Experimental Nonlinear Modal Analysis of an F-16 Aircraft Using Phase-Locked Loop Control

This study leverages phase-locked loop (PLL) control and adaptive filtering for the experimental identification of the nonlinear modal parameters of an F-16 aircraft. Specifically, PLL effectively tracks the backbones of three aircraft modes, enabling the extraction of resonance frequencies, mode shapes, and damping ratios, all of which vary with vibration amplitude. Additionally, the nonlinear frequency responses of 3:1 superharmonic resonances are identified. The results reveal that the F-16 aircraft exhibits softening effects due to joint friction in the wing-to-payload connections, as well as clearance-induced nonlinearity. The onset of contact is further illustrated through time-harmonic analysis of modal deflection shapes.