FlightGear Ardupilot SITL for custom UAV

1)How to simulate a multirotor fixed wing UAV modelled in CATIA with FlightGear simulator and Ardupilot SITL?
2)Which files need to be generated while importing it from CATIA to FlightGear?
3) I want to know how to generate an XML file for UAV.
I just tried replacing c172p.ac with my model.ac, editing fg_plane_view batch file --aircraft=c172p(My model was renamed) and running sim_vehicle.py