Optimal speed scheduling with arrival time constraint for solar-augmented aircraft

Improvements in solar cell weight and performance have enabled the development of small solar-powered aircraft that operate at low altitudes. Unlike high-altitude pseudosatellites, these aircraft must contend with significant stochastic variations in wind and solar energy. This paper examines speed scheduling for aircraft equipped with solar panels, but which do not necessarily supply their entire energy budget from solar power. Soaring speed-to-fly theory is extended to incorporate both solar and updraft energy. When used to optimize shadow crossings for solar aircraft, it allows pure solar flight with 20% greater cloud coverage. The requirement for pure solar flight is relaxed and the use of stored energy onboard allows derivation of a speed to fly with an arrival time constraint, allowing the exploitation of stochastic energy while satisfying 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 the variance in final energy state by approximately 3%. The algorithm is also tested in flight on a small unmanned aerial system, satisfying an arrival time condition within 1% of the nominal flight time.