Periodically alternating between climbing and gliding flight can result in a range advantage. This periodic cruise can benefit high-aspect-ratio aircraft especially, which are primary candidates for electric flight due to a low power demand. Electric aircraft typically operate at low speeds. At low speeds, the influence of wind on performance becomes more pronounced, making airspeed adaption to local winds beneficial. This paper proposes a system of wind-dependent range-optimal reference generation by direct collocation and its integration into periodic control. Optimization includes specific characteristics and limitations of battery electric aircraft. With the optimization outside of the real-time control, a Total Energy Control System (TECS) is used to control these range-optimal references. The control approach includes undervoltage protection through battery-state-dependent power limitation, and managing transitions between segments at low speeds is detailed. Periodic control and optimized references are assessed in simulation of an electric-powered unmanned aerial vehicle glider, considering vertical Dryden turbulence. The results are compared to level cruise with an optimized static airspeed reference, also determined via direct collocation, and show increased range.
Spark et al. (Thu,) studied this question.