Method of operating a high altitude long endurance aircraft for maximizing solar capture

A method, comprising:

• determining, by at least one flight control computer (FCC) associated with at least one UAV, a direction of travel of a first UAV of the at least one UAV relative to a Sun;
• adjusting, by the at least one FCC, an airspeed of the first UAV to a first airspeed if the determined direction of travel of the first UAV is towards the Sun;
• and
• adjusting, by the at least one FCC, the airspeed of the first UAV to a second airspeed if the determined direction of travel of the first UAV is away the Sun;
• adjusting, by the at least one FCC, an angle of the first UAV to a first angle relative to a horizontal plane if the determined direction of travel of the first UAV is towards the Sun;
• and
• adjusting, by the at least one FCC, the angle of the first UAV to a second angle relative to the horizontal plane if the determined direction of travel of the first UAV is away from the Sun;
• wherein the angle of the first UAV is relative to a plane of the first UAV parallel to an upper surface of the first UAV, wherein the first angle is substantially parallel to the horizontal plane, wherein the second angle causes the first UAV to tilt up such that the solar array is closer to perpendicular to the Sun's rays;
• controlling, by the at least one FCC, the first UAV to loiter within a set distance of a ground control station in a large-area D-loop flight pattern having portions toward the Sun and portions away from the Sun;
• wherein the at least one FCC is further configured to adjust the airspeed of the first UAV to the first airspeed and adjust the angle of the first UAV to the first angle while traveling toward the Sun;
• wherein the at least one FCC is further configured to adjust the airspeed of the first UAV to the second airspeed and adjust the angle of the first UAV to the second angle while traveling away from the Sun;
• wherein the solar array is disposed on an upper surface of a wing panel of the first UAV and is rearwardly angled in level flight due to a leading-edge-up attitude such that solar capture is primarily maximized when the UAV travels away from the Sun;
• capturing, by a solar array covering at least a portion of the first UAV, solar energy to propel the first UAV and charge a battery of the first UAV with the captured solar energy, wherein the battery is configured to power the first UAV;
• receiving, by a power tracker in communication with the battery and the solar array, power from the solar array;
• supplying, by the power tracker, an electrical charge of the received power from the solar array to the battery, wherein when the power tracker supplies the electrical charge of the received power to the battery while regulating a steady battery-bus voltage despite variation in solar array output with Sun position;
• wherein the power tracker is configured to taper charging, responsive to at least one of:
• a battery temperature and an upper-voltage limit, by adjusting a boost ratio and by commanding a propulsion system of the first UAV to absorb surplus current while maintaining the steady battery-bus voltage;
• wherein the first airspeed is greater than the second airspeed to maximize solar capture of the solar array.