This paper presents the setup and results of a flight test campaign performed to identify the longitudinal motion of a small unmanned fixed-wing aircraft. The flight test experiments include manoeuvres to excite short-period and phugoid dynamics, as well as gliding flights to determine drag coefficients. Frequency ranges of the manoeuvre inputs are selected based on the dynamics of an initially derived linear approximation of the aircraft dynamics using aerodynamic vortex lattice method computations. By applying grey-box system identification, the corresponding aerodynamic parameters are estimated from recorded measurement data. The gathered results indicate satisfactory correlation with the mathematical modelling of the aircraft. This not only enables the development of suitable model-based control algorithms but also validates the entire mathematical model development chain for small fixed-wing unmanned aerial vehicles, i.e., from the initial approximation to flight test validation.