Change of model origin does not export to .ac format I'm trying to modify a model of a windturbine for use in Flightgear. The origin is at present set at turbine level, so when the model is placed in the scenery, it is buried in the ground. I want to change the origin, so that it is at the base of the tower.

In Blender I have "set origin to 3D cursor" with the cursor at the base of the tower. I export to .ac, place the object in the scenery and the origin is still at the turbine level
Some file formats can't store object center information, or simply don't have a concept of a "local origin", and some exporters also don't take into account local coordinates or object origin information.

In these cases all objects centers are generally considered to be at the scene origin or world coordinate [0,0,0]

Try moving all your objects so that their desired centers rest at Blender's scene origin.