China Flanker Thread II

[plawolf]

Or maybe as its batch 1 the remaining service life did not justify an AESA upgrade.

Maybe, but if that was the case, why even bother to re-engine them at all?

They could have done the re-engine work on later batches with more airframe hours remaining and just kept these flying with the stripped out AL31s if there aren’t many airframe hours remaining.

 

[Maikeru]

Maybe, but if that was the case, why even bother to re-engine them at all?

They could have done the re-engine work on later batches with more airframe hours remaining and just kept these flying with the stripped out AL31s if there aren’t many airframe hours remaining.

Later batches use WS10 anyway only the first batch of J11B used Russian engines because WS10 was not reliable at that time.

 

[Tirdent]

That depends on the load bearing structure. It’s not like you’re going into a material swap blind. Just from your own structural testing you should have a good idea of what kinds and magnitudes of loads you should expect for each fitting and part and how reasonable it would be to swap materials, and which materials are appropriate to pair for the swap. This also btw applies to actual changes in shape. Most shape changes are not dramatic new geometries but additions or subtractions with well known and predictable effects on load distribution. It’s not just a dichotomy of skin vs structure. Real analysis goes into this stuff, and that can be done pretty straightforwardly. And that real analysis cannot be avoided because you *are* reverse engineering a whole production process so you need to do frame testing from scratch anyways just to make sure you’re reproducing comparable results from your reference copy. The shorthand you’re using undersells, imo, how much material swapping is possible.

The problem isn't the analysis, it's that CFRP really isn't "black metal", first and foremost because its properties are strongly anisotropic. A primary strutcural member designed to take a particular load is necessarily going to be significantly different from an aluminium or titanium equivalent, to the point that you might for example use 4 where previously you had 5. You also tend to need markedly larger rivets with wider spacing to fasten composite parts. Both these things would be visible on the outside of the aircraft even for parts hidden inside the airframe (say, a wing carry-through bulkhead), and the former can have cascading effects that make the whole thing prohibitive.

Well, AV-8B's dimensions changes have multiple reasons and should not be simply put down to "changing materials MUST lead to major changes in exterior dimensions".

Of course. The problem is finding an example that doesn't include significant alterations because, as mentioned, the effort is so big that generally you take the opportunity to make far deeper changes. Wholesale replacement of metallic primary structure while artificially constraining yourself like that isn't a very cost-effective thing to do, as I said. There's a reason why there are few if any such examples The F-15E with its SPF/DB aft fuselage might fit, but that is titanium -> titanium, not metal -> composite.

The paper I quoted also stated that the russians took a similar approach with titanium bulkheads when designing the su-35, but this in no way indicates that the Chinese flankers made very little structural changes, unless your definition of "structural changes" exclude changing designs and materials of individual componants. As to the book, there are paragraphs with accompanying pictures that clearly showcase the flanker's intake. In case you aren't aware, official Chinese publications seldom outright state what paticular model is discussed unless it is considered suffciently "Un-advanced", such as the J-8 in this case.

My point is not about structural changes in general, but composites specifically. That's the rationale Bronk invoked for his argument, and in any case the Su-35 (incidentally, be interesting to know which Su-35 was being referred to in the paper - Su-27M or Su-35S?) also takes advantage of increased integral machining.

 

[Schwerter_]

The problem isn't the analysis, it's that CFRP really isn't "black metal", first and foremost because its properties are strongly anisotropic. A primary strutcural member designed to take a particular load is necessarily going to be significantly different from an aluminium or titanium equivalent, to the point that you might for example use 4 where previously you had 5. You also tend to need markedly larger rivets with wider spacing to fasten composite parts. Both these things would be visible on the outside of the aircraft even for parts hidden inside the airframe (say, a wing carry-through bulkhead), and the former can have cascading effects that make the whole thing prohibitive.



Of course. The problem is finding an example that doesn't include significant alterations because, as mentioned, the effort is so big that generally you take the opportunity to make far deeper changes. Wholesale replacement of metallic primary structure while artificially constraining yourself like that isn't a very cost-effective thing to do, as I said. There's a reason why there are few if any such examples The F-15E with its SPF/DB aft fuselage might fit, but that is titanium -> titanium, not metal -> composite.



My point is not about structural changes in general, but composites specifically. That's the rationale Bronk invoked for his argument, and in any case the Su-35 (incidentally, be interesting to know which Su-35 was being referred to in the paper - Su-27M or Su-35S?) also takes advantage of increased integral machining.

I agree with your point that switching from metal to composites in large scale is rare and usually comes with significant redesign and work input. However this doesn't necessarily translates to "This degree of changes are not present on the J-11B". According to multiple Chinese sources the J-11B fits this catagory (relatively large-scale switches to composites with redesigns on various parts) and does indeed have very little exterior change. Whether you choose to believe said sources is not my concern.

 

[Schwerter_]

The problem isn't the analysis, it's that CFRP really isn't "black metal", first and foremost because its properties are strongly anisotropic. A primary strutcural member designed to take a particular load is necessarily going to be significantly different from an aluminium or titanium equivalent, to the point that you might for example use 4 where previously you had 5. You also tend to need markedly larger rivets with wider spacing to fasten composite parts. Both these things would be visible on the outside of the aircraft even for parts hidden inside the airframe (say, a wing carry-through bulkhead), and the former can have cascading effects that make the whole thing prohibitive.



Of course. The problem is finding an example that doesn't include significant alterations because, as mentioned, the effort is so big that generally you take the opportunity to make far deeper changes. Wholesale replacement of metallic primary structure while artificially constraining yourself like that isn't a very cost-effective thing to do, as I said. There's a reason why there are few if any such examples The F-15E with its SPF/DB aft fuselage might fit, but that is titanium -> titanium, not metal -> composite.



My point is not about structural changes in general, but composites specifically. That's the rationale Bronk invoked for his argument, and in any case the Su-35 (incidentally, be interesting to know which Su-35 was being referred to in the paper - Su-27M or Su-35S?) also takes advantage of increased integral machining.

Also, the paper didn't specifically mention which version of the su-35 was specifically talked about, but from the time of publishment I would say the su-35s is more likely.

 

[Tirdent]

Wait, what exactly is the matter of debate here?

The issue is whether Justin Bronk's assertion that Chinese Flankers have dramatic weight reductions compared to their Russian counterparts is tenable.

Is the question whether J-11B (and by extension, other SAC Flankers afterwards) uses composite materials in their construction?
Or is the question about whether J-11B uses composite materials in specific parts of its construction, such as the load bearing elements of the airframe?

By implication, the latter.

Even the basic Su-27 has a tiny amount of composite construction and there was never a reason to doubt that modest increases could have been made in the J-11. Bronk's assertion however requires the introduction of composite on a frankly massive scale which necessarily means the inclusion of primary load-bearing structure. These are the heaviest and most highly-stressed parts of the airframe, so it is here that the largest reductions can be obtained. If you want to get a Flanker below 16t, you're going to run out of moderately stressed skin to replace before approaching that figure.

(If you don't know the language, you'll just have to take the word of people who can understand the language. Though of course you can ask for clarifications, but simply rubbishing it is frankly non-constructive and borderline insulting)

Where have I rubbished anything? It's just that the scale of application is quite frankly a very important point in this discussion. Without having a handle on that, it's impossible to safely make the kind of assertion Bronk made.

If it's about specifically whether composite materials are used in the specific load bearing elements of the airframe, that is not something we know, but I don't think anyone else brought it up before you did in #8847.

Sure - Bronk did (indirectly), before we even get into my contributions! And I in fact made the point rather plain in #8829 (the first really elaborate message on the subject):

You don't get massive weight reductions (I think the rumoured saving was several hundred kilograms, bringing OEW below 16t) with minor surgery that does not manifest in externally visible differences.

You requested a translation of the video, while also expressing doubt as to whether it was even for J-11B in the first place, and translations have been provided to you.

And thanks were given to the contributor responsible! The statements just happened to be too vague to really add much to the discussion.

That video in turn was linked, because previously you'd suggested that the use of composites in SAC Flankers "hadn't been conclusively proven," and suggesting it was only based on external views of primer colour.

Well, until this thread I had never seen the claim properly supported in all these years that it has been around, and not for lack of searching, either. Only in English, obviously, and with that caveat the argument *was* at best supported by the primer colour reasoning in the resources available to me until now. Trust me, I'm happy that finally this debate has yielded a proper source for something I've been wondering about for longer than I've been a member round here!

That second video with the J-11 fins unambiguously referred to in the subtitles is gold - but as I said, required about 40 minutes of effort to get the information content of 40 seconds. A verbatim translation of the text from that segment would have made the whole thing orders of magnitude more accessible:

关键材料的每一次突破 - Every breakthrough in key materials

都凝聚着创新与拼搏 - Are all condensed with innovation and hard work

而在航空工业 - And in the aviation industry

也有一个口号 - There is also a slogan

"为每一克减重而奋斗。- "Fight for every gram of weight loss.

因为 - because

轻质高强度材料 - Light high strength material

历来是航空材料攻关的方向 - It has always been the direction of aviation materials research

新型复合材料 - New composite materials

是目前航空强国 - it's an aviation strong country.

最关注的核心材料之一 - One of the most concerned core materials

航空人是如何实现材料突破升级的呢 - How did the aviation people achieve material breakthroughs and upgrades?

在航空工业沈飞的部装车间里 - In the assembly workshop of Aviation Industry Shen Fei

中国第一款三代重型战机 - China's first three-generation heavy fighter

开-11B正在组装 - Kai-11B is being assembled

它绿色的尾翼 - Its green tail [at this point the J-11 tails are shown]

正是由高强度复合材料制成 - It is made of high-strength composite materials

That is as good as it gets as a source, the link between composites and the J-11 tails is made absolutely plain. But each of the lines above is one screenshot that you have run through the translator which, just to keep you entertained, will every now and then ask you to solve a captcha for sending such a flood of requests.

Now that evidence has been provided, and translated as well, which definitively states that composite use is present in the J-11B (with specific elements of the airframe mentioned as including wing, fuselage and tails), what exactly remains to be clarified?

Nothing really, unless we want to discuss whether such things as the wing skins, spars and wing carry through bulkheads are composite. But clearly we've established that the J-11 and subsequent Chinese Flankers have composite fins and rudders, which is more than the Su-35 and admittedly more than I thought. Will it save >500kg and justify Bronks assertion? Probably not, we should be looking at 100 to 200kg, but it's not entirely trivial.

 

[Schwerter_]

The issue is whether Justin Bronk's assertion that Chinese Flankers have dramatic weight reductions compared to their Russian counterparts is tenable.



By implication, the latter.

Even the basic Su-27 has a tiny amount of composite construction and there was never a reason to doubt that modest increases could have been made in the J-11. Bronk's assertion however requires the introduction of composite on a frankly massive scale which necessarily means the inclusion of primary load-bearing structure. These are the heaviest and most highly-stressed parts of the airframe, so it is here that the largest reductions can be obtained. If you want to get a Flanker below 16t, you're going to run out of moderately stressed skin to replace before approaching that figure.



Where have I rubbished anything? It's just that the scale of application is quite frankly a very important point in this discussion. Without having a handle on that, it's impossible to safely make the kind of assertion Bronk made.



Sure - Bronk did (indirectly), before we even get into my contributions! And I in fact made the point rather plain in #8829 (the first really elaborate message on the subject):





And thanks were given to the contributor responsible! The statements just happened to be too vague to really add much to the discussion.



Well, until this thread I had never seen the claim properly supported in all these years that it has been around, and not for lack of searching, either. Only in English, obviously, and with that caveat the argument *was* at best supported by the primer colour reasoning in the resources available to me until now. Trust me, I'm happy that finally this debate has yielded a proper source for something I've been wondering about for longer than I've been a member round here!

That second video with the J-11 fins unambiguously referred to in the subtitles is gold - but as I said, required about 40 minutes of effort to get the information content of 40 seconds. A verbatim translation of the text from that segment would have made the whole thing orders of magnitude more accessible:

关键材料的每一次突破 - Every breakthrough in key materials

都凝聚着创新与拼搏 - Are all condensed with innovation and hard work

而在航空工业 - And in the aviation industry

也有一个口号 - There is also a slogan

"为每一克减重而奋斗。- "Fight for every gram of weight loss.

因为 - because

轻质高强度材料 - Light high strength material

历来是航空材料攻关的方向 - It has always been the direction of aviation materials research

新型复合材料 - New composite materials

是目前航空强国 - it's an aviation strong country.

最关注的核心材料之一 - One of the most concerned core materials

航空人是如何实现材料突破升级的呢 - How did the aviation people achieve material breakthroughs and upgrades?

在航空工业沈飞的部装车间里 - In the assembly workshop of Aviation Industry Shen Fei

中国第一款三代重型战机 - China's first three-generation heavy fighter

开-11B正在组装 - Kai-11B is being assembled

它绿色的尾翼 - Its green tail [at this point the J-11 tails are shown]

正是由高强度复合材料制成 - It is made of high-strength composite materials

That is as good as it gets as a source, the link between composites and the J-11 tails is made absolutely plain. But each of the lines above is one screenshot that you have run through the translator which, just to keep you entertained, will every now and then ask you to solve a captcha for sending such a flood of requests.



Nothing really, unless we want to discuss whether such things as the wing skins, spars and wing carry through bulkheads are composite. But clearly we've established that the J-11 and subsequent Chinese Flankers have composite fins and rudders, which is more than the Su-35 and admittedly more than I thought. Will it save >500kg and justify Bronks assertion? Probably not, we should be looking at 100 to 200kg, but it's not entirely trivial.

just a bit of additional information, iirc Yankee once mentioned in an article on his wechat official account (the account's now gone, sadly) that the weight reductions on the J-11B due to composites is "X00KG" and he specifically said it's not 700, which was (and still is) a figure circulating around the internet. If yankee's word is to be taken as true then a 100-200kg reduction as suggested by you is quite likely, cheers!

 

[weig2000]

The issue is whether Justin Bronk's assertion that Chinese Flankers have dramatic weight reductions compared to their Russian counterparts is tenable.



By implication, the latter.

Even the basic Su-27 has a tiny amount of composite construction and there was never a reason to doubt that modest increases could have been made in the J-11. Bronk's assertion however requires the introduction of composite on a frankly massive scale which necessarily means the inclusion of primary load-bearing structure. These are the heaviest and most highly-stressed parts of the airframe, so it is here that the largest reductions can be obtained. If you want to get a Flanker below 16t, you're going to run out of moderately stressed skin to replace before approaching that figure.



Where have I rubbished anything? It's just that the scale of application is quite frankly a very important point in this discussion. Without having a handle on that, it's impossible to safely make the kind of assertion Bronk made.



Sure - Bronk did (indirectly), before we even get into my contributions! And I in fact made the point rather plain in #8829 (the first really elaborate message on the subject):





And thanks were given to the contributor responsible! The statements just happened to be too vague to really add much to the discussion.



Well, until this thread I had never seen the claim properly supported in all these years that it has been around, and not for lack of searching, either. Only in English, obviously, and with that caveat the argument *was* at best supported by the primer colour reasoning in the resources available to me until now. Trust me, I'm happy that finally this debate has yielded a proper source for something I've been wondering about for longer than I've been a member round here!

That second video with the J-11 fins unambiguously referred to in the subtitles is gold - but as I said, required about 40 minutes of effort to get the information content of 40 seconds. A verbatim translation of the text from that segment would have made the whole thing orders of magnitude more accessible:

关键材料的每一次突破 - Every breakthrough in key materials

都凝聚着创新与拼搏 - Are all condensed with innovation and hard work

而在航空工业 - And in the aviation industry

也有一个口号 - There is also a slogan

"为每一克减重而奋斗。- "Fight for every gram of weight loss.

因为 - because

轻质高强度材料 - Light high strength material

历来是航空材料攻关的方向 - It has always been the direction of aviation materials research

新型复合材料 - New composite materials

是目前航空强国 - it's an aviation strong country.

最关注的核心材料之一 - One of the most concerned core materials

航空人是如何实现材料突破升级的呢 - How did the aviation people achieve material breakthroughs and upgrades?

在航空工业沈飞的部装车间里 - In the assembly workshop of Aviation Industry Shen Fei

中国第一款三代重型战机 - China's first three-generation heavy fighter

开-11B正在组装 - Kai-11B is being assembled

它绿色的尾翼 - Its green tail [at this point the J-11 tails are shown]

正是由高强度复合材料制成 - It is made of high-strength composite materials

That is as good as it gets as a source, the link between composites and the J-11 tails is made absolutely plain. But each of the lines above is one screenshot that you have run through the translator which, just to keep you entertained, will every now and then ask you to solve a captcha for sending such a flood of requests.



Nothing really, unless we want to discuss whether such things as the wing skins, spars and wing carry through bulkheads are composite. But clearly we've established that the J-11 and subsequent Chinese Flankers have composite fins and rudders, which is more than the Su-35 and admittedly more than I thought. Will it save >500kg and justify Bronks assertion? Probably not, we should be looking at 100 to 200kg, but it's not entirely trivial.

I want to commend you on your persistence and professionalism and the effort to wade into a foreign language to get to the bottom of the thing. Even if we still have different understandings among members here with regards to the matter due largely to the absence of clear evidence, there is no doubt that we have made progress in our understanding collectively. And you have contributed to the discussion.

 

[latenlazy]

The problem isn't the analysis, it's that CFRP really isn't "black metal", first and foremost because its properties are strongly anisotropic. A primary strutcural member designed to take a particular load is necessarily going to be significantly different from an aluminium or titanium equivalent, to the point that you might for example use 4 where previously you had 5. You also tend to need markedly larger rivets with wider spacing to fasten composite parts. Both these things would be visible on the outside of the aircraft even for parts hidden inside the airframe (say, a wing carry-through bulkhead), and the former can have cascading effects that make the whole thing prohibitive.

Not every structure in a frame that uses metal is incompatible with anisotropic materials. No one’s suggesting that the J-15 is using carbon fiber bulkheads. There are plenty of structural details that aren’t the bulkheads.

 

[Blitzo]

The issue is whether Justin Bronk's assertion that Chinese Flankers have dramatic weight reductions compared to their Russian counterparts is tenable.



By implication, the latter.

Even the basic Su-27 has a tiny amount of composite construction and there was never a reason to doubt that modest increases could have been made in the J-11. Bronk's assertion however requires the introduction of composite on a frankly massive scale which necessarily means the inclusion of primary load-bearing structure. These are the heaviest and most highly-stressed parts of the airframe, so it is here that the largest reductions can be obtained. If you want to get a Flanker below 16t, you're going to run out of moderately stressed skin to replace before approaching that figure.



Where have I rubbished anything? It's just that the scale of application is quite frankly a very important point in this discussion. Without having a handle on that, it's impossible to safely make the kind of assertion Bronk made.



Sure - Bronk did (indirectly), before we even get into my contributions! And I in fact made the point rather plain in #8829 (the first really elaborate message on the subject):





And thanks were given to the contributor responsible! The statements just happened to be too vague to really add much to the discussion.



Well, until this thread I had never seen the claim properly supported in all these years that it has been around, and not for lack of searching, either. Only in English, obviously, and with that caveat the argument *was* at best supported by the primer colour reasoning in the resources available to me until now. Trust me, I'm happy that finally this debate has yielded a proper source for something I've been wondering about for longer than I've been a member round here!

That second video with the J-11 fins unambiguously referred to in the subtitles is gold - but as I said, required about 40 minutes of effort to get the information content of 40 seconds. A verbatim translation of the text from that segment would have made the whole thing orders of magnitude more accessible:

关键材料的每一次突破 - Every breakthrough in key materials

都凝聚着创新与拼搏 - Are all condensed with innovation and hard work

而在航空工业 - And in the aviation industry

也有一个口号 - There is also a slogan

"为每一克减重而奋斗。- "Fight for every gram of weight loss.

因为 - because

轻质高强度材料 - Light high strength material

历来是航空材料攻关的方向 - It has always been the direction of aviation materials research

新型复合材料 - New composite materials

是目前航空强国 - it's an aviation strong country.

最关注的核心材料之一 - One of the most concerned core materials

航空人是如何实现材料突破升级的呢 - How did the aviation people achieve material breakthroughs and upgrades?

在航空工业沈飞的部装车间里 - In the assembly workshop of Aviation Industry Shen Fei

中国第一款三代重型战机 - China's first three-generation heavy fighter

开-11B正在组装 - Kai-11B is being assembled

它绿色的尾翼 - Its green tail [at this point the J-11 tails are shown]

正是由高强度复合材料制成 - It is made of high-strength composite materials

That is as good as it gets as a source, the link between composites and the J-11 tails is made absolutely plain. But each of the lines above is one screenshot that you have run through the translator which, just to keep you entertained, will every now and then ask you to solve a captcha for sending such a flood of requests.

Fair enough, though some of the posts subsequent to 8829 conveyed the impression that you doubted that SAC Flankers used any composites at all.

Nothing really, unless we want to discuss whether such things as the wing skins, spars and wing carry through bulkheads are composite. But clearly we've established that the J-11 and subsequent Chinese Flankers have composite fins and rudders, which is more than the Su-35 and admittedly more than I thought. Will it save >500kg and justify Bronks assertion? Probably not, we should be looking at 100 to 200kg, but it's not entirely trivial.

Yes, but it's not just the composite fins and rudders.
Recall, there were two videos, one talking about the tails -- the other talking about using composites for J-11B's blended wing fuselage, at the 27:48 timestamp I mentioned in my last post.
The exact portion of the text -- "歼11B大的机翼叫翼身融合体, 它用到复合材料".


And just for the record, I have no specific estimate or guess as to how much weight is saved in the J-16's use of composites.