Exploring aeroelastic stability of very flexible solar powered UAV with geometrically large deformation

A very flexible solar powered UAV under aerodynamic loading undergoes large deformation, thus changing the stiffness characteristics and mass distribution of its wing structure. It is impossible to obtain its precise aeroelastic stability with the linear theory. Therefore we use the co-rotational theory to develop the aeroelastic stability analysis algorithm suitable to a very flexible aircraft, derive the expression of tangent stiffness matrix and mass matrix of a spatial two-node beam element, and establish the dynamic model of a geometrically nonlinear structure. Using the unsteady aerodynamic strip model and the quasi-mode assumption, we derive the aeroelastic motion equations. We use the P-K method to analyze the aeroelastic stability characteristics of a solar-powered UAV with the layout similar to Helios under geometrically large deformation. The analysis results on a test are compared with other analysis results given in Table 2, and they show good agreement: as the wing deformation increases, the nonlinear flutter speed decreases by 10%, and the nonlinear flutter frequency decreases by 8%; the aeroelastic stabilities of a solar-powered UAV will be improved by increasing torsional rigidity or by moving its elastic axis and the mass center of its wing section toward the leading edge.