J-20 5th Generation Fighter VII

taxiya · Nov 30, 2022

tphuang said:
btw, someone did a lot work in RCS analysis of j-20. Keep in mind these figures are posted without considering the RAM layer. He clearly stated how he did the simulation, so you can make your own judgement of these things

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Here is the end result of J-20 in his simulation

vs F-35

Based on his analysis, you'd see that average RCS of J-20 faired the worst vs F-35A at X-band. From VHF to L band, the numbers look quite comparable. It seems like F-35A is also very much focused on just S to X band radar directly in front of its nose. Its stealth gets a lot worse as frequency decreases and angles are further away from the center.

Just to point out that the 0.41sqm average RCS of J-20 is significantly larger than what J-20 was required to be which is less than 0.3sqm.

Besides, I am puzzled by lots of people doing this kind of simulation without accurate 3D model of J-20. In radar reflection, every 1 degree matters, every centimeter matters. These people either have direct access to such model from CAC, or just bullshitting.

Why I doubt? Everybody who has been to engineering university must have the experience to match their experiment results in the lab to the expected results from their professors. Some times, +-5% is acceptable, other times +-1% is wrong, without knowing if the input is reliable, the output is just rubbish even one get a number close.

My very latest experience, I found a bug in our product that has been there for years because nobody has tested a specific range of numbers. It looks perfect omitting that range, but results weird behaviour when the range is used as input. This kind of seemingly weird behaviour is the most difficult bug to be discovered. My motto is questioning everything, nothing is to be assumed right until all known corners have been swiped, even after that error should still be expected because one does not know if one know.

ZeEa5KPul · Nov 30, 2022

Blitzo said:
I think that while they numbers are certainly is not representative of the real world aircraft, the efforts taken by the author to do so can still be appreciated.

I've given this some thought and on balance, it would have been better for everyone if this individual just hadn't bothered. We've now wasted several pages discussing this zero-value exercise and it's going to be another anti-fact like "the J-20 is an interceptor" added to the pile.

phrozenflame said:
I had been recently bugging him to do the analysis. Some of his other work is quite interesting. Anyway, it's something useful that we will find in public domain. Ofcourse it isn't perfect but if anyone got better analysis they should raise their hands.

No, it's really not.

Gloire_bb · Nov 30, 2022

ZeEa5KPul said:
No, it's really not.

We probably need to wait for full photogrammetric models to get sufficiently close to the actual thing, especially in X/S bands - and probably need a good civilian specialist on RAMs to enter this discussion. At this point we may be reasonably close to the truth, stealth planes aren't witchcraft in the end.

For now - '3 aircraft of this general configuration can get within one order of magnitude of each other; it is likely that x/s Su-57 aimed for ~somewhat less of an order of magnitude higher numbers within X/S, but is still decent in L and especially VHF'.

latenlazy · Nov 30, 2022

taxiya said:
Just to point out that the 0.41sqm average RCS of J-20 is significantly larger than what J-20 was required to be which is less than 0.3sqm.

Besides, I am puzzled by lots of people doing this kind of simulation without accurate 3D model of J-20. In radar reflection, every 1 degree matters, every centimeter matters. These people either have direct access to such model from CAC, or just bullshitting.

Why I doubt? Everybody who has been to engineering university must have the experience to match their experiment results in the lab to the expected results from their professors. Some times, +-5% is acceptable, other times +-1% is wrong, without knowing if the input is reliable, the output is just rubbish even one get a number close.

My very latest experience, I found a bug in our product that has been there for years because nobody has tested a specific range of numbers. It looks perfect omitting that range, but results weird behaviour when the range is used as input. This kind of seemingly weird behaviour is the most difficult bug to be discovered. My motto is questioning everything, nothing is to be assumed right until all known corners have been swiped, even after that error should still be expected because one does not know if one know.

As I’ve been trying to say about this, if you want to model low noise floor you cannot use a noisy model. And I think that’s probably the comment I’m just going to default to wrt to these kinds of modeling exercises.

taxiya · Nov 30, 2022

latenlazy said:
As I’ve been trying to say about this, if you want to model low noise floor you cannot use a noisy model. And I think that’s probably the comment I’m just going to default to wrt to these kinds of modeling exercises.

I wish you good luck with the approach, but I doubt you will succeed

. I think it is almost impossible to convince people lacking basic knowledge in the subject even if you point at the fault, they would not see what is wrong with it.

From the latest experience, I pointed out what is wrong with the formular to the author who just don't see how it is wrong until I asked him to run his formular with the specific range of inputs and compare the result to his expectation. I was lucky that he could eventually be convinced because at least he can do the convincing by himself.

taxiya · Nov 30, 2022

Gloire_bb said:
We probably need to wait for full photogrammetric models to get sufficiently close to the actual thing, especially in X/S bands - and probably need a good civilian specialist on RAMs to enter this discussion. At this point we may be reasonably close to the truth, stealth planes aren't witchcraft in the end.

For now - '3 aircraft of this general configuration can get within one order of magnitude of each other; it is likely that x/s Su-57 aimed for ~somewhat less of an order of magnitude higher numbers within X/S, but is still decent in L and especially VHF'.

That actually leads to false confidence to one's input, one think one knows but actually doesn't. We are talking about accuracy down to millimeter (resolution to accurately represent object of centimeter which is related to the band), photogrammetric modeling isn't accurate enough. Only laser based 3D modeling can do the job, and we know that is not going to happen.

taxiya · Nov 30, 2022

My last comment about RCS simulation in general. Such effort without accurate model, mockup or real aircraft are wrong, this applies to any aircraft from any country. It isn't about national pride, it is science.

tphuang · Nov 30, 2022

taxiya said:
Just to point out that the 0.41sqm average RCS of J-20 is significantly larger than what J-20 was required to be which is less than 0.3sqm.

Besides, I am puzzled by lots of people doing this kind of simulation without accurate 3D model of J-20. In radar reflection, every 1 degree matters, every centimeter matters. These people either have direct access to such model from CAC, or just bullshitting.

Why I doubt? Everybody who has been to engineering university must have the experience to match their experiment results in the lab to the expected results from their professors. Some times, +-5% is acceptable, other times +-1% is wrong, without knowing if the input is reliable, the output is just rubbish even one get a number close.

My very latest experience, I found a bug in our product that has been there for years because nobody has tested a specific range of numbers. It looks perfect omitting that range, but results weird behaviour when the range is used as input. This kind of seemingly weird behaviour is the most difficult bug to be discovered. My motto is questioning everything, nothing is to be assumed right until all known corners have been swiped, even after that error should still be expected because one does not know if one know.

This is just a best effort model at rcs between f35 and j20. I wouldn't take the value themselves that seriously. What I got out of this is that f35 is really focused just on the narrow sphere in front of its nose and at the x band radar range. You don't really see that as much with j20. It seems to maintain similar level of stealth all across frontal sphere.

latenlazy · Nov 30, 2022

tphuang said:
This is just a best effort model at rcs between f35 and j20. I wouldn't take the value themselves that seriously. What I got out of this is that f35 is really focused just on the narrow sphere in front of its nose and at the x band radar range. You don't really see that as much with j20. It seems to maintain similar level of stealth all across frontal sphere.

I think what we’re trying to say is that the model simply isn’t high resolution enough to even conclude that the F-35’s shaping is focused on just the narrow sphere in front of the nose.

taxiya · Nov 30, 2022

tphuang said:
This is just a best effort model at rcs between f35 and j20. I wouldn't take the value themselves that seriously. What I got out of this is that f35 is really focused just on the narrow sphere in front of its nose and at the x band radar range. You don't really see that as much with j20. It seems to maintain similar level of stealth all across frontal sphere.

As @latenlazy has pointed out, I have also stated in my post 6355 that we can't take the simulation seriously for any conclusion, not only J20, but also F35, regardless the result looks good or bad for any of them. Computer simulation can only give designers a general direction on how and where to tweak their design, but is far from enough to settle the design spec which can only be obtained by actually measuring in a radio dark room.

J-20 5th Generation Fighter VII

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taxiya

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taxiya

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