Development of unmanned aerial vehicle has attracted attention of several agencies and university laboratories over the past decade, due to their great potential in military and civilian applications. There are a dozen of commercial autopilots which combine tiny dimensions, low weight and quite efficient navigation capabilities but have limited CPU which restricts the control of the airplane to PID loops and doesn't allow the onboard execution of complex algorithm. On the other side, there is a lot of research in Universities on UAV autopilot but whether they are done on VTOL systems or fixed-wing model airplane, the embedded system is often over-dimensioned, compared to the airplane itself, in order to have high computational capabilities and efficient sensors. Consequently, the UAV becomes very heavy, needs high electrical power and the flight endurance reduces dramatically which is not in correlation with the targeted application. In this paper, we present the airplane developed for the project Sky-Sailor which aim is to build a solar autonomous motor glider by taking care of all aspects, not only the autopilot system but as well the mechanical structure, the solar generator, the energy storage, etc. The final airplane only weighs 2.5 kg with 0.5 kg payload.