The addition of a horiz. stab. will move the neutral point aft. In order to maintain a similar static margin, the CG will also need to move aft. First, find (calculate) MAC of the Rookie's wing. The distance from 25% MAC to the original CG, expressed as a % of MAC is the static margin. Now, calculate the neutral point with the horiz. stab. using the linked website. The CG can now be moved to a position that yields a static margin (SM) similar to the flying-wing version. Tailed aircraft usually use a SM smaller than that for a flying wing, due to the longer tail-moment. A SM of 10-15% would be a good starting-point. Hope this helps.[link]http://www.geistware.com/rcmodeling/cg_super_calc.htm[/link]