本文由Th.Theodorsen给出的二维不可压缩流谐和振动升力面理论出发,利用线性空气动力系统频率响应函数与脉冲响应函数的关系,推演出非定常气动力指示升力函数近似表达式。并以活塞理论和三维定常流结论加以修正,无需做大量的数值计算和拟合工作。最后导出考虑三阶弹性振型的飞行器纵向状态空间方程。 Based on the theory of two-dimensional incompressible flow and vibration lifting surface given by Th. Theodorsen, the approximate expression of lift function of unsteady aerodynamic force is deduced by using the relationship between frequency response function and impulse response function of linear aerodynamic system. And the piston theory and three-dimensional steady flow conclusions to be corrected, without having to do a lot of numerical calculations and fitting work. Finally, the longitudinal state space equation of the aircraft considering the third-order elastic modes is derived.