Structural sizing is a further step in the aeroelastic design process. The objective is to dimension the structure with realistic component thicknesses on the basis of the loads that are determined for selected load conditions. This results in a stiffness distribution that is as realistic as possible and which takes other non-structural masses and mass distributions into account. Coupling of these factors results in a dynamic structural model for the aeroelastic analysis, or load analysis.
Sizing is usually carried out in MSC.NASTRAN. The modelling stage provides a finite element model without specified component wall thicknesses. On the basis of the loads catalogue, a small number of load conditions are selected, which are most relevant for structural sizing. These loads in particular, these include manoeuvring loads, can be calculated in MSC.NASTRAN., or they can be obtained from external analyses; for example, landing loads can be generated in the multi-body simulation.
A complete aircraft structure is sized from a large number of different load cases. This is illustrated with the example of the main areas on the underside of the wing of the iGREEN configuration in the image on the right. For this reason, careful selection of the load conditions that are used for sizing dimensioning is necessary.
After structural sizing of the components, a model of the entire aircraft is created. These models are provided to partners for static and dynamic investigations as ‘GFEM’ (Global FEM) models in the context of internal DLR projects, as well as for national and international projects.