The aerodynamic characteristics of a diamond wing shape unmanned aerial vehicle (UAV), the so called SAGITTA demonstrator configuration, are investigated. Reynolds Averaged Navier-Stokes computations as well as wind tunnel force measurements are applied to generate an aerodynamic data set for two different configurations. On the one hand, the diamond wing UAV is considered as tail-less configuration, while on the other hand, a double vertical tail is attached to the SAGITTA demonstrator configuration. The results of the computed and measured aerodynamic force and moment coefficients and their corresponding derivatives are compared to each other for both the longitudinal and the lateral motion. A good agreement between the numerical and experimental data is observed for both regarded configurations. For the tail-less diamond wing UAV, no lateral yaw stability is present without control surface deflection. Therefore, lateral stability is provided by vertical tails constituting the first flight configuration within the SAGITTA demonstrator program.