This paper presents in the first part the conception and construction of a mini 4 rotors helicopter for indoor and outdoor applications. The proposed UA V, named XSF, has a very manoeuvrable platform and is indicated to work in inaccessible spaces such as per forming inspection tasks under bridges as well as inside pipes or tanks. Its main advantage with respect to classical4 rotors helicopters is the ability of flipping two motors in order to obtain two more control inputs. This feature allows

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... the XSF to have a better horizontal displacement or to create a yaw movement without translation. In. the second part, we present a stabilization strategy around a position of equilibrium. The model is highly nonlinear, we use a methodology based on the linearization. The dynamic of the system involves six. control inputs which will be computed to stabilize the engine with regard to extemal perturbations.