大展弦比飞机运动稳定性建模及分析

随着飞机设计技术的提高和新型材料的应用，现代飞机气动弹性效应越来越显著，刚体运动和弹性体振动互相解耦的关系不再明显，在分析弹性飞机相关问题时，应该综合地、统一地考虑飞行动力学与气动弹性力学问题。本文在一般体轴系下综合考虑了飞机刚体运动自由度和弹性振动自由度，建立弹性飞机刚弹耦合运动的方程，通过在配平状态下引入小扰动运动假设，以及利用有理函数拟合技术将偶极子格网法计算所得到的频域非定常气动力转化为时域形式，建立了大柔性飞机刚弹耦合小扰动状态空间方程，并对纵向运动稳定性进行分析计算。针对文中构型飞机，运用本文所采用的方法计算所得结果与传统的线性及刚体计算所得结果进行对比分析，非线性计算方法所得颤振速度更小，而且失稳模态亦发生变化，对于飞行力学模态而言，长周期模态稳定性变差，在计算速度范围内出现失稳的现象，由此说明机翼大变形对飞机稳定性所带来的影响。

Stability modeling and Analysis of high-aspect-ratio aircraft

Accompanying with the improvements in design technology and application of advanced materials, the structure of modern aircraft is much lighter and more flexible, which induced significant aeroelastic effects. Decoupling of the rigid-body motion and the elastic vibration is not always present. As a result, this dissertation works in the interdisciplinary field of flight dynamics and aeroelasticity to search for an integrated flight dynamic modeling methodology for flexible aircraft. The Lagrange equations of motion of the flexible aircraft are derived, which considered the rigid-body degrees of freedom and elastic degrees of freedom. With the assumption of small disturbance on the nonlinear trim equilibrium state, the state-space equations describing the motion with rigid-body degrees of freedom and elastic degrees of freedom are established. The unsteady aerodynamics in the frequency domain is computed by the doublet-lattice method, and then it is transferred into the time domain by the rational function approximation. The state-space equations are applied to analyze the stability of the very flexible aircraft, and the results are compared to the rigid method and linear method, in order to illustrate the effects of geometric nonlinearity and the coupling between rigid-body motion and elastic vibration. The results of nonlinear analysis indicate that the critical stability flight speed is even lower than the result of linear analysis.