J-20 5th Gen Fighter Thread V

[Air Force Brat]

To admit externally - especially with only the exhaust visible - they are the same and as such it is not possible to know.
However since CAC specifically demanded a modified version of the trusted AL-31F with the gear-box relocated to the bottom of the engine for the J-10 that became the AL-31FN, since exactly the same was demanded for the FC-1/JF-17's engine when Klimov relocated the gear-box of its RD-33 to the bottom to develop the RD-93 ... I simply can't think that CAC uses an engine with its gear-box back on top as on the AL-31F or RD-33. Otherwise the J-10 and JF-17 could have easily used the original engines too.

As such ... only my estimated guess.

Deino


PS: by the way what's about these batch 02 J-15s ???

Proof positive

I'm speculating the dimension of the engine nacelle has already been fixed to that of the new engine and not the AL-31F/N, or whatever it currently is. This explains why a gab is left between the engine nacelle and the engine. This may be an indication that an engine change is going to happen sooner that later

Quite likely the case, (pun intended), the J-20 has likely been designed to take the WS-15, the engine nacelles are stressed skins that carry much of the load of the J-20, and it would involve a little work to "enlarge them", so the less of that the better, it would effect lots of other aspects of the airframe and dynamics?

I have speculated that the fuse was designed to accept the larger case without modification, the engine and cases being centered within the nacelle by the mounts which are comparatively simple to change or modify.

 

[Deino]

I just tried to find a few similar shots of the other J-20 prototypes ... and quite interesting, '2016' is again more similar to the early birds '2001' & '2002" than to the last four. Biggest change IMO is however that the engine itself seems to be positioned deeper into the airframe ... or that serrated ring is longer !

Deino

 

[Quickie]

It looks like to me the slight bend on the top surface of the nacelle just before the serrated edge is less pronounced on the new prototype than the rest of the older prototypes.

 

[Totoro]

fuselage cover seems longer on 2016, removing the need for the row of sawtooth lines on the engine itself, as it is now approximately where the engine line previously was.

 

[duncanidaho]

It looks like to me the slight bend on the top surface of the nacelle just before the serrated edge is less pronounced on the new prototype than the rest of the older prototypes.

It seems to me that the serrated ring reach further back, so the way to become narrower getting longer, therefore it looks less pronounced.

 

[huitong]

Aqreed, but IMO the use of the "old-style gear-box on top-design-solution" for all these Flanker-versions is mostly regarded to the fact that a change to a new engine would have required yet another redesign. Just look at these slim nacelles.

Also, the J-31 uses two "gear-box on the bottom" RD-93, when it could have easily taken the standard RD-33.

Deino

IMO gearbox-on-top is definitely more convenient to maintain than on the bottom. It is similar to fixing a car engine. 99% mechanics would prefer doing the job from above rather than getting underneath and having oil spilling on your face. Keep in mind maintainability is also part of the requirement when you design a 4th/5th generation stealth fighter. Also if J-20 uses the FN series then that would put the F-M series out of question. The Chinese would have only FN and FN Series 3 to play with. And that could make the production J-20 underpowered since FN Series 3 is only rated at 13.7 ton. As for the FC-31 case, since they don't have RD-33 in their inventory, it makes sense to use RD-93 rather than importing a few RD-33s from Russia which would be much more expensive. So from that point of view RD-33 is not necessarily an "easy" option.

 

[taxiya]

Awww no serrations. Disappoint.

May not matter. I've always gotten the sense that the silver coating is a custom job they have to do on their own. May not wanted to use that time or resource, especially if it wasn't necessary.

I think we will never see serrations as long as it is AL-31. It is off-the-shelf product. I don't believe Russia will or China want to invest in making a special variant of it for J-20. It is meant to be there temporarily until Chinese engines are ready which is likely serrated, be it WS-10G or WS-15. I believe China expects them to be ready in the near future say 5 years. During this time China will use J-20 in a more defensive role which means that the aft stealthness is not a serious issue, after all AL-31 is not powerful enough for J-20 to go deep behind enemy line.

I agree with you that Chengdu just got "lazy". I heard somewhere that the it is silver colored ceramic plate attached to the nozzle. So I guess one can just put it on and take it off any time like normal maintenance. This again suggest that Chengdu does not expect AL31 to be on J20 for long. The domestic engine will likely have ceramic nozzle panels serrated.

 

[vesicles]

I just tried to find a few similar shots of the other J-20 prototypes ... and quite interesting, '2016' is again more similar to the early birds '2001' & '2002" than to the last four. Biggest change IMO is however that the engine itself seems to be positioned deeper into the airframe ... or that serrated ring is longer !

Deino

View attachment 18768

The obvious differences between the engines of the latest 2016 and those of other protypes suggest an interesting possibility: they are planning to put the new engines on this very prototype, 2016, in the very near future.

It is apparent that the CAC is "slacking off" on the engine dept on the 2016. However, this does not make any sense if we actually assume that the engineers actually got lazy. The J-20 project is almost the crème de la crème of China's defense industry. It would be completely unlike that any kind of "slacking off" can be tolerated. Let alone these top notch engineers take their work very serious. In fact, it is this serious attitude that got them where they are now. Why would they allow themselves to "slack off"?

Then why did they decide to "skip a few steps" on the engines of the 2016? So far, we have not spotted any other disappointing "skipping" elsewhere on the plane. Again, why? An obvious possibility would be that the current engine is very temporary, hence not worth the time and energy to put all the little detailed stuff on. On the other hand, they planned to keep the AL31 engines on other early prototypes. So they paid a lot of attention to all the little details. My speculation would be that they are planning to swap the engines on the 2016 in the very near future, like in days / weeks ahead. completely my guess/ speculation...

 

[Ali Qizilbash]

The obvious differences between the engines of the latest 2016 and those of other protypes suggest an interesting possibility: they are planning to put the new engines on this very prototype, 2016, in the very near future.
........................................
My speculation would be that they are planning to swap the engines on the 2016 in the very near future, like in days / weeks ahead. completely my guess/ speculation...

Thinking about your speculation the question comes to mind as to why bring 2016 out with the present engine. They could have waited days / weeks and fit in the new engine. So it seems the present engine will continue to be on 2016 for quiet some time, even if a replacement is on the cards.

 

[manqiangrexue]

Thinking about your speculation the question comes to mind as to why bring 2016 out with the present engine. They could have waited days / weeks and fit in the new engine. So it seems the present engine will continue to be on 2016 for quiet some time, even if a replacement is on the cards.

Perhaps there were some flight software updates (such as to combat pilot-induced oscillation) or some slight physical differences in the air-frame (maybe on the DSI or even inside the intake) so they want to use the AL-31 first to verify the flight-worthiness/new flight characteristics of 2016. Maybe they will tweek the software again after the first few flights. So I think it will definitely take off and fly, maybe a few times, maybe more, with the current engines, and if Vesicles is right, then they will do the engine swap.