If you are a total noob and are just beginning in converting, trying to convert the "Ratte" is probably VERY difficult.
I did this myself some months ago and really, the Ratte is one of the most complex objects avaible. It has many very special code lines in use and tricks quite a lot to get things working. E.g. the ~20 PCOs avaible on the Ratte are impossible to include in one model, so most of the turrets have simply be added with "holdObject". Has the cool side effect one can destroy single turrets of the Ratte

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But rest assured it will be very time-consuming and difficult to import all necessary meshes, appropiate textures used, sounds, weapon& exhaust effects, additional weapons used (like the 20mm AA guns on top), the projectiles used etc.
You have to look through all the referencenes and links to other files in the .cons, and that can take hours, considering the Ratte has more code than all BF42 air vehicles combined...