Abstract: A rotor system with flexible damped support has been investigated experimentally under the conditions of simulated blade loss.Some results of the transient response dynamics are presented.Experiments under different sudden unbalances applied to the rotor system with various Squeeze Film Damper (SFD) film clearances were performed at different rotational speeds.The instability conditions characterized by limiting circle orbits for large amplitude at damper location can be determined,and some particular phenomena caused by nonlinearity of the rotor system such as lock up,bistable jump and subharmonic etc.have been observed.The effectiveness and the capability of SFD for suppressing instability of the rotor system are analyzed.