AutoCAD has a FLATTEN command that will created a D object from a 3D view (I.E.. SW Isometric). Though this will not show the "true length" of the object. Unfortunately AutoCAD does not have the functionality for this.
To determine the true length of the object within AutoCAD, my suggestion would be to trace the arcs with a polyline. Through the properties window, you can determine the actual true length of said arc.
Steve Bessette Support Specialist Product Support Autodesk, Inc.