Robotic lighter-than-air vehicles (type of unanimated air vehicle UAV), provide a promissory strategic platform for the transport, exploration and surveillance. This paper presents an approach to the control of a small sized airship in cruise flight phase; specifically, non-linear control by extended linearization is considered. In order to make this control, a study of the dynamic model and some hypothesis for its reduction are presented. These reduced models enable to develop the control laws and the stabilization of the aerodynamic speed, altitude and heading of the airship. A technique of dynamical decoupling is considered in order to have a more stable altitude when the airship turns. Tests in simulation were made.