A Survey of Recent Developments in Rotorcraft Design Optimization

OTORCRAFT engineering is highly interdisciplinary because the flexibility of the main rotor blades couples with the aerodynamics, dynamics, and control system. In addition, interaction between the rotor and fuselage further complicates helicopter system predictions. The multidisciplinary nature of the helicopter engineering problems has led researchers to investigate formal optimization methods for the design process. Applications of formal optimization methods for helicopter problems started in the early 1980s. Miura 1 provided a review of some of the early work on application of numerical optimization to helicopters. Friedmann, 2 Adelman and Mantay, 3 and Celi 4 provide further reviews of helicopter optimization. Sobieszczanski-Sobieski and Haftka 5 give a review of recent developments in multidisciplinary design optimization for aerospace problems and Gieseng and Barthelemy 6 provide an industrial perspective of multidisciplinary optimization research. Whereas considerable studies have been conducted on helicopter design optimization, several issues have prevented it from becoming as popular or successful as structural optimization. Many finite element-based design packages today have builtin optimization capacity. However, the predictive capacity of even the most sophisticated helicopter aeroelastic analysis codes remains quite poor, as evidenced in a recent study by Hansford and Vorwald, 7 where hub load predictions from several codes are compared with flight-test data. In addition, because of the nature of helicopter problems, comprehensive aeroelastic codes are highly multidisciplinary and very difficult to understand and alter except by domain experts. This is because of the complexity of the physical modeling. For example, as the blade moves over one revolution, it encounters transonic flow, reverse flow, stall, and unsteady effects including dynamic stall. Large azimuthal variations in lift result from changes in dynamic pressure