Nonlinear aeroelastic coupled trim analysis of a cyclocopter in hover
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2017 by the American Helicopter Society International, Inc. In this paper, detailed development of a nonlinear aeroelastic coupled trim model of a twin-cyclocopter, consisting of two cycloidal rotors (also known as cyclorotors) as main rotors and a conventional horizontal tail-rotor for anti-pitch torque and control, is presented. Coupled trim analysis requires simultaneous computation of trim controls, vehicle orientation and blade structural responses so that both blade response equations and vehicle trim equations are satisfied. To obtain the blade structural response and the hub loads in the vehicle frame for the cyclorotors, a nonlinear aeroelastic model of cyclorotor is developed. For this purpose, a high-fidelity unsteady aerodynamic analysis of a cyclorotor is developed, which includes rigorous modeling of effects such as dynamic virtual camber, effects of near and shed wake, and leading edge vortices. To include effect of blade deformations on cyclorotor performance, a structural framework consisting of fully nonlinear geometrically exact beam model and an FEM based solver is developed. An aeroelastic framework of cyclorotor is developed by coupling the aerodynamic and structural models and the coupled aeroelastic model is validated with in-house experiments with flexible cyclorotors. To obtain the performance of the conventional horizontal tail rotor a modified BEMT based model with CFD-based airfoil lookup tables is developed and validated with test data. Once the complete aeroelastic framework of cyclocopter is developed, coupled trim analysis is performed by simultaneously solving blade response equations and vehicle trim equations until trim controls, blade response, inflow and circulation converge all together. Variation of control inputs required for hover trim is investigated with change in gross-weight and longitudinal center of gravity location of the vehicle.
