5 Investigating Nonlinearities in a Demo Aircraft Structure Under Sine Excitation 43 Fig. 5.1 CAD models of (left) the full aircraft and (right) the pylon subassembly Fig. 5.2 Preliminary FE model 5.3 Experimental and Numerical Analysis of the Aircraft The main objective of the paper is, as mentioned, to present a step-by-step procedure that allows in the end to obtain a validated non-linear Finite Element of the test object, which in this case is the aircraft model with the pylons. Obviously, the first step is to deal with what we know (or can know) fairly accurately, which in this case is the aircraft without the pylons. Consequently, this section will present the preliminary and simplified aircraft model built starting from the CAD, the Experimental Modal Analysis campaign and the model upgrading and updating phases to increase the accuracy of the FE model. 5.3.1 Preliminary FE Model Based on the nominal dimensions of the aircraft components, a preliminary FE model was built, with the objective of getting a first idea of the global modes and plan the experimental campaign accordingly, in particular with respect to the number and positions of the sensors. The model is shown in Fig. 5.2. Each main element (Fuselage, Wings and Tail) is modelled using nominal dimensions and material properties as illustrated in Table 5.1. Solid elements are used for the fuselage bar (to allow taking into account
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