Aeroelastic optimization of a composite tilt rotor

Abstract

Composite tilt rotor aeroelastic optimization is performed by using a mixed variational formulation based on exact intrinsic equations of motion for moving beams and a finite-state dynamic inflow theory. 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 24 laminated orthotropic 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 mass. 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. Results are presented for effects such as extension-twi st coupling, choice of layups, and cross-sectional geometry of the blade. Significant improvements in the objective function are shown to be possible.