Hilbert-Huang transform stability spectral analysis applied to flutter flight test data

A new method, the Hilbert-Huang transform (HHT), has been applied to analyze the aerostructures test wing (ATW) flight flutter data from NASA Dryden Flight Research Center. The analysis shows the yielding of the wing after the onset of flutter, but just before breaking off of the wingtip. Based on HHT, a new stability spectral analysis is also proposed that shows both positive (stable) and negative (unstable) damping. The stability spectral analysis further shows that the flutter of ATW bending occurs at 2-5 Hz in addition to 18 Hz as determined by modal analysis and identification. Both HHT and the Teager energy operator based nonlinearity indicator show that the vibrations of the ATW are nonlinear throughout the flight-test flutter maneuver.