Advanced Techniques for Flutter Clearance by Laurent Guillaume Duchesne

In this thesis, a new methodology for flutter boundary prediction using experimental data is developed. Due to the complexity of the aircraft's structure and aerodynamics, it appeared necessary to rely on a simplified wing model to create a low order state space representation that would capture all the essential dynamics of a flutter problem. The methodology is the following: first, a low order finite element model was derived using linear aerodynamic theory and a Pade approximation. The technique also relies on a time-frequency analysis which selectively eliminates noise from the recorded signals in order to estimate the transfer function of the system. A graphical interface was developed to perform this task more efficiently. Then, a state space model parameterized by the dynamic pressure q is identified with a quasi-Newton optimization based on a frequency domain cost function. Finally, the flutter boundary is determined based on the domain of stability of the parameterized model. This methodology has been validated first on a theoretical example, then on wind tunnel data through the Benchmark Active Controls Technology (BACT) model and finally on the F18 System Research Aircraft. Thesis Supervisor: Eric Feron Title: Assistant Professor Acknowledgments First of all, I would like to thank my advisor Eric Feron for the interest and enthusiasm that he has showed throughout my stay at MIT. I would also like to thank Jim Paduano who acted as a co-advisor for this project. I wish to acknolewdge all the NASA Dryden Flight Research Center engineers with whom I have interacted with a special thank to Marty Brenner with whom I have shared many productive discussions. Finally, I would like to thank all my lab mates who provided useful advice and more importantly friendship. This work was supported by NASA under the Consortium program NCC 2-5116 entitled "Advanced Techniques for Flutter Clearance" and the cooperative research agreement DFRCU-95-025 entitled "Methods for In-Flight Robustness Evaluation".