Fuel sloshing is seen as a potential mechanism to reduce the loads in aircraft due to atmospheric turbulence and gusts via an increase in the effective damping. A series of steprelease experiments have been performed on a cantilever beam structure with a tank at its end filled with different levels of liquid in order to provide experimental data to characterise the amount of damping caused by the sloshing motion and to validate future numerical models. This paper presents an analysis of some of the acceleration data sets acquired during the experiments and shows how the frequency and damping behaviour varies during the time decay resulting from the step-release. Correlation is made between the amount of effective damping and the different fluid motions in the tank. The analysis is repeated for the dry beam configurations as well as different test conditions including tank level filling and number of compartments in the tank.