J-20 5th Gen Fighter Thread V
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I think it should be important for us to acknowledge the legitimacy of whatever test they are running as a sign that they are obviously interested in modelling J-20's RCS.
However, it is something else entirely for anyone to claim that their modelling is an accurate reflection of the real thing, unless we have evidence of them being able to replicate the other aspects of the aircraft's RCS reduction measures specifically in terms of RAM application and structures... and it is even something else entirely to compare what they may estimate to be J-20's RCS versus other publicly available supposed RCS for other stealth fighters in the world.
So IMO there is no problem with taking the NCIST's RCS modelling for what it is -- a model that they've estimated, in effort to try and gauge what the aircraft's RCS profile is like.
But if anyone tries to claim that their RCS estimate accurately reflects on what the real thing's RCS is, or if anyone tries to compare that with the RCS of other aircraft, then that is overextending.
Pretty simple logic really.
Blitzo's general argument is usually that evidence is not sufficient when unpleasant evidence is offered. However, we are playing on rumors, and the conclusions I've proposed are not unreasonable to assume, because the alternative we are seeing is just denying the evidence.
The thing is, we're comparing RCS derived from RCS models made by competitors. For instance, the F-35 model I've mentioned (you can google it) is based off a Chinese study on the probable RCS of the F-35. This yields a negative 20 to negative 30 dBsm range. Using similar methodologies, we get negative 20 minimum dBsm for the J-20, which suggests that the J-20 is still less stealthy than the F-35.
If you seriously want to argue based on this, consider the reflective LERX on the J-20 prototype. These use continuous curvature, but reflect outwards. The current J-20 uses straight LERX instead of curved LERX, which should reduce RCS to some extent. Alternatively, if we wish to attack the model, we can simply claim it's not conducted in sufficient resolution; it is definitely less detailed (i.e, samples and calculations are made for less degree values than on the Kopp simulation) than the Chinese F-35 RCS simulation.
The thing is, we're comparing RCS derived from RCS models made by competitors. For instance, the F-35 model I've mentioned (you can google it) is based off a Chinese study on the probable RCS of the F-35. This yields a negative 20 to negative 30 dBsm range. Using similar methodologies, we get negative 20 minimum dBsm for the J-20, which suggests that the J-20 is still less stealthy than the F-35.
If you seriously want to argue based on this, consider the reflective LERX on the J-20 prototype. These use continuous curvature, but reflect outwards. The current J-20 uses straight LERX instead of curved LERX, which should reduce RCS to some extent. Alternatively, if we wish to attack the model, we can simply claim it's not conducted in sufficient resolution; it is definitely less detailed (i.e, samples and calculations are made for less degree values than on the Kopp simulation) than the Chinese F-35 RCS simulation.
The value of the Taiwanese RCS is in establishing a baseline. It lets us claim that the J-20 is LO, that is to say, it has at most -20 dBsm in certain areas. Perhaps with more accurate models, such as with better clipped canards, using the modern LERX, or increasing the resolution of the modeling, we can find lower minimum RCS figures, pushing it closer to the -30 dBsm peak of the F-22 and F-35 within the Chinese models.
In all actuality, it may be the case that the F-35, the F-22, and J-20 are all -40 dBsm to -50 dBsm coatings. But we can't know that, because the actual polar diagram is classified. Instead, the best we can do is to work on the open extrapolations, which imply that the J-20 is roughly 5 to 10 dBsm noisier than the F-35 and F-22.
In all actuality, it may be the case that the F-35, the F-22, and J-20 are all -40 dBsm to -50 dBsm coatings. But we can't know that, because the actual polar diagram is classified. Instead, the best we can do is to work on the open extrapolations, which imply that the J-20 is roughly 5 to 10 dBsm noisier than the F-35 and F-22.
And your general argument is that bad evidence is sufficient and tells us as much or more as good evidence, usually based on a faulty understanding of the subject areas needed to interpret evidence in the first place.
The NCSIST's RCS does provide a baseline, but it doesn't allow us to compare what it may be compared to F-35 or F-22 or others, because we do not know the RCS of other aircraft or how they were measured.
My suggestion is that the F-35 RCS developed by competitors (China in this case, if you say) cannot be measured with the Taiwan NCIST's RCS, because we do not know whether the methodology that resulted in both of their RCS was consistent across the two results.
And that goes for all RCS estimates made by various different parties as well. Unless we know their methodology for modelling the RCS for different aircraft is consistent, the "inter-aircraft RCS baseline" is not very useful.
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.
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.
@Totoro: if you look closely, the minimum RCS is achieved on the 90 degree angle. Functional forward RCS is closer to -20 dBsm or .01 m^2. I have the same sentiment you do: the RCS is not bad for a first attempt, and I'm confident later variations on the J-20 can drop the frontal RCS even further.
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