I use an OS61FX in mine and the only mod I had to make to get it to balance first time with no extra weight added was to reposition the rudder servo to a hole I cut under the rear of the fuselage, using a double push/pull rod to two rudder horns.

I must have had at least 200 flights by now, and it still is the only model (of many!) that I have that always seems to be ready to fly without any effort.

I great model in every way.

-David C.