Static aeroelastic characteristics analysis of a very flexible solar powered UAV with geometrical nonlinear effect considered

Very flexible solar powered UAV under aerodynamic loading undergoes large deformation and aerodynamic load distribution is not possible to be obtained sufficiently precisely by means of linear theory. Starting from Ref.12 by Crisfield et al, we develop a static aeroelastic characteristics analysis algorithm suitable to very flexible aircraft; this is explained in sections 1 and 2 of the full paper. The core of section 1 is that, using the co-rotational theory, we derive the expression of tangent stiff matrix and that of internal force of a spatial two-node beam element of a geometrically nonlinear structure. The static aeroelastic equations are set up in section 2. Section 3 analyzes the static aeroelastic characteristics of a solar powered UAV with the layout similar to Helios. The results given in Figs.5 through 8 and their analysis show preliminarily that: the distortion of the flexible wing leads to lift loss, when the wingtip displacement is 13% of span, the lift-drag ratio decreases by 4.2%, the rolling moment coefficient derivative increases by 300%, and the yawing moment coefficient derivative increases by 350%; the geometrical nonlinear bending effect improves the aerodynamic load distribution along the span, thus benefiting structure design. The investigation is believed to be of some reference value to the design of very flexible solar powered UAV.