Hi Stearmandriver,

from my knowledge, the database is stored in Users\[YOUR USERNAME]\Documents\Plan-G Files\Data
Here are some sdf files called PLANG3_* for each simulator. In my case (I am using XPlane) it is PLANG3_XPX.sdf
There is also a UserWPTS3.sdf and a MEF.sdf
sdf files from simulators you are not using have a really small size - the big one is the one, that contains the data.

Perhaps it helps,

happy flying

Joerg