I am also interested in knowing if this is possible.
If two craft can be housed in one facility are both craft's base sprites rendered overlapping on the hanger's tile or can you choose which one is displayed?
(EDIT)
I did some quick tests with this code:
extraStrings:
- type: en-US
strings:
STR_HANGAR_TEST: "HANGAR TEST"
facilities:
- type: STR_HANGAR_TEST
spriteShape: 9
spriteFacility: 9
size: 2
buildCost: 200000
buildTime: 2
monthlyCost: 25000
crafts: 2
mapName: XBASE_16
(These are the results):
(1) You can have two craft (or theoretically more) stored in one hangar.
(2) The first craft placed in the hangar will have it's base sprite displayed, the other will not.
(3) Even when the first craft is airborne and the second craft is still in the hangar it will not be displayed, the hangar will appear to be empty visually.