Optimal speed scheduling for hybrid solar aircraft with arrival time condition

Improvements in solar cell weight and performance has enabled the development of small solar powered aircraft which operate at low altitudes. Unlike high altitude pseu-dosatellites, these aircraft must contend with significant stochastic variations in wind and solar energy. This paper examines speed scheduling for solar augmented aircraft (i.e. an aircraft equipped with solar panels and a supplementary energy source which cannot be recharged in flight). We show that solar energy can be considered as identical to vertical air motion exploited by a sailplane. This permits soaring speed to fly theory to be extended to incorporate both solar energy and atmospheric vertical motion. The use of stored energy onboard allows derivation of a speed to fly theory with an arrival time constraint, allowing the exploitation of stochastic energy during a flight plan. The speed schedule is tested in Monte Carlo simulations and shows the ability to satisfy an arrival time constraint while reducing energy consumption by approximately 2% and reducing variation in final energy state by approximately 3%. The algorithm is also tested in flight using a small uas, and shows the ability to satisfy an arrival time condition within 1%.