支柱柔性对起落架缓冲器摩擦力的影响

Effect of Shock Strut Flexibility on Landing Gear Shock Absorber Friction Force

旨在通过缓冲支柱柔性对起落架缓冲器摩擦力的影响研究,为起落架缓冲器摩擦力建模方法和柔性起落架防卡滞设计提供技术指导。伴随着超高强度钢的逐步应用,刚度问题成为起落架设计中日益突出的矛盾问题,传统的缓冲支柱刚性假设可能并不适用于一些新类型起落架的分析。本文结合某无人机飞行试验中出现的主起落架缓冲器卡滞问题,首次建立了考虑支柱柔性影响的起落架缓冲器摩擦力模型,计算了最严重工况下的摩擦力值,并与缓冲支柱刚性假设计算得到的摩擦力值进行了对比分析。分析表明在考虑支柱柔性和理想平面滑动轴承约束的情况下,摩擦力大小为原来的6倍,缓冲器发生卡滞。分析了平面滑动轴承的实际约束情况,提出了轴承支承变形协调系数的概念,并分析了其与摩擦力和卡滞的关系,进而研究了支柱外筒和活塞杆刚度对于缓冲器摩擦力的影响。研究表明在变形协调系数不小于0.53时,缓冲器发生卡滞;适当改变活塞杆和外筒的刚度使其相匹配可以降低缓冲器的摩擦力。

In order to provide a new modeling method of the landing gear shock absorber friction force and offer technical advice about shock absorber binding, influence of the shock strut flexibility on landing gear shock absorber friction force is researched. With the use of high-strength steel, stiffness becomes an ever more serious issue. Traditional rigid shock strut presupposition may not be suitable for analysis of new types of aircraft landing gear. To address the binding occurring to an unmanned aircraft, a landing gear shock absorber friction force model is established with the shock strut flexibility taken into consideration. The friction force under the most serious case is calculated, and is compared with the force calculated without taking shock strut flexibility into account. The study shows that in the case when the shock strut flexibility is considered and under the ideal planar slide constraint, the friction force is 6 times that of the rigid model. The friction force thus can lead to shock absorber binding. Furthermore, the actual constraint forms are analyzed, and the coefficient of bearing deformation consistency is presented. The relationships of this coefficient with the friction force and shock absorber binding are analyzed. The influence is studied of the flexibility of the shock strut inner cylinder and outer cylinder on the value of the friction force. The study shows that the shock absorber will get stuck as the coefficient of bearing deformation consistency becomes no less than 0.53. Decreasing the inner cylinder＇s flexibility or increasing the outer cylinder＇s flexibility can decrease the shock absorber friction force.