Interesting, thx for passing on the chart. I'll need more info on this to believe it. The electronic engineer in me thinks this is more propaganda than science.
J-20 5th Gen Fighter Thread V
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If true then it does confirm the theory that the RCS is at the lowest in the front.
plawolf
Lieutenant General
At best that's what a full metal J20's RCS might look like.
With RAM and composites as well as likely measurement and modelling errors on the part of the team trying to build a model from just photos, that chart is not going to look anything like what the RCS profile of a real world J20 would look like.
With RAM and composites as well as likely measurement and modelling errors on the part of the team trying to build a model from just photos, that chart is not going to look anything like what the RCS profile of a real world J20 would look like.
Exactly. Unless they have a J-20, this must be a computer model. Models are by nature guesses, the guess is only as good as the information feed into the computer. Nobody has the information required to produce that graph. Even if the red on the graph was accurate( I don't think it is) , the numbers on it are not sensible. If the numbers were correct and the graph is accurate and exact it still has little or no relevance in the real world.
No actually I think anyone who's seen enough doctored pictures should easily be able to tell this picture does not have any of the hallmarks of a doctored picture.
I don't know what you mean by "the two departing aircraft are very close" -- I assume you know what a two ship takeoff is like.
From the angle of the picture, the two J-20s look exactly like what we would expect for a two ship takeoff.
Not quite -- I think the EOIRST in the J-20 in the picture is obviously a functional one and looks the same to the functional EOIRSTs that we've seen in some of the prototypes and the first LRIP #2101 -- i.e.: we can tell the EOIRST has glass windows.
OTOH, what plawolf and I were talking about a while back, were about the LRIP J-20s that we saw in the parades in service colours... their EOIRSTs OTOH were grey and opaque and did not look like they had windows like what we see in the J-20 in this picture.
Even if RAM is not modelled (it almost certainly isn't), there is still value in computations like this. Otherwise they wouldn't be done. There is stuff like error budgets, partial differentials of the result with respect to input errors etc that are usually found in scientific papers. A proper rebuttal of the result would require the full study and much more expertise than the average (dare I say any) forum member has.
The diagram does imo capture the potential rcs hotspots of the J-20. The tail/exhaust, and the reflecting "pockets" caused by the canard, LERX, and wing leading edge.
There would have been more value if they included another design using the same methodology for comparison.
plawolf
Lieutenant General
Models are only as good as the underlying assumptions and underlying data, and stealth is about so much more than just external shaping.
A core part of the J20 preliminary design evaluation and selection process would have been extensive tests on scale models in a real RCS test chamber to assess their underlying shaping RCS characteristics. At a stretch, this is what all these public RCS maps can show.
But that is only the most basic starting point, and conveniently for certain interest groups, they also show the worst possible RCS profile of the J20.
The Chinese would have done their own, exhaustive RCS modelling and testing to better refine the shape. Then the real hard work beings of using materials and internal structures to mitigate any RCS hotspots from the basic shaping.
When even with all that real world data to help refine their models, and supercomputers with which to crunch the numbers, the Chinese still put real J20s on RCS ranges, and made tweaks and modifications through the prototype stage to better refine their stealth, aerodynamic and other properties of the airframe.
That should give you some idea of how complex and difficult accurate RCS modelling can be.
Which in turn shows how woefully inadequate any conclusions drawn from using photos to model a highly complex object and then using commercially available civilian RCS modelling software on it would be.
To me, data we know with almost certainty to be critically flawed is worse than no data. As in the absence of any real, authoritative data to contradict this bad data, it would be all too easy for people with an agenda or preconceptions to use this fundamentally flawed data to shut down contrary views, no matter how logical and reasonable.
It's not good, but neither is it bad. It looks like an odd diagram; there's lots of asymmetries which you would not expect from a real model. Moreover, it doesn't look like it's fully-detailed: if you compare it to F-35 and F-22 diagrams, theirs shows much greater variation depending on angle.
On the other hand, from diagrams of the F-35 and F-22, we see between -30 and -20 dBsm radar returns, while minimum RCS on the J-20 diagram is about -20. So it's about an order of magnitude stealth difference, or about a 44% reduction in detection range.
On the other hand, from diagrams of the F-35 and F-22, we see between -30 and -20 dBsm radar returns, while minimum RCS on the J-20 diagram is about -20. So it's about an order of magnitude stealth difference, or about a 44% reduction in detection range.
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