Study on Interaction Between a Stability Augmentation System and an Active Flutter Suppression Controller

This work presents the research carried out using the latest update of the F-XDIA model – a wind tunnel model designed for experimentally studying active flutter suppression technologies (AFS) and freeplay induced nonlinear aeroelastic behavior of representative commercial aircraft configurations. The model was tested repeatedly during last years in the framework of an international cooperation between Politecnico di Milano and the University ofWashington. The pylon support for the wind tunnel test was modified, hosting a gimballed connection between the model and the pylon itself, allowing the rigid rotation of the model around the pitch and roll axes, separately or simultaneously. The model is unstable around the roll axis. For thisreason a Stability Augmentation System (SAS) had to be designed and implemented, and its interaction with AFS controllers is studied. The results show that the two controllers, "rigid body" stability-augmentation and AFS, have to be designed considering their interactions and that a gain scheduling w.r.t. the air speed is necessary to stabilize both rigid body motion and the aeroelastic modes. As the tests demonstrate, the model was successfully tested in the wind tunnel beyond its open-loop flutter point in the free-to-roll configuration.