Aeroelastic of transient blade dynamics during shipboard engage/disengage operations

An analysis has been developed to predict transient aeroelastic rotor response during shipboard engage/disengage sequences. The blade is modeled as an elastic beam undergoing deflections in flap and torsion. The blade equations of motion are formulated using Hamilton's principle and they are spatially discretized using the finite element method. The discretized blade equations of motion are integrated for a specified rotor speed run-up or run-down profile. Blade element theory is used to calculate quasisteady or unsteady aerodynamic loads in linear and nonlinear regimes. Three different simple wind-gust distributions are modeled. Basic ship-roll motion characteristics are also included in the shipboard airwake environment. An H-46 rotor system model is developed and shows excellent correlation with experimental static tip deflection and blade natural frequency data. Parametric studies are conducted to systematically investigate the effects of collective and cyclic pitch control settings, droop stop angle, and ship motion on blade response. These studies indicate that collective and cyclic control inputs have a moderate effect on maximum negative tip deflections. Torsion is shown not to be required for rotorcraft with small amounts of pitch-flap coupling. Unsteady aerodynamics is shown only to be important to the blade response at high wind speeds for spatially varying gusts. A flap damper is incorporated and is effective in reducing tip deflections if the flap stop angle is increased.