小型油动无人直升机机架振动特性与试验研究

农用油动植保无人直升机在航空作业时因受到发动机、旋翼、传动箱动力载荷激励作用与无人机表面附面层紊流强度的影响,导致机身及相连施药关键部件的振动。若机架与喷杆连接点的激励频率与喷杆固有频率接近或相等,则会引起两者共振,强烈的振动甚至会影响无人机的飞行姿态。因此,为了保证植保无人机的安全飞行,获得机架的振动特性是研究的首要任务。为此,以小型油动无人直升机为研究对象,建立无人机机架的有限元模型,应用ANSYS Workbench对模型进行自由振动状态下的模态分析,获得前8阶非刚体模态固有频率和振型,通过模态试验验证模型的准确性。试验中,试验模态与解析模态模态频率差均小于10%,模态置信准则均大于0.8,试验结果表明:有限元模型能够反映机架振动特性,随着机架固有频率的增长,振型变化越来越复杂,由机体单向摆动向机体多向同时扭摆转变,变形最大部位在喷杆、起落架、尾管处。该研究为后续展开谐响应分析与喷杆结构优化研究提供了理论依据,旨在避免喷杆与机体产生共振。

Vibration Characteristics Analysis and Test Verification Based on Small Engine Driving Agricultural Plant Protection Unmanned Helicopter Frame

The agricultural plant protection engine driving unmanned helicopter is excited by the dynamic loading from the engine, rotor and transmission case, as well as the effect of surface layer turbulence intensity on the surface of unmanned aerial vehicle when the unmanned helicopter is in the air, leading to the vibration of fuselage and lance. If the frequency of the connection point between the rack and the spray lance is close or equal to the nature frequency of the spray lance, it will be going to resonate, strong vibrations can even affect the flight stance of unmanned aerial vehicle, so in order to ensure the safe flight of the unmanned helicopter, the primary task of the study is to obtain the vibration characteristics of the frame. This paper focus on the small engine driving agricultural plant protection unmanned helicopter frame,establishing finite element model of unmanned helicopter frame, applying on ANSYS Workbench to analyze the modal of the finite element model under free vibration condition, obtaining the natural frequencies and modes of the first eight non-rigid modes. The accuracy of the model is verified by modal test and the results are analyzed. The result showed that the unmanned helicopter frame finite element model is correct and it can be used to reflect the vibration characteristics of the frame, with the increase of the natural frequency of the frame, the change of frame vibration is more and more complicated,and the most deformed parts are in the spray, landing gear and stern tube, so to enhance stability, it is very important to avoid the resonance of the spray and the body. This paper provide theoretical basis for subsequent research work, based on this,the study of harmonic response analysis and structure optimization can be carried out, thereby solving the optimization problem of spray structure which cannot be easy to achieve under test conditions, to avoid resonance of spray and unmanned helicopter frame.