Multidisciplinary optimization and design variable sensitivity of helicopter rotor blades using a composite box beam model

The paper addresses a fully integrated optimization procedure, for helicopter rotor blades, with the coupling of blade dynamics, aerodynamics, aeroelasticity and structures. The goal is to reduce vibratory shear forces at the blade root with constraints imposed on critical dynamic, aerodynamic, aeroelastic and structural design requirements. The blade is modeled with a composite box beam as the principal load carrying member. Nonlinear chord and twist variation are assumed. A wide range of both structural and aerodynamic design variables are used along with several subsets to determine the sensitivity of the design variables on the optimum design. The optimization problem is formulated with two objective functions and the Kreisselmeier-Steinhauser (K-S) function approach for multiple design objectives is used. A nonlinear programming technique and an approximate analysis procedure are used for optimization. The procedure yields substantial reductions in the vibratory root forces and moments along with significant improvements in the remaining design requirements. Comparisons with previous work where isotropic beam elements were used indicate that the use of a composite box beam yields significant improvements in the blade design. Results are presented for several different cases of design variable vectors and are compared with a baseline, or reference blade.