How to keep Air Force sustainable

it depends if I went for expensive tech trees I might annex some rare city.

also if I get a day of inactivity for whatever reason I mgiht use the resources to annex

Buckeyechamp wrote:

deathfromabove wrote:

annexation is a resource shift

and takes like 10 days to recoup costs.

It is more, typically at east 13 (for a city with decent morale AND population) or even close to 20 (in low morale areas, like most recent conquests)!

For a specific example, in a late-ish game at Day 54 I got an occupied city's morale 38% and population 6.8; this produces 181 rares/day. So the ROI here is 181/1500=12 days for the rares.

A 10 day return-of-investment would be fairly good, as CON economy goes. But that is hardly ever achievable with annexation (or subsequent AI building).

Well you keep missing the point. If you need rares, it is wasteful to annex (you'd be lacking the invested amount for the long duration of ROI). And a single day of inactivity does not matter for the timescale it takes for the annexation cost to be earned back.

You'd be much better off occupying more cities or provinces that yield the desired resource.