Symmetric/Antisymmetric Flutter Identification and Control Beyond the First Flutter Speed

It is important for aircraft design and certification to gather aeroelastic test data for system identification as close as possible to the critical flutter speeds. Such data are used for fine-tuning and validation of aeroelastic math models and the establishment of safety margins. Physically symmetric aircraft configurations usually exhibit both symmetric and antisymmetric flutter mechanisms. Both symmetric and antisymmetric mechanisms should, desirably, be studied by tests, especially if there is a potential for the flutter critical mechanism to switch from symmetric to antisymmetric due to configuration variations. A method is presented here, using active control, that allows the experimental identification of both the first symmetric and the first antisymmetric mechanisms of a physically symmetric configuration close to their flutter speeds. The aeroservoelastic wind-tunnel model used for demonstration has two flutter mechanisms in the operative range of the wind tunnel. With a proper design of active control laws, it is possible, after the first mechanism was studied experimentally, to increase dynamic pressure, reach, and experimentally identify the second flutter mechanism without modifying its behavior. Simple static output feedback control laws were used to suppress the symmetric and reach the antisymmetric flutter without affecting it and then to suppress the antisymmetric flutter. In addition to a successful demonstration of the concept, the paper also offers certain lessons and insights regarding active flutter suppression technology in general that are, hopefully, useful.