J-20 5th Gen Fighter Thread VI

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by78

General
Very recent (November 25, 2019) publication of "Research on impact of canard to RCS" by 611. The article seems to have been submitted in 2017.
Summary:
  1. Comparison of conventional and canard configurations of otherwise the same fuselage, based on F-35.
  2. Before improvement on canard configuration, compared to conventional layout, Canard has
    1. Slightly worse RCS return in frontal area from 0 to 30 degrees because:
      1. Canard aft edge reflection is exposed while conventional horizontal stabilizer is blocked by main wing.
      2. Sharp end of aft edge of canard.
      3. The gap between canard and fuselage is another strong contributor, but mostly to high frequency (C band).
    2. Much less RCS return from the side, from 30 to 90 degrees, because conventional horizontal and vertical stabilizer forms a strong reflector while canard does not.
  3. Improvement
    1. Use radar absorbent structure (not paint) on all edges, the light grayish green area. It is much better than paint in terms of frequency band and size.
    2. Smooth curvature and seal of the inner edge of canard.
    3. Cut the corner of canard aft edge.
  4. After improvement, the conclusion is that canard configuration with proper measures is equal to conventional configuration in RCS.
  5. As to the "canard moving increase RCS":
    1. the test shows that within +- 5 degree movement (in cruising), there is both increase and also decrease (-5 degree). Overall neglect-able.
    2. When the canard must be turned more than 5 degrees, the aircraft is in a situation where the whole RCS has drastically increased (close dog fight or violent maneuver) making canard's contribution neglect-able or the whole stealth thing non-existent.
It is interesting to note 2.2 where Canard configuration is inherently better than conventional on the side.
View attachment 55945


Here's the paper in full for those who are interested. It's beyond my limited Chinese to translate this. Anyone wants to take a crack at it? It might just resolve the ongoing endless back-and-forth. Or am I too optimistic?

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Brumby

Major
First:

Single-figure RCS is an extremely ambiguous measurement of an aircraft's stealthiness. For instance, the Russians can correctly claim that the F-22 has a -10 dBsm RCS by averaging a polar diagram of the F-22's RCS.

Even when you have a polar diagram, that's not good enough. A polar diagram only accounts for one azimuth, and moreover, it usually accounts for only one frequency band as well.

When you go through the multi-azimuth polar diagram and then go through frequency, you still have remaining ambiguities. For instance, what's the functional RCS of the aircraft; i.e, stealth aircraft tend to have complex emissions control systems that maintain a specific angle toward detection platforms. What is the practical RCS against one radar? Against five? Against twelve?

===

Second, -10 dBsm typically accounts for a 44% decrease in detection range. A variance of -20 dBsm from the listed figure only results in a reduction of radar range by 68%, although it can reach 99% if jamming is effective.

===

Third, the actual stealth level of the F-35 is an unknown. Some sources claim that the F-35 is stealthier than the F-22 due to improvements in material. Others claim it's less stealthy.

The minus 50 dBsm comes from a Chinese RCS study of a F-35 model at about 10 Ghz, which people have argued is flawed (in the sense of being biased against the F-35) due to the intake shaping. That's the minimum RCS seen, so the F-35, if its emissions control and detector positioning permits, can reach -50 dBsm.

Of course the range varies because of different aspect angles - that is the not the point of the conversation. Your original quote of -50dBsm in my view is an outlier. It is so far out there that I have never seen such a low number either in AWST, Jane, Flight Global. technical literatures or any of the conventional aviation magazines .In any sensible conversation we deal with norms that the general body consider to be representative of its RCS even though the actual details are classified. If you think -50dBsm is representative then quote your source. Are you now attempting a Muhammad Ali maneuver?

As to which platform is more stealthy - the F-35 of F-22, the answer is pretty straight forward from public information. It is the F-22. The reconciliation to the comment that the F-35 is more stealthy in dealing with threats is the idea that the F-35 has a superior sensor fusion capability (multi spectral vs RF only) and due to its superior SA is able to position its flight profile with less probability of detection.

This is all OT and will be my last on this topic.
 

Air Force Brat

Brigadier
Super Moderator

This is actually very helpful, and we see in the modeling that indeed the main wing is pushed far aft of its normal position with the addition of the canard, just as I speculated.... I do note that there is only a partial overlap on the trailing edge of the main wing with the vertical stab/rudder, but there is indeed an overlap forming a reflector...

Note that there is NO mention of any RCS spike as a result of the main wing moving aft, and while the spike may be small, it seems to have been omitted from the paper??

So this is one of the cascading effects Mr. Brumby alerted SDF members to be aware of....

also note the author mentioning the importance of construction using meta-material on highly reflective areas, ie leading edges of canards and main wings, inlets, etc. etc. we see this on the LockMart 5 Gens as well..

respectfully Air Force Brat

since this originated with 611, I think its a safe bet that they are doing apologetics on the canard/aft delta main wing configuration, and their decision to build the J-20 in this configuration...

all good, but I would again caution readers that this is a highly subjective paper, and ask readers to note that my speculation as to configuration and effects of same were indeed verified by the modeling.....
 

lgnxz

Junior Member
Registered Member
This is actually very helpful, and we see in the modeling that indeed the main wing is pushed far aft of its normal position with the addition of the canard, just as I speculated.... I do note that there is only a partial overlap on the trailing edge of the main wing with the vertical stab/rudder, but there is indeed an overlap forming a reflector...

Note that there is NO mention of any RCS spike as a result of the main wing moving aft, and while the spike may be small, it seems to have been omitted from the paper??

So this is one of the cascading effects Mr. Brumby alerted SDF members to be aware of....

also note the author mentioning the importance of construction using meta-material on highly reflective areas, ie leading edges of canards and main wings, inlets, etc. etc. we see this on the LockMart 5 Gens as well..

respectfully Air Force Brat

since this originated with 611, I think its a safe bet that they are doing apologetics on the canard/aft delta main wing configuration, and their decision to build the J-20 in this configuration...

all good, but I would again caution readers that this is a highly subjective paper, and ask readers to note that my speculation as to configuration and effects of same were indeed verified by the modeling.....
Or maybe your opinion of such an RCS spike is just too exaggerated? You said before that they should move the main wing back for weight balance, and they did, and the rest of the calculation is done by computer simulation, which presented into the graph on page 5. Whether they talk about your hypothesis in the paper is irrelevant, just simply look at the result and it shows that there's no such thing as a big RCS spike on the back that you want it to be. Between your mere words and their research, sorry to say that they have more proofs that their conclusion is correct.

And what's so apologetic about the paper? Is the computer simulation suddenly biased and omit your so called RCS spike from the moving the main wing? Are the conclusion the researchers made by showing the similar RCS between delta vs conventional configuration is false/biased if you look at the result graph? Let's reverse the position, if for example lockheed martin makes a stealth wing configuration research, are you going to call them apologetic/subjective from the start due to their involvement with US stealth aircrafts or do you have to actually look at their research and point out the flaws in their research? Having said that, do you find any flaws in the result (mainly from page 5 which talks about the comparison) that justify calling it an apologetic paper instead of just research paper??
 

Air Force Brat

Brigadier
Super Moderator
Or maybe your opinion of such an RCS spike is just too exaggerated? You said before that they should move the main wing back for weight balance, and they did, and the rest of the calculation is done by computer simulation, which presented into the graph on page 5. Whether they talk about your hypothesis in the paper is irrelevant, just simply look at the result and it shows that there's no such thing as a big RCS spike on the back that you want it to be. Between your mere words and their research, sorry to say that they have more proofs that their conclusion is correct.

And what's so apologetic about the paper? Is the computer simulation suddenly biased and omit your so called RCS spike from the moving the main wing? Are the conclusion the researchers made by showing the similar RCS between delta vs conventional configuration is false/biased if you look at the result graph? Let's reverse the position, if for example lockheed martin makes a stealth wing configuration research, are you going to call them apologetic/subjective from the start due to their involvement with US stealth aircrafts or do you have to actually look at their research and point out the flaws in their research? Having said that, do you find any flaws in the result (mainly from page 5 which talks about the comparison) that justify calling it an apologetic paper instead of just research paper??

Apologetics describe a positive argument in favor of something, in this paper the argument is "FOR" the canards, even if there is a slight (according to the authors), RCS spike here and there, overall the canard is only slightly more "noisy" than a conventional configuration..... they do in fact acknowledge that.

I don't object to any of the authors arguments, they are all sound arguments, I simply point out that they did NOT in fact get into every aspect of moving the main wing aft. They did NOT include any data caused by the interface of the main wing with the rudder/vertical stabs.

More notable is the fact that the authors have the data for an F-35, and that they are using the F-35 as an example of a very clean low L/O artifact in their research, a null in their research, it also lends weight that the J-20 fuselage is a very close rendition in that they are using the F-35 fuselage as a proxy for the J-20.....
 

lgnxz

Junior Member
Registered Member
They did NOT include any data caused by the interface of the main wing with the rudder/vertical stabs.
And what kind of data is that supposed to be?? Didn't they already take the whole 3D model of the delta wing planes into simulation? Again, all the RCS calculation are obtained through computer, which should have automatically take into account all geometric changes of the wings during the simulation, giving you the final RCS result presented in that final graphs that you see on page 5. It's illogical to think there's more 'missing data' that you're still looking for; it's already aggregated in there.
 

Inst

Captain
Of course the range varies because of different aspect angles - that is the not the point of the conversation. Your original quote of -50dBsm in my view is an outlier. It is so far out there that I have never seen such a low number either in AWST, Jane, Flight Global. technical literatures or any of the conventional aviation magazines .In any sensible conversation we deal with norms that the general body consider to be representative of its RCS even though the actual details are classified. If you think -50dBsm is representative then quote your source. Are you now attempting a Muhammad Ali maneuver?

As to which platform is more stealthy - the F-35 of F-22, the answer is pretty straight forward from public information. It is the F-22. The reconciliation to the comment that the F-35 is more stealthy in dealing with threats is the idea that the F-35 has a superior sensor fusion capability (multi spectral vs RF only) and due to its superior SA is able to position its flight profile with less probability of detection.

This is all OT and will be my last on this topic.

file.php


Note that this is for metallic RCS (no-coating), and minimal RCS is roughly -50 dBsm.

The other source is roughly
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.

Further discussion of the F-35's RCS belongs in the F-35 / USAF thread, but I want to point out that the F-35 is a physically smaller airframe than the F-22, and that it uses more advanced and modern RAM than the F-22. It is very plausible that the F-35, in certain bands and angles, is stealthier than the F-22.

@Air Force Brat

Basically, when the J-20's canards are discussed, it comes up that the space between the canards and the main body is basically a corner reflector that's exposed to the front. This corner reflector is addressed by highly aggressive use of RAM. Incidentally, the F-22 ALSO has frontal corner reflectors, but this is created by its intake system with a gap between the intakes and the main body to act as a diverter. In the F-22's case, the F-22 slathers ram aggressively in this gap to mitigate the effects of the corner reflection.
 
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