Electric aircraft propulsion requires electrical components achieving very high power-to-mass ratios regardless of the architecture considered, whether turboelectric or with fuel cells. Among the components that constitute an electrical powertrain, electric motors and generators are the heaviest components [1], [2]. It is therefore essential to develop technologies of light and efficient machines and breakthrough technologies such as high temperature superconductivity (HTS) might be a mean to achieve it. Indeed, HTS allows reaching the magnetic field level of conventional motors without the need for any ferromagnetic components, which can provide a significant mass reduction. In this context, we have started in 2020 a three and a half year project called FROST (Flux barrier ROtating Superconducting Topology) which aims to build a 250 kW partially superconducting prototype using the so-called flux modulation machine topology. This topology employs a static DC HTS coil generating a large magnetic flux, which is trapped and deviated by HTS bulks located on the rotor. The resulting machine has a controllable excitation while being brushless. A first 50 kW prototype, built in 2019 [3], used first generation of HTS tapes for the coil and multi-seeded YBaCuO bulks for the rotor. For our current project FROST, an increased power of 250 kW is targeted without increasing the rotor’s diameter thanks to the following improvements: -HTS coil employing second-generation HTS tapes -Single seeded GdBaCuO bulks for the rotor -Implementation of a liquid cooling for the conventional armature. In this presentation, the construction of the 250 kW prototype is presented as well as its technical challenges.