Passive and active load alleviation technologies for UHARW wings

ifasd2024 Tracking Number 167

In the framework of the Ultra High Aspect Ratio Wing Advanced Research and Designs (U-HARWARD) CS2JU founded project, different gust load alleviation (GLA) technologies were developed and studied. GLA is a key enabler for the development of new generation UHARW, indeed the GLA allows to limit the gust loads and as a direct consequence it can reduce the structural weight of the wing itself, and considering the snowball effect of the entire aircraft. This overall weight reduction improves the global aircraft efficiency allowing an increase in the aspect ratio. GLA technologies can be divided into two main categories: the passive ones where no action is needed to reduce the load and the active ones where a control system modifies the aerodynamic loads automatically. In this case, the passive GLA is performed with a Folding Wing Tip (FWT) developed by the University of Bristol and the GLA is performed with a Static Output Feedback controller developed by Politecnico di Milano. Both cases are compared with the baseline aircraft. A flutter assessment is performed to prove that the FWT do not introduces aeroelastic instabilities and the aircraft is flutter free across the entire flight envelope. A comprehensive comparison of the load envelopes obtained is provided, considering almost 2000 load cases for different flight points and mass configurations for the baseline aircraft and the GLA solutions. The gust cases are compliant with CS25 regulations and account for positive and negative cases, providing the bending-torsion envelopes in different spanwise placed monitoring stations. Thanks to NeOPT it was possible to realize a hybrid FEM model of the aircraft, where the wingbox is modelled with a detailed GFEM while the other components are modelled as stick elements. This model was used to perform linear gust analyses in Nastran with the hinge locked and released. The results of this HI-FI structural solution are used to compare the wing failure indexes in the two conditions, assessing the effectiveness of the GLA.