Investigation about the structural nonlinearities of an aircraft pylon

The goal of the present work is to develop a high-fidelity nonlinear finite element (FE) model able to describe the mechanical response of an aircraft structure composed of a pylon, sway braces, and a store system with an applied external load. Unstable phenomena (such as limit cycle oscillations) on aircraft pylons have been shown to occur because of the presence of nonlinearities (structural and aerodynamic). Most previous investigations mainly focused on aerodynamic effects while almost neglecting structural effects. The present paper, however, focuses on the building and assessment of a nonlinear FE structural model of a pylon, starting from experimental evidence, showing that nonlinearities are concentrated in the joint between the pylon and the suspended store. The static results of the numerical model were assessed by means of an experimental stiffness test. The dynamical reliability of the model was assessed when linked to a delta cropped wing comparing its vibration modes with experimental values and with a linear model. The results demonstrate that the FE model is able to accurately replicate both the static and dynamic behavior of the system.