Aeroelastic Concepts for Flexible Aircraft Structures

Abstract: In this thesis, aeroelastic concepts for increased aircraft performance are developed and evaluated. Active aeroelastic concepts are in focus as well as robust analysis concepts aiming at efficient analysis using numerical models with uncertain or varying model parameters.The thesis presents different approaches for exploitation of fluid-structure interaction of active aeroelastic structures. First, a high aspect ratio wing in wind tunnel testing conditions is considered. The wing was developed within the European research project extit{Active Aeroelastic Aircraft Structures} and used to demonstrate how structural flexibility can be exploited by using multiple control surfaces such that the deformed wing shape gives minimum drag for different flight conditions. Two different drag minimization studies are presented, one aiming at reduced induced drag based on numerical optimization techniques, another one aiming at reduced measured total drag using real-time optimization in the wind tunnel experiment. The same wing is also used for demonstration of an active concept for gust load alleviation using a piezoelectric tab. In all studies on the high aspect ratio wing, it is demonstrated that structural flexibility can be exploited to increase aircraft performance.Other studies in this thesis investigate the applicability of robust control tools for flutter analysis considering model uncertainty and variation. First, different techniques for taking large structural variations into account are evaluated. Next, a high-fidelity numerical model of an aircraft with a variable amount of fuel is considered, and robust analysis is applied to find the worst-case fuel configuration. Finally, a study investigating the influence of uncertain external stores aerodynamics is presented. Overall, the robust approach is shown to be capable of treating large structural variations as well as modeling uncertainties to compute worst-case configurations and flutter boundaries.