Any file that is made in 3Ds Max [a rather expensive design tool] will have the extention *.3DS. Gmax [a free design tool] can import this file so that you can can model it. You can download Gmax and register it at
www.turbosquid.com.
Be warned. In Gmax, or in any design tool, modeling an addon for FS is not going to be easy. 3D modeling never is easy. There are tutorials available
www.freeflightdesign.com. The turbosquid website provide basic tutorials on how to model a P-38 using simple objects.
There are a handleful of websites that can provide tutorials that range from basic modeling to complex techniques and steps for exporting a model to FS. When you install Gmax, you need the following gamepack from Microsoft:
Make Model SDK -
http://www.microsoft.com/games/flightsi ... ds_sdk.aspJust scroll down a little and click on the highlighted link that says Make Model SDK.
EDIT: The Gmax Gamepack SDK also provides important files needed for exporting.