Formula is:
aircraft sortie ammo x number of total planes / 20000 + number of total planes
Thanks for your reply.
I can't determine 'aircraft sortie ammo' from the unit info screen, so I loaded an old save from 1/1/42 and returned everything to the national reserve and then committed one air group of each type to an air base.
It looks like all the airbases have a base support need of 16. Beyond that is for the aircraft.
There's a pretty wide variance (e.g. ~1 per LaGG-3, 1.6 per IL-2, 3.2 per IL-4, 5.13 per Pe-8)
This info would be nice on the unit screen, because just three Pe-8 air groups would never be able to get sufficient support, whereas 9 LaGG-3 air groups would be fine.
Because the new air base construction rule is dependent on air groups per base calculations, being able to figure out what you can support in an air base without several lost weeks of trial and error (awaiting the update of support/need, and trying to calculate for less than full complements of aircraft) would be appreciated.