| Helicopter air-resonance is the most complex problem of hingeless helicopter dynamic design.It’s caused by coupling of low frequency blade regressive flap, regressive lag modes and coupledfuselage modes. This thesis mainly researches the influence of dynamic stall on helicopterair-resonance stability.Firstly, a modified dynamic stall model which based on Leishman-Beddoes model and isappropriately applied on a nonlinear rotor/airframe coulped dynamic model is dervied.Secondly, a nonlinear rotor/airframe coulped dynamic model which also takes into account ofrotor dynamic stall is established. The model is appropriate for investigations of air-resonance inhovering and forward flight. When the airframe is fixed, the model is also appropriate for isolate rotorstability analysis. The predictions of regressive lag mode damping from time-domain analysis of thenonlinear system by the model correlate experimental data even in the large collective pitch and highrotor load situations.Thirdly, the case helicopter air-resonance stability is calculated from time-domain analysis.During the calculation, only reckoned in airframe rolling and pitching which are the conclusivefreedoms to air-resonance; rotor load was changed by adjusting the weight of helicopter. Resultsdemonstrate that helicopter air-resonance stability for forward flight is lower than for hovering.Moreover, during maneuvering flight and heavy load flight, dynamic stall makes helicopterair-resonance stability drop drastically. |
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