Efficient ground vibration testing of aircraft based onoutput-only modal analysis during taxi

The work presented in this paper shows a simple way how to obtain eigenfrequencies, damping ratios and mode shapes of an aircraft prototype. The only prerequisite is flight test instrumentation (FTI) including a set of acceleration sensors with sufficient number and distribution over the aircraft components and data acquisition hardware. For the excitation of the structure the aircraft is towed by a tractor on the runway. The enforced motion at the landing gears will induce distributed inertia excitation causing airframe vibrations that can be measured with acceleration sensors. Time recordings of all acceleration channels are converted to cross-power spectral densities and later on analyzed using the means of operational modal analysis. The work presented here demonstrates how this method was used to verify the proper operation of the FTI right before entering into the flight testing. However, with more intensive installation, the method can also be used for a complete modal identification of the aircraft on ground, equivalent to ground vibration testing (GVT).