During an in-flight lightning strike, the relative motion between the arc channel and the aircraft causes a sweeping of the attachment point on the aircraft skin. To predict the behaviour of the arc channel and therefore the potential locations for further restrikes, this study aims at investigating the phenomenon with an innovative method for producing sweeping arcs based on a stationary arc and an electromagnetic launcher propelling aeronautical samples. This article focuses on characterisation of the arc channel, aiming at establishing the evolution of its physical properties during swept-stroke for various experimental conditions. Firstly, the experimental coupling of the lightning generator with the electromagnetic launcher and with a wind tunnel is described with a discussion on the representativeness of the experiment. Then, high-speed cameras and voltage and current probes are used to measure the electrical and geometrical behaviour of the electric arc channel during a swept-stroke. The shape, the length, the voltage and the power evolution of the arc channel are evaluated for different input parameters such as speed, polarity, arc current and sample length. Furthermore, the influence of these parameters on the temperature of the arc channel is studied, resorting to an optical emission spectroscopy technique. The results are presented and discussed with the objective of providing a physical insight into arc elongation phenomenology during a swept-stroke.