Benefiting from their compact structure and high-power density, axial flux permanent magnet synchronous motors have attracted extensive global research interest. Nevertheless, Yokeless and Segmented Armature (YASA) topologies still face several challenges concerning their electromagnetic and output characteristics, which remain key obstacles for further application. For the design and manufacturing of YASA, precise evaluation of electromagnetic performance is therefore essential. In this study, a 12 kW YASA motor intended for electric aircraft applications is developed, and the effects of different structural parameters on its overall performance are systematically investigated. And the accurate calculation of the electromagnetic performance and output characteristics is carried out. These research results provide an important reference for the design and development of YASA motors for electric aircraft.