CG Balance
if a little nose heavy no problem, lot of nose heavy big problem,can run out of up elevator then will not fly.Can add weight at the bottom end of plane on the surface,drill hole in weigh then screw weigh to plane,make a door at the back of the plane and move battery to rear of plane ,or again,drill hole in weigh and door and bolt weigh to inside of door or hatch,even with stick on weigh I drill the weigh then screw or bolt to plane,seen to many problems when weigh shifted or fell off plane.
Have a goodun,John.