Ground Vibration Testing for Validation of Large Aircraft Structural Dynamics.

Abstract

To perform aeroelastic analyses such as flutter calculations, the knowledge of both the unsteady airloads and the structural dynamic behaviour is a mandatory requirement. The modal parameters are determined either mathematically by means of a finite element model of the aircraft or experimentally by means of suitable test methods and facilities. The accurate structural dynamics prediction of large and complex aircraft needs mathematical models with several thousand degrees of freedom. Although much progress has been achieved in the predictive capabilities of modern finite element codes, experimental investigations are necessary to validate the respective mathematical model. Furthermore, in most cases realistic damping values and struc-tural unsymmetries or nonlinearities can only be determined and studied experimentally. The present paper emphasizes the experimental requirements and exper-iences with respect to large aircraft structures. These topics are exemplified by ground vibration tests performed on twodistinct air- craft: the new airbus A321 and the high-altitude aircraft STRATO 2C. The experiences gained with both airplanes are summarized. Similar investigations on helicopter structures are presented allowing for a comparative study of the respective structural dynamics. This includes test performance and identification methods. Special emphasis is given to the investigations of structural unsymmetries and nonlinearities. Finally, the results of the correlation and validation of the respective finite element models are outlined.