Modal Identification of Large Aircraft

Abstract

The modal identification of a structure consists in providíng the parameters representing this specific system and allowing the prediction of its dynamic behaviour for several environment conditions. The ground vibration test producing the modal identification is one of the main tools used by aircraft manufacturers to verify the aircraft flutter clearance in their flight domain, prior to the first certification flight. Today, the experimental parameters coming from the ground vibration tests are not only used to verify the aeroelastic stability of the aircraft, but also to update the Finite Element Model. The specificities of the modal identification of large aircraft come mainly form the very low resonance frequencies, the high modal density, and the necessary equipment to perform the ground vibration test. To succeed in reducing the test duration, both the Phase Resonance method (modal appropriation), generally used to perform such a test, and the Phase Separation method will be applied complementarily and supported by the Finite Element Model.