Recent developments in operational modal analysis for ground and flight vibration testing

Abstract

In this paper, recent advances are presented in ground vibration testing and flight vibration testing of aircraft as applied at DLR, the German Aerospace Center. New test procedures have been developed with specific focus on efficient certification of experimental aircraft operated by DLR. These research aircraft quite often are modified to fulfill scientific missions, e.g. to carry scientific equipment for atmospheric research or to demonstrate and assess new aircraft technology in flight. For this reason, DLR is interested in the development, maturation and application of advanced test methods for ground vibration testing and flight vibration testing, because the selection of the test method to demonstrate compliance with certification requirements has strong impact on the cost for certification and the availability of the aircraft for the intended scientific missions. The new methods are based on output-only modal analysis. Fast data analysis tools have been implemented which enable automated real-time modal analysis. This paper demonstrates the ability of the new methods to monitor the aeroelastic stability in flight by tracking the changes of eigenfrequencies and damping ratios continuously and in real time.