An aerodynamic performance figure of merit for sailplanes

Abstract

The comparison of the cross-country abilities of different sailplanes is limited by the fact that they are designed for operation under varying thermal strengths and, hence, the performance curves cannot be directly compared.  This article proposes a single figure of merit which may be used as a general indication of the cross-country performance of all sailplanes under a variety of conditions though naturally the best sailplane under any particular thermal conditions is not necessarily the one with the best figure of merit since it may have been designed for thermals of entirely different strength.