Speed To Fly

Speed to fly is a principle used by soaring pilots when flying between sources of lift, usually thermals, ridge lift and wave. The aim is to maximize the average cross-country speed by optimizing the airspeed in both rising and sinking air. The optimal airspeed is independent of the wind speed, because the fastest average speed achievable through the airmass corresponds to the fastest achievable average groundspeed. The idea is usually attributed to Paul MacCready, although an early version of the theory was first described by Wolfgang Späte in 1938. However Späte may not have considered sinking air between thermals, and there is no mention of this until 1947 when Ernest Dewing and George Pirie independently included this aspect. Paul MacCready, however, certainly invented the "ring", which allowed an easy indication of the optimal speed to fly.