Study Of Aircraft-pylon Vibration Transmission Characteristics Under Unbalance State Of Windmilling

A large number of aviation events show that the unbalanced state of the windmill will jeopardize the flight safety of the aircraft.Based on the aviation accidents caused by windmill imbalance,33.74 clauses and 25.903(c)of chinese civil aviation regulations clearly stipulate that the continuous rotation of the engine can't endanger the safety of the aircraft.The pylon as the engine bearing and connected to the engine and wing connecting structure can decrease vibration caused by engine continuous rotation,for safe flight of civil aircraft,it is necessary for the analysis of aircraft engine pylon windmilling in unbalanced vibration characteristics under the condition.This paper takes a typical aircraft pylon as the research object,established the finite element model of aircraft suspension and simulation analysis,the vibration characteristics of the pylon,and the finite element power flow based on the theory of transfer path analysis method of pylon-wing transfer path analysis,the typical pylon in the windmilling unbalanced transfer path under the condition of pylon-wing,provide a reference for the dynamic simulation of windmilling state analysis.The study involved the airworthiness CCAR25.903 and CCAR33.74 interpretation and analysis,combined with the Advisory circular 25-24 for pylon windmilling unbalanced airworthiness verification made analysis,gives a dynamic windmilling pylon structure under unbalanced analysis goal,criteria and corresponding modeling method.Through the analysis of the pylon structure,pylon-wing connection,after establishing suitable geometric properties of hanging,by applying the accord with the actual condition of suspended load and constraints,a pylon structure finite element model and beam finite element model;after the modal analysis of the two models,modal based on the results of the analysis,found that two kinds of model natural frequency value is large,the need for beam model optimization,the optimization results show that the beam model and entity model dynamic similarity.The finite element model of pylon structure based on the influence of the output of the windmilling balance six parameters(i.e.,load / stator friction coefficient between the rotor mass unbalance,rotor speed,stator stiffness and rotor stator rub impact rotor clearance and damping)simulation analysis of the transmission path characteristic and pylon-wing vibration transfer between different conditions formed under;finally,obtained the flow curves of six parameters in different operating conditions of suspended solid model and beam model of the vibration displacement,acceleration and power analysis of the main transmission path characteristics and response under different working conditions pylon-wing solid model and beam model of vibration six reference variables.The analysis results show that for the solid model and the beam and girder model,the main transmission path is the same as the vibration source transferred to the points of the diagonal strut at the connection between the pylon and the wing,and then transferred to the wing.