Research On Methods Of Establishing Load Spectrum For Helicopter’s Transmission System

Abstract:The fatigue reliability of the helicopter is an important guarantee for helicopter flight safety. As one of the core components of helicopter, transmission system has always been the key of fatigue check. In order to get the load spectrum which is needed for fatigue test, the whole process of generating load spectrum is discussed in detail.Firstly, this paper introduced the whole process of generating load spectrum, proposing some issues that should pay attention to. Meanwhile, according to the task requirements of load measurement, it illustrated a general method of determining the helicopter’s mission spectrum, ana lyse ways of statistics and related hypothesis test, and gave computing results. In the course of data processing, following work was completed: the first is the implementation of row of pseudo processing, including the elimination of interference signal, the failure signal diagnosis, and the excluding of fault. The second is the load separation. According to a reasonable load cycle, with the fundamental frequency load processing method, the static load and dynamic load is isolated. The third is the retrieval of peak and valley value. Extract peak and valley value which reflects the information of load cycles, and further data compression through the establishment of certain range threshold. The forth is the cycle count. After comparison of several common methods of counting, the paper focused on the rain flow counting method which is often used in engineering practice, and explain it from three aspects. The fifth is the classification statistics. For count results obtained for each flight state, dynamic and static loads were hierarchically counted. Considering the fact that the fatigue load of the same state, the thesis adopted the single parameter classification statistical method. For the flight test data, sometimes it’s difficult for us to find the hidden failure data, just through the preliminary rows of pseudo processing. Therefore, the paper analyzed the validity of test data from five aspects as periodic, consistency, relevance, regularity and repetition. After getting the classification statistics data, the paper used different calculation methods to generate vibration fatigue load spectrum and power spectrum which reflect the high cycle fatigue properties, and generate transient fatigue load spectrum and transient fatigue power spectrum which reflect maximum cycle characteristics of low cycle fatigue separately, according to load characteristics of the high cycle fatigue and low cycle fatigue load.Finally, to meet the actual needs of fatigue test, we simplified the vibration fatigue load spectrum, transient fatigue load spectrum, power spectrum and transient fatigue power spectrum into different stages, which based on the needs, through the life curve and the Miner theory. In addition, baseded on power spectrum gotten by computing, the paper modeled on the surface stress of key wheel gear, and calculated the biggest contact stress of the wheel gear. There are fifty nine pictures, tweeny one tables, and sisty two references.