About the Instant Cross-country Speed

Abstract

The instant cross-country-speed of gliders is defined and a formula given which is discussed in detail, explaining for instance why the classical theory is failing to provide suitable instantaneous results, why the instant cross-country speed may be regarded to be the shadow speed of the glider if the sun rays are inclined in the right manner and the shadow is cast on flat ground, or how energy is gained and transformed into cross-country speed.  Igc-files of two flights are evaluated to test the formula, showing promising results suggesting its implementing into modern flight computers for the purpose of helping pilots to improve their cross-country-speed and flying performance.