Engineless unmanned aerial vehicle propulsion by dynamic soaring

Dynamic soaring is a flight technique which extracts energy from wind gradients with the potential to power small unmanned aerial vehicles in maritime applications. Wind gradients of the required magnitude naturally occur at the air-sea interface due to friction between the waves and the moving air. Suitability of dynamic soaring as a means of propulsion requires clarification of the achievable flight performance and the likelihood of favorable winds. Optimal trajectories for minimal and maximal wind conditions are generated as well as trajectories for optimal cross-country travel. The flight model's differential flatness property is used to simplify the optimization problem. The likelihood of favorable winds is predicted based on long term weather statistics and knowledge of the minimal and maximal permissible wind strengths. Comparison of the likelihood of favorable winds for the wandering albatross and an unmanned aerial vehicle of similar size shows that the ability to fly close to the surface is a key factor governing dynamic soaring performance