Multidisciplinary optimization of helicopter rotor blades including design variable sensitivity

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 variations 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 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. Results are presented for several different cases of design variable vectors and are compared with a baseline, or reference blade.