Updating a Finite Element Based Structural Model of a Small Flexible Aircraft

The generation of a finite element based structural model of a small, flexible unmanned aircraft is presented. The paper focuses on obtaining a simple model suitable for control design based on a two step procedure. In an initial step, static and dynamic tests of the wings are conducted. These experiments give first estimates of the material properties (e.g., stiffness) of the aircraft. A finite element model consisting of simple beam elements is constructed based on these first estimates. In the next step, the modal data of the aircraft is extracted from a ground vibration test. The initial finite element model is then updated using this modal data. An optimization problem is proposed to minimize the difference in the modal properties, i.e. the modal frequencies and mode shapes, between the model and the experimental data. The free parameters of the optimization are chosen based on physical insights of the system. The resulting finite element model closely matches the experimental data both in terms of modal properties as well as input/output behavior.