A gearless one-motor concept for contra-rotating fans is presented in this article. The rotors are mounted to an electric motor using only one shaft. The coupling between both rotors is realised by utilising the conservation of angular momentum. The contra-rotating fans has a diameter of 200mm at a design speed of 2100min(-1) for the first stage and 1200min(-1) for the second stage. It has been designed and investigated through a series of experiments by the Institute of Air Handling and Refrigeration in Dresden. The performance map and 2D particle image velocimetry measurements have been conducted. Numerical models for 3D quasi-steady state and transient simulations have been implemented and carried out by the Institute of Mechanics and Fluid Dynamics. The results show a good agreement between the quasi-steady, the transient simulations and the experiment. However, when close to stall, the time-resolved simulations show a superior performance compared with steady-state computations.