Evaluation and Comparison of Sailing Flight Optimization Algorithms for a Stratospheric Dual Aircraft Platform Concept

Dual-aircraft platform (DAP) is a novel stratospheric satellite concept that features two tethered glider-like unmanned aerial systems which exploit wind speed differential across altitudes (i.e. vertical wind shear) to literally sail without propulsion, analogous to a kitesurfer. This paper describes a sailing flight optimization algorithm/strategy for refining the DAP sailing flight target requirements which accounts for uncertainties (error) in the precomputed (initial guess) target flight conditions. This autotuning strategy is a passive calculation method utilizing a performance index (PI) which consists of cost functions for control actuation and trajectory tracking to identify optimal flight requirements for sailing. The performance index is used in combination with autonomous angle sweeps in the roll, pitch, and yaw axes to determine a new sailing condition. Flight simulation results are presented for two scenarios involving uncertainties in the wind conditions and aircraft aerodynamics, respectively. The potential benefits and drawbacks of the strategy are discussed.