Rotor's unbalance is a synchronous dynamic load which is source of vibrations, especially on Aircraft engines. These vibrations could lead to hardware failure because of High Cycle Fatigue and it could impact the overall performance of the machine, with even the possibility of a catastrophic event in case the rotor operates at one of its critical speeds. The main goal of rotordynamic analysis is to study the effects of rotor unbalance, predicting and optimizing the modal response of the machine and verifying it through measurements of the resulting vibrations. Residual unbalance is intrinsic of any rotor assembly process and cannot be completely removed.