The effect of nonlinear elastic materials on swept aeroelastic wings

Kurzfassung

Aircraft design under the terms of regulations postulates load cases between 2.5g and ‑1.0g. According to statistical load data, high manoeuvre and gust loads (-1.0g and 2.5g) occur seldom, but they determine aircraft structures. In contrast to linear aircraft materials (e.g. aluminium, carbon), rubber like materials show nonlinear elastic behaviour. Hence, the aim is to create passive load alleviation with nonlinear elastic materials. The idea is to increase the performance during low load cases around cruise and to decrease the loading for high load cases. In other words, we want to create a wing which is stiff during cruise and which gets more flexible at high loading cases. To examine this, an iterative process computes three trimmed quasi steady manoeuvres (1.0g, 2.5g, -1.0g). In doing so, the process considers the aeroelastic coupling. It iteratively calculates loads and deformations, using the Vortex Lattice Method (VLM) for the aerodynamic analysis and the Nonlinear Solution of MSC Nastran (SOL400) for the structural analysis. Also, Solution 400 computes the deformation due to the loads iteratively. The process utilises a rectangular 30° aft swept wing with a wingspan of 60 m which is close to common long range aircraft. A finite element model with beam elements represents the load carrying structure. A vortex lattice simulates the aerodynamics. The reference wing structure with the linear material is untwisted. To compare two different approaches of nonlinear elastic materials, the corresponding wing structures are pretwisted. This ensures an equal lift distribution of the 1g load cases. The root bending moment decreases of about 3.98% for the material with the stiffer area at cruise conditions.