Average RCS values, F-35 vs S-400

[stealthflanker]

Great @TR1

----

Other than that is.. why "Average RCS" being used as measure for usually Russian publication (e.g PAKFA Patent) ? While the US one often only cites a value from a certain angle.

 

[flanker]

Because "average RCS" is extremely vague and non-descriptive. Which is excellent when you are telling a highly secret RCS value without actually telling it.

 

[stealthflanker]

Because "average RCS" is extremely vague and non-descriptive. Which is excellent when you are telling a highly secret RCS value without actually telling it.

I see. Thanks.

Kinda feel bad however as some people just go ahead and use the one in patent and pit it against the US value without actually paying more thought on it. Similar as one which just use RCS value without specifying frequency or any other information.

 

[overscan (PaulMM)]

The whole point of stealth design is to concentrate radar energy into spikes. Averaging the spikes and the troughs makes little sense except as a desperate attempt to make your non-stealthy design seem comparable - any radar energy not absorbed has to go somewhere, so averaging reduces the disparity between stealth and non-stealth designs.

 

[stealthflanker]

The whole point of stealth design is to concentrate radar energy into spikes. Averaging the spikes and the troughs makes little sense except as a desperate attempt to make your non-stealthy design seem comparable - any radar energy not absorbed has to go somewhere, so averaging reduces the disparity between stealth and non-stealth designs.

Yet it used, i'm curious on why. The Russians can just do the same as US by telling a value without disclosing the frequency. That is already confusing enough.

I am however criticizing the use of it for comparison with value taken from a single aspect. e.g one comparing the averaged RCS of 0-30 degrees aspect with one taken only from 0 degrees. in this respect they are apple vs watermelon, add frequency (which also rarely mentioned) then they can be apple vs human. To be apple vs apple then it has to be compared with same (average vs average or single angle value vs single angle value + frequencies if possible) Which i wonder rarely done.

 

[Saber]

The whole point of stealth design is to concentrate radar energy into spikes. Averaging the spikes and the troughs makes little sense except as a desperate attempt to make your non-stealthy design seem comparable - any radar energy not absorbed has to go somewhere, so averaging reduces the disparity between stealth and non-stealth designs.

Yet it used, i'm curious on why. The Russians can just do the same as US by telling a value without disclosing the frequency. That is already confusing enough.

I am however criticizing the use of it for comparison with value taken from a single aspect. e.g one comparing the averaged RCS of 0-30 degrees aspect with one taken only from 0 degrees. in this respect they are apple vs watermelon, add frequency (which also rarely mentioned) then they can be apple vs human. To be apple vs apple then it has to be compared with same (average vs average or single angle value vs single angle value + frequencies if possible) Which i wonder rarely done.

Average RCS is a more applicable number for a combat situation, especially given mobile nature of aircraft and the huge variety of illumination angles and actuator usage.

 

[overscan (PaulMM)]

The whole point of stealth design is to concentrate radar energy into spikes. Averaging the spikes and the troughs makes little sense except as a desperate attempt to make your non-stealthy design seem comparable - any radar energy not absorbed has to go somewhere, so averaging reduces the disparity between stealth and non-stealth designs.

Yet it used, i'm curious on why. The Russians can just do the same as US by telling a value without disclosing the frequency. That is already confusing enough.

I am however criticizing the use of it for comparison with value taken from a single aspect. e.g one comparing the averaged RCS of 0-30 degrees aspect with one taken only from 0 degrees. in this respect they are apple vs watermelon, add frequency (which also rarely mentioned) then they can be apple vs human. To be apple vs apple then it has to be compared with same (average vs average or single angle value vs single angle value + frequencies if possible) Which i wonder rarely done.

Average RCS is a more applicable number for a combat situation, especially given mobile nature of aircraft and the huge variety of illumination angles and actuator usage.

Nope, it really isn't. If all the radar energy is returned in four widely separated 1 degree wide spikes, for example, the "average RCS" over 360 degrees many be roughly the same as a non-stealthy aircraft, but you will only see it fleetingly at very specific angles.

The only use I can see for quoting "average RCS" is to cover up your inability to do effective planform alignment signature control.

 

[Saber]

The whole point of stealth design is to concentrate radar energy into spikes. Averaging the spikes and the troughs makes little sense except as a desperate attempt to make your non-stealthy design seem comparable - any radar energy not absorbed has to go somewhere, so averaging reduces the disparity between stealth and non-stealth designs.

Yet it used, i'm curious on why. The Russians can just do the same as US by telling a value without disclosing the frequency. That is already confusing enough.

I am however criticizing the use of it for comparison with value taken from a single aspect. e.g one comparing the averaged RCS of 0-30 degrees aspect with one taken only from 0 degrees. in this respect they are apple vs watermelon, add frequency (which also rarely mentioned) then they can be apple vs human. To be apple vs apple then it has to be compared with same (average vs average or single angle value vs single angle value + frequencies if possible) Which i wonder rarely done.

Average RCS is a more applicable number for a combat situation, especially given mobile nature of aircraft and the huge variety of illumination angles and actuator usage.

Nope, it really isn't. If all the radar energy is returned in four widely separated 1 degree wide spikes, for example, the "average RCS" over 360 degrees many be roughly the same as a non-stealthy aircraft, but you will only see it fleetingly at very specific angles.

The only use I can see for quoting "average RCS" is to cover up your inability to do effective planform alignment signature control.

Yup, it really is. I suppose you think aircraft constantly fly around with their nose perfectly pointed at any threat emitters around? Aircraft frequently move in all axis, especially when performing combat maneuvers. Not to mention aerodynamic actuators and bay door opening.

And there's multi-source illumination.

 

[overscan (PaulMM)]

That's precisely why stealth works. The chance of you being aligned precisely at the correct angle to receive radar from any of the the target spikes is actually very low, and when the target and source move, the target disappears as the spike now points somewhere else.

If there are only 4 azimuth positions of 1 degree where you can detect the target, that leaves (360 -4) - 354 degrees in azimuth where you can't detect it. In a dynamic battle, you might get a brief glimpse of a target at range, but it would be very hard to do anything with.

An aircraft with say 0.3 sq m RCS in all directions is pretty detectable. An aircraft with 0.001 sq m RCS in most directions and 5 sqm RCS in specific small angle ranges is much less detectable, even if it averages to the same value of 0.3 sq m.

 

[Trident]

Nope, it really isn't. If all the radar energy is returned in four widely separated 1 degree wide spikes, for example, the "average RCS" over 360 degrees many be roughly the same as a non-stealthy aircraft, but you will only see it fleetingly at very specific angles.

No disagreement. The target will appear to "glint" very briefly when the aspect aligns with one of the exceedingly narrow spikes - too briefly to take advantage of for reliable long range tracking.

The only use I can see for quoting "average RCS" is to cover up your inability to do effective planform alignment signature control.

Well, that's plainly not the case (emphasis mine), is it? A further fundamentally plausible rationale has been offered above - whether one accepts it as valid in the specific case of the Su-57 is another matter entirely.

 

[Saber]

That's precisely why stealth works. The chance of you being aligned precisely at the correct angle to receive radar from any of the the target spikes is actually very low, and when the target and source move, the target disappears as the spike now points somewhere else.

If there are only 4 azimuth positions of 1 degree where you can detect the target, that leaves (360 -4) - 354 degrees in azimuth where you can't detect it. In a dynamic battle, you might get a brief glimpse of a target at range, but it would be very hard to do anything with.

An aircraft with say 0.3 sq m RCS in all directions is pretty detectable. An aircraft with 0.001 sq m RCS in most directions and 5 sqm RCS in specific small angle ranges is much less detectable, even if it averages to the same value of 0.3 sq m.

Sure, except how true is the notion of .001 sq m "in most directions" and 4 azimuth positions is in practical and combat terms? This is the biggest problem in discussing 5th gens, their classified nature as well as veritability of open source theoretical data.

In my view, facts like the multi-billion dollar rework of the B-2 for low level flight penetration of the Soviet Union, or the total unwillingness of LM/USA to allow export of F-35 to Turkey after S-400 acquisition which would allow for a final settlement of the 5th gen vs IADS argument to be rather deflating for the arguments of "metal marble" RCS.

 

[sferrin]

Turkey after S-400 acquisition which would allow for a final settlement of the 5th gen vs IADS argument to be rather deflating for the arguments of "metal marble" RCS.

How do you figure? Do you actually believe the US would sell it's most recent stealth aircraft to a country likely to have Russian 'tech support" with access to it, no matter what it's actual RCS is?

 

[overscan (PaulMM)]

"Stealth scepticism" on this level is just stupid. Other countries have verified the basic techniques, even if few have gone as far down that path as the US.

Feel free to doubt if its worth the money, doubt that the maintenance of the coatings is easy, doubt that a fighter plane needs stealth to be effective, even imagine that possible counters to stealth are plentiful, but doubting it works in principle is just conspiracy minded garbage.

Any system will have possible counters, of course. The best possible way to enable their development is let the other side have access to it.

 

[Saber]

Turkey after S-400 acquisition which would allow for a final settlement of the 5th gen vs IADS argument to be rather deflating for the arguments of "metal marble" RCS.

How do you figure? Do you actually believe the US would sell it's most recent stealth aircraft to a country likely to have Russian 'tech support" with access to it, no matter what it's actual RCS is?

Turkey purchases S-400, therefore Russians get access to F-35? Is that your logic? Why would Turkey compromise its premier fighter to the Russians, who have directly killed Turkish troops and supplied and reinforced Turkish enemies? Or do you believe Turks are stupid and wouldn't check and let S-400s hoover up data somehow on the F-35 and email to the Kremlin?

And why only reply on my mentioning of Turkey/F-35? Didn't want to talk about B-2s low level redesign? NG itself admits it was redesigned.

"Stealth scepticism" on this level is just stupid. Other countries have verified the basic techniques, even if few have gone as far down that path as the US.

Feel free to doubt if its worth the money, doubt that the maintenance of the coatings is easy, doubt that a fighter plane needs stealth to be effective, even imagine that possible counters to stealth are plentiful, but doubting it works in principle is just conspiracy minded garbage.

Any system will have possible counters, of course. The best possible way to enable their development is let the other side have access to it.

Seventh Method "Pugna"

" A method closely related to the previous one. It is based on assigning a false designation to the defended conception or to opponent himself and since that point the entire debate is waged against this arbitrarely taken position. This technique is most often used in so-called principled debates. The enemy is accused of some obscene "ism" and then this "ism" is handily defeated. "

1. Never said it's not worth the money

2. Never once mentioned coatings

3. Never doubted necessity of stealth or its effectiveness.

4. Never doubted the the principles of LO/VLO

But good job smearing me as a "stealth skeptic" .

I want to make one thing very clear, my entire statement was that standard claims of "golf ball RCS" and such are simply not accurate in my view.

Don't compare me to fucking Pierre "Turkey" Sprey.

 

[stealthflanker]

How do you figure? Do you actually believe the US would sell it's most recent stealth aircraft to a country likely to have Russian 'tech support" with access to it, no matter what it's actual RCS is?

Maybe UAE but well they can only test it against Pantsyr. hahaha.

 

[overscan (PaulMM)]

Turkey purchases S-400, therefore Russians get access to F-35? Is that your logic? Why would Turkey compromise its premier fighter to the Russians, who have directly killed Turkish troops and supplied and reinforced Turkish enemies? Or do you believe Turks are stupid and wouldn't check and let S-400s hoover up data somehow on the F-35 and email to the Kremlin?

S-400 will come with Russian technicians. They would love to test S-400 against the F-35s. Turkey might agree to it. How were they planning to prevent the S-400 shooting down their F-35s? They won't discclose anything to Russia to help with IADS integration? What if Russia say they need detailed RCS signature profiles for their NCTR system in S-400 radar?

I think its wrong to conclude, as you appear to, that the US is frightened Turkey will prove that the S-400 defeats the F-35 was the motivation to stop F-35 sales to Turkey.

And why only reply on my mentioning of Turkey/F-35? Didn't want to talk about B-2s low level redesign? NG itself admits it was redesigned

The switch to support low level flight was made to prolong the lifespan of the B-2 in the event that counters to stealth were developed, at at time when the Soviet Union was still going on 20% GDP defence spending. It was also the USAF's decision, not Northrop's. Not sure why this is relevant?. Post Soviet collapse, development of the main adversary systems went glacially slow for 20 years, and B-2 has never had to fly low in the 30 years since.

I want to make one thing very clear, my entire statement was that standard claims of "golf ball RCS" and such are simply not accurate in my view.

Don't compare me to fucking Pierre "Turkey" Sprey.

Apologies if I misunderstood your point, but I still think you are factually off base. The breakthough of stealth was realising that a shape that only has controlled narrow lobe spikes (4, 6 or 8 main directions depending on type) in its RCS plot will not be visible on radar long enough to be tactically relevant. Nobody every said that the B-2 has the RCS of a golf ball from every single direction in every possible wavelength. "Golf Ball" or "marble" is a way of visualising the RCS equivalent area from a tactically relevant direction and radar wavelength (e.g front quarter for F-117A) which is memorable and showy. There's a bit of marketing there, for sure.

The art of designing a successful stealth aircraft is to make sure the most likely threat directions and wavelengths are covered, and the radar energy as far as possible is not sent back to the sender from tactically meaningful directions. This is also why early stealth aircraft systems include detailed route planning, to ensure threats as far as possible don't lie in those directions.

 

[Evgeniy]

Gentlemen, this whole situation with the S-400 and F-35 in Turkey, this is more from the field of politics than technology.

 

[Saber]

S-400 will come with Russian technicians. They would love to test S-400 against the F-35s. Turkey might agree to it. How were they planning to prevent the S-400 shooting down their F-35s? They won't discclose anything to Russia to help with IADS integration? What if Russia say they need detailed RCS signature profiles for their NCTR system in S-400 radar?

I think its wrong to conclude, as you appear to, that the US is frightened Turkey will prove that the S-400 defeats the F-35 was the motivation to stop F-35 sales to Turkey.

Turkey would love to test both S-400 and F-35, no need for Almaz-Antei personnel there, or LM ones for that matter, it's a simple matter of one country being able to control for all variables when testing each of them in battlefield-like field exercises.

Also, Almaz-Antei had no problem exporting this system to Turkey, unlike LM/USA. Had these claims/estimations of .0001 sq m RCS and 23km detection ranges against F-35 on part of the S-400 been combat accurate, then it would have been an absolute crushing blow to a system frozen in design characteristics, removing any and all export potential for the system, and a perfect counter-will op against Russia, India, China, and any other country operating the system. And it would solidify Turkey's position in USA/NATO's orbit as it remove Russia as a "alternative" to them.

And it wouldn't require any data leakage to Russia, after all, highly doubt Turkey would buy a system they couldn't use against Russia.

The switch to support low level flight was made to prolong the lifespan of the B-2 in the event that counters to stealth were developed, at at time when the Soviet Union was still going on 20% GDP defence spending. It was also the USAF's decision, not Northrop's. Not sure why this is relevant?. Post Soviet collapse, development of the main adversary systems went glacially slow for 20 years, and B-2 has never had to fly low in the 30 years since.

Well, the USSR didn't spend 20 percent of its GDP on defence, that's a misconception formed due to the result of USSR folding in a large part of societal benefits such as schools/hospitals being attached to say, UVZ or such. And when funding for UVZ dried up, so did the funding for the school and hospital.

And yes, NG redesigned the B-2 according to USAF orders, I was more referring to the pdf that was published by NG. https://www.northropgrumman.com/wp-content/uploads/B-2-Spirit-of-Innovation.pdf

And how do you know it was lifespan-prolonging and not an rethinking of parameters and expected performance of S-300 and its variants? Original purpose and mission for B-2 was gravity nuclear bomb drop on tactical Warsaw Pact formations from high cruising altitude utilizing VLO against long range SAMs and altitude against short-range AAA

Evidently much changed, now both missions for B-2 and B-21 are fulfilled with nuclear LRSO. And yes, B-2 never had to fly low, it never faced Soviet S-300s in the missions it was thought necessary.

Apologies if I misunderstood your point, but I still think you are factually off base. The breakthough of stealth was realising that a shape that only has controlled narrow lobe spikes (4, 6 or 8 main directions depending on type) in its RCS plot will not be visible on radar long enough to be tactically relevant. Nobody every said that the B-2 has the RCS of a golf ball from every single direction in every possible wavelength. "Golf Ball" or "marble" is a way of visualising the RCS equivalent area from a tactically relevant direction and radar wavelength (e.g front quarter for F-117A) which is memorable and showy. There's a bit of marketing there, for sure.

The art of designing a successful stealth aircraft is to make sure the most likely threat directions and wavelengths are covered, and the radar energy as far as possible is not sent back to the sender from tactically meaningful directions. This is also why early stealth aircraft systems include detailed route planning, to ensure threats as far as possible don't lie in those directions.

Yes, we agree on a small basis, and I mainly say metal marble to avoid having to type .001 sq RCS everytime.

As I said before, our main argument lies in what accuracy average RCS measurements and specific angle measurements have to combat usefulness. From your view, outside of certain angles, detectability is zero in tactical sense. From my view, even outside these certain angles(such as directly perpendicular to the wing edge of a B-2) stealth aircraft can still be detected at tactically relevant ranges, especially when considering multi-aspect and multi-wavelength illumination, and in near and long term future, terahertz and photonic circuit based radars.

This is why I believe that average RCS measurements hold more weight when regarding "threat envelopes" for VLO aircraft.

 

[Ronny]

Turkey would love to test both S-400 and F-35, no need for Almaz-Antei personnel there, or LM ones for that matter, it's a simple matter of one country being able to control for all variables when testing each of them in battlefield-like field exercises.
Also, Almaz-Antei had no problem exporting this system to Turkey, unlike LM/USA. Had these claims/estimations of .0001 sq m RCS and 23km detection ranges against F-35 on part of the S-400 been combat accurate, then it would have been an absolute crushing blow to a system frozen in design characteristics, removing any and all export potential for the system, and a perfect counter-will op against Russia, India, China, and any other country operating the system. And it would solidify Turkey's position in USA/NATO's orbit as it remove Russia as a "alternative" to them.

And it wouldn't require any data leakage to Russia, after all, highly doubt Turkey would buy a system they couldn't use against Russia.

Stealth aircraft are more static in nature than surface to air missile system. You can change the software of a surface to air radar, you can change the radar aperture.
But it would be much more impractical to change the whole airframe of the aircraft.
It would not be beneficial for US if the Russian know exactly which distance their radar can detect an F-35, which angle is the easiest to detect it, and how the signature characteristic of an F-35 different from a MALD.

And how do you know it was lifespan-prolonging and not an rethinking of parameters and expected performance of S-300 and its variants? Original purpose and mission for B-2 was gravity nuclear bomb drop on tactical Warsaw Pact formations from high cruising altitude utilizing VLO against long range SAMs and altitude against short-range AAA
Evidently much changed, now both missions for B-2 and B-21 are fulfilled with nuclear LRSO. And yes, B-2 never had to fly low, it never faced Soviet S-300s in the missions it was thought necessary.

The design of B-21 seem to suggest that it come back to high altitude mission though

terahertz and photonic circuit based radars.
This is why I believe that average RCS measurements hold more weight when regarding "threat envelopes" for VLO aircraft.

Consider the atmosphere absorption of terahertz frequency, any radar working with that frequency will be quite useless for air defense purposes.
And the so called photonic radar is probably mostly marketing hype, it is very unlikely to come here anytime soon, we probably only have them once B-21 already retired

 

[overscan (PaulMM)]

Turkey would love to test both S-400 and F-35, no need for Almaz-Antei personnel there, or LM ones for that matter, it's a simple matter of one country being able to control for all variables when testing each of them in battlefield-like field exercises.

Also, Almaz-Antei had no problem exporting this system to Turkey, unlike LM/USA. Had these claims/estimations of .0001 sq m RCS and 23km detection ranges against F-35 on part of the S-400 been combat accurate, then it would have been an absolute crushing blow to a system frozen in design characteristics, removing any and all export potential for the system, and a perfect counter-will op against Russia, India, China, and any other country operating the system. And it would solidify Turkey's position in USA/NATO's orbit as it remove Russia as a "alternative" to them.

And it wouldn't require any data leakage to Russia, after all, highly doubt Turkey would buy a system they couldn't use against Russia.

You seem oddly keen to ascribe miraculous powers to the S-400.

Whole load of ifs, buts and maybes and your conclusion is wildly off base. If the S-400 has a detection range of 23km against the F-35 (which isn't demonstrated) and if it can successfully track it (which we don't know) and if it can fire at a tactically useful distance (20km?) and if the missile seeker is able to track it and if the proximity fusing work correctly and if the warhead detonates.... unless you are building an IADS for the Vatican City you are going to need one giant shedload of S-400 systems to cover your country. And of course, the F-35 could use stand off weapons from outside 23km range...

 

[Josh_TN]

My understanding is that a key enabler of stealth technology is an ESM system that can plot bearings to threat emitters. The B-2 apparently 'tacts' into the radar wind to reach its targets - that is it's flight path has to be intentionally inefficient to take the angle of incidence of threat emitters into account ("film my best side"). The USAF believes it is significantly ahead in this area of technical expertise relative to other nations producing low RCS aircraft.

 

[Saber]

Stealth aircraft are more static in nature than surface to air missile system. You can change the software of a surface to air radar, you can change the radar aperture.
But it would be much more impractical to change the whole airframe of the aircraft.
It would not be beneficial for US if the Russian know exactly which distance their radar can detect an F-35, which angle is the easiest to detect it, and how the signature characteristic of an F-35 different from a MALD.

The changes you describe are significant to a SAM system, and its not just radar that might require a change, but missile design as well, these are all expensive to modify especially a deep in production stage system like S-400. The same goes for F-35.

The design of B-21 seem to suggest that it come back to high altitude mission though

Absolutely, especially with LRSO integration.

Consider the atmosphere absorption of terahertz frequency, any radar working with that frequency will be quite useless for air defense purposes.
And the so called photonic radar is probably mostly marketing hype, it is very unlikely to come here anytime soon, we probably only have them once B-21 already retired

Terahertz radar's biggest problem was creation of components such as waveform generators and waveguides not necessarily its attenuation in atmosphere. It's a very useful waveband due to its high detail, and with use of pencil beams its range can be quite high plus its high accuracy and near immunity to RCS reduction.

On photonic circuit based radars, several prototypes have been created, I'd be willing to bet that Su-57M will be carrying it in serial.

You seem oddly keen to ascribe miraculous powers to the S-400.

Whole load of ifs, buts and maybes and your conclusion is wildly off base. If the S-400 has a detection range of 23km against the F-35 (which isn't demonstrated) and if it can successfully track it (which we don't know) and if it can fire at a tactically useful distance (20km?) and if the missile seeker is able to track it and if the proximity fusing work correctly and if the warhead detonates.... unless you are building an IADS for the Vatican City you are going to need one giant shedload of S-400 systems to cover your country. And of course, the F-35 could use stand off weapons from outside 23km range...

I'm ascribing miraculous powers to the S-400? I think it the other way, you've taken one figure given(.001 sq m RCS) and suddenly that's the benchmark for the S-400? How are you so sure? LM doesn't lie but Almaz-Antei does?

In my view, S-400 can detect/track/engage F-35s from quite a bit further, but I'd rather not find out due to real life engagements.

 

[overscan (PaulMM)]

In my view, S-400 can detect/track/engage F-35s from quite a bit further, but I'd rather not find out due to real life engagements.

I'm really struggling to understand your point. What are you basing this view on? A hunch you have?

My point was we don't know enough about the F-35 OR the S-400 to be able to form an opinion. You appeared to suggest earlier that the US stopping F-35 sales to Turkey somehow proved how awesomely the S-400 would perform against it. I simply don't follow the logic here. Plenty of other explanations.

 

[overscan (PaulMM)]

Split off from Su-57 topic.

 

[Ronny]

The changes you describe are significant to a SAM system, and its not just radar that might require a change, but missile design as well, these are all expensive to modify especially a deep in production stage system like S-400. The same goes for F-35.

You don't seem to understand, it is much easier to change the aperture or the software of a surface radar than it is to change the airframe or internal RAS of an aircraft

Absolutely, especially with LRSO integration.

I don't think that is the key, even the old AGM-86 and AGM-129 could allow the B-52 stay outside the engagement range of any SAM

Terahertz radar's biggest problem was creation of components such as waveform generators and waveguides not necessarily its attenuation in atmosphere. It's a very useful waveband due to its high detail, and with use of pencil beams its range can be quite high plus its high accuracy and near immunity to RCS reduction.

No, the biggest problem of Terahertz radar is exactly atmosphere attenuation. The absorption rate at 1 THz is literally 10,000 dB/km and dB unit scaled exponentially, in other words, every 1 km that the signal pass through the atmosphere, the signal strength reduced by 10^1000, can you even imagine how big is that number? you would be lucky if your THz radar can see past the 10 meters range. And why would THz radar be immune to stealth? the wavelength would be too short that all reflection will be specular reflection, literally the type that stealth aircraft most optimized against

On photonic circuit based radars, several prototypes have been created, I'd be willing to bet that Su-57M will be carrying it in serial.

in the labs sure, but it is decades from being reality, just like dozens others catchy invention

 

[marauder2048]

This is why I believe that average RCS measurements hold more weight when regarding "threat envelopes" for VLO aircraft.

Not really. Because of Swerling target assumptions, which is about the ratio of instantaneous to average RCS, you end up for
say a 0.9 probability of detection for a Swerling 1 target, needing the ability to detect 1/10th of the average RCS i.e. 10 dB below the
average RCS.

I think just about every air defense radar out there uses some form of Swerling target model.

 

[Josh_TN]

This discussion has so far also omitted any references to how much more effective any ECM will be with a smaller target reflection. Perhaps you get a fleeting glance and can focus your energy in that area, but with a modern aircraft that is unlikely to not go unnoticed and might provoke active countermeasures.

 

[Ronny]

This discussion has so far also omitted any references to how much more effective any ECM will be with a smaller target reflection. Perhaps you get a fleeting glance and can focus your energy in that area, but with a modern aircraft that is unlikely to not go unnoticed and might provoke active countermeasures.

 

[Saber]

In my view, S-400 can detect/track/engage F-35s from quite a bit further, but I'd rather not find out due to real life engagements.

I'm really struggling to understand your point. What are you basing this view on? A hunch you have?

My point was we don't know enough about the F-35 OR the S-400 to be able to form an opinion. You appeared to suggest earlier that the US stopping F-35 sales to Turkey somehow proved how awesomely the S-400 would perform against it. I simply don't follow the logic here. Plenty of other explanations.

Yet again, you're the one putting words in my mouth. Never said "awesomely". My entire point was that LM/USA seemed loathe to let F-35s fly in an area monitored by an S-400 with the same nationality operators, thereby controlling all variables.

And you're correct, we DON'T know about they would fare against each other, yet natural assumptions you have are that it would only engage F-35 at around 20km. Is this a hunch you have?

You don't seem to understand, it is much easier to change the aperture or the software of a surface radar than it is to change the airframe or internal RAS of an aircraft

Lol, I don't understand? I just told you that those two are not the only characteristics of an IADS system. And those two characteristics are not as easy as you think, software refinement takes time, and limited in how much improvement there is, rather difficult to squeeze another 20 percent performance through just software improvements.

And aperture? Sure, comes with more power draw, difficult to cope with on a limited powerbase available. I highly doubt you'll see a S-400M anytime soon, compared to a brand new system like S-500.

And sure internals are difficult to change on aircraft, my point exactly, both systems are frozen in most part for their primary design characteristics.

I don't think that is the key, even the old AGM-86 and AGM-129 could allow the B-52 stay outside the engagement range of any SAM

I'm referring to nuclear role.

No, the biggest problem of Terahertz radar is exactly atmosphere attenuation. The absorption rate at 1 THz is literally 10,000 dB/km and dB unit scaled exponentially, in other words, every 1 km that the signal pass through the atmosphere, the signal strength reduced by 10^1000, can you even imagine how big is that number? you would be lucky if your THz radar can see past the 10 meters range. And why would THz radar be immune to stealth? the wavelength would be too short that all reflection will be specular reflection, literally the type that stealth aircraft most optimized against

Really? Considering until recently Thz devices were practically lab based, "existing" was the biggest problem for it. Second of all, yes attenuation is enormous at THz range, yet still being worked on for radar/imagery, due to the fact that THz doesn't care at all shaping, I fail to see how stealth aircraft would be "optimized" against Thz.

Not really. Because of Swerling target assumptions, which is about the ratio of instantaneous to average RCS, you end up for
say a 0.9 probability of detection for a Swerling 1 target, needing the ability to detect 1/10th of the average RCS i.e. 10 dB below the
average RCS.

I think just about every air defense radar out there uses some form of Swerling target model.

I'm not referring to target model, I'm referring to actual distribution of RCS measurements in azimuth and vertical illumination angles.

 

[marauder2048]

I'm not referring to target model, I'm referring to actual distribution of RCS measurements in azimuth and vertical illumination angles.

I don't think you understand how these distributions get used in air defense radars...

 

[Saber]

I'm not referring to target model, I'm referring to actual distribution of RCS measurements in azimuth and vertical illumination angles.

I don't think you understand how these distributions get used in air defense radars...

I don't think you understand the crux of the argument, what targeting models radars currently use is of no bearing to my discussion of how practical using average RCS calculations versus measurements taken at certain points.

Not to mention how pervasive these certain sweet spots of VLO are on aircraft.

 

[marauder2048]

I'm not referring to target model, I'm referring to actual distribution of RCS measurements in azimuth and vertical illumination angles.

I don't think you understand how these distributions get used in air defense radars...

I don't think you understand the crux of the argument, what targeting models radars currently use is of no bearing to my discussion of how practical using average RCS calculations versus measurements taken at certain points.

Well aside from the fact that your premise is ill-posed...do you want arithmetic mean, log mean, geometric mean, harmonic mean?
Some of the radar literature would prefer that you use the median since that might be more representative of the target type of interest.
In fact, some of the literature on LO aircraft suggests medians are more representative.

Rather goes back to the target models which you don't like.

 

[Saber]

Well aside from the fact that your premise is ill-posed...do you want arithmetic mean, log mean, geometric mean, harmonic mean?
Some of the radar literature would prefer that you use the median since that might be more representative of the target type of interest.
In fact, some of the literature on LO aircraft suggests medians are more representative.

Rather goes back to the target models which you don't like.

Arithmetic mean, a simple average of the values measured over a horizontal range at a certain vertical value, at a specified wavelength. What is the reality for them? are they all .001 sq m RCS at all angles except four specific degrees thereby rendering them tactically invisible? Or is there some truth to the standard average RCS claims of .3-.5 sqm RCS?

This is what I wish to discuss.

 

[stealthflanker]

Really? Considering until recently Thz devices were practically lab based, "existing" was the biggest problem for it. Second of all, yes attenuation is enormous at THz range, yet still being worked on for radar/imagery, due to the fact that THz doesn't care at all shaping, I fail to see how stealth aircraft would be "optimized" against Thz.

Yeah. but may not necessarily be used for something like combat or air defense application. It's much more valuable in instrumentation radar or sensors.

The THz frequency is valued because it's almost like laser and giving you a very fine resolution, this allows you in field of industry to spot a small cracks (tho there is X ray for that but i guess cant always bring a large X-ray machine) Or in terms of RCS testing. This allows much smaller subscale model to be used.

The possible means for "counter stealth" with THz however looks enticing as it's basically allows you to see more imperfections thus spikes. Though atmosphere may work heavily against you, but one can find a "window" frequency where the absorption is smaller, plus expect RAM against this frequency to be more easily implemented as it would be thinner. In short, you may not get sort of useful range unless you're stealth yourself and more stealthy than the one you hunted. It may have missile seeker application but that's gonna be far in future. Another problem is getting enough power. Higher frequency transmitter tend to have rather small power generation capability and difficult to build. If you want a phased array, it cant be AESA as its gonna need thosands or even hundred thousands of elements to fill even modest aperture (e.g missile seeker)
---------


And i wonder why there should be S-400 into equation. Nonetheless. The radar can actually "do" something to improve its detection range like special modes. Increasing pulsewidth or duty cycle and to actually lowers the detection threshold which can be done by integrating more pulses (to the limit of correlation time of course for coherent) In my previous "thought experiment" The detection range can be increased about twice or 1.95 times if anyone wants that detail. So 31 km can be 61.2, ability to lower the detection threshold further to say 18 dB the range would be 91 Km. But the technology is the limit here. Mostly in signal processing as very low noise receiver does exist in PESA realm and the one Russian used doesnt even need duplexer or protector and being a space feed array the graph in 2nd edition of Stimson's introduction to airborne Radar may not necessarily apply (It does however applies to Zaslon and B1 Radar)

There of course some ifs like whether the transmitter is really capable of doing that, whether the radar can resolve the ambiguity resulted from higher PRF's or whether such modes really exist in first place. However as i said previously, radar range equation is not just 4th root of RCS like people often like to use.

But the biggest issue for me of course to find what RCS value i should use as input, which the whole point of me asking why Russian use average and why US one likes to use one from just an angle.

So for my future reference, what i should use as input ?

The point i gathered so far is that the average appears to be more representative in combat, because aircrafts can move 3 dimensionally so the radar may see various parts of the aircrafts and thus "average" it. The counter points is that stealth aircraft may have "Most" of its spikes managed that the "relevant" angle may have low RCS and thus put a doubt on usefullness of average RCS in terms of comparison.

Single angle RCS have benefit of exact value, tho the applicability may be limited to that particular angle and whether the target can retain that angle and whether the target can retain the RCS in the relevant wavelength. However average RCS also mentioned without consideration of frequency so there's that both are the same.

 

[marauder2048]

Well aside from the fact that your premise is ill-posed...do you want arithmetic mean, log mean, geometric mean, harmonic mean?
Some of the radar literature would prefer that you use the median since that might be more representative of the target type of interest.
In fact, some of the literature on LO aircraft suggests medians are more representative.

Rather goes back to the target models which you don't like.

Arithmetic mean, a simple average of the values measured over a horizontal range at a certain vertical value, at a specified wavelength. What is the reality for them? are they all .001 sq m RCS at all angles except four specific degrees thereby rendering them tactically invisible? Or is there some truth to the standard average RCS claims of .3-.5 sqm RCS?

This is what I wish to discuss.

The reality is that different practitioners prefer different methodologies based on different target types.
Example: TsAGI traditionally used median RCS.

 

[marauder2048]

But the biggest issue for me of course to find what RCS value i should use as input, which the whole point of me asking why Russian use average and why US one likes to use one from just an angle.

The formulation I like is from Kabama et al.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/76140/AIAA-14303-218.pdf?sequence=1

They have the instantaneous probability of radar detection based on aspect/bank angle dependent RCS for
which you could use median RCS; they have a simplified ellipsoid model of aspect/bank angle dependent RCS.

You then more-or-less average the instantaneous probs over the track time.

The Kabama paper has a huge impact factor and you can follow the citation chain forward for
more elaborate analytic RCS modeling:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.876.9358&rep=rep1&type=pdf

 

[Ronny]

Lol, I don't understand? I just told you that those two are not the only characteristics of an IADS system. And those two characteristics are not as easy as you think, software refinement takes time, and limited in how much improvement there is, rather difficult to squeeze another 20 percent performance through just software improvements.

And aperture? Sure, comes with more power draw, difficult to cope with on a limited powerbase available. I highly doubt you'll see a S-400M anytime soon, compared to a brand new system like S-500.
And sure internals are difficult to change on aircraft, my point exactly, both systems are frozen in most part for their primary design characteristics.

I don't think you got the point,
Apertures, software of radar are not super easy to change, but they can be changed and much much easier than changing the airframe shape or the internal radar absorbing structure of an aircraft. Take for example: the F-15 airframe has changed its radar many times in its life cycle from APG-63 to APG-70 to APG-63v1 to APG-63v2 to APG-63v3 then APG-83. Now how many times have you seen the production version of F-15 change the fuselage shape or wing shape?

I'm referring to nuclear role.

AGM-129 has nuclear warhead

Really? Considering until recently Thz devices were practically lab based, "existing" was the biggest problem for it. Second of all, yes attenuation is enormous at THz range, yet still being worked on for radar/imagery, due to the fact that THz doesn't care at all shaping, I fail to see how stealth aircraft would be "optimized" against Thz.

All THz devices are labs based because the sheer idea of using THz radar for air defense purposes is even less practical than using a toy water gun to intercept ballistic missiles.
"Enormous" is still a massive understatement when talking about the THz absorption rate of the atmosphere. So let me put it this way for you: Atoms are very very small while the universe is very very big, but it is estimated that there are only 10^78 to 10^82 atoms in the known, observable universe. Compare that to the number I gave you earlier, every km that the signal of a 1 THz radar pass through atmosphere, the signal strength will reduced by 10^1000 times. So unless you want your radar to have maximum range of 5-10 meters forget about THz frequency.
And THz care a lot about shaping, even more than the common X-band since at 1 THz the wavelength is barely 0.3 mm, so most if not all features of the stealth aircraft will be in optical region for a THz radar.