An enhanced integrated aerodynamic load/dynamic optimization procedure for helicopter rotor blades

An enhanced integrated aerodynamic load/dynamic optimization procedure is developed for minimizing vibratory root shears and moments of a helicopter rotor blade. The optimization problem is formulated with 4/rev inplane shears at the blade root as objective functions. Constraints are imposed on 3/rev radial shear, 3/rev flapping and torsional moments, 4/rev lagging moment, blade natural frequencies, weight, autorotational inertia, centrifugal stress and rotor thrust. The "global criteria approach" is used for formulating the multiobjective optimization. Design variables include spanwise distributions of blade bending stiffnesses, torsional stiffness, nonstructural mass, chord, radius of gyration and blade taper ratio. The programme CAMRAD is coupled with an optimizer, which consists of the programme CONMIN and an approximate analysis. The optimization procedure is applied to an advanced rotor as a reference design. Optimum blade designs, obtained with and without a constraint on the rotor thrust, are presented and are compared to the reference blade. Substantial reductions are obtained in the vibratory root forces and moments. As a byproduct, improvements are also found in some performance parameters which were not considered during the formulation of the optimization problem. The effect of thrust constraint on the values of the vibratory forces and moments is demonstrated by varying the magnitude of the prescribed thrust. A proper choice of the "move limit" parameter, used in the approximate analysis, is shown to have significant effect on the optimum results.