If you want a DF trainer that flies well on a hot sport engine like the O. S. .46FX, try to find a Fantrainer kit. They are no longer in production (that I know of, at least), but the Fantrainer is a simple D/F plane. It uses a 10" 3-bladed prop in a plywood duct mounted a little behind the wing. It will give you some of the flying characteristics of a more complex D/F for about the same price as a sport plane. Since the fan is out in the open, it is farily simple to maintain and fly. The only drawback is that the Fantrainer has a face only a mother could love. If you can't find the kit anywhere and are a good builder, I think that Model Airplane News sells the plans. Good luck!