Effects of Span Morphing on Flutter Characteristics of Subsonic Wing

This paper focuses on the dynamic behavior of variable-span morphing wings (VSMW) oscillating in pitch and plunge motions under subsonic flight conditions. The unswept cantilevered wing is modeled as three-stepped Euler-Bernoulli beam. The aerodynamic loads acting on the wing are represented by Theodorsen's unsteady aerodynamic theory. The differential equations of motion that describe the behavior of the dynamics of Euler-Bernoulli beam are derived through the Hamilton's principle. The differential transformation method (DTM) is implemented to equations of motion and boundary conditions. The solution of the aeroelastic system is obtained by the classical frequency domain solution, k-method. Goland wing and High-Altitude Long-Endurance (HALE) wing are used as the basis for this study. Prior to analyzing flutter characteristics of VSMW, validation cases are conducted to ensure that the developed algorithm works well. Furthermore, flutter speed and flutter frequency are analyzed for different elongation ratios of wing. There is a significant difference in flutter values of fully retracted and fully extended wing configurations. It can be concluded that both flutter speed and flutter frequency decrease dramatically as wing span extends. Another important finding is that the flutter speed and flutter frequency reductions are relatively high at the initial stages of wing span extension.