Transient loads control of a variable speed rotor during lagwise resonance crossing

Transient aeroelastic response of a stiff in-plane rotor system undergoing variable speed operation in forward flight is simulated using a finite element model. During crossing of the fundamental lag mode near 2/rev, high transient lag bending moments are observed. Flapping amplitude and duration of the resonance crossing event have a strong influence on the peak lagwise root bending moments. Embedded chordwise fluidlastic dampers are introduced to control the transient lagwise loads of the variable speed rotor during resonance crossing. The design of the fluidlastic damper is based on the analysis of a two degree-of-freedom blade-damper system. Results indicate more than 6% critical damping can be provided to the blade around the resonance rotor speed. Results indicate that approximately 65% peak-peak moment reduction can be achieved with reasonable damper devices (i.e. less than 5% blade mass). The stroke of the damper is limited to less than 2.5% blade chord length in worst case scenarios (i.e. high flapping). Parametric studies show that tuning port ratios, loss factors, and device mass can be utilized to enhance the performance of the damper, and control the stroke. Damper performance is shown to be relatively independent of rotor thrust and advance ratio.