A very flexible solar powered UAV under aerodynamic loading undergoes large deformation, thus chan-ging the stiffness characteristics and mass distribution of its wing structure.It is impossible to obtain its precise aero-elastic stability with the linear theory.Therefore we use the co-rotational theory to develop the aeroelastic stability a-nalysis 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 analy-sis 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.%大柔性太阳能无人机在气动载荷的作用下产生较大的弯曲变形，机翼结构的刚度、质量分布等特性亦发生较大改变，线性理论无法满足这类飞机气动弹性稳定性分析的精度要求。基于Cor-ota -tional（CR ）理论，推导了结构变形后的切线刚度矩阵和质量矩阵，建立了大柔性机翼结构动力学模型；采用建立在局部气流坐标系下的片条非定常气动力模型，建立了考虑几何非线性效应的大柔性无人机气动弹性运动方程。引入准模态假设，采用P-k法研究了几何大变形对类＂太阳神＂布局太阳能无人机的气动弹性稳定性的影响。研究结果表明：随着弯曲变形的增加，非线性颤振速度可降低10％以上，非线性颤振频率可下降8％；合理的增加扭转刚度、前移弹性轴、前移剖面质心等，均可以有效改善几何大变形引起的不利影响。研究工作对大柔性飞机的气动弹性设计具有一定的参考意义。
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