Deterministic Design Optimization of a Bendable Load Stiffened UAV Wing
Vijay N. Jagdale, Peter Ifju, Abhishek Patil, Bret Stanford · 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition · 2010
A bendable UAV wing, developed at the University of Florida, shows the ability to load stiffen in positive flight load direction, while remaining compliant in the opposite direction. Such a wing enables UAV storage inside smaller packing volumes. The present paper utilizes a multidisciplinary approach for conceptual design of a bendable load stiffened UAV wing having 24 inch span and 7 inch root chord via a multi-objective optimization problem. The wing shape definition parameters and the layup scheme used to manufacture the wing are treated as design variables. Two types of wing geometry definitions are discovered: constant camber and variable camber wing design. Aerodynamic performance of the wing is studied using extended vortex lattice method (Athena Vortex Lattice, AVL) software. An arc length method based nonlinear FEA routine in ABAQUS is used to evaluate the structural performance of the wing and to determine the maximum flying velocity that the wing can withstand without buckling or failing under flight loads. An analytical approach is used to monitor the stresses developed in the composite wing during storage and the Tsai-Wu criterion is used to check failure of the wing due to the rolling stresses to determine minimum storage diameter. Wing shape optimization is performed using an elitist nondominated sorting genetic algorithm: NSGA-II. Experimental long term storage creep testing showed wing twist angle being the dominant factor in wing creep deformation. Optimization studies are performed by fixing the twist angle to zero. Compact storage volume requirements constrain the UAV horizontal stabilizer dimensions and an appropriate pitching moment constraint is added in the problem definition. Variable camber wing geometry definition leads to improved wing designs over constant camber wing geometry definition. The design points on the Pareto optimal fronts thus achieved give improved performance over a baseline wing design.