I think there have been 11 in service so far based on huitong's page. However, that number may go a lot this years as the deliveries from 2021 enter service. Keep in mind that the number of Z-18s are dependent on the number of carriers serving PLAN. So, we maybe looking at 20+ Z-18s by the time Shandong air wing fully forms.
Beyond that, it really depends on the success of the AC-313A project and what the future air wing for PLAN carriers and LHDs look like. I would assume they no longer need Z-18Js for CATOBAR carriers, but could use them for future LHDs. Another question is whether or not the Navy is interested in a naval version of AC-313A or if they are just looking to continue purchasing Z-18 series. The Z-18s would have lower payload and using less powerful engines than AC-313A variants. That may not matter all that much to PLAN.
I want to be careful and not treat the original Z-8, the current Z-18s, Z-8Cs and the future AC-313A military versions as the same thing. They are vastly different. The improved engine performance, fuselage changes, increased composite usage, rotor blades, reduction gears and all new avionics have resulted in a new helicopter. But in the context your question, we can talk about how many Z-18/Z-8C type of helicopters they would need. I would say they probably need 10 per STOBAR carrier, 6 per CATOBAR carrier, 3 per LPD and maybe up to 8 per LHD and a small number for other large ships. Maybe upwards of 150 helicopters of this class. Between this and Z-20, I would think PLAN would want to order more of the latter.
I don't know if that sounds like a lot, but it's a pretty significant fleet size. They've really done a lot in this program. Watching Z-8 is like watching someone growing up and experiencing ll the growing pains until he/she finally figures everything out. It suffered through the lack of engine options more than any other domestic helicopter program. Even now, WZ-6C is not as powerful as PT6B. A 15 ton transport version with WZ-10s and capable of carrying Lynx ATV will probably be the ultimate transport helo for PLA. I see this series getting more order from PLA LH in the long run than even Z-20.
