Thanks for the info. I can probably move the battery back into the servo area of the tail, this will reduce overall weight. I'm a reasonably accomplished flyer and I think that adding this much weight at the extremities of an airframe will dramatically increase the momenent around the COG i.e. once the tail weight begins to move it's momentum will tend to keep it moving. Hence my problems trimming. I'm way overpropped too with a 15X6 as the OS91 FX runs at near idle most of the time and gives me 30 min flights.