Aerodynamics-Structural Coupled Analysis of a Bearingless Rotor using a Flexible Multi-body model

A bearingless rotor has been used to take advantage of the reduced number of helicopter hub components and maintenance expense. It comprises of three primary components: a main rotor blade, torque tube, and flexbeams. It has another advantage that its structure is simple. But large nonlinear bending-torsion is induced because the flexbeams have low torsional stiffness. Furthemore, since it has multiple load path, its structural modeling and structure-aerodynamics coupled analysis will be complicated. In this paper, a geometrically exact beam formulation was used to describe nonlinear behavior of the rotating beam elements. To conduct the multi-body analysis, multiple beam elements were assembled. The present structural model was coupled with the finite-state dynamic inflow aerodynamics. Finally, trim analysis was carried out, and the blade deformation/internal load was predicted. Its results were compared with those obtained by the rotorcraft comprehensive analysis, CAMRAD II. The blade deformation discrepancies were less than 5% and internal loads average difference was smaller than 10%.