It's possible to import aircraft graphical design to the FlightGear from AutoCAD or other similar file formats?Thanks for your answers

If you still read this, the answer is yes. You will also need 3D Max Studio, however.To convert, save the .dwg file in 2000 format, then import it into 3D Studio. Then, from 3D Studio, export the file into .3ds (file extension must be lower case).FlightGear is capable of reading .3ds. But if you want to further convert the model into .ac3d, you could import the model from .3ds in AC3D as well.

Thanks very much.I have one more question. I need to know if I can use or import other types of terrain model, perhaps from Google Earth. Or FlightGear web is only the one source of terrain files?

Terrain files are custom-built from SRTM data, so yes, they can only be obtained from FlightGear's website.If you are on Linux, you can make use of TerraGear that comes with FlightGear to download the terrains as you fly.