Testing of Active Flutter Suppression for Wings Incorporating Floating Wingtips

A recent proposal in aircraft design is the incorporation of floating wingtip (FWT) devices to alleviate in-flight loads, enabling higher aspect ratios while meeting airport gate limitations. Previous research has shown that these devices can lead to aeroelastic instabilities, such as flutter, which may prove catastrophic to the aircraft. In the effort to improve the stability characteristics of the FWT, a consideration has been the implementation of a control surface placed on the wingtip, the wingtip tab, which can be used to command the orientation of the wingtip in flight. Numerous studies have investigated the effect of a wingtip tab on the flutter onset speed and gust load alleviation performance, concluding that the stability envelope can be extended and that there is scope for further load reduction. However, no experimental data currently exists for the active control of a wingtip tab for the suppression of flutter. The work presented herein details an experimental campaign exploring the effect of a proportional-derivative controller on the modal properties, flutter speed, and gust response of an aeroelastic wing model. Comparison with a low-fidelity numerical model shows that, for flutter dominated by coupled out-of-plane bending and wingtip-flapping motions, active control of the wingtip tab provides a mechanism-specific source of aerodynamic damping that is sufficient to suppress the instability over all realistic airspeeds. Repeating the approach with the inboard aileron yields a comparable response, indicating that the same stabilising mechanism can be realised without the need for an additional wingtip control surface.