The CG is a point at which the plane needs to balance if it is going to fly well. On a flying wing The CG is back about 23% of the total wing area including elevons. This means that 77% of your plane and the motor are behind the center of gravity. On a conventional plane with a tail the CG can be back as far as 32% with 68% of the length of the plane behind the CG. With most of the plane behind the CG you still have to make it balance. Placement of the battery and radio help to move the CG forward but it is also just as important to keep the back or tail of the plane light. It takes 2-3 ounces of lead in the nose to balance one oz of added weight in the tail.