Chengdu J-20 news and analysis Part III

Ainen said:

CALF, 1.42

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Typo on my part, meant to say "current and currently proposed (forthcoming)"

sferrin said:

PaulMM (Overscan) said:

Presumably "J-20A" will have the new WS-15 engine and stealthy TVC nozzles similar to the J-10B TVC demonstrator.

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Wonder if we'd ever see that engine on the T-50/Su-57. That would be quite a twist.

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We already saw Izd. 30 almost year ago. So what's the point?

Ainen said:

From everything we saw, j-20 bay is a wide and shallow, raptor-like bay of a pure air superiority breed.

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From hundreds of images we saw, we're pretty much able to size up most dimensions on J-20. Some image include the weapons bay, there are several fairly hi res images of it. You're welcome to do your own measurements, like anyone else. I'll just post measurements I did:

Total length of the bay around 4.5 meters. Total width of (one) bay around 1 meter (give or take 5 cm)
560mm depth at the deepest point of deepest structural support brace. Of course, only a small portion of the length is that deep, as intakes curve above them. (theoretically something like the tip of a fin might extend into the area between support braces)
Some 4.3 meter long stretch of the bay is 310mm deep (or more)
Some 3.7 meter long stretch of the bay is 380mm (or more)
Some 3.2 meter long stretch of the bay is 440mm (or more)

Objects the size of JSOW and JSM should fit in there. Perhaps even a bit larger. Certainly the length is there to allow for something slightly longer. Depending on how much clearance is needed between the roof of the bay and the actual ordnance, due to various interfaces and/or ejecting mechanisms, even something similar in size to JASSM *might* fit. (I'm not saying that's likely)

I suggest using these images, for people wanting to do their own measurements:
http://i1.wp.com/inews.gtimg.com/newsapp_match/0/3488645501/0
https://qph.fs.quoracdn.net/main-qimg-9dca705385690c98c55cf7ae28fd0685
https://cdn-images-1.medium.com/max/1200/0*bbS9m0tvTogu7xg0.jpg

Wingspan to engine nozzle (since its round) and then nozzle to depth of the bay is a practical way to do it. Also, width of the weapon bay doors is also helpful, as it is known from overall wingspan.

GARGEAN said:

sferrin said:

PaulMM (Overscan) said:

Presumably "J-20A" will have the new WS-15 engine and stealthy TVC nozzles similar to the J-10B TVC demonstrator.

Click to expand...

Wonder if we'd ever see that engine on the T-50/Su-57. That would be quite a twist.

Click to expand...

We already saw Izd. 30 almost year ago. So what's the point?

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Is the "Izd.30" simply an AL-31 variant or a completely new engine?

PaulMM (Overscan) said:

Yep, its Google translate. 'Sidebar controller' is obviously sidestick controller - it improves visibility of the cockpit displays by not blocking valuable real estate near the centre with a control stick, plus its argued to help pilots carry on manouvering under heavy g load as their elbow is supported, not resting on their thigh, as LowObservable says.

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Agree, visibility concerns the instrument panel, not the view out of the canopy. In addition to what LowObservable, um, observes, a sidestick is probably better suited to accommodate F-16-style semi-reclined seating for increased g-tolerance. I've also read that in formation aerobatics (such as the relevance of that is to combat ops) inflation of the g-suit trouser legs can upset the pilot's inputs with a conventional stick.

latenlazy said:

I’m actually not as sure they would have arrived at an F-22 like configuration without the engine bottleneck. I get the feeling that even without the engine bottleneck CAC would have probably gone with a delta canard of some sort anyways. They may have struck a different set of compromises though, but it probably would have the same planform, as it was the one they had the most familiarity with. Meanwhile, if what we’ve heard about the J-XX’s history is correct then its unlikely CAC wouldn’t have gotten the tender, given how much more proactively inventive they supposedly were than SAC in their approach to the contest.

To be clear to the original question I don’t think an inability to copy the F-22’s physical features had anything to do with the approach they ended up choosing for the J-XX. Nothing in their capabilities prohibited them from going with a design like the J-31 for example. An F-22 like design wasn’t pursued because it probably didn’t fit their set of requirements and conditions.

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Yes, I also suspect the J-20 was always going to be a canard. Depending on your requirements, it's perfectly possible to find good arguments for a canard configuration even with access to world-class engine technology (consider for example the Eurocanards). As you say, with the J-10 as previous experience, the delta-canard is the high-performance fighter configuration most familiar to and best understood by CAC. For them, anything other than a canard could arguably have been considered a departure from convention.

Blitzo said:

And as far as current flying and proposed 5th generation fighters go, I think one has to admit J-20's aerodynamic configuration is among the more unique. Bringing up Song's paper back here naturally would spark some more discussion about the aircraft's aerodynamic configuration

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While the J-20 layout is somewhat unusual for a stealthy 5th generation fighter (and even so, it's not the first time such a configuration was considered for this purpose: Northrop/MDD NATF, JAST/CALF, Saab FS2020, Yakovlev MFI...), I don't see anything truly novel about a delta-canard by now. Between the J-10 and Eurocanards, comfortably in excess of 1000 are in service all over the world today - upgrades of existing 4th generation fighters (some of which acquired canards in the process!) notwithstanding, you could even say it was the default choice for clean-sheet 4.5 generation fighters. There's been a lot of prior art and while it's definitely no more a copy of anything else than the Rafale is a Typhoon rip-off (in other words, not at all), I don't consider the J-20 as particularly radical. Certainly not YF-23-radical and (IMHO) not even Su-57-radical, aerodynamically speaking.

Sundog said:

Something interesting to note with the Lockheed JAST design is the canards weather-vane at subsonic speeds and became "active" at supersonic speeds, to minimize trim drag and increase supersonic maneuverability.

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There's also the MiG Ye-8 which used its canards to counteract the rear-ward shift of the centre of pressure in supersonic flight in a similar manner, anticipating the F-14's glove vane idea by a couple of years.

sferrin said:

Is the "Izd.30" simply an AL-31 variant or a completely new engine?

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Clean sheet. Why would they bother with another AL-31 evolution when they've already pushed that architecture about as far as it will practically (i.e. with acceptable life & TBO) go in the current 147kN Izd. 117 engine? The latter is an improved version of the 142kN Izd. 117S in the Su-35S, so arguably twice (or thrice, counting the AL-31FP from the Su-30MKI which pioneered the TVC nozzle & integration) removed from the basic 122kN AL-31F by now.

Trident said:

Blitzo said:

And as far as current flying and proposed 5th generation fighters go, I think one has to admit J-20's aerodynamic configuration is among the more unique. Bringing up Song's paper back here naturally would spark some more discussion about the aircraft's aerodynamic configuration

Click to expand...

While the J-20 layout is somewhat unusual for a stealthy 5th generation fighter (and even so, it's not the first time such a configuration was considered for this purpose: Northrop/MDD NATF, JAST/CALF, Saab FS2020, Yakovlev MFI...), I don't see anything truly novel about a delta-canard by now. Between the J-10 and Eurocanards, comfortably in excess of 1000 are in service all over the world today - upgrades of existing 4th generation fighters (some of which acquired canards in the process!) notwithstanding, you could even say it was the default choice for clean-sheet 4.5 generation fighters. There's been a lot of prior art and while it's definitely no more a copy of anything else than the Rafale is a Typhoon rip-off (in other words, not at all), I don't consider the J-20 as particularly radical. Certainly not YF-23-radical and (IMHO) not even Su-57-radical, aerodynamically speaking.

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A lot of later generation fighter aerodynamics innovations focus on how to generate ever more powerful vortices at high AoA to improve the L ratio in different flight conditions, to expand the flight envelope, or ever more sophisticated methods to control these more powerful vortices. While I don’t think the J-20 is as radical as say the Su-57 in the fundamental principles it employs I think a case can be made that there looks to be some pretty significant iterative innovations with multiple different vortex generation methods. In other words, one could argue the aerodynamic design itself is innovative even if the aerodynamic principles aren’t. That said, I’ve said elsewhere before that the J-20 and Typhoon have a lot in common, and whether by intent or convergence they seem to have arrived at very similar aerodynamic solutions.

Trident said:

While the J-20 layout is somewhat unusual for a stealthy 5th generation fighter (and even so, it's not the first time such a configuration was considered for this purpose: Northrop/MDD NATF, JAST/CALF, Saab FS2020, Yakovlev MFI...), I don't see anything truly novel about a delta-canard by now. Between the J-10 and Eurocanards, comfortably in excess of 1000 are in service all over the world today - upgrades of existing 4th generation fighters (some of which acquired canards in the process!) notwithstanding, you could even say it was the default choice for clean-sheet 4.5 generation fighters. There's been a lot of prior art and while it's definitely no more a copy of anything else than the Rafale is a Typhoon rip-off (in other words, not at all), I don't consider the J-20 as particularly radical. Certainly not YF-23-radical and (IMHO) not even Su-57-radical, aerodynamically speaking.

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Canard deltas certainly are not unique, and there have also been other proposals for 5th gen canard deltas in the past at varying points, but I was saying that as far as current and future forthcoming 5th gen aircraft go, J-20's configuration is quite unique (in a world of F-22/F-35 esque fighters), and that is part of the reason why so much heat was being expended talking about J-20's design (in reply to lowobservable)

sferrin said:

Is the "Izd.30" simply an AL-31 variant or a completely new engine?

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Completely new. Not drastically more powerful (it's not like with AL-41F1 T-50 was underpowered), but pretty significant upgrade in all areas like production coplecity, maintetance weight, work hours, fuel consumption...

GARGEAN said:

sferrin said:

Is the "Izd.30" simply an AL-31 variant or a completely new engine?

Click to expand...

Completely new. Not drastically more powerful (it's not like with AL-41F1 T-50 was underpowered), but pretty significant upgrade in all areas like production coplecity, maintetance weight, work hours, fuel consumption...

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I’d say going from 15,000 kg of thrust to 17,500 kg of thrust is a pretty big difference in power.

latenlazy said:

A lot of later generation fighter aerodynamics innovations focus on how to generate ever more powerful vortices at high AoA to improve the L ratio in different flight conditions, to expand the flight envelope, or ever more sophisticated methods to control these more powerful vortices.

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This has been the case pretty much ever since the F-5 introduced LERX - but it was a process of continuous evolution, as the new tool in the box was understood better and better and new design instruments such as CFD became available. For this reason a fighter designed in 2000 is going to be better than one from 1980 (whether it has a conventional tail or canard) and I expect the J-20 is no exception.

latenlazy said:

That said, I’ve said elsewhere before that the J-20 and Typhoon have a lot in common, and whether by intent or convergence they seem to have arrived at very similar aerodynamic solutions.

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Rafale is even closer, arguably (LERX, wing planform, inlet positioning). Its canards are more closely coupled to the wing than those on the J-20, but equally the Typhoon has an even longer moment arm, so you can't really say it's more similar to one rather than the other in this respect.

Trident said:

latenlazy said:

A lot of later generation fighter aerodynamics innovations focus on how to generate ever more powerful vortices at high AoA to improve the L ratio in different flight conditions, to expand the flight envelope, or ever more sophisticated methods to control these more powerful vortices.

Click to expand...

This has been the case pretty much ever since the F-5 introduced LERX - but it was a process of continuous evolution, as the new tool in the box was understood better and better and new design instruments such as CFD became available. For this reason a fighter designed in 2000 is going to be better than one from 1980 (whether it has a conventional tail or canard) and I expect the J-20 is no exception.

latenlazy said:

That said, I’ve said elsewhere before that the J-20 and Typhoon have a lot in common, and whether by intent or convergence they seem to have arrived at very similar aerodynamic solutions.

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Rafale is even closer, arguably (LERX, wing planform, inlet positioning). Its canards are more closely coupled to the wing than those on the J-20, but equally the Typhoon has an even longer moment arm, so you can't really say it's more similar to one rather than the other in this respect.

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I think how the J-20’s LERXes interact with its other aerodynamic features is much more similar to the interaction between the Typhoon’s canards and strakes than the Rafale’s canards and LERXes. I wouldn’t say any of them are identical to one another, but I would argue the J-20’s is closer in kind to the Typhoon than the Rafale. That said, while each design goes for the vortex coupling approach I would argue the J-20’s seems more ambitious and might be taking that concept further than the other designs. There were some very clear modifications in the aerodynamics between the demonstrator and production prototype models, in ways that went beyond what was described in the original design study, that I thought were pretty interesting, and which I think tells us a lot about the ideas behind the J-20’s design.

Trident said:

Sundog said:

Something interesting to note with the Lockheed JAST design is the canards weather-vane at subsonic speeds and became "active" at supersonic speeds, to minimize trim drag and increase supersonic maneuverability.

Click to expand...

There's also the MiG Ye-8 which used its canards to counteract the rear-ward shift of the centre of pressure in supersonic flight in a similar manner, anticipating the F-14's glove vane idea by a couple of years.

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However, the Ye-8s were fixed at supersonic speeds, just as on the MiG E-152M. They weren't fixed on the Lockheed design, they were control surfaces at supersonic speeds. Also, the Ye-8 and MiG E-152M weren't tailless designs at subsonic speeds.

latenlazy said:

GARGEAN said:

sferrin said:

Is the "Izd.30" simply an AL-31 variant or a completely new engine?

Click to expand...

Completely new. Not drastically more powerful (it's not like with AL-41F1 T-50 was underpowered), but pretty significant upgrade in all areas like production coplecity, maintetance weight, work hours, fuel consumption...

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I’d say going from 15,000 kg of thrust to 17,500 kg of thrust is a pretty big difference in power.

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Those are not exactly official numbers. And official ones are pretty vague, usually just "5-10% thrust increase".

Sundog said:

However, the Ye-8s were fixed at supersonic speeds, just as on the MiG E-152M. They weren't fixed on the Lockheed design, they were control surfaces at supersonic speeds. Also, the Ye-8 and MiG E-152M weren't tailless designs at subsonic speeds.

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Yup, hence "similar manner". It's not quite the same thing and the closer analogue is, as mentioned, the F-14's glove vane. FCS technology wasn't yet up to more than that at the time.

B)

Blitzo said:

B)

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That, combined with the fact that the planes had to travel from the airport in Foshan (200KM round trip), means that they carried decent load while performing the maneuvers.

siegecrossbow said:

Blitzo said:

B)

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That, combined with the fact that the planes had to travel from the airport in Foshan (200KM round trip), means that they carried decent load while performing the maneuvers.

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indeed, though I missed the live broadcast and I'm now waiting for a recording lol

==

Also, for those who missed the pics cause it's the last post on last page:

Blitzo said:

siegecrossbow said:

Blitzo said:

B)

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That, combined with the fact that the planes had to travel from the airport in Foshan (200KM round trip), means that they carried decent load while performing the maneuvers.

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indeed, though I missed the live broadcast and I'm now waiting for a recording lol

==

Also, for those who missed the pics cause it's the last post on last page:

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Spoilers:

It is the exact same thing they did on the 6th and 9th.

siegecrossbow said:

Blitzo said:

siegecrossbow said:

Blitzo said:

B)

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That, combined with the fact that the planes had to travel from the airport in Foshan (200KM round trip), means that they carried decent load while performing the maneuvers.

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indeed, though I missed the live broadcast and I'm now waiting for a recording lol

==

Also, for those who missed the pics cause it's the last post on last page:

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Spoilers:

It is the exact same thing they did on the 6th and 9th.

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Yeah but it’s interesting to compare the different runs.

http://video.weibo.com/show?fid=1034:4305126329153018

Video of weapons bays closing.

Only 2 BVR missiles per main weapons bay's? gone are the day's when we all thought that the J-20 carried 3 BVR missiles per bay.

FighterJock said:

Only 2 BVR missiles per main weapons bay's? gone are the day's when we all thought that the J-20 carried 3 BVR missiles per bay.

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Over the last few years I think most people have agreed 4 PL-15s was the total.

Though there are good rumours a new missile is in the works so 6 can be carried and use up all the space

FighterJock said:

Only 2 BVR missiles per main weapons bay's? gone are the day's when we all thought that the J-20 carried 3 BVR missiles per bay.

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We've known for a while now that the PL-15 load out was probably going to be 4 due to the size of the fins, but we've heard from a source who corroborated the 4 PL-15 load out that the J-20 can mount 6 PL-12s. This suggests, to me at least, that sooner or later we will eventually see 6 for a modified PL-15, or some successor to it. As always with PLA watching, time will tell.

latenlazy said:

we've known for a while now that the PL-15 load out was probably going to be 4 due to the size of the fins, but we've heard from a source who corroborated the 4 PL-15 load out that the J-20 can mount 6 PL-12s. This suggests, to me at least, that sooner or later we will eventually see 6 for a modified PL-15, or some successor to it. As always with PLA watching, time will tell.

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May be you got that the other way around. Pl-12 fins are larger than pl-15 fins.
Pl-12 dimensions:
752mm rear fins pan
670mm wingspan

If trying to stagger 3 such missiles, one would get over 1200mm of width of three such missiles in a package. Without a single mom of clearance. That's visibly over the width of j20 bay. So 3 pl12 is a no go.

3 pl-15 miiiight be able to fit but judging by the photos it's looking like a terribly tight fit with almost non existing clearance. Until we actually get images of three pl12 per bay, I would say it's safer to assume two per bay are carried.

probably Chinese will reduce fin size as US did

Video from the 11th.

https://www.youtube.com/watch?v=tNss2y__xGE

Nice shot of the weapons bays:

https://www.youtube.com/watch?v=TVDqqRM83ZE

Note the black edging on the doors in the pics below.

Blitzo said:

FighterJock said:

Only 2 BVR missiles per main weapons bay's? gone are the day's when we all thought that the J-20 carried 3 BVR missiles per bay.

Click to expand...

Over the last few years I think most people have agreed 4 PL-15s was the total.

Though there are good rumours a new missile is in the works so 6 can be carried and use up all the space

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From volume, not from suspension point of view.
I honestly am not as sure, if 6 vs. 8 is that critical of a difference or not.

sferrin said:

Nice shot of the weapons bays:

https://www.youtube.com/watch?v=TVDqqRM83ZE

Note the black edging on the doors in the pics below.

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The background music from the first Captain America movie is a nice touch.

totoro said:

latenlazy said:

we've known for a while now that the PL-15 load out was probably going to be 4 due to the size of the fins, but we've heard from a source who corroborated the 4 PL-15 load out that the J-20 can mount 6 PL-12s. This suggests, to me at least, that sooner or later we will eventually see 6 for a modified PL-15, or some successor to it. As always with PLA watching, time will tell.

Click to expand...

May be you got that the other way around. Pl-12 fins are larger than pl-15 fins.
Pl-12 dimensions:
752mm rear fins pan
670mm wingspan

If trying to stagger 3 such missiles, one would get over 1200mm of width of three such missiles in a package. Without a single mom of clearance. That's visibly over the width of j20 bay. So 3 pl12 is a no go.

3 pl-15 miiiight be able to fit but judging by the photos it's looking like a terribly tight fit with almost non existing clearance. Until we actually get images of three pl12 per bay, I would say it's safer to assume two per bay are carried.

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Nope, the leaker (pb19980515) definitely said 6 PL-12 and 4 PL-15. If I recall correctly the PL-12 that fit 6 was supposed to have cropped or folded fins, but I’d have to peruse the original Chinese thread to confirm. Here’s the SDF discussion on this back in February. I’m not saying this source is for sure correct, just that this is what they said. Make what you will of it.

https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-vi.t8169/page-196#post-497243

PL-12 and PL-15 seem to have the same diameter body (203mm) with PL-15 being fractionally longer. I don't see why you'd design a version of PL-12 in order to fit in 6 AAMs when the only dimension you save space is length unless PL-15 is actually fatter.

https://www.youtube.com/watch?v=SEsWCUhLMlE

latenlazy said:

Nope, the leaker (pb19980515) definitely said 6 PL-12 and 4 PL-15. If I recall correctly the PL-12 that fit 6 was supposed to have cropped or folded fins, but I’d have to peruse the original Chinese thread to confirm. Here’s the SDF discussion on this back in February. I’m not saying this source is for sure correct, just that this is what they said. Make what you will of it.

https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-vi.t8169/page-196#post-497243

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Some new variant, sure. 6 missiles might be possible if overall width of the package can be reduced. Folding fins is unlikely in my opinion as no one has done it. Cropped fins is... well, basically pl-15. Sure, pl-15 also has redesigned fins as well, but essentially, they're also cropped when compared to pl-12.

So if they're going to redesign fins once again, then they're more likely to use the pl-15 internals of that body than the pl-12. The body casing is shared by the two missiles anyway. With pl-15 only having slightly more pointy tip. (difference in length is literally one cm or so) Of course, internals of the body are likely different between pl-12 and pl-15.

Question is - since they were making the fins on pl-15 smaller than pl-12, why not go that extra bit and make them as small as needed to fit inside j-20, if carrying 6 missiles was a requirement?

totoro said:

latenlazy said:

Nope, the leaker (pb19980515) definitely said 6 PL-12 and 4 PL-15. If I recall correctly the PL-12 that fit 6 was supposed to have cropped or folded fins, but I’d have to peruse the original Chinese thread to confirm. Here’s the SDF discussion on this back in February. I’m not saying this source is for sure correct, just that this is what they said. Make what you will of it.

https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-vi.t8169/page-196#post-497243

Click to expand...

Some new variant, sure. 6 missiles might be possible if overall width of the package can be reduced. Folding fins is unlikely in my opinion as no one has done it. Cropped fins is... well, basically pl-15. Sure, pl-15 also has redesigned fins as well, but essentially, they're also cropped when compared to pl-12.

So if they're going to redesign fins once again, then they're more likely to use the pl-15 internals of that body than the pl-12. The body casing is shared by the two missiles anyway. With pl-15 only having slightly more pointy tip. (difference in length is literally one cm or so) Of course, internals of the body are likely different between pl-12 and pl-15.

Question is - since they were making the fins on pl-15 smaller than pl-12, why not go that extra bit and make them as small as needed to fit inside j-20, if carrying 6 missiles was a requirement?

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Perhaps because the PL-12 and PL-15 are very different missiles (and if what we're hearing about the PL-15 is right they really are), and whatever cropping they were able to do to preserve the PL-12's performance they were unable to or have not yet been able to do for the PL-15.

Oh, absolutely the pl-12 and pl-15 have different internals. There's 10+ years of progress between them. The same way amraam A and amraam D are much different. Different rocket motor, different seeker electronics, different fuze, warhead, different comm links. And those aren't just slot for slot upgrades but they, at times, take up a different volume than their previous incarnations.

I'd very much expect pl-15 to be doing the same. larger rocket motor section, less voluminous electronics. One can actually see that, unlike with amraam, pl-15 has mid body wings placed slighty more aft compared to pl-12. Suggesting a different center of gravity perhaps?

Huge image of weapons bay opening sequence
https://c1.staticflickr.com/5/4887/32189846368_362f0d82b3_o.jpg

https://www.sinodefenceforum.com/j-20-5th-gen-fighter-thread-vi.t8169/page-415

Awesome zoom shots

If width of the black line is whole gap between the IWB door and fuselage, it is too wide for the most aircraft.

That is not a gap. It is edge treatment that looks as if there is a gap.