Design of a high altitude long endurance flying-wing solar-powered unmanned air vehicle

The low-Reynolds number environment of high-altitude flight places severe demands on the aerodynamic design and stability and control of a high altitude, long endurance unmanned air vehicle (HALE UAV). The aerodynamic efficiency of a flying-wing configuration makes it an attractive design option for such an application and is investigated in the present work. The proposed configuration has a high-aspect ratio, swept-wing planform, the wing sweep being necessary to provide an adequate moment arm for outboard longitudinal and lateral control surfaces. A design optimization framework is developed under a MATLAB environment, combining aerodynamic, structural and stability analysis. Low-order analysis tools are employed to facilitate efficient computations, which is important when there are multiple optimization loops for the various engineering analyses. In particular, a vortex-lattice method is used to compute the wing planform aerodynamics, coupled to a two-dimensional panel method to derive aerofoil sectional characteristics. Integral boundary-layer methods are coupled to the panel method in order to predict flow separation boundaries during the design iterations. A quasi-analytical method is adapted for application to flying-wing configurations to predict the wing weight and a linear finite-beam element approach is used for structural analysis of the wing-box. Stability is a particular concern in the low-density environment of high-altitude flight for flying-wing aircraft and so provision of adequate directional stability and control power forms part of the optimization process. At present, a modified Genetic Algorithm is used in all of the optimization loops. Each of the low-order engineering analysis tools is validated using higher-order methods, to provide confidence in the use of these computationally-efficient tools in the present design-optimization framework. This paper includes the results of employing the present optimization tools in the design of a high-altitude, long endurance, flying-wing unmanned air vehicle to indicate that this is a viable design configuration option