Currently right now in my Wonder is a OS 15 FP, but like I said I building a second one with a OS 25 FP up front, dual aileron servos, and maybe rudders, I haven't decided yet. I dont know if I built the first one with a little offset in the rudder or if it is the wait of the muffler to one side but it will do a hammer head when you stall vertical, always to the muffler side it looks kind of neat, but rudders would give some more options. I have most of the pieces cut out, and as soon as I finish up my Up Roar I will start on the Wonder.