Comprehensive risk assessment method for weak components of encased differential planetary gear train in coaxial helicopter

ObjectiveThe encased differential planetary gear train of a coaxial helicopter consists of numerous components with varying failure probabilities. Identifying weak components and potential failure modes is critical for implementing targeted measures, such as structural optimization or material substitution, to enhance the system's service life and reliability.MethodsFirstly, a comprehensive risk assessment model was developed by integrating fuzzy set theory with the technique for order preference by similarity to an ideal solution (TOPSIS). Secondly, trapezoidal fuzzy numbers were utilized to construct a robust fuzzy evaluation matrix, and a hybrid weighting scheme combining the analytic hierarchy process (AHP) and the entropy weight method (EWM) was implemented to determine objective and subjective index weights. Finally, an expert scoring framework was established, and a ranking index was calculated for each component to prioritize failure risks.ResultsThe analysis results demonstrate that among the gear components, the sun gear of the differential stage exhibits the highest risk index, identifying it as the weakest part of the system. The primary failure modes are determined to be tooth surface wear and tooth root cracks. This study offers a quantitative theoretical reference for the reliability design and maintenance of complex aviation transmission systems.