Abstract

Consideration of standard landing cases from technical guideline document is the traditional design practice followed to ascertain aircraft landing loads. A rationale approach on landing load generation and its impact on flexible airframe dynamic response is explored, considering multi-variate landing conditions for the first time on land-base high performance aircraft. Methodology on nonlinear landing dynamic response simulation is developed by amalgamating inputs such as nonlinear nose and main landing gear dynamic models, aircraft rigid body dynamics, low speed aerodynamic and thrust forces. True representation of landing gear nonlinear oleo-pneumatic strut and tire characteristics, variable geometric strut structural stiffness and nonlinear spin-up friction resulted in satisfactory correlation of vertical and longitudinal dynamic response simulation with experimental drop test results. The adequacy of lateral dynamic model is established from the compatibility condition of landing gear and tire dynamics. A down selection methodology is worked out considering total probability and first order sensitive multi-variate landing parameters such as pitch, roll and vertical descent speed, taking into account the plausible statistical variation. Transient dynamic response simulation is then performed for the critical landing cases, on a flexible airframe finite element model by inputting landing load time history as base excitation motion. The dynamic amplification of acceleration response on flexible fuselage nose location from the simulation, is verified with flight data accelerometer frequency response. The application of flexible dynamic responses in ensuring the structural integrity of airframe is elaborated. The proposed methodology on landing load generation is pragmatic, in comparison with the traditional design practice and provides insight during early design phase thereby achieving landing gear subsystem development in-unison with airframe structural clearance aspects.

摘要

考虑技术指南文件中的标准着陆情况是确定飞机着陆载荷的传统设计实践。首次考虑陆基高性能飞机的多变量着陆条件，探讨了着陆载荷产生的基本原理及其对灵活机身动态响应的影响。非线性着陆动态响应仿真的方法是通过合并非线性机头和主起落架动力学模型、飞机刚体动力学、低速空气动力学和推力等输入而开发的。起落架非线性油压气动支柱和轮胎特性的真实表现，可变几何支柱结构刚度和非线性旋转摩擦导致垂直和纵向动态响应模拟与实验跌落测试结果的令人满意的相关性。从起落架和轮胎动力学的兼容性条件建立横向动力学模型的充分性。考虑总概率和一阶敏感的多变量着陆参数（例如俯仰、滚转和垂直下降速度）并考虑合理的统计变化，制定了向下选择方法。然后通过输入着陆载荷时间历史作为基础激励运动，在柔性机身有限元模型上对关键着陆情况进行瞬态动态响应模拟。利用飞行数据加速度计频率响应验证了来自仿真的柔性机身机头位置加速度响应的动态放大。阐述了柔性动力响应在保证机身结构完整性中的应用。与传统设计实践相比，所提出的着陆载荷生成方法是务实的，并在早期设计阶段提供洞察力，从而实现起落架子系统开发与机身结构间隙方面的协调。