A universal dimensionless model for the MacCready sailplane theory

Abstract

An improvement of the MacCready speed-to-fly theory used in sailplanes cross-country flights is outlined. Two different parameters characterizing the thermal are introduced (the vertical speed of the air inside the thermal and the thermal radius) and a universal dimensionless model is proposed, which can be applied to any sailplane. The maximum average cross-country speed, the optimum airspeeds in descent and climb, the rate of climb in the helical trajectory and other flight variables are calculated versus two abbreviated parameters condensing thermal and sailplane data.