Boeing rotorcraft experience with rotor design and optimization

Abstract

This paper reviews 12 years of progress in applying optimization to the helicopter rotor design problem. This involves multiple disciplines, multiple objective functions, a large number of design variables and irregular design space. The initial step was to develop a single interdisciplinary analysis to evaluate the objective function. By understanding the problem, approaching it incrementally and learning how to adapt optimization techniques, dramatic progress has been made. Numerous optimization techniques have been tried, including: gradient-based methods (with finite difference and automatic differentiation), biological models, surface approximations and direct search. Each of these methods had to be properly adapted to the problem. Initial progress was made using a gradient-based method along with numerous prodding techniques to avoid local minima. Though successful, it required extensive labor hours. In search of more efficient methods, a scaled down representative problem was defined and multiple derivative free optimization (DFO) methods were investigated. All this has led to a hybrid approach that we are currently using in rotor design.