Aeroelasticity, the interaction between inertial, elastic and aerodynamic forces, plays a vital role in aircraft design. And as aircraft get optimized and more flexible, aeroelastic behavior has evolved becoming more and more complex. Large, four-engine aircraft are characterized by a very high modal density, and their first mode is situated at a very low frequency. Along with aircraft optimization, modal identification methods used during flutter testing have evolved to assure correct parameters identification. Frequencies and damping values estimations have to be as accurate as possible in order to be compared to the aeroelastic model results and to tune it. This paper will compare the traditional parameter estimation approach using Frequency Response Functions, with an Operational Modal Analysis approach that only requires the aircraft response time histories. Also different excitation techniques will be discussed such as control surface sine sweep or pulse excitation. Data from a four-engine aircraft in-flight test in which more than 100 accelerometers have been used will be exploited in this paper.
