The design of a new-concept aircraft wing is strongly connected to the analysis of the effects of the fuel sloshing on the wing structural dynamics properties. The objective of the paper is the experimental investigation on the damping mechanism that characterizes wing/tank-like systems in actual operating conditions. A cantilever beam, carrying a tank filled with fluid located at its free end has been considered. The dynamic response of the system at different amplitudes and frequencies in a controlled loop seismic excitation framework will mimic the typical wing operating conditions. The operational modal analysis methods called Frequency Domain Decomposition (FDD), Stochastic Subspace Identification (SSI) and Hilbert Transform Method (HTM) have been used to study the effects of the fuel tank filling level, the amplitude, and the frequency of vibration on the damping, for this experimental investigation, the structure is excited with a random excitation. Moreover, sine sweep seismic excitation has been also used to characterize the damping of the system from harmonic response. In addition, the paper investigates the correlation between the different regimes inside the fuel tank corresponding to previous considered seismic excitations.