A Mathematical Model of a Conceptual Design Approach of High Altitude Solar Powered Unmanned Aerial Vehicles

Abstract

High-altitude aircraft flying in the stratosphere (around 20-30 km altitude) can provide a useful platform for sensors to support a range of surveillance tasks. Flying at high altitudes comes with a number of challenges. The air at high altitudes is thin and can considerably impact on the generation of sufficient lift and thrust. Moreover, powering the aircraft by solar energy with the aim of long-term operation adds extra challenges such as power management and system requirements. Therefore, the balancing of the energy and mass is usually taken to initiate the design process. In this paper, an analytical approach has been developed to conceptually design a solar-powered aircraft operating for long endurance at high-altitude. The total mass of the aircraft was defined as the summation of all aircraft elements. Each element was represented as a fraction of the total mass or the required power. These fractions were obtained from existing data of similar solar powered high-altitude UAVs. Also, a study has been conducted to explore the influence of mission requirements such as the flight level, the geographic location and the start & end date of the mission on the main characteristics of the aircraft. The design approach proved its capability by producing acceptable results for the weight and the power of the aircraft elements. This approach facilitates exploring the possible design space for a given mission in which the optimal weight and its corresponding set of characteristics can be easily concluded. The study of the mission parameters shows that designing the aircraft for high altitude operations can lead to a heavier aircraft despite the harvested solar energy at higher altitude being higher. Also, it was shown that the required surface area for solar panels is less than that required to generate adequate lift forces due to low air density. The duration of the daylight hours along with the intensity of solar radiation has a marked influence on achieving the design objective.