Tasks for improvement in ground vibration testing of large aircraft

Abstract

The European aircraft industry plans to extend their product offer towards high capacity aircraft. The prototypes of these aircrafts are dynamically characterized by a high modal density in the very low frequency range. This requires a high effort for the experimental modal analysis. On the other hand the test time should be reduced to a minimum for cost reduction. In order to meet these requirements the test teams of the French ONERA and the German DLR agreed upon a cooperation for future joint performance of ground vibrations tests on large aircraft . The cooperation is based on a new test strategy, new test methods, and new test equipment. An essential part of the improved test strategy is the combination of the classical phase resonance test method with phase separation techniques. The improved test strategy was investigated during a research GVT on the Airbus A340-300 MSN 1 in October 1999 and partly applied during the GVT of the prototype of the A340-600 in January 2001. The paper elucidates the improved test strategy and discusses the experiences gained during the GVT's. Different tasks for further investigation of GVT methods for large flexible aircraft are derived from these experiences. Since the combination of different test methods delivers a larger data base, the establishment of unique modal confidence parameters are required in order to get the most reliable modal model of the aircraft. The paper summarizes the state of the art of different criteria which were used within the A340 GVT's. The investigation of the structural dynamics linearity is a second field of further GVT methods improvement. The paper elucidates the state of the art of the experimental investigation of nonlinearities during GVT.