Thanks so much for all the information you have given us. I am going with two YS 63FZ-S four strokes. They are rated at 1.6HP compared to the OS 70 which has 1.1HP. I will be using the APC 13x6 two blade prop's. I would like to try the Graupner 13x6 prop's also. Will be looking forward to more of your flight test reports so we will be able to pick the best combination prop's for this plane. Thanks again.