FULLY INTEGRATED AERODYNAMIC DYNAMIC OPTIMIZATION OF HELICOPTER ROTOR BLADES

This paper describes a fully integrated aerodynamic/dynamic optimization procedure for helicopter rotor blades. The procedure combines performance and dynamics analyses with a general purpose optimizer. The procedure minimizes a linear combination of power required (in hover, forward flight, and maneuver) and vibratory hub shear. The design variables include pretwist, taper initiation, taper ratio, root chord, blade stiffnesses, tuning masses, and tuning mass locations. Performance constraints consist of limits on power required in hover, forward flight, maneuver, airfoil section stall, drag-divergence Mach number, minimum tip chord, and trim. Dynamic constraints are on blade natural frequencies, minimum autorotational inertia, and maximum blade weight. The procedure is demonstrated for two cases. In the first case, the objective function involves power required (in hover, forward flight, and maneuver) and vibratory hub shear. In the second case, the objective function involves power required in hover and vibratory hub shear. For both cases, the designs from the integrated procedure are compared with designs from a sequential optimization approach. In the sequential optimization approach, the blade is optimized first for performance (minimum power) using only aerodynamic design variables and performance constraints. Then these optimized aerodynamic design variables are held fixed, and the blade is optimized for minimum vibratory hub shear, using only dynamic design variables and dynamic constraints. In both cases, the integrated approach is superior to the sequential approach.