Ground Vibration Testing of Large Aircraft - State-of-the-Art and Future Perspectives

Abstract

A ground vibration test (GVT) on the prototype of a new aircraft is often regarded as necessary to update the mathematical model of the aircraft in order to make reliable flutter predictions for flight tests. Due to very high development costs for such aircraft, the goal is to strive for a significantly shorter testing time by simultaneously increasing the amount and quality of the test data. In the past, the duration of such GVTs was reduced significantly due to the combined application of the phase resonance method (sine-dwell) and phase separation techniques instead of using only the time consuming phase resonance method for modal identification (extraction of mode shapes, frequencies and damping parameters). This switch in test philosophy, including the application of a sufficient amount of equipment, caused a reduction in testing time of large aircraft by 1/3. Nowadays, the application of the common GVT strategy is more or less a standard process, depending on the size of the investigated structure. Nevertheless, the scope of requirements of the aircraft manufacturers regarding the test program has increased in the last years in order to cover new issues like passenger comfort, fan-blade-off (wind-milling) or aero-servo-elasticity within the same time-window as for the modal identification topic during past GVTs. Mid-term improvements are continuously achieved due to test strategy improvements or enhanced soft- and hardware developments. However, a great leap with respect to test time reduction, quality enhancement and cost efficiency can only be made if the complete aeroelastics process is taken into account. Thus, it must be scrutinized if the classical GVT will play the same role in the future within the aeroelastics process as nowadays or if equivalent data required for aircraft certification can also be gained from other tests which are performed anyway during aircraft development. In this paper the advanced GVT strategy of the transnational ONERA and DLR team is presented. After that, midterm improvements are shown which are related directly to the test strategy issue. A vision with respect to ground vibration testing in the future, which will have a significant effect on the complete aeroelastics process, is discussed and will complete this publication.