To make more room for batteries in mine I moved the horizontal "tray" that Pierre mentioned, to the bottom of the fuselage. This also further strengthened the floor for belly landings. http://personal.rdu.bellsouth.net/rd...d/skimmer.html
I used 8 x 600AE cells with a direct drive speed 400 or 10 x 600AE when using a geared speed 400. With the geared setup I had trouble getting the CG back far enough because the battery was all the way back against the servos. And to do that I had to move the receiver behind the servos.