The Optimum Center of Gravity Position for Minimum Overall Energy Loss

Abstract

The effect of center of gravity position on the additional induced drag due to the tail lift force is considered for both the circling and gliding phases of a cross-country flight.  The loss of energy height per hour is then derived as a function of CG position for soaring conditions requiring various gliding speeds, assuming the usual MacCready theory to apply.  The optimum CG position to minimize the loss of energy height per hour is found to be a function of the gliding speed (or of the corresponding rate of climb).  However, if typical Standard and l5-Meter sailplanes are considered, it is found that a single CG position will provide near-optimum conditions over a reasonable range of gliding speeds.  The optimum CG position, in the cases considered, was somewhat forward of the likely aft limit.  Varying the CG position in flight to maintain zero tail load at all times does not appear to be worthwhile.