You can find Felix's site at
http://www.freeflightdesign.com/Your 3ds to mdl converter - are you sure it's for Microsoft's flight simulator - or might it be for making objects and levels for Quake or one of those other first person shooter type games? About three or four of those games use object files that are ".mdl" files. I suspect that your converter is for those games and not the MS flight sims. Also - when you get a mesh ready for use in the flight sim, the parts have to be named or "tagged" in a certain way in order to work or animate properly when converted to mdl.
The plugin that Microsoft made available for making mdl files for use in their flight sims requires the mesh be in the ".x" file format.
There are a few other requirements in getting an object or mesh ready before it can get converted and be made ready to "fly" in the flight sim world. (orientation, animation postions, texture maps have to be square, etc.) You can find out about most of these "extra" requirements from asking questions on this forum.
If you plan to make more than one aircraft - I'd recommend looking into buying a copy of FSDS 2. It is designed specifically for making MS flight sim aircraft objects and automatically handles all the "extra" steps involved in the process.
If you're familiar with 3DStudio Max - then you'll be right at home in using Gmax. Gmax is free but it doesn't have any manuals for getting objects ready for conversion to mdl and use in MS flight sims - and right now you have to have the two plugins that come with FS2k2 PRO to properly export Gmax meshes into .mdl files as well. Maybe better gmax support and how-to-do-it information will be available when the Century of Flight gets released this summer.
