Power Optimization of Solar-Powered Aircraft with Specified Closed Ground Tracks

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Power Optimization of Solar-Powered Aircraft with Specified Closed Ground Tracks

Spangelo, Sara C. / Gilbert, Elmer G.

This paper considers the optimization of flight trajectories for solar-powered aircraft. This work is unique relative to past work because flight path is constrained to repeatedly traverse a specified closed ground path. Constraints of this form are of interest in a variety of missions where the goal is to loiter near a fixed point on the ground. The performance index to be maximized is the average input power to the battery over each cycle of the ground path. It is advantageous to allow the periodic flight path to have altitude variations because during both ascent and descent there are opportunities to increase the angle of sun exposure to the aircraft solar array. A novel procedure for solving the related optimization problem is described that addresses the implementation of a difficult state constraint: the flight path must belong to the surface of the vertical cylinder whose base is the closed ground path. Results for a wide collection of optimization examples are described, which lead to an important conclusion. By allowing aircraft speed and altitude to vary it is possible to obtain an average input battery power greater than the optimal power for constant speed and constant altitude.