直升机-吊挂耦合系统平衡特性和稳定性分析

基于单质点吊挂假设，建立了直升机-吊挂耦合系统的非线性动力学模型。在该假设下，吊挂将引入额外的自由度和约束，使运动方程增加4阶，且为隐式的微分代数方程组。通过将惯性力中的广义加速度项与广义速度的二次项分离，可将运动方程转化为显式的微分方程组。针对无吊挂的直升机本体和直升机-吊挂耦合系统这两种模型，采用直接数值方法，计算了它们以不同速度做零侧滑定直平飞的配平状态，并结合飞行试验数据进行对比。进一步对两种模型进行了小扰动线化处理，分析其运动模态并进行对比。结果表明，单质点吊挂会给系统引入两个新的运动模态，使得吊挂两个自由度上的运动与直升机高度响应产生耦合，同时改变直升机本体各个模态的特性，会使部分模态响应品质变坏。

Equilibrium characteristics and stability analysis of helicopter-slung-load coupling system

A nonlinear dynamical model of the helicopter-slung-load coupling system was presented, based on single mass-point hypothesis. Under this hypothesis, the consideration of the slung-load brought in extra degrees of freedom and constraints, which made the equations of motion increased by 4 orders, and being a set of implicit differential algebraic equations. By distinguishing the generalized acceleration terms from the quadratic generalized speed terms in the inertia forces, the equations of motion can be turned into a set of explicit ordinary differential equations. For the helicopter model and the helicopter-slung-load model, trim states for zero-side-slipping forward flight were first computed, using direct numerical approach, and the results were compared with flight test data. Then, both of the two models were linearized under small-perturbed conditions, and modal decomposition was performed on these linearized models. Results show that 2 new dynamical modes would be introduced by the single-mass-point slung-load. Motions of the slung-load's 2 degrees of freedom would be coupled with the helicopter's altitude response, and modify the characteristics of helicopter's inherence modes, make some of them worse.