On the Design of Coreless Permanent Magnet Machines for Electric Aircraft Propulsion

This paper presents design and prototyping studies for coreless and slotless permanent magnet (PM) machines, which have the potential for high power density and efficiency, and discusses their feasibility for electric aircraft propulsion. The emphasis is on axial flux permanent magnet (AFPM) machines with printed circuit board (PCB) stators that have advantages over their wired counterparts in terms of design flexibility, coil accuracy, manufacturing process reliability, and heat dissipation. Detailed electromagnetic finite element analysis models were developed and employed alongside analytical sizing equations to evaluate the performance of two dual-rotor single-stator coreless AFPM designs employing wave and spiral PCB winding patterns. Design considerations for a 10kW 2,600rpm rating similar to the NASA X-57 electric aircraft propulsor motors are included. A 26-pole prototype machine has been developed and experimental testing results are presented.