As a long endurance unmanned aerial vehicle (UAV) platform, a solar powered airplane is a powerful candidate, and the airplane is expected to carry out the mission of artificial satellite partly as well as the continuous reconnaissance and surveillance. Under the limited conditions of solar radiation, solar cell efficiency and battery gravimetric energy density, sustainable flight of an UAV is a challenge issue.
In this paper an energy saving flight operation by adjusting flight altitude is proposed to prolong flight time of a solar powered UAV. The proposed method is based on the use of surplus energy from solar radiation to get higher altitude in the daytime and then the obtained altitude is used for descending flight without power consumption during the night. Also the method maximizes the energy saving by optimizing the flight profile, such as the flight altitude, the rate of climb and the time of free descending according to the unexpected solar radiation in real time under the real weather conditions. The proposed method reduces the use of battery energy in the night, so that, the method improves the feasibility of sustainable flight of UAV powered by solar energy only. The flight simulations and discussions are presented to validate the effectiveness of the proposed method.
In addition, the virtual flight system for evaluation of solar powered unmanned aerial vehicle (UAV) is designed and summarized. This system will provide the flight data for evaluating the possibility of continuous flight of a solar UAV. This system consists of the control and monitoring part, the power management part and the fuselage and the propulsion part. The mechanism part is designed for simulating the motion of the aircraft. This is equipped with the three stepper motors and motor drivers and controlled by the LabVIEW CRio. The power measurement circuit is designed in order to monitor the flow of the energy. By using the Zigbee module, the measured data can be monitored by the wireless communication. The power management part is comprised of the maximum power point tracking (MPPT), the solar modules and the charging controller. The fuselage and propulsion part consisted of the aircraft wing, fuselage and propulsion motor. The airfoil and wing are designed considering the aerodynamic characteristics. The required power for the flight is calculated and the data of flight path and attitude is generated to simulate the motion of the aircraft. The experiment of virtual flight is carried out under the real weather conditions and the monitoring of acquisition and consumption of solar energy is performed.