OPTIMIZING FIGURE-8 SOARING FOR HILL AND WAVE LIFT

Abstract

Flying to and fro along a line of hill or wave lift we often pass through local patches of stronger lift. Traffic and other conditions permitting, we sometimes try to work this lift either by circling, by flying short beats through the good patch, or by doing figures of eight. Unlike thermals, which drift downwind, hill and wave lift tend to be associated with the ground features producing them. Shifts certainly occur, but there are periods when the area of lift seems to be fixed near some point on the ground, and we try to stay fairly close to it. This note suggests ways to optimize the gain from the figure-8 method. In what follows we will take the direction from which the wind blows as 0 degrees ( = 360 degrees) and the line of lift as running across wind (090 degrees to 270 degrees). We will first consider a simple case, consisting of a sequence of reverse
turns.