Aeroelastic Optimization Using Laminate Fiber Orientation on a Composite Wing Structure

Abstract

Composite materials use increases significantly in aerospace structures, especially wing structures, primarily due to their attractive strength-weight ratios. Nevertheless, the increasing use of light and slender wings in modern unmanned aerial vehicles (UAVs) leads to structural configurations featuring low natural frequencies and high flexibility, which can easily experience aeroelastic phenomena that might cause potentially catastrophic failure. This paper aims to present an investigation to achieve an optimal fiber orientation of laminates layup for the UAVs’ wing skin to meet aeroelastic design requirements. The wing ribs and spars are made from aluminum alloy, while the wing skin is a composite plate made of woven carbon laminates. The flutter speeds for each configuration layup were analyzed numerically using MSC Nastran. The doublet-lattice method is adopted to predict three-dimensional unsteady aerodynamic forces acting on the oscillating wing. According to the numerical analysis, it is evident that the fiber orientations of the wing skin influence the critical flutter onsets. Since the fiber orientation change can significantly affect the wing's stiffness, particularly in the torsion modes. Thus, the aeroelastic performance can be improved without increasing the mass by modifying the fiber orientation on the wing skin laminates. The angle of 45° can improve the critical flutter speed by more than 400 m/s and static-divergence up to 330 m/s or 50% higher in static-divergence speed and more than 260% in flutter speed compared to angles of 0 and 90°.