Conceptual Multidisciplinary Design Optimization (MDO) of Solar Powered UAV
CHALLENGE - The paper describes the design of a solar unmanned air vehicle (UAV). It starts with a review of the various models used during the design process, including the solar radiation model, the aerodynamic model, the mass estimation method and the energy balance model. To make a solar powered air vehicle successful, namely to have sufficient design margins, two technological hurdles should be considered: the first one is the efficiency of the solar panels and the second one is the energy storage system (i.e. the battery pack).The design problem has had the objective of staying aloft for an unlimited time, by loitering at high altitude (70,000 ft) during daytime and then descending and cruising at a lower altitude during the night. During daytime the power requirements of the vehicle are fulfilled by the solar panels and during the night by the batteries. The batteries are charged by the surplus solar power at daytime. The main challenge of the solar air-vehicle design is to reach a positive energy balance, while keeping the vehicle mass and drag and power requirements at a minimum.
SOLUTION - Two design cases are presented. The design goal of the first case is to minimize the vehicle total mass and maximize the night flight altitude, while the payload has a fixed value of 2 kg. The design goal of the second case is to maximize the payload mass and minimize the total vehicle mass; this is done for a fixed night flight altitude (two values are used: 50,000 ft and 65,000 ft). The above mentioned two opposing objectives are defined through complex functions of the design variables, whereas the design process is based on a multidisciplinary design optimization (MDO) approach, implemented using the modeFRONTIER platform. Pareto fronts for different design goals are presented, followed by discussions of design trends and tradeoffs. The results emphasize the importance of the MDO approach during the conceptual design process for this type of air-vehicles.
BENEFITS - modeFRONTIER enabled the integration of different simulation models into a single synergetic design tool using the Matlab direct integration node. In addition, the designers took advantage of various optimization procedures available in modeFRONTIER, which are an essential part of the MDO approach.