To create control systems, mathematical models of objects are required, which often have to be obtained experimentally. In this case, the numerical data of experiments on the identification of essentially nonlinear objects can be satisfactorily approximated only in certain areas, which leads to fragmentary models that are not analytical. In these cases, when only fragmentary models are adequate, it is proposed to apply the new Cut-Glue approximation method, which allows obtaining a model with analytical properties. The proposed approach to the unification of the Cut-Glue approximation method is demonstrated by solving the problem of synthesizing a nonlinear airship altitude control system and studying it.