A vehicle's in-flight behavior can be represented by the Newton-Euler equations of motion: usually, such a model has a nonlinear and continuous description based on ordinary differential equations. The model structure can be altered using analytic transformations-such as transformation into a quasi-LPV structure-and, when the model is supposed to reflect an existing physical system, some of its parameters might be uncertain. This paper's objective is twofold: firstly, to investigate if a quasi-LPV model does accurately replicate the physical behavior of a large-caliber spin-stabilized projectile in free flight; and secondly, to verify if the available embedded sensors data could be used to determine non-identifiability of uncertain model parameters. In order to investigate these prospects, a permutation-based global sensitivity analysis is employed. The proposed study has highlighted the non-identifiable parameters of the model, either during the whole flight or some periods of it. These results can help to enhance the preparation of free flight experiments at the open-range test site of the French-German Research Institute of Saint Louis. Nomenclature M = Mach number V = airspeed, m s −1 α, β, α t = angle of attack, angle of sideslip, total angle of attack, deg C X , C N α , C y pα = axial force, normal force slope, and Magnus force slope coefficients C lp , C mα , C mq , C npα = roll damping, pitch moment slope, pitch damping and Magnus moment slope coefficients

A vehicle's in-flight behaviour can be represented by the Newton-Euler equations of motion: usually, such a model has a nonlinear and continuous description based on ordinary differential equations. The model structure can be altered using analytic transformations and, when the model is implemented, its numerical precision may depend on the selection of a numerical solver. Hence, the selection of a model's structure and an appropriate numerical solver can become the key development issues, if the model's numerical stability, convergence, and computational complexity are to be improved. This paper assesses the influence of a model's reference frame and a numerical solver on the accuracy of calculating a projectile's trajectory, for a case study of free-flight long-range ballistic experiments. The analysis is based on two model structures: the first is a six-degree-of-freedom nonlinear description of a spin-stabilized projectile, expressed in a rolling reference frame; the second is a quasi-LPV reformulation of the same projectile model, but expressed in a non-rolling reference frame. It is shown that inappropriate selection of a numerical solver can hinder the accuracy of the nonlinear model. At the same time, the model represented in a non-rolling reference frame offers a solution with higher accuracy, better convergence properties, and significantly reduced computation time.

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