ACFTools
Here goes small external utility that converts X-Plane aircraft model to AC3D format. Then you can edit aircraft bodies (wings
not supported!) in AC3D which is more cooler than internal Plane-Maker modeler, and import them back to X-Plane.
From
http://www.x-plane.com/descrip.html:
"X-Plane is the world's most comprehensive, powerful flight simulator, and has the most realistic flight model available for personal computers."
Users can develop and fly their own designed planes, thus there exists ~1900 real & fictional aircrafts located in central repository
X-Plane.Org, which you can now import to AC3D 8)