I just cannot believe how much extra weight I have had to add to the motor box to get this plane balanced. So far I have added 6oz plus I have moved the 6v 2500 nimh battery to the top of the motor box and she still needs more weight. It looks like I will have to add another 6oz. I did have to move the firewall back 1" to get the OS 70 FS to fit into the cowl. I just hope the plane can handle this extra weight and be a good flyer