J-20 5th Gen Fighter Thread V

[latenlazy]

At this point what reason do we have to doubt that China isn't capable of achieving RCS comparable to the F-22 or F-35?

 

[Blitzo]

Blitzo, if you have to ask that the methodologies are exactly the same, no comparison would be possible. For instance, if we look at weapons ranges reported on data, what altitudes are we talking about? At different altitudes, the air is thinner and therefore projectiles achieve a higher maximum range, and therefore Chinese grenade launchers and Western grenade launchers do not have comparable features.

The funny thing is, RCS is being measured by a computer, without a scale mock-up. The equations for designing stealth aircraft are more or less the same globally, so that we can assume the methodology is the same.

What is your point about methodology? Do you have something specific as opposed to something abstract? Let me guess, are we talking about whether RAM is included? That's the thing. If we look at Chinese RCS estimates for the F-22 and F-35, the RCS is abnormally high compared to reported RCS figures from the US military, implying that the F-22 and F-35 projections made by the Chinese ignore RAM. Likewise, we can assume the figures given for the J-20 by the Taiwanese are either a high or low figure. If it's a low figure, i.e, coatings are included, the J-20 is not very stealthy at all, given the -40 dBsm achievable by the F-35 and F-22. If it's a high figure, then the Taiwanese projections ignore RAM. But the Chinese RCS projections on the F-22 and F-35 also likely ignore RAM, so the Chinese and Taiwanese figures are reasonably close as an apples to apples comparison.

The only real arguments for a lower J-20 RCS figure would be that the Taiwanese model seems to be using the 2001 demonstrator instead of the current aircraft. That may push the RCS difference to 0 to 5 dBsm.

When you reply to me in future can you quote me, so that I can receive a notification?

Anyway, regarding methodology -- yes you're absolutely right. For weapons ranges it is difficult to compare as well. For certain weapons systems like A2A missiles, SAMs I have quite a bit of skepticism towards cross applicability as well.


In this particular case, all I'm saying is to let's give the right degree of skepticism to any sort of attempts of comparison between RCS from different groups/sources unless we have some kind of evidence to suggest their methodology allows accurate cross comparison. Everything from the level of detail to which they've modelled (overall shape of the aircraft, down to details like panels with or without serrations), the frequencies which they're modelling and the conditions they're modelling under. Considering we are only looking at the RCS of these aircraft, yet also considering how important RCS is to these aircraft's performance, then yes I think it is worth treading carefully.

That isn't to say that any attempts of comparison are entirely illegitimate, but I do think it means we should significantly temper the confidence to which we can extrapolate with.

 

[Blitzo]

At this point what reason do we have to doubt that China isn't capable of achieving RCS comparable to the F-22 or F-35?

something something J-20 design compromise of stealth vs aerodynamics, something something RCS calculations for shaping, something something RAM?


Personally I'm not saying J-20's RCS is as good or better than F-22 or F-35 or anything, however I do think that if people want to start to throwing RCS modelling results out and start comparing them, then that means we need to treat the modelling results with the skepticism and vigilance that their methodology should deserve... and comparisons of different results as well.

 

[Inst]

I think I see the crux of our problem. Others are perfectly willing to use loose epistemology to make technology comparable, whereas you rarely do so. But here's the thing, the board at large has a tendency to compare. A positive comparison claiming that Chinese equipment is better than so and so goes unchallenged, but if someone like, say, myself, mentions that the Chinese technology is still not up to par, you guys come out of the woodwork. I don't think that you, as an individual, often do compare, and when you make an aggressive claim, such as the idea that the J-20 is intended to be deployed as an air superiority fighter, you insinuate, instead of making the actual claim. We don't have the same epistemology. I am willing to extrapolate from available evidence to form hypotheses: strictly speaking, we don't know what the J-20's RCS is. That's a secret held only by Chengdu and the PLAAF, and perhaps foreign espionage services that have compromised them. But we do have these models, and from the available information we can make deductions and arrive at conclusions with regards to these models, which is that the J-20 is probably 5 to 10 dBsm less stealthy than American stealth fighters.

@latenlazy: up until recently, the Chinese had a pronounced technology gap with Western leaders, but with the Great Financial Crisis and curbs on military spending, the gap is being closed. As Blitzo said, it's about China having to make do with inferior engines, something that only the most deluded of fanboys would disagree with. The J-20 is definitely innovative in many ways, but while it highly prioritizes stealth, it still compromises it by using canards; every additional control surface, or any surface that juts out, reduces the stealth of the aircraft. This is why I'm so enthusiastic about potential tailfinless variations of the J-20, wherein better engine technology allows Chengdu to jettison the tailfin control surface, reducing weight, drag, and detection distances.

 

[Blitzo]

I think I see the crux of our problem. Others are perfectly willing to use loose epistemology to make technology comparable, whereas you rarely do so. But here's the thing, the board at large has a tendency to compare. A positive comparison claiming that Chinese equipment is better than so and so goes unchallenged, but if someone like, say, myself, mentions that the Chinese technology is still not up to par, you guys come out of the woodwork. I don't think that you, as an individual, often do compare, and when you make an aggressive claim, such as the idea that the J-20 is intended to be deployed as an air superiority fighter, you insinuate, instead of making the actual claim. We don't have the same epistemology. I am willing to extrapolate from available evidence to form hypotheses: strictly speaking, we don't know what the J-20's RCS is. That's a secret held only by Chengdu and the PLAAF, and perhaps foreign espionage services that have compromised them. But we do have these models, and from the available information we can make deductions and arrive at conclusions with regards to these models, which is that the J-20 is probably 5 to 10 dBsm less stealthy than American stealth fighters.

You're not wrong, and there is definitely a bias for more favourable comparisons to go unchallenged depending on which forum or board one is on, that's just the way it goes.

However, at the same time that doesn't invalidate the criticisms of this specific model, and the proposals to compare the results of this model with other ones.
Again, I'm not saying we can't compare the models, but I do think it means there needs to be significant skepticism and caution to the generalizability of the "results".


As for J-20 as an air superiority fighter, I hope you're not trying to compare debates over J-20's role, versus that of one model's RCS versus that of models of other aircraft from other sources?

And frankly if you believe that J-20 being an air superiority fighter is still an aggressive claim these many years on I question whether we've been reading the same forums over the last decade or so.


edit: and again, can you please quote me when you reply to me? So I can see the notifications when you direct a reply to me, otherwise it means I could miss them in future...

 

[FORBIN]

Remember that Kopp's model showed between -20 and -30 dBsm, with spots approaching -40 or even -50 dBSM. I would still say that the J-20 quite possibly is somewhat less stealthy than the F-35 and F-22, but it's up in the air whether it's a 5 or 10 dBSM difference.

Under reserves but confirm previous "infos" for F-22 minimum frontal - 40, F-35 - 30 it is certain. To - 20 J-20 between US and Su-57.

 

[FORBIN]

At this point what reason do we have to doubt that China isn't capable of achieving RCS comparable to the F-22 or F-35?

If you talk for now simple coz USA have yet do since 40 years 4 stealth aircrafts the first for China and Russia USA have much more experience, things similar to noise for submarine.

 

[latenlazy]

If you talk for now simple coz USA have yet do since 40 years 4 stealth aircrafts the first for China and Russia USA have much more experience, things similar to noise for submarine.

Experience isn't a durable or insurmountable gap.

 

[latenlazy]

I think I see the crux of our problem. Others are perfectly willing to use loose epistemology to make technology comparable, whereas you rarely do so. But here's the thing, the board at large has a tendency to compare. A positive comparison claiming that Chinese equipment is better than so and so goes unchallenged, but if someone like, say, myself, mentions that the Chinese technology is still not up to par, you guys come out of the woodwork. I don't think that you, as an individual, often do compare, and when you make an aggressive claim, such as the idea that the J-20 is intended to be deployed as an air superiority fighter, you insinuate, instead of making the actual claim. We don't have the same epistemology. I am willing to extrapolate from available evidence to form hypotheses: strictly speaking, we don't know what the J-20's RCS is. That's a secret held only by Chengdu and the PLAAF, and perhaps foreign espionage services that have compromised them. But we do have these models, and from the available information we can make deductions and arrive at conclusions with regards to these models, which is that the J-20 is probably 5 to 10 dBsm less stealthy than American stealth fighters.

@latenlazy: up until recently, the Chinese had a pronounced technology gap with Western leaders, but with the Great Financial Crisis and curbs on military spending, the gap is being closed. As Blitzo said, it's about China having to make do with inferior engines, something that only the most deluded of fanboys would disagree with. The J-20 is definitely innovative in many ways, but while it highly prioritizes stealth, it still compromises it by using canards; every additional control surface, or any surface that juts out, reduces the stealth of the aircraft. This is why I'm so enthusiastic about potential tailfinless variations of the J-20, wherein better engine technology allows Chengdu to jettison the tailfin control surface, reducing weight, drag, and detection distances.

I wasn't talking about the J-20. I was asking why we should presume today that China can't match the F-22 or F-35 in their ability to reduce RCS. Do we have any actual reasons, or just a bunch of presumptions based on preferred conjectures?

Using your arguments, are you suggesting the J-31 has a lower RCS than the J-20? If so, why didn't the PLAAF simply go with a design more akin to the J-31? China didn't *have* to go with a canard configuration.

On the matter of epistemology, no amount of extrapolation can account for information you don't have. Before we invented microscopes it was fair to extrapolate that illnesses must be caused by bad humours. How does that extrapolation stand up to scrutiny today? An epistemology that doesn't account for what isn't known is nothing more than self selected superstitions, or circular self affirming confirmation bias. Right now we don't know how the model was constructed, what the methods and parameters of the model were, and how other designs using the same methodology would compare. To draw confident conclusions without accounting for these questions is nothing less than analytical malpractice.

 

[Inst]

@Bltizo The Taiwanese results are a datapoint, just as Kopp's results are also datapoints. We consider them all in the context of each other, giving them different weighs. As to the J-20 being designed as an air superiority fighter, once again, I'd argue instead that it's designed as a developmental fighter whose primary roles change as its technologies improve. It is not suitable to go one-on-one vs the F-22 yet, nor is it best used trying to attrition F-22s in that role. Against the F-35, interceptor aircraft have done quite well against strikers or multi-role aircraft; the only US air-to-air loss in the first Iraq War was to a MiG-25 with the victim being an F-18.