I think we might see a land based version of the J-XY for the PLANAF land based aircraft component. But I am skeptical it will ever enter service in high numbers in the PLAAF itself. A single engine aircraft will be cheaper. Even the Russians are developing a single engine 5th gen aircraft. Once China has the WS-15 high-thrust engine then making a new single engine aircraft with much better performance characteristics than the J-10 will become possible. All that will be necessary will be a new airframe since all the other components can be borrowed from other programs. The WS-15 is supposed to have theoretically about the same performance as two WS-13 class engines while only having roughly the same number of parts as a single one. For a massive air force like China's this cost advantage cannot be underestimated.
The dual engine J-XY is most well suited for coastal patrol and naval carrier missions where the redundancy of dual engines is required.
This thread and the other one has had fruitful discussions over this topic before, and in the time since then, to be honest I have only just become even more convinced that I think a single engine, land based 5th generation aircraft may not be desirable for the PLA.
I'm going to call it "SEFA" for short (Single Engine Fifth-gen Aircraft), to describe a 5th gen fighter of medium weight, that can for all intents and purposes be considered as J-XY/FC-31 but powered by one large thrust engine rather than two medium thrust engines.
===
Now that we are in late 2021, I think there are a few contextual realities that any prospective PLA SEFA needs to be considered in:
1: Any SEFA that enters service would require an engine of WS-15 class to be viable. IMO this is important, because going into the next 10-20 years, WS-15 production will be prioritized for other aircraft first -- specifically J-20 for the next decade or so, but also as we approach 2030, I can see a variable cycle variant of WS-15 being prioritized for the PLA 6th gen effort, as we all expect 6th gen fighters to use VCEs, and WS-15 is really the only plausible basis for a 6th gen viable VCE.
That is to say, I expect the production of any prospective SEFA to be dependent on the availability of WS-15 production, and I do not expect WS-15 production into the next 20 years to be able to meet the production of J-20s, PLA 6th gen, and a SEFA itself, when the SEFA would be third/last in line for WS-15 priority.
If a JH-XX does emerge, then it is possible that any prospective SEFA might even be
fourth in line for WS-15 priority, as WS-15 would obviously also be the powerplant of choice for a modern stealthy theater bomber as well.
Meanwhile, J-XY will use WS-19, an engine of a similar generation to WS-15, but a medium thrust rather than large thrust engine and whose production and commitment is already guaranteed and whose production may well be easier to achieve in the immediate to near term future given for various reasons not least the size of the blades.
2: J-XY/FC-31 is simply so much further ahead of any prospective SEFA in development and testing, and the aerospace resources of the industry is finite.
Developing and producing an entirely new fighter -- which SEFA will be, i.e.: a clean sheet aircraft -- takes up the time and energy of designers, computing power, engineers, subsuppliers, factories, all of which could be spent doing other things.
J-XY has already flown and is guaranteed to be developed and produced for the PLAN, and we expect a land based variant to be developed that will likely share massive overlap in subsystems and logistics -- that is to say, the aerospace resources for J-XY is already "committed". Furthermore, we expect at least a reasonable sized order of the J-XY (in both carrier based and land based forms), meaning the production and tooling and expertise will all be there by the time they become familiar with producing it.
The question is whether it makes sense to commit additional aerospace resources to build a whole new clean sheet SEFA, when J-XY is already there, and when (imo this is important) the aerospace resources could be used
doing other things.
Does it make sense to develop a brand new SEFA when the aerospace resources could be used to develop a couple of new UCAVs instead, or maybe if they could be used to develop the PLAAF's 6th generation fighter in a faster manner, or if they could be applied onto a notional JH-XX theater bomber instead? Is it maybe more wise to just buy additional land based J-XYs whose development, subsystems, logistics, are already mature and paid for, and just accept that at the national and industry and strategic level, that the economical/maintenance benefits of a single engine for SEFA is not actually worth it?
3: UAVs/UCAVs. This is another big factor imo, that we can start to describe with more confidence.
Everyone is focused on wanting a capable yet affordable fleet of modern combat aircraft. Part of the rationale for a SEFA is wanting to operate an aircraft that's cheaper than a twin engine aircraft by virtue of having one powerplant versus two powerplants.
But IMO, the role of cheaper UAVs/UCAVs and loyal wingmen systems may greatly change what is considered "capable yet affordable".
A SEFA will have to be a medium weight fighter powered by a WS-15, yet still be relatively high end enough to have 5th gen or 5.5th gen capabilities.
However, emerging UAVs/UCAVs and loyal wingmen have the potential to be significantly lower in cost than a SEFA, and also require less strenuous powerplants to be effective. For example, a loyal wingman UCAV of the near future may only require a single WS-10 variant or even a single WS-13 variant engine to be effective.
UAVs and UCAVs and loyal wingmen drones are not a choice -- regardless of whether the PLA gets a SEFA or not, a robust unmanned capability and fleet is basically guaranteed to be a significant part of their fleet makeup into the 2030s, and likely to be a determining capability that we use to describe 6th gen and maybe 5.5th gen fighters.
So the question is whether a slightly more affordable (but still manned, relatively high performance, 5th gen fighter airframe) SEFA is worthwhile in context of the large scale emergence of UAVs/UCAVs in the near future that are likely to be much more affordable than a SEFA will be -- and in context of both premises 1 and 2.
Now, on paper, if everything were held equal, then yes it goes without saying that a SEFA would be more economical than a twin engine fighter of the same class/type/weight, by virtue of having one powerplant rather than two.
The logic of it, is very very reasonable.
But for the PLA and for China's aerospace industry, I think as of our current time in late 2021 the combination of contextual factors:
1. in terms of powerplant availability and higher priority projects that will require powerplants that SEFA depends on, and
2. the much greater maturity of the existing J-XY/FC-31 solution for a land based medium weight 5th generation fighter relative to a notional SEFA, plus the priorities of other aerospace projects where resources are better used on, and
3. the emergence of UAVs/UCAVs/loyal wingmen as a credible, capable and affordable makeup of tactical air fleets in a way that is far more affordable than a SEFA would be.....
..... all of that makes me strongly believe that at this point in time, developing and producing a SEFA doesn't make sense for the PLA, and is better spent on other things.
(The other factor of course, which I don't describe but which is obvious enough to go without saying, is that any new SEFA will introduce a whole new line of logistics and maintenance that is separate from J-20 family and the J-XY (carrier and land based) variants, introducing a
third manned 5th generation aircraft type).
If some of the above factors change, then I think I would revise my assessment.
- For example, if they were able to produce something like 200 WS-15s a year from 2025 rising to 300+ WS-15s a year in 2030 and beyond, then in that case I could certainly believe a strong case for a SEFA could be made because the powerplant would no longer be a bottleneck.
- If they are able to develop a SEFA that uses far less aerospace resources than they would traditionally (either through new methods or design technologies etc) and be produced with greater speed and less retooling as well, then it might be reasonable to argue for a SEFA.
As it stands though, I don't think the logic of "single engine fighter is more economical than twin engine" is enough for them to actually develop and buy a new clean sheet SEFA.
