The Best-speed Diagram for Soaring in Isolated and Aligned Lift

Abstract

Speed-to-fly theory optimizes the average speed of a glider based on the climb rate in circling flight and on the vertical air motion in straight flight.  This paper looks at the optimized average speed when aligned upward motion is available in the straight flight between the circling climbs in isolated lift.  The optimized average speed is visualized in a diagram with the climb rate in isolated lift on one axis and the aligned upward motion of the air on the other axis.  For aligned upward motion of sufficient strength the pure straight flight mode is faster than the circle-and-glide flight mode.  A transition line separates the two flight modes in the best-speed diagram.  The diagram is an essential component for the meteorological planning of soaring flights with predictions of isolated and aligned lift.