See:
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html
for a program that calculates the mean Aerodynamic Chord (MAC). The placement of the CG on the MAC depends on the tail volume coefficient. For configurations with typical tail moment arms (in multiples of MAC) and tail areas (as a percentqge of wing area) a safe place for the CG, in order to begin flight testing, is at about 28 to 30 % of the MAC. This will probably result in moving the CG aft some to get the desired handling qualities.