Shenyang FC-31 / J-31 Fighter Demonstrator

plawolf said:

Well, it looks like you guys have figured it out, the J31 is in fact the secret love child of the F22 and F35 (which also explains why the F35 has been getting more and more bloated ever since it first flew).

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sdleio said:

I need to point out here, aircraft design isn't the problem of China Aviation Industry.But the heart disease is domestic aircraft engine manufacturing (including basic materials research for aircraft engine).
As long as J-20 and J-31 still use Russia AL-31 and RD-93 engines to fly, they r just China stealth prototypes,testing aircrafts. PLAAF won't equip these fighters until WS-15 or other more powerful engines mass produce.

The time of the whole J-20/J-31 projects finish totally depend on WHEN domestic new engine come out.
What China Aviation Industry lack is Chinese GE,Pratt & Whitney engine company.

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plawolf said:

That is all assuming that the back end of those aircraft were designed to take a specific engine.

The J10 famously had to switch from the WS10 to the AL31 during development, but there is every chance that the original design allowed to WS10(or rather WS10A now) to be retro-fitted later. The fact that there appears to be no external changes between J10Bs with AL31 and WS10As would support this theory.

Similarly, the J20 was always designed to use WS15s, which may well have slightly different dimensions to the AL31/WS10A they have installed already.

Even the JF17 has been designed with modular design from the start, which would allow for the installing of different engine options based on the requirements of the customers.

If spacing was required for some fundamental purpose, you would expect to see that quite consistently on planes of all nationalities. But most designs from other countries, many of which which use the same engines as the J10 and JF17, do not have similarly sized gaps between their engines and their nacelles.

SAC itself is no stranger to switching engines, as they have done with the AL31 and WS10A on their various flanker variants.

With all that in mind, I think it is quietly likely that the gaps we can see on many modern Chinese designs are put there because China's engine sector still lags behind the rest of it's aviation industry, and as such, the designers were forced to make do with engines that were available instead of what they wanted. However, in order to not limit the potential of their designs, they could have designed the aft of their fighters to allow for the easy installation of engines of slightly different dimensions so that their designs can meet their full potential once the suitable engines become available. As such, it is entirely possible that the J31 was designed and built with oversized engine nacelles to allow for the retrofitting of a more powerful fifth gen engine once that because available.

Leaving such a large gap in the fuselage of a plane is ever a great idea, because all sorts of foreign objects can easily get into the plane that way, and exposing the insides of the plane to the elements like that could also cause you all sorts of maintenance headaches down the line. Considering the tiny effort it would take to design and install a cover, I would be pretty surprised if they do not both to cover that gap up at some point.

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plawolf said:

Well, that's pretty much what I have been saying for some time now.

I think the current plan is to have the WS15 ready by the time the J20 is ready for serial production, but if the WS15 is significantly delayed for whatever reason, I have no doubt that the PLAAF will still order J20s to be inducted with whatever engines they are using now.

The most important thing for the PLAAF with the J20 is to get them to operational units ASAP so pilots could start converting to the type and new tactics and doctrines could be developed to make best use of the new possibilities offered by a 5th gen fighter.

The first J20s would no doubt go to the PLAAF 'Blue Force' aggressor units, so regular PLAAF pilots can train and practice with their J10s and J11s against a true 5th gen opponent to hopefully help to train them to counter such fighters at the same time as allowing the PLAAF Blue Force pilots to develop tactics to use 5th gens against conventional opponents.

The fact that the J20 running on WS10X or AL31 will not be as capable as a full spec J20 with WS15s would not matter so much, since the most different and important tactics and aspects with 5th gens is the fundamental way they would change BVR combat.

Even at full specs, a J20 would not really teach PLAAF pilots anything about WVR combat they could not already learn from DACT against other types, and as the Typhoon showed in recent exercises, in WVR, they have nothing to fear of the Raptor, so a 5th gen is little different from a 4th gen in WVR. It is at BVR that the Raptors and other 5h gens truly come into their own.

Having underpowered engines would not really make much of a meaningful difference to the J20's BVR combat potential, so no matter if it's in terms of training, or even real combat, a WS10X powered J20 would be as good as a full spec J20 in most of the fields that really matter. The only noticeable exception might be the lack of supercruise, but that is hardly a deal-breaker. With the J20 airframe designed to take WS15s, the first WS10X powered J20s could be retro-fitted with WS15s and be brought up to full specs with little difficulty at a later date, so the PLAAF really have very little to loose and a hell of a lot to gain by ordering WS10X powered J20s rather than wait for the full specs version.

That is all, of course a worst case contingency plan. Ideally, the WS15 would be ready in time, and the first J20s delivered would be full spec versions, and CAC can move on to designing a newer J20 to incorporate any new technologies that became available during the J20 development, and/or 6th gen fighters etc.

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plawolf said:

Did the lack of a Chinese engine stop the J10, J11A or JF17?
I have already written about this so to save from repeating myself.

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sdleio said:

Of course not, i had said the biggest problem is China aircraft engine research,not aircraft design.

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(We had seen many J-10A or J-11B with WS-10 engines)?

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plawolf said:

Urgh, I'm an idiot. I managed to somehow misquote myself.

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escobar said:

Never see J-10A with WS-10A. Only J-10B PT-1035 has WS-10A.

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