F-22 given identical radars.

Given they use their radars, which is no-go in a fight between stealth fighters.

A lower RCS means ECM is potentially more effective, and also will likely affect missile seekers more. There may even be a floor value below which the seeker cannot ever lock on. In this case, you are down to IR missiles only.

ECM also gives the plane away. And I think you are being really optimistic if you think a maneouvering plane is going to show a RCS of 0.0001 sqm to every opponent every time. This is simply non realistic, even if we accept (no-one has ever proven it) that such RCS is real for some given sweet spots in the frontal aspect. As to the minimum detection floor, do you think a F-35 or F-22 pilot is just going to stay on course in the presence of an incoming missile trusting it will not de detected? Would like to see that... It is perfectly possible that missiles are guided in the best path to get return from the fighter. Coming from above they should get a fair signal from the plane's tail for instance, or line with the wings sweep. Tactics are developed for a reason.

So, even if the Su-57 pilot knows roughly where the F-22 is from early warning radars, the F-22 pilot will have the advantage of knowing exactly where the Su-57 earlier.

As said above it makes no sense to empoy radars from stealth planes since they will be given away hundreds of km before they detect anything, specially if the other plane is also a low detectable one. If you are thinking about LPI magic, I think it is pretty obvious such techniques are valid against militaries that have still not get in touch with digital processing, of course against any modern rival this is simply useless.

Lastly, "narrow band stealth has been defeated" when all aircraft, SAMs, ground radars in service are able routinely to track and shoot down stealth aircraft. I think we are very far from that world. Even if Russia develops such a radar and SAM and aircraft and AAM today, until every threat nation buys them, then stealth still has value.

Stealth has special value, today as always, against weak countries without advanced IADS, where all that is needed to defeat are isolated SAM sites. Against Russia, China and any other advanced military it has already lost a good part of its value and that is the reason we see the development of new platforms intended for broad band stealth from the onset.

 

[Ronny]

They are visible in lower frequency radars, that is all is needed to know. Of course they show useful reductions on L band and even below, but that is simply not enough today.

Stealth aircraft aren't invisible, they only intended to reduce detection range enough so that they detect and attack enemy before they are attacked themselves.
Contrary to popular belief, modern stealth aircraft do implement methods to reduce their RCS value at low frequency
Firstly, the total radar reflection of a complex body such as aircraft made from several different kinds of reflections:

Specular return: this is the most significant form of reflection in optical region (when structure circumphere > 10 times wavelength) ,surface acts like a mirror for the incident radar pulse. Most of the incident radar energy is reflected according to the law of specular reflection ( the angle of reflection is equal to the angle of incidence).This kind of reflection can be reduced significantly by shaping
Traveling/Surface wave return: an incident radar wave strike on the aircraft body can generate a traveling current on surface that propagates along a path to surface boundaries such as leading edge, surface discontinuous …etc, such surface boundaries can either cause a backward traveling wave or make the wave scattered in many directions .This kind of reflection can be reduced by radar absorbing material, radar absorbing structure, reduce surface gap or edges alignment ( so that their lobes occur in low priority region )
Diffraction: wave striking a very sharp surface or edge are scattered instead of following law of spectacular reflection.
Creeping wave return: this is a form of a traveling wave that doesn’t face surface discontinuous and not reflected by obstacle when traveling along object surface ,so it is able to travel around the object and come back at the radar. Unlike normal traveling wave, creeping wave traveled along surface shadowed from incidence wave (because it has to go around the object). As a result, the amplitude of creeping wave will reduce the further it has to travel because it can’t feed energy from the incident wave in the shadow region. Creeping wave mostly traveled around a curved or circular object. So, stealth fighters and stealth cruise missiles do not use tube fuselage. Nevertheless, the creeping wave return is much weaker than the specular return.
The percentage which each type of return will contribute to the total RCS value of an object depending on which region that object located in.
A high-frequency regime (or optical region) applies when the circumference of the object is at least 10 times longer than the wavelength of the incident radar wave. In this regime, specular mechanisms dominate the radar reflection ,(the angle of reflection equals the angle of incidence), like billiard balls colliding. Reflection towards the emitting radar – is reduced by angling surfaces so that they are rarely perpendicular to radars and suppressing the reflections from re-entrant structures such as engine intakes and antenna cavities with combinations of internal shaping, radar-absorbent material (RAM) or frequency selective surfaces. In this regime, “surface wave” mechanisms are small contributors to RCS, but are still present. If the wavelength is small relative to the surface, these waves are weak and their overlap will generate maximum backscatter when the radar signal is at grazing angles. When these currents encounter discontinuities, such as the end of a surface, they abruptly change and emit “edge waves.” The waves from different edges interact constructively or destructively due to their phases. The result is that they can strengthen the reflection in the specular direction and create “sidelobes” – a fan of returns around the specular reflection which undulate rapidly and weaken as the angle deviates from the specular direction. Surface wave reflections are generally very small in the optical region.
Mie region or also known as the resonance region : applies when object circumference*0.1 ≤ wavelength ≤ object circumference*1 in this region the surface wave can also swing around a structure’s back side, becoming “creeping waves” that shed energy incrementally and contribute to backscatter when they swing back toward the threat radar. This creeping wave can interferes constructively or destructively with the specular backscatter to produce a variation in the object’s RCS. So why is stealth less effective at low frequency? Creeping wave doesn’t follow mirror like reflection rule, thus the common angular shape of stealth aircraft doesn’t help deflect them away from the threat radar direction

secondly, as the radar wavelength of radar grows, the intensity of specular reflections is reduced but its lobes width are widened (the same phenomenon also happened to radar, if aperture size remained the same, the reduction in frequency will increase radar beamwidth). Because the specular reflection lobes are widen ,shaping become less effective because it will be harder to deflect radar wave away from the source ( it is important to note that, while this lobe widening phenomenon making shaping less effective, it also reduce the intensity of the reflection because the energy will be distributed over a wider volume )

Specular reflections from flat surfaces decrease with the square of the wavelength but widen proportionally: at 1/10th the surface length(approaching Mie region) they are around 6 deg. wide.

At lower frequency, the effect of traveling wave and diffraction is also more pronoun. For flat surfaces, traveling waves grow with the square of wavelength and their angle of peak backscatter rises with the square root of wavelength: (at 1/10th the surface length, it is over 15 deg). As the power of surface wave grow, the power of creeping wave return also grow. Tip diffractions and edge waves from facets viewed diagonally also grow with the square of wavelength. The end result is that the net value of stealth aircraft’s RCS often increases in Mie region. Maximum RCS is often reached when the wavelength reaches the circumference of the structure
There is a common misconception that any low-frequency radar can render stealth aircraft useless regardless of their transmitting power or aperture size, that is wrong however. While it is true that stealth aircraft will often have higher RCS in Mie region. It is important to remember that given equal radar aperture area, lower frequency radars will have much wider beam compared to high-frequency radars, thus, the concentration of energy is much lower making them more vulnerable to jamming, lower gain also result in lower accuracy. Moreover, as mentioned earlier lower frequency also resulted in wider reflection beamwidth, hence weaker reflection. As a result, most low-frequency radars have much bigger transmitting antenna compared high-mid frequency radar (to get narrow beamwidth) ,it is also the reason that fighters fire control radar still work in X-band, because a L-band, VHF band radars of similar size would be too inaccurate for any purpose others than early warning.

So, is there any way for modern stealth aircraft to reduce their return even in Mie region? YES.
To begin with, the negative effect of traveling wave and diffraction can be reduced by: aligning discontinuities to direct traveling waves towards angles of unavoidable specular return, such as the wing leading edge, thus limit their impact at other angles.
For example: serrated edges are used in places where there is current discontinuity such as weapon bay door so that traveling wave return reflected toward less important aspect

Another common method to reduce the effect of surface wave is designing airframe facets with non-perpendicular corners and so radars view them along their diagonals, at low angles and across from the facets’ smallest angles, limits the area of edge-wave emission. Surface wave diffraction can also be reduced by blending facets. The first stealth aircraft, the F-117, was designed with a computer program that could only predict reflections from flat surfaces, necessitating a fully faceted shape, but all later stealth aircraft such as B-2 , F-35 , F-22, X-47 use blended facets. Shapes composed of blended facets are not only more aerodynamic but also allow currents to smoothly transition at their edges, reducing surface-wave scattering. Therefore, blended bodies have the potential for a lower RCS than fully faceted structures, especially at low-frequency regime. And blending the curves around an aircraft in a precise mathematical manner can reduce RCS around the azimuth plane by an order of magnitude. The penalty is often a slight widening of the specular return at the curves, but in directions at which threat radars are less likely to be positioned. This was one of the great discoveries of the second generation of stealth technology.

It is, however, important to remember that, even though a blended body shape can benefit stealth characteristics because they reduce surface scattering compared to sharp facet design. A full circular (tube) body is extremely bad for stealth application, the reason is that the surface wave doesn’t get scatter but will travel a full circle around the object and come back to the source (also known as creeping wave return).

While it is possible to reduce the number of sharp edges with blended edge design, it is not possible to get rid of them all, for example an aircraft will always have wing and inlet edges. Thus, there are the need for trailing edge and leading edge treatment. As mentioned earlier, the edge diffraction is more pronoun at lower frequency. To reduce the effect of edge diffraction, the wing and inlet leading edge can be made to be a soft electromagnetic surface, to achieve this, a tapered resistive sheet can be stuck or painted on the edge. Additionally, the edge can be made from bulk absorber to improve the result. Similar to the previous example, the resistivity of the sheet will reduce from the maximum at the front tip of the edge to near zero at the rear. The resistivity of the sheet can be increased by adding holes and reduce by adding metal particles in it. This allows the surface current to transition slowly rather than abruptly as well as be absorbed and thus reduce the edge diffraction as well as surface waves

As mentioned earlier, the resistive strip/tape must have a WIDTH at least half the wavelength of the lowest frequency of interest to be effective (read image carefully, the width not the thickness) , so it is plausible to estimate the lowest frequency where the edge treatment can remain effective.
For example the inlet edge strip/tape treatment of F-35 has a width between 22- 25.4 cm, which would indicate the lowest frequency where the treatment can still be effective is around 0.5-0.7 GHz

Finally, Rayleigh Region applies when the circumference of the object is smaller than the radar wavelength. A common misconception is that the lower the operating frequency of the radar ( longer wavelength ), the better it would perform again stealth assets. That is wrong, however. It is important to remember that aircraft RCS does not necessarily grow linearly with an increase in frequency. Once the radar wavelength grows past the target’s circumference, the specifics of target geometry cease to be important and only its general shape affects reflection. The radar wave is longer than the structure and pushes current from one side of it to the other as the field alternates, causing it to act like a dipole and emit electromagnetic waves in almost all directions. This phenomenon is known as Rayleigh scattering. At this point, the RCS for aircraft will then decrease with the fourth power of the wavelength and can get exponentially smaller as the frequency reduced.

 

[Ronny]

Historically is the right word. Radars today use complex adaptive digital processing that make useless all that is known from historical performance of analog radars. Nor even talking about interferometric radars like the ones being developed in China to increase the precision at low frequencies. On the other hand, no cm-precise guidance is needed when missiles have seekers themselves.

Low frequency radar are less accurate because their beam width are wider than high frequency radar of the same aperture area. Return of two or more targets within the same resolution cell will be merged into one so when your beam width is wider, it is more likely to happen, and it is harder to determine true target location That is a physical characteristic that remain true regardless your radar is analog or digital. Think of it like how bigger optic focus light better.

Given they use their radars, which is no-go in a fight between stealth fighters. As said above it makes no sense to empoy radars from stealth planes since they will be given away hundreds of km before they detect anything, specially if the other plane is also a low detectable one. If you are thinking about LPI magic, I think it is pretty obvious such techniques are valid against militaries that have still not get in touch with digital processing, of course against any modern rival this is simply useless.

I agree that radar isn't very useful in the fight between stealth aircraft but that mainly because their radar won't be powerful enough to detect each other from extended range rather than the assumption that a stealth fighter should never use its radar for fear of detection. Because detection alone isn't enough, to attack target you need to track and have a firing solution. Missiles don't move at speed of light so to attack an aircraft, the missile must LEAD it. In other words you don't launch missile at the current location of your target but the expected future location, this is even more true for BVR air to air missile because they don't fly a direct path to target but climb to high altitude then dive down on target location.

To do that, you need to know the distance to the stealth aircraft, as well as its direction, heading, altitude and speed. But when an enemy stealth aircraft uses its radar and show up on your RWR screen, the only thing that you will know is the general direction of that aircraft, but not the distance or altitude or speed or heading, so you can't get a firing solution for your missile. As a result, you can't launch your missiles. There are methods used by SEAD aircraft to geolocate ground radar by passive ESM system, but most of them don't really work on airborne moving target, especially a non-cooperative one

There is a method often used by the so called passive radar such as VERA-E called TDOA - time different of arrival, this method is done by having receivers at separate locations, when they all receive a pulse from the target, you can compare the pulse arrival time between the separate receivers to draw circles and their intersection point will be the target location. You can locate an airborne emitter by this technique, but it required the separate receivers at very different place to receive the same pulse. This create a big problem when the targets aren't conventional aircraft but stealth aircraft.

Because having low radar cross section isn't the only characteristic of stealth aircraft. Their design also pay attention to radio emission stealth for example: AESA radar has much weaker side lobes compared to normal radar combined with very narrow beam width, it is much harder for two receivers at separate location to receive the same pulse. Stealth datalink such as MADL, IFDL transmit data through very narrow directional beam instead of omi direction like Link-16. Last but not least, data can be shared through stealth datalink, so only 1 aircraft in the squadron needed to emit, the others can remain silent.

ECM also gives the plane away.

Unless the jammer and the plane are at very different locations

Stealth has special value, today as always, against weak countries without advanced IADS, where all that is needed to defeat are isolated SAM sites. Against Russia, China and any other advanced military it has already lost a good part of its value and that is the reason we see the development of new platforms intended for broad band stealth from the onset.

There are ways to reduce effectiveness off stealth aircraft, but the counter of stealth technologies also have many weakness themselves that can be exploited
for example: OTH radars are huge stationary targets that can't be camouflaged, that make them easy to find on satellite image and priority targets for long range cruise missile strike and hypersonic missile strike.

 

[kaiserbill]

Can we stick with the Su-57, please?
These extra long posts detailing a particular technology in detail but in a generic overall way, but not even mentioning the aircraft that is the actual topic, make the thread unreadable.
It has in the past been a feature of other forums, and has the effect of slewing the thread hopelessly off course.
Not singling anyone out, just that this gets predictable and tiresome.
A separate (or existing?) thread is surely more suitable for a generic discussion on the subject?
In my humble opinion, and with no malice intended.

 

[ubiquitous08]

I learned ALOT and to be fair understanding the principles of RCS fully allows a more informed opinion of the Su-57 but agreed with that very useful primer on the subject now done (cheers), specific thoughts on RCS and operational concept of Su-57?

 

[LMFS]

@Ronny

That was a very good summary about stealth. To be honest I am familiar with most of that, let me answer a couple of issues you mention

Contrary to popular belief, modern stealth aircraft do implement methods to reduce their RCS value at low frequency

It is just a matter of physics, as you say later on:

Once the radar wavelength grows past the target’s circumference, the specifics of target geometry cease to be important and only its general shape affects reflection. The radar wave is longer than the structure and pushes current from one side of it to the other as the field alternates, causing it to act like a dipole and emit electromagnetic waves in almost all directions.

So yes, if most of your RCS reduction on a fighter comes from shaping and that is taken away by decameter band radars, plus the RAM's depth is not sufficient against them, your stealth has been greatly defeated.

secondly, as the radar wavelength of radar grows, the intensity of specular reflections is reduced but its lobes width are widened (the same phenomenon also happened to radar, if aperture size remained the same, the reduction in frequency will increase radar beamwidth). Because the specular reflection lobes are widen ,shaping become less effective because it will be harder to deflect radar wave away from the source

Further evidence that those back-scatter lobes which are popularly claimed to be almost infinitely narrow and hence practically undetectable are not, more the lower the frequency of the radar.

Low frequency radar are less accurate because their beam width are wider than high frequency radar of the same aperture area. Return of two or more targets within the same resolution cell will be merged into one so when your beam width is wider, it is more likely to happen, and it is harder to determine true target location That is a physical characteristic that remain true regardless your radar is analog or digital. Think of it like how bigger optic focus light better.

Of course, I am not referring to the ultimate physical limitation but to the popular dismissal of such radars because "they are imprecise", without giving the topic a further thought and without analisying what level of precision is necessary for them to work effectively. Anyone taking a look at available data for Nebo-M or similar modern system understands that with a detection cell of a few hundreds of meters they are more than enough to put a missile in the right direction and close enough for the seeker to do its job. Plus the fact that knowing the plane is there is already eliminating the surprise effect, allowing to cue higher frequency radars in that direction, sending interceptors etc. As said such disadvantages are also being addressed with interferometric radars that will provide way better precision by increasing massively the effective "size" of the antenna used. Konteyner radars are also boing to be built with overlapping fields for that purpose too.

I agree that radar isn't very useful in the fight between stealth aircraft but that mainly because their radar won't be powerful enough to detect each other from extended range rather than the assumption that a stealth fighter should never use its radar for fear of detection. Because detection alone isn't enough, to attack target you need to track and have a firing solution. Missiles don't move at speed of light so to attack an aircraft, the missile must LEAD it. In other words you don't launch missile at the current location of your target but the expected future location, this is even more true for BVR air to air missile because they don't fly a direct path to target but climb to high altitude then dive down on target location.

A fighter's radar in scan mode is going to reveal regularly the position of the carrier and so allow to calculate course and speed. ESM has the advantage that it is receiving orders of magnitude more power than the emitting radar so it is obviously going to detect the emitter much before the emitter detects anything. This allows to estimate a targetting solution and send a missile to the calculated interception point. ARH does the rest and there is still improvement room there with multispectral seekers starting to be used.

There are ways to reduce effectiveness off stealth aircraft, but the counter of stealth technologies also have many weakness themselves that can be exploited
for example: OTH radars are huge stationary targets that can't be camouflaged, that make them easy to find on satellite image and priority targets for long range cruise missile strike and hypersonic missile strike.

This race between technologies is the basis of what I am writing, current stealth on fighters has many weak spots and they get corrected with newer developments, the same counter stealth technology progresses too. If new platforms with focus on broad band are developed, stand-in jamming appears and also stand -off weapons and unmanned systems, it is because it is understood that current ones are threatened.

An OTH radar like Konteyner is an strategic asset, deep in the territory, that is crucial for Russia to track possible nuclear-tipped CMs, so it being attacked would mean the conventional phase of the conflict is over and air combat irrelevant.

To all: sorry for the recurring detour through RCS issues, but the same way some have the right to permanently question the Sukhoi's stealth approach, others like me have the right to reply and put in context the issue.

 

[Josh_TN]

Lower frequency radars seem largely limited to ground stations. That seems like a bit of a win for low RCS aircraft. The one exception I know of is the E-2D, which is supposed to be a UHF band radar and apparently uses some form of computer black magic to generate target grade tracks. But we are still talking about a dedicated multi-engined platform with a huge fairing.

But the bigger question to me is whether a row RCS aircraft is really cost prohibitive in the first place. The F-35 is now at nearly the same price per copy as an F-18. There probably is a lot of sunk cost in R&D specifically related to composite materials and shaping, but that is spread across about 600 examples and counting. The main drawback the Su-57 seems to have in that regard is that the production rate and number of users of the aircraft are going to be much lower than F-35, which makes it harder to justify some program costs. This may or may not have influenced Russian attitudes and requirements for RCS; I don't think anyone definitively knows.

 

[BLACK_MAMBA]

But the bigger question to me is whether a row RCS aircraft is really cost prohibitive in the first place. The F-35 is now at nearly the same price per copy as an F-18. There probably is a lot of sunk cost in R&D specifically related to composite materials and shaping, but that is spread across about 600 examples and counting. The main drawback the Su-57 seems to have in that regard is that the production rate and number of users of the aircraft are going to be much lower than F-35, which makes it harder to justify some program costs. This may or may not have influenced Russian attitudes and requirements for RCS; I don't think anyone definitively knows.

I think a more accurate statement would be that while LO is very expensive it can be cheap, if there is a big buy in. Russia's long time strength and advantage was that it could produce very capable aircraft in large quantities thanks lower unit costs compared to the west. Those aircraft often lacked the finer finish in some areas to keep costs low.

To have LO or even VLO attention to detail is everything. While the fit of the first production aircraft looked very good finish wise there was little change to some LO no-no's witnessed in the prototypes and quite rightly pointed out by experts in the field. But like you yourself or many others mentioned, Russia might well not have requested VLO - even if their propaganda portrays it as such. For the aircraft to enter production it means it clearly meets what was requested of it. And if that provides an aircraft that will keep the US/NATO on their toes at least in their continued power play over the globe then I guess the RuAF are happy.

 

[Ronny]

That was a very good summary about stealth. To be honest I am familiar with most of that, let me answer a couple of issues you mention
It is just a matter of physics, as you say later on:
So yes, if most of your RCS reduction on a fighter comes from shaping and that is taken away by decameter band radars

Once the radar wavelength grows past the target’s circumference, the specifics of target geometry cease to be important and only its general shape affects reflection. The radar wave is longer than the structure and pushes current from one side of it to the other as the field alternates, causing it to act like a dipole and emit electromagnetic waves in almost all directions.

I want to clarify something: Firstly, the part that you quoted referring to Rayleigh region when the wavelength is longer than the circumference of the aircraft, normally an aircraft is 15-16 m long, so you need HF frequency to view them in Rayleigh region. The interaction of VHF, UHF, L band radar with normal aircraft is mostly in Mie region. In Mie region, the blended curve, serrated edges, serrated panels, conductive paint over gaps, trailing and leading edge treatment, still have great impact on RCS reduction.
Secondly, even though in Rayleigh region stealth design have no impact, in this region RCS will be reduced when wavelength get longer, this is opposite to Mie region. So while I can see OTH-B radar immune to stealth, OTH-SW radar will struggle.

plus the RAM's depth is not sufficient against them, your stealth has been greatly defeated.

Ferrite magnetic RAM can be much thinner than dielectric RAM because their electrical thickness is much greater than mechanical thickness

Further evidence that those back-scatter lobes which are popularly claimed to be almost infinitely narrow and hence practically undetectable are not, more the lower the frequency of the radar.

Low frequency radar has the benefit of making the reflection lobes wider but at the same time, wider lobes resulted in lower intensity. In the photo I posted earlier, you can see that the energy return intensity at 300 MHz is about 0.09% of 10 GHz

Of course, I am not referring to the ultimate physical limitation but to the popular dismissal of such radars because "they are imprecise", without giving the topic a further thought and without analisying what level of precision is necessary for them to work effectively. Anyone taking a look at available data for Nebo-M or similar modern system understands that with a detection cell of a few hundreds of meters they are more than enough to put a missile in the right direction and close enough for the seeker to do its job. Plus the fact that knowing the plane is there is already eliminating the surprise effect, allowing to cue higher frequency radars in that direction, sending interceptors etc. As said such disadvantages are also being addressed with interferometric radars that will provide way better precision by increasing massively the effective "size" of the antenna used. Konteyner radars are also boing to be built with overlapping fields for that purpose to

Resolution cell isn't a fixed volume, it has the same size as: (vertical beam width)*(horizontal beam width)* (pulse width) so it will get bigger with range.


Secondly, Konteyner radars are build with overlapping field because it is an OTH-B radar, and OTH-B radar has very big blind spot around them called the skip zone because they need to be reflected from the ionosphere. This blind skip zone is anywhere from 1000-3000km in diameter

A fighter's radar in scan mode is going to reveal regularly the position of the carrier and so allow to calculate course and speed. ESM has the advantage that it is receiving orders of magnitude more power than the emitting radar so it is obviously going to detect the emitter much before the emitter detects anything. This allows to estimate a targetting solution and send a missile to the calculated interception point. ARH does the rest and there is still improvement room there with multispectral seekers starting to be used.

AESA/PESA radar can perform scan very rapidly in irregular pattern so they won't need to reveal position of the carrier for very long, and the pilot has option to use their radar only once a while.
geolocate a noncooperative moving airborne target with ESM system is very implausible in most cases because the change of bearing for a fast target at long range and a slow target at close range can be the same. Motion analysis method might allow a guesstimate of the range and target velocity but you need your target to maintain the same course, speed, altitude for a while or your estimation will get a huge error and become useless.



Think of it like this, there are 5 different radio emitters on Su-57, and these things are expensive. If using radar remove all advantage of stealth, Russian wouldn't put that many on Su-57

 

[Ronny]

Can we stick with the Su-57, please?
These extra long posts detailing a particular technology in detail but in a generic overall way, but not even mentioning the aircraft that is the actual topic, make the thread unreadable.
It has in the past been a feature of other forums, and has the effect of slewing the thread hopelessly off course.
Not singling anyone out, just that this gets predictable and tiresome.
A separate (or existing?) thread is surely more suitable for a generic discussion on the subject?
In my humble opinion, and with no malice intended.

Sorry if my post is off topic, but I think since we are talking about the stealth characteristic of Su-57, it make sense to understand the general idea why a specific part of a stealth aircraft is designed in a specific way. So we can make informed assessments

 

[LMFS]

I understand the discussion is too general for the thread so we may take it somewhere else.