i have to agree with pat, i also have the sd50 and using a os91fx and to get the cg i just made a balsa mount for the battery just behind the canopy and it cg'd great and still under the max weight limit per horizon. just had to look at it to make it and it works great. the only problem with mine it's i really have a hard time landing, i'm used to 3d planes and it's hard for me to land fast but that's my issue and not the planes. i'll get i hope because i love flying this plane.