A COUPLED ROTOR WING OPTIMIZATION PROCEDURE FOR HIGH-SPEED TILT-ROTORAIRCRAFT/

A multidisciplinary optimization procedure is developed to investigate the design trade-offs associated with coupled rotor/wing performance in high speed tilt-rotor aircraft. The aerodynamic efficiency of the r otor in both hover and high speed cruise are improved along with the a erodynamic and aeroelastic performance of the wing while maintaining s tructural integrity of the wing/rotor configuration. The objectives ar e to maximize the hover figure of merit and the high speed cruise prop ulsive efficiency of the rotor and to minimize the wing weight. Constr aints on the rotor include the first natural frequency in hover, the a utorotational inertia and the blade weight. To avoid whirl flutter ins tabilities, constraints are imposed on the real part of the stability roots in the windmill flight condition. Constraints are also imposed o n wing root stresses in both hover and cruise. An isotropic box beam m odel is used to represent the structural properties of the wing-box se ction. Design variables include rotor and wing planform variables and individual wall thicknesses in the wing. The Kreisselmeier-Steinhauser function approach is used to formulate the multiobjective optimizatio n problem and the Broyden-Fletcher-Goldfarb-Shanno method is used as t he optimization algorithm. The two-point exponential expansion approxi mation technique and a variable move limit scheme are used to reduce t he computational effort. The optimum design performance is compared wi th an existing advanced tilt-rotor performance which is used as the ba seline design. The results show significant improvements in both aerod ynamic and structural performance while maintaining aeroelastic stabil ity.