Selection of Rotorcraft Models for Application to Optimal Control Problems

Abstract

The maneuver characteristics of rotorcraft are analyzed using a nonlinear optimal control theory. The flight path deviations from a prescribed maneuver trajectory are penalized in the optimal control formulation to avoid numericaldifficulties.Thesystemoptimality isrepresented byatwo-point boundaryvalue problemandsolved viaa multiple-shooting method. The focus of this paper is on the model-selection strategies for resolving the problems of numerical instability and high computational overhead when complex rotor dynamics are included in the mathematical model. Four different types of rotorcraft models are identified, two of which are linear models with or without rotor dynamics, as well as two models that include nonlinear dynamics for the rotor in its formulation. The effect each modelwas found to impart on the numerical analysis isreported. Therelative computational efficiency is assessed in terms of computation time and the number of function calls for each model. The applications encompass the analyses for bob-up, turn, and slalom maneuvers and the results are used as guidelines for the selection of appropriate rotorcraft models.