Just a stab at a suggestion. If you have the plane model and all you want in Poser is the propeller, take it into Carrara's vertex modeller (I don't know for sure if that's what it's called, as I have RayDream Studio, but it's basically the same thing). Go to a side view. Select all the verteces on the model except the propeller. Delete them. Leave the vertex modeller, then export the propeller as an .obj. If you need the rest of the plane you'd have to save working copies of the full model, do what I described for the propeller, but backwards -- that is to say, select only the propeller verteces and delete them. Hope this helps.