EFFICIENT TREATMENT OF MODERATE AMPLITUDE CONSTRAINTS FOR HELICOPTER HANDLING QUALITIES DESIGN OPTIMIZATION

This paper describes a new technique for the calculation of gradients of constraints associated with the moderate amplitude criteria of the ADS-33 helicopter handling qualities specifications, The gradients are calculated using low-order linear approximations to the full nonlinea r model of the helicopter, The low-order models approximate the gradie nts well and reduce the additional cost of calculating the gradient by a factor of about 50. Most of the reduction in the objective function obtainable using the exact gradients are retained, with no additional infeasible intermediate designs. The accuracy of linear Taylor-series expansions of the constraint in terms of the design variables is foun d to depend on the size of the changes of each design variable, The ac curacy is not improved by using intermediate design variables, such as reciprocals and cubes of the design variables, but it improves if the bandwidth or derivative ratios such as L-theta 1c/L-p are used as int ermediate variables in the expansions.