| Composite tilt rotor aeroelastic optimization is performed by using a published formulation of mixed variational exact intrinsic equations of motion for dynamics of beams along with a finite-state dynamic inflow theory for rotors.; A composite box beam model is used to represent the principal load carrying member of the rotor blade. The blade is discretized using finite elements. Each wall used to model the box beam is made of laminated composite plies. For the optimization, design variables are blade twist, box width and height, horizontal and vertical wall thicknesses, the ply angles of the laminated walls and nonstructural masses. The rotor is optimized for the figure of merit in hover and the axial efficiency in forward flight while keeping the same thrust levels in both flight modes. Blade weight, autorotational inertia, geometry, and aeroelastic stability are considered as constraints. The feasible direction technique is used for optimization. The results are validated by earlier test results. A trim calculation procedure is added to the analysis to keep the desired values of the thrust. Sensitivities of the rotor performance to design variables are studied.; The effect of structural couplings on rotor performance is studied. Of all the couplings extension-torsion is found to be the most effective parameter to improve the performance. The ply angles of the laminates are assumed to be the same over the span and through the thickness of walls. Such a model can be built by the filament winding technique and offers manufacturing ease. Isolated rotor stability is investigated for both flight regimes. Some values of elastic coupling result in isolated rotor instability. However, the optimized configuration was free of instability.; Optimization results are presented for effects such as extension-torsion coupling, choice of layups, twist distribution, and cross-sectional geometry of the blade. Optimum designs are compared with XV-15 tilt rotor performance, which is used as a baseline. Significant improvements in the objective function are shown to be possible even when optimizing only the extension-torsion coupling of the rotor blade. |
