J-20 5th Generation Fighter VII

Blitzo · Nov 29, 2022

gongolongo said:
Didn't the article say that the Su-57 and F-35 didn't have leading edge treatment while the J-20 did?

No, what it said more specifically was: "the trailing edge treatment on the canard and main wing of J-20 in the form of edge serration will be simulated because they are very easily to identify visually"

I.e.: only the trailing edge of the canard and main wing is represented because of the structurally visible serrations, and is represented in the form of structural edge serrations on the trailing edges only. Not on the edges of the entire aircraft, and not as RAM treatments.
F-35 and Su-57 as aircraft do not have serrated trailing edges that are structurally present, so they were not factored in.

So if you're asking whether J-20 in that simulation had any sort of RAM treatment advantage, I do not think so.

gelgoog · Nov 30, 2022

In the Su-57 they did not want to compromise aerodynamic performance to gain more stealth. The F-35 is limited to Mach 1.6. Su-57 is Mach 2. Despite the F-35 having the best engine of its generation with a thrust to weight ratio of 11.47:1 compared with Su-57 engine at 9.04:1, the F-35 has a loaded thrust to weight ratio of 0.87 while the Su-57 outmatches it at 0.99.

stannislas · Nov 30, 2022

latenlazy said:
Well, I’m not trying to be harsh to the person who chose to do this exercise. I’m just cautioning against drawing any strong conclusions about it.

Like sure, in real life R&D work engineers prefer simpler over more sophisticated models, but that’s because the point of the model is to provide a study tool to explore the general characteristics of your system of interest. That kind of simulation work is just very different from what we seem to be trying to do here, which is to use simulation as an analytical tool to substitute for lack of better methods to derive conclusions about performance.

Well, in general i found what you said make no sense here, can you give like one single example that an model is not used as an anlytical tool in any sort of ways? being an analytical tool is the fundamental purpose of any model, it need to be first as an analystical tool than evaluation or estimation. So, there is no different at all in terms of a model being used, you of couse can have your feeling of this model is too rough, but from a general point of view have a flewed simple model with less details is better than nothing, at least it give a base line.

let me put it further, even if this model is as bad as a 'golf ball' as long as it treat every aircrafts in the same standard, than it has its value. why? because we then can ask something like, why J-20 golf ball has less RCS than Su-57 golf ball? oh it's because central lifting structure has make the su-57 golf ball an extra ditch in its belly. As long as it won't round all aircrafts into perfect balls, the effectiveness of comparision stands.

latenlazy · Nov 30, 2022

stannislas said:
Well, in general i found what you said make no sense here, can you give like one single example that an model is not used as an anlytical tool in any sort of ways? being an analytical tool is the fundamental purpose of any model, it need to be first as an analystical tool than evaluation or estimation. So, there is no different at all in terms of a model being used, you of couse can have your feeling of this model is too rough, but from a general point of view have a flewed simple model with less details is better than nothing, at least it give a base line.

let me put it further, even if this model is as bad as a 'golf ball' as long as it treat every aircrafts in the same standard, than it has its value. why? because we then can ask something like, why J-20 golf ball has less RCS than Su-57 golf ball? oh it's because central lifting structure has make the su-57 golf ball an extra ditch in its belly. As long as it won't round all aircrafts into perfect balls, the effectiveness of comparision stands.

?? I never said models weren’t used as analytical tools?

I just said that in R&D the purpose of a model is to provide a tool to study system characteristics, which is why they don’t have to be as sophisticated. But that’s very different from using a model to derive accurate information about performance.

If your model has low resolution comparing two objects with the same model doesn’t tell you how they perform relative to each other in reality, just in context of the model. This again isn’t always problem if you’re just using a model to study very general dynamics, but it doesn’t tell you anything meaningful about actual performance comparisons. Details that matter and could change conclusions get obscured by the low resolution of the model.

stannislas · Nov 30, 2022

latenlazy said:
?? I never said models weren’t used as analytical tools?

I just said that in R&D the purpose of a model is to provide a tool to study system characteristics, which is why they don’t have to be as sophisticated. But that’s very different from using a model to derive accurate information about performance.

If your model has low resolution comparing two objects with the same model doesn’t tell you how they perform relative to each other in reality, just in context of the model. This again isn’t always problem if you’re just using a model to study very general dynamics, but it doesn’t tell you anything meaningful about actual performance comparisons. Details that matter and could change conclusions get obscured by the low resolution of the model.

of course, but from what we can see, the J-20 model is no where near the 'low resolution as treated as the same thing', in this case F-35 and Su-57, right?

Blitzo · Nov 30, 2022

stannislas said:
of course, but from what we can see, the J-20 model is no where near the 'low resolution as treated as the same thing', in this case F-35 and Su-57, right?

The J-20 model (and the author's other models) is nice, but it is not sufficiently accurate, detailed or representative of the real world aircraft for us to derive accurate information about their real world performance, and we should not draw any significant strong conclusions from it.

Whether it's as low or high resolution as the F-35 and Su-57 model that the author made is irrelevant.

The only conclusion I would be comfortable confidently drawing from this study is "J-20 is designed with significant RF signature management shaping" (i.e.: something we've all already known anyway since J-20 first emerged).
Anything else beyond that gets more dicey, due to (as latenlazy said), the limitations of the accuracy of the model.

latenlazy · Nov 30, 2022

stannislas said:
of course, but from what we can see, the J-20 model is no where near the 'low resolution as treated as the same thing', in this case F-35 and Su-57, right?

From what I can see I absolutely think this model is too low resolution. A model this rough should be able to give us some insight on where the intended hotspots are for radar reflection but imo you can’t tell much about how effectively it actually reflects EM energy because the shape of the planes aren’t continuous but low dimensional polygons, which is going to give you inherently noisy reflections.

stannislas · Nov 30, 2022

Blitzo said:
The J-20 model (and the author's other models) is nice, but it is not sufficiently accurate, detailed or representative of the real world aircraft for us to derive accurate information about their real world performance, and we should not draw any significant strong conclusions from it.

Whether it's as low or high resolution as the F-35 and Su-57 model that the author made is irrelevant.

The only conclusion I would be comfortable confidently drawing from this study is "J-20 is designed with significant RF signature management shaping" (i.e.: something we've all already known anyway since J-20 first emerged).
Anything else beyond that gets more dicey, due to (as latenlazy said), the limitations of the accuracy of the model.

that's not what latenlazy was argue about, I was saying, given how the model is like, may be 'the method has flews and the missing in some deteails' but if this hold the same for all three aircrafs (F-35 and Su-57), than the model is meaningful, it will give us a realitive idea on how each aircraft is comparing with each other, in terms of how accurate they are, that's a judgmental call.

latenlazy · Nov 30, 2022

stannislas said:
that's not what latenlazy was argue about, I was saying, given how the model is like, may be 'the method has flews and the missing in some deteails' but if this hold the same for all three aircrafs (F-35 and Su-57), than the model is meaningful, it will give us a realitive idea on how each aircraft is comparing with each other, in terms of how accurate they are, that's a judgmental call.

If the thing you’re trying to measure with a model is the noise floor a noisy model won’t tell you what you are trying to look for, even relatively between three objects that are being observed by the same model.

stannislas · Nov 30, 2022

latenlazy said:
From what I can see I absolutely think this model is too low resolution. A model this rough should be able to give us some insight on where the intended hotspots are for radar reflection but imo you can’t tell much about how effectively it actually reflects EM energy because the shape of the planes aren’t continuous but low dimensional polygons, which is going to give you inherently noisy reflections.

but you do understand, computer made of 0 and 1 ticked in discrete clock right? so for any simulation it's going to be polygons anyway, just how many polygons they are. what i was saying is that, as long as they can hold the polygons resolution asame on three aircraft, the simulation comparision is valid

latenlazy said:
If the thing you’re trying to measure with a model is the noise floor a noisy model won’t tell you what you are trying to look for, even relatively between three objects that are being observed by the same model.

that's why i use the golf ball as a figure of speach before, can you distiguish between these three 'golf balls'? are they represent their characteristics in same polygons resolution? if they are, why not?

J-20 5th Generation Fighter VII

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