Active Flutter Suppression of a Highly Flexible Swept Wing through Multiple Flap Control

Abstract

Future commercial aircraft designs tend to light-weight wing structures for energy and cost saving reasons. The slenderness and flexibility of these higher aspect-ratio wings might show susceptibility not only to lower flutter flight speeds. Also, the danger of a larger number and variety (e.g. through sweep induced coupling) of potentially wing-dominated flutter modes is impending. The main objective of the submitted work is to depict a suitable control methodology, and show how dynamic stability of highly flexible wings can be achieved by actively influencing the aeroelastic behaviour of the overall deformed structure. On the prediction side, the design, build-up and analysis of aero-servoelastic simulation models become necessary. The incorporation of active control elements like sensors, actuators and controllers leads to closed-loop models. On simulation side, the strategic goal of this investigation is to reach the capability of completely erasing any kind of flutter occurrence, with no restrictions, neither in composition (e.g. heave, torsion, in-plane sway or flap dominated) nor in number (e.g. up to 4) of eigenmodes. The design of the controller transfer functions turned out to be crucial. In order to have the desired variety of eigenmodes at disposal, here a number of three configurations of the nominal generic wing design (baseline with five deflection-controlled flaps plus two modifications) underwent the analyses. By means of active flutter suppression (AFS), formerly unstable wing configurations could be transferred into aeroelastic stable flight conditions at any point of a potential flight envelope.