Determination of Model Structure from Flight Test with Generalized Additive Models

The determination of an appropriate structure for an aerodynamic model developed from flight-test data can be challenging, particularly if a physical interpretation of the model is required. This paper introduces generalized additive models (GAMs) as an efficient and effective means to this end. GAMs provide an intuitive method to determine the structure by allowing the various aerodynamic effects to be separated into an additive model. Individual effects can be modeled by a number of nonlinear smooth functions. The suitability of this method is demonstrated on the example of a simple pitching moment coefficient model that is developed using flight-test data. The ability to separate and visualize effects together with a number of statistical indicators, the relatively low computational costs, and the availability of efficient software packages make GAMs attractive for practical applications. For the work presented in this paper, the "mgcv" package of the open-source statistical software R is used.