舰面状态直升机机体在起落架上的固有频率分析

Analysis of Helicopter Natural Frequencies on Landing Gear at Ship-Borne Conditions

针对起落架缓冲支柱和轮胎的非线性特性,应用等效线性模型,提出一种预估刚性机体在弹性起落架上的固有频率计算方法。利用缓冲支柱和轮胎的刚度和阻尼试验数据,采用循环迭代方法计算了机体耦合振动的固有频率;分析了直升机重量、旋翼拉力、舰面运动状态、舰面风力等因素对机体模态固有频率的影响。对最不稳定的机体侧向二阶模态而言,最大设计重量和大升力状态时其固有频率最低,与最小重量、零升力状态相比其稳定转速余度减少约133 r/min;文中假设的舰面运动状态和舰面风力对机体模态的固有频率影响很小,而采用纵、横侧向独立的简化模型来预估机体模态固有频率具有足够的精度。

Aiming at nonlinear properties of landing gear oleo shock absorber and tire, a calculation method was presented to predict the natural frequencies of rigid body fuselage free vibrations on elastic landing gears from equivalent linear model. Application of oleo shock absorber and tire equivalent stiffness and damping test data, an iterative procedure was utilized to solve the fuselage natural frequencies. The various effects such as helicopter gross weight, rotor lift, ship motion state and wind ship-borne to natural frequencies were analyzed. For the fuselage second lateral mode, which is the least stable fuselage mode, its natural frequency is the lowest for the case of maximum gross weight with high rotor lift. In such a case the stability margin of rotary revolution will be reduced about 133r/min compared to the case of minimum gross weight with zero rotor lift. All types of ship motion state and wind ship-borne hypotheses in this paper had hardly effects to fuselage natural frequencies. A simple decoupling model, independent in fuselage longitudinal-pitch and lateral-roll motions, showed enough precisions in natural frequency predictions.