If using the Saito 91. Put the throttle servo up front. You will need to use a band saw or scroll saw and cut some area out of the ply. I just put a saito 91 in my first one and it is way tail heavy. But I also have the engine mounted rearward. Might be wise to bend the landing gear out a bit, so it doesn't want to tip so easy in a little wind. Other than that it is a breze to build and way fun to fly...........