Actuator-friendly flutter control design using robust control and blending of inputs and outputs

Kurzfassung

A novel active flutter control, or damping augmentation, method for civil aircraft is presented. The approach leverages the link between the acceleration sensitivity of second-order systems and the damping ratio of their modes to express minimum damping constraints as frequency-domain criteria. This enables the use of modern, robust frequency-domain control design techniques, thereby taking advantage of their advanced capabilities while explicitly incorporating damping-related constraints. A similar approach was proposed in the past, using the transfer function from a (indirect) perturbation on the mode generalized acceleration to the generalized velocity of that mode. The advantage of using the acceleration sensitivity over the acceleration-to-velocity transfer function is explained. The application example, based on the DLR F-25 configuration, shows the practicality of the new approach. A structured synthesis is used, which allows comparing this new approach to the input/output blending approach by using a similar controller structure. The ability to use the method on models with a large number of modes (more than 50), many damping constraints, with robustness margin constraints, and minimizing the actuator activity (only optimization criterion) is demonstrated. The input/output blending method, even in its recently published relaxed version, does not seem suitable for such cases, whereas the proposed method is applicable for industry-scale problems. The properties and differences between the proposed method and already established approaches for damping augmentation / flutter control are summarized at the end.