Maximizing Net Power in Circular Turns for Solar and Autonomous Soaring Aircraft

Abstract

This study investigates maximizing net power input from a solar-photovoltaic array and/or a thermal updraft while performing constant bank angle, circular flight-path turns (that is, an orbit). The process inputs are the aircraft sink polar (or, equivalently, the power required curve), the date, the time, the location, and the flight altitude. A solar insolation model is combined with a best-turn performance calculation to determine the bank angle that maximizes power input from a solar-photovoltaic array at varying sun elevation angles. In general, for low sun elevation angles, the maximum net power gain from solar input and drag output is found at higher bank angles and shows 15% (absolute) gain over the limiting case of wings-level orbits in the same conditions. For high sun elevation angles, the maximum net power is found at low bank angles. The break point between high and low sun elevation angles varies with aircraft parameters and is approximately 25 deg for the example aircraft in this paper. The relative power losses of off-optimum orbits at a given bank angle are quantified. Finally, a thermal-updraft model is included in the net power calculations to determine an optimal bank angle that maximizes the average power input from a combination of solar photovoltaics and thermal updrafts. This paper shows that soaring and solar photovoltaics can be mutually beneficial, and it provides a method to calculate losses at off-optimum conditions.