China Flanker Thread II

[optionsss]

Well, since I don't understand Chinese I can only go by the footage, and that shows generic composite manufacturing of small parts and a cockpit windscreen. Apart from the latter, they may or may not belong to the J-11 (or to bike frames, for all the evidence to the contrary), but they sure as hell are not of a size which would be suitable to shave off hundreds of kilograms. Can you (or anyone else) provide a summary of what is being said on the subject? Is it stated which parts of the J-11 airframe are supposed to be composite?

they did not say exactly which part, just the the wings and fuselage used composites.

 

[Tirdent]

they did not say exactly which part, just the the wings and fuselage used composites.

Thanks! Since the division of the airframe into individual parts remains identical going by photographic evidence it's hard to see where a large weight reduction is supposed to come from. If we (*very* optimistically) assume the full 30% density reduction for a 1:1 part replacement, as opposed to a total redesign, that means we'd be looking at replacing more than 2 tons worth of parts to eke out 700kg. That is almost certainly the majority of the entire wetted area of a Flanker-size fighter aircraft worth in skin panels. If you replace a couple of aluminium maintenance access covers the sum of which does not even amount to several hundred kilograms, there's only so much you can save.

 

[weig2000]

I don't think J-11B use of composites are rumors, in the CCTV documentary on J-11 they mentioned the development and use of composites materials. Here is the YouTube video, composite material part starts at 27 minute mark. It is in chinese.

The part relevant to composite materials: The experiment with composite started with 2nd generation aircraft, but had no real applicable composite to 3rd-gen aircraft (J-11B) then. The domestic development of composite (for J-11B) started around 97/98, and lasted about a decade until it's completed. The documentary mentioned that the composite materials were applied to wing and fuselage of J-11B. Subsequently, composites were also used in other aircraft such as J-10 and J-20. J-16 is not mentioned, but it's pretty obvious it's included (it's similar to and in the same category as J-11B in that aspect).

 

[Blitzo]

Clearly, it's theoretically possible - I'm just pointing out why in practice even Yankee may have no way of knowing, and that there are reasons to remain on the fence.

For the (export?) ESM component of the Su-35 suite quite a few technical specs are available, but (as with Izd. 30 and WS-15) there is hardly anything on the Chinese side to compare them to. Jumping to the conclusion that they must be better is - given the relative merits of the Chinese and Russian industries involved - much more justified than in the engine case, but still a bit of a leap.

On the subject of ECM, even the Russian L-265 (a Khibiny derivative) is largely shrouded in mystery. There have been unconfirmed rumours that it may use AESA antennas, which isn't as outlandish as it may sound at first - Rafale's SPECTRA also used AESA emitters long before the main radar got an active array. You need far fewer TRMs and lower power levels per module to equip a jammer, making the whole proposition economically viable at a much earlier stage of TRM maturity.

In fact, similar considerations mean that it is easier in general to make a cutting-edge jammer than a cutting-edge radar - we can refer back to the F-15C and Su-27S for an example. Sorbtsiya with its (passive) phased array emitters was generally considered superior to the ECM component of TEWS, even though the US clearly had access to more advanced radar technology.

Still, largely rumours on both sides, and the one more believable data point (Yankee's assessment) is also open to doubt on this particular issue.

Well, we literally know nothing about J-16's ESM and ECM suite, we only know about its relative performance to the Su-35s that the PLAAF bought from Russia.

Or that may be because, as with the Su-35, there simply aren't any worth mentioning. Again, it is in part high quality photographs of the J-16 that I'm referring to when I say the Chinese derivatives are structurally closer to the basic Flanker.

No... what I mean is that composites are definitely used on recent SAC Flankers starting from J-11B, but we've just never had any rumours about specific numbers or percentages.
That is not abnormal -- in fact, I don't think we have any rumours for specific numbers of composites used in any contemporary Chinese military aircraft, aside from J-11B back in the mid 2000s, and that has proven to be the exception rather than the norm.

If I had to summarize the situation here, I would say "it is widely accepted that J-16, similar to other contemporary SAC Flankers (as well as other recent Chinese military aircraft), use composite materials, however similar to other Chinese military aircraft, the extent of which composites are used is not known and a specific number cannot be estimated".

 

[Volpler11]

Thanks! Since the division of the airframe into individual parts remains identical going by photographic evidence it's hard to see where a large weight reduction is supposed to come from. If we (*very* optimistically) assume the full 30% density reduction for a 1:1 part replacement, as opposed to a total redesign, that means we'd be looking at replacing more than 2 tons worth of parts to eke out 700kg. That is almost certainly the majority of the entire wetted area of a Flanker-size fighter aircraft worth in skin panels. If you replace a couple of aluminium maintenance access covers the sum of which does not even amount to several hundred kilograms, there's only so much you can save.

It should be noted that the bulk of the aircraft parts are not visible from the outside. You can't just look at the skin of the aircraft and estimate now much composite material is used. In fact most of the know composite parts are internal to the aircraft.

 

[siegecrossbow]

There was a table released by SAC or AVIC on percentage of composite material used in aircraft. Unfortunately I can’t find where it is.

 

[Tirdent]

It should be noted that the bulk of the aircraft parts are not visible from the outside. You can't just look at the skin of the aircraft and estimate now much composite material is used. In fact most of the know composite parts are internal to the aircraft.

It should also be noted that the internal load bearing structure is the most challenging to make out of composite on the entire aircraft, and I have in fact mentioned that here before. Changing these parts over from metal is, apart from the difficulty in designing the parts themselves, akin to a clean-sheet effort - you might as well engineer a new aircraft from scratch at that point. It would completely alter the geometry of the structure (e.g. bulkhead/rib spacings), and therefore result in very visible external differences, i.e. different rivet patterns - as I've also pointed out already. No such differences are discernible on J-11 or J-16 aircraft, so if anything we should be looking at skin panel replacements for the most part.

More generally, even in the latest 5th generation fighters, the majority of the internal structure remains metallic and most of the composite content is on the surface. I don't know where you're taking your claim from.

The part relevant to composite materials: The experiment with composite started with 2nd generation aircraft, but had no real applicable composite to 3rd-gen aircraft (J-11B) then. The domestic development of composite (for J-11B) started around 97/98, and lasted about a decade until it's completed. The documentary mentioned that the composite materials were applied to wing and fuselage of J-11B. Subsequently, composites were also used in other aircraft such as J-10 and J-20. J-16 is not mentioned, but it's pretty obvious it's included (it's similar to and in the same category as J-11B in that aspect).

Thanks. Yes, no doubt anything done with composites on the J-11B would at least carry over to the J-16 (and possibly be improved upon). My point was merely that even if we look at dozen-megapixel close-up photos of the newest Chinese Flanker variant (i.e. the J-16) there is little if any evidence of extensive composite construction. It is more similar to the basic Su-27 and Su-30 than the Su-35 that Justin Bronk so confidently asserts has less advanced structure.

 

[Tirdent]

Well, we literally know nothing about J-16's ESM and ECM suite, we only know about its relative performance to the Su-35s that the PLAAF bought from Russia.

Exactly right - I was merely pointing out that the corollary is that this may not reflect accurately on its performance relative to the Su-35s *operated by* Russia. And explained that this isn't a wholly academic possibility, because there are some concrete reasons why the Su-35 ESM/ECM suite might have certain advantages (e.g. band coverage due to array sizes).

It's all speculation, but Bronk confidently makes far-reaching assertions in that video that he cannot have researched very deeply, as then he would have encountered the very caveats we are discussing here.

No... what I mean is that composites are definitely used on recent SAC Flankers starting from J-11B, but we've just never had any rumours about specific numbers or percentages.
That is not abnormal -- in fact, I don't think we have any rumours for specific numbers of composites used in any contemporary Chinese military aircraft, aside from J-11B back in the mid 2000s, and that has proven to be the exception rather than the norm.

If I had to summarize the situation here, I would say "it is widely accepted that J-16, similar to other contemporary SAC Flankers (as well as other recent Chinese military aircraft), use composite materials, however similar to other Chinese military aircraft, the extent of which composites are used is not known and a specific number cannot be estimated".

And here too, stated like that, I have no problems with it. Yet again, that is NOT the argument Justin Bronk makes - he seems to unquestioningly buy into the rumours that claim composite application to an extent that saves several hundred kilograms. The photographic evidence strongly suggests this is not the case, which doesn't mean SAC didn't make a few conservative improvements by replacing a few metal panels here and there.

Even the basic Su-27 has CFRP h-stab actuator fairings - but those are parts which, at a reasonable guess, weigh less than 5kg total. On a 16 ton airframe, even increasing that by 20 times isn't really worth making much of a song and dance about. The weight saving over metal analogues would come to a mere 40kg - the variation between individual pilots is probably in the same ball park!

 

[optionsss]

It should also be noted that the internal load bearing structure is the most challenging to make out of composite on the entire aircraft, and I have in fact mentioned that here before. Changing these parts over from metal is, apart from the difficulty in designing the parts themselves, akin to a clean-sheet effort - you might as well engineer a new aircraft from scratch at that point. It would completely alter the geometry of the structure (e.g. bulkhead/rib spacings), and therefore result in very visible external differences, i.e. different rivet patterns - as I've also pointed out already. No such differences are discernible on J-11 or J-16 aircraft, so if anything we should be looking at skin panel replacements for the most part.

More generally, even in the latest 5th generation fighters, the majority of the internal structure remains metallic and most of the composite content is on the surface. I don't know where you're taking your claim from.



Thanks. Yes, no doubt anything done with composites on the J-11B would at least carry over to the J-16 (and possibly be improved upon). My point was merely that even if we look at dozen-megapixel close-up photos of the newest Chinese Flanker variant (i.e. the J-16) there is little if any evidence of extensive composite construction. It is more similar to the basic Su-27 and Su-30 than the Su-35 that Justin Bronk so confidently asserts has less advanced structure.

that's the message from SAC, with the J-11B, they are basically redesigning a new aircraft using with a proven aerodynamic. It's not just the composites, but China also wanted to use other aerospace material they developed. In the documentary, they mentioned the need for static and dynamic strength/stress test. They needed to make sure the new airframe is strong enough, but not too strong, as then you are just logging around dead weight.

As for how much weight savings or other performance gain, I don't think that was never publicly announced. At the minimum China wanted to improve the lifetime of the airframe, Su27 was designed at the late 1970, using material available at that time.

 

[Tirdent]

I'm aware of that, there are even photos of the J-11 structural test article on airliners.net. That alone isn't necessarily indicative of a total redesign though:

And in any case, it bears repeating that making major changes to airframe materials (even changing between alloys of the same base metal, sometimes) is a huge undertaking.

Much as the Soviets did when adapting the B-29 to their own industrial base (alloy specs, also metric instead of imperial units in this case), that is a normal part of reverse engineering. A more recent example would be the Il-476/Il-76MD-90A (Russia's ill-thought-out counterpart to the much better Y-20) where they incurred most of the effort and delays of a clean-sheet aircraft without the performance benefits.

Doing a radical redesign of the Flanker that replaces the internal structure with composite goes far beyond even that, and (I can only repeat) would have resulted in tell-tale external signs that are conspicuous by their absence in real J-11s/J-16s.

Since we're repeating previous arguments to the point that I've started self-quoting, I think this debate has run its course.