The scope of this report is the development of a mathematical model and a control system for a three degrees of freedom (3DOF) helicopter rig. This 3DOF-system offers a good simplification of a real world tandem helicopter for evaluating performanceof different automatic control principles. A mathematical model of the system is developed using free-body diagrams. This mathematical model is then linearized and a controller is developed by decoupling the system. Due to model imperfections external disturbances and similar effects integral action is added as well as feed-forward compensation to reduce nonlinear effects. After the controller has been decoupled the two different controllers are tuned. The Linear-Quadratic Regulator, described in section 3.6, is used for selectingstate-feedback gains. Due to the highly nonlinear nature of the system an Extended Kalman Filter is developed to estimate unmeasurable states. The model and controller is then implemented on the actual rig and evaluated. The results displayed that the elevation controller had good performance. The travel controller also showed good performance but not as good as the elevation controller. The main goal of this thesis was to develop a controller for the 3DOF helicopter system. The results clearly show that an LQR-controller is able to successfully control a system like this with decent performance characteristics despite the highly nonlinear system.