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In this paper, we consider the problem of estimating the parameters in mathematical models of complex systems from experimental observations; the methods and procedures that we develop are general, but in this work we make specific reference to the problem of parameter estimation for multibody-based rotorcraft vehicle models from flight test data. We consider methods that are applicable to unstable systems, since rotorcraft vehicles are typically unstable at least in certain flight regimes. Unstable vehicles must be operated in closed-loop, and this must be explicitly accounted for when formulating parameter estimation methods. We describe two alternative classes of methods in the time domain, namely, the recursive filtering and the batch optimization methods. In the recursive approach, we formulate a novel version of the extended Kalman filter that accounts for the presence of unobservable states in the model. In the case of the batch optimization methods, we present a formulation based on a new single-multiple shooting approach, specifically designed for models with slow and fast solution components. We perform some initial steps toward the validation of the proposed procedures with the help of applications regarding manned and unmanned rotorcraft vehicles.

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In this paper, the authors present a procedure for the global solution by the use of evolutionary algorithms of trajectory optimization and parameter estimation problems for rotorcraft vehicles. The proposed approach makes use of a novel repair heuristic based on a sequential quadratic programming method to handle problem constraints. The resulting formulation effectively deals with the complex, highly constrained, optimization and optimal control problems plagued by multiple local minima or maxima that are often encountered in practical rotorcraft flight mechanics applications. The performance of the proposed procedures is assessed with applications dealing with the design of optimal inputs for the estimation of model parameters, with the determination of the optimal way of flying continued take-offs under category A requirements, and with the determination of the most dangerous areas of the height-velocity (H-V) plane in terms of impact velocity with the ground