Performance enhancement of a composite tilt-rotor using aeroelastic tailoring

An optimization technique is applied in an attempt to improve the performan ce of a tilt-rotor aircraft with composite blades that are enhanced by aero elastic tailoring. The aeroelastic analysis is based on a published mired v ariational formulation of the exact intrinsic equations of motion of beams, along with a finite-state dynamic inflow theory for the rotor. The composi te rotor blade is modeled structurally as a composite box beam with nonstru ctural mass included. For optimization the design variables are blade twist , box dimensions and wall thicknesses, ply angles of the laminated walls, a nd nonstructural mass. The rotor is optimized using an objective function t hat is weighted equally between the figure of merit in hover and the axial efficiency in forward flight. Constraints are considered on blade weight, a utorotational inertia, geometry, and aeroelastic stability. The effects of all structural couplings on rotor performance are studied. Of all possible couplings, extension-twist coupling is found to be the most effective param eter to enhance performance. The effects of accounting for pretwist and thi n- vs thick-walled theories in the blade cross-sectional analysis are discu ssed. Significant improvements in the objective function are shown to be po ssible even when optimizing only the extension-twist coupling of the rotor blade.