Flutter suppression

Successful demonstration of active flutter suppression

An international team of researchers, including scientists from the DLR Institute of System Dynamics and Control, has developed a control system that suppresses flutter of the aircraft structure. The researchers successfully demonstrated this in a flight campaign with a specially designed and constructed Unmanned Aerial Vehicle (UAV). One of the main goals of the EU project FliPASED (Flight Phase Adaptive Aero-Servo-Elastic Aircraft Design Methods) was to demonstrate suppression of flutter in the aircraft structure by active means, using on board sensors, existing control surfaces and intelligent control algorithms. Active flutter suppression is of great importance for future wing designs, these are prone to unstable aeroelastic behavior due to lighter structures and increasing aspect ratio. “New control and modelling methods developed at our institute were successfully applied in the flight test," reports Dr Gertjan Looye, head of the Aircraft System Dynamics department at the DLR Institute of System Dynamics and Control. "As far as we know, this has been the first successful flight test of these methods", says Looye. For the flutter suppression algorithm, the researchers extended and applied the "input-output blending" method. "This algorithm is particularly suitable for control functions that directly affect the airframe structure like active gust load alleviation and flutter suppression," explains Looye.

The scientists used their model integration environment VarLOADS to develop the control design and verification models, based on CAD, Finite Element, mass and modal data provided by their partners. This also includes data from Ground Vibration Tests (GVT) performed at the DLR Aeroelasticity Institute in Göttingen, conducted by a team from ONERA. Before the critical flutter speed was reached and exceeded in the last flight test campaign, it was crucial to accurately estimate the actual flutter speed and the corresponding modal behaviour. To this end, the scientists developed new model updating algorithms that allow to incorporate test results obtained from the GVT, or even flight test data in the simulation models. “Model updating algorithms combine phenomenological and behavioural model structures This is very practical from a control law design point of view, as it allows for a smooth continuation from initial theoretical to test-validated model data in the course of the design process”, explains Looye. The final flight test, performed without flutter suppression control laws, impressively confirmed the accuracy of the updated model regarding predicted flutter mechanism and flutter speed. Further information Successful demonstration of active flutter damping Project participants DLR Institut für Systemdynamik und Regelungstechnik in Oberpfaffenhofen, DLR-Institute für Aeroelastik in Göttingen, Institut für Computerwissenschaft und Kontrolle (SZTAKI) aus Ungarn, Französisches Labor für Luft- und Raumfahrt (ONERA),