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.
This paper describes numerical procedures for the solution of trajectory optimization problems in rotorcraft flight mechanics. Specifically, procedures are considered that can be easily interfaced with black box flight simulators, with minimal assumptions on such third-party software components, and that can cater to a wide range of vehicle models of increasing complexity. First, the direct approach to the solution of maneuver optimal control problems is identified as the method of choice for this class of problems. Next, the direct transcription and the direct multiple shooting approaches are formulated, their characteristics are discussed, and their respective optimal application areas are identified. Finally, the functionality and architecture of a general-purpose code implementing both methods is described. The capabilities of the proposed procedures are demonstrated with the help of practical examples of industrial relevance, regarding both helicopters and tiltrotors
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