Performance enhancement of a composite tilt-rotor using aeroelastic tailoring

An optimization technique is applied in an attempt to improve the performance of a tilt-rotor aircraft with composite blades that are enhanced by aeroelastic tailoring. The aeroelastic analysis is based on a published mired variational formulation of the exact intrinsic equations of motion of beams, along with a finite-state dynamic inflow theory for the rotor. The composite rotor blade is modeled structurally as a composite box beam with nonstructural mass included. For optimization the design variables are blade twist, box dimensions and wall thicknesses, ply angles of the laminated walls, and nonstructural mass. The rotor is optimized using an objective function that is weighted equally between the figure of merit in hover and the axial efficiency in forward flight. Constraints are considered on blade weight, autorotational 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 parameter to enhance performance. The effects of accounting for pretwist and thin- vs thick-walled theories in the blade cross-sectional analysis are discussed. Significant improvements in the objective function are shown to be possible even when optimizing only the extension-twist coupling of the rotor blade.