Where are you getting the idea that the J-20's stealth coating is painted on and that the J-31 is getting "baked in stealth materials" ? These ideas runs counter with the notion that the J-31 can be lower spec enough to justify it's existence. At this point of time we have no idea what kind of stealth technology will be applied to the J-31. And seeing that the J-20 is the primary focus of the PLAAF, for it not to receive the best level of tech ridiculous at best. Chengdu has far more experience with stealth tech then SAC so how on earth would the latter stole a leap over the former ?Point 1
The number 400 comes from:
- The Chinese Air Force continuing with a fleet of 2000 combat aircraft, so 400 medium-weight stealth fighters is not unreasonable.
- If you look at geography, China has so many neighbours near its borders. eg. Taiwan is 200km away, Korea is only 350km away, Vietnam/India share a border etc. So a requirement for 400 lower-spec J-31 is not unreasonable.
- A 15 year production run at 24 aircraft per year. That is a large enough production run that unit costs and maintenance are reasonable, and can justify the upfront R&D costs. But if they were only producing 100 J-31s, it would be cheaper just to stick with additional J-20 instead.
As for a carrier version, again, we're looking at low production numbers for a carrier variant. Call it a a maximum of 200 aircraft over the course of the next 15 years. Plus I imagine that maintenance of the J-20 stealth coatings is a nightmare due to the salt-water environment.
So I reckon there will still be a requirement for a *common enough* medium-weight stealth fighter with baked-in stealth materials between the Chinese Air Force and Chinese Navy.
And where comes the idea that the PLAAF wants a 2000 combat aircraft, and even if they do. What would be the ratio of stealth aircraft vis a vis the rest of the very serviceable and capable 4.5 gen fighters that are still in existence ?
Even if we cite the low number of fighters for carrier ops, the J-20 with it's existing production line can still potentially come up with a lower price tag than the J-31 that has to create a new line entirely from scratch again.
And finally, wherein comes the claim of a 15 year production run if 24 units per year ?
Mind you, I am open to discussions on how the J-31 can possibly find it's way into the China's air force roster. But as of now we have literally no proof or evidence than the PLAAF or the PLAN is planning for anything of the sort, or for that matter even the potential price tag and production of the plane in general.