This Master Thesis deals primarily with experimental studies on a vertical Jefcott-Rotor test stand. The main topics addressed in this work are the dynamical properties of a multi-station supported elastic rotor with some imperfections, and a new method to estimate critical speeds by measurements below that speed. The rst part of this thesis is devoted to improvements on an already existing rotor test stand. A new front end based on a recent version of the software in use for the measurement system and the rotor speed control are developed and documented. The rotor shaft was originally supported by two roller bearings. In the course of this work, two additional bearing stations have been introduced. The main feature of these additional bearing stations are rubber elements, to increase the external damping in the system. These design modications have a signicant impact on the dynamical properties of the rotor. In the experimental part, vibration measurements on the non-rotating rotor and, of course, on the rotor running at various constant speeds are carried out. Numerous test runs have been measured and the acquired data are analysed and investigated. Measurements of the free vibrating rotor are analysed with respect to the natural frequencies of the system. Frequency response functions due to unbalance excitation are acquired by measurements at various rotor conditions. A new method to estimate a critical speed of the rotor has been reported recently in the literature and is tested and conrmed for the rst time on a multi-station rotor with imperfections. In addition to the experimental work, a numerical model, based on a commercially available FE-software, is also established. Numerical results and experimental measurements are compared, primarily with respect to the critical speeds and the vibration modes. Several conclusions can be drawn based on the results of the various experimental studies. The newly introduced rubber-bearing-supports introduce a signicant amount of external damping and moreover change the dynamic properties of the rotor system signicantly. A strong dependency of the actual temperature of the rubber material was noted. Also non-linear behaviour was detected. A newly proposed method to estimate the critical speed based on measurements well below that speed was tested under non-ideal conditions, since the rotor system shows some imperfections. However, the experiments showed that this new method is quite reliable and may be used also for multi-bearing station rotors with imperfections. The numerical analysis of the rotor system, based on a FE-model did conrm the measured critical speeds and the vibrational modes.