This thesis suggests that with air-cooled direct-drive ring-type machines it is very likely to incur into a weight penalty for the application of main propulsion of civilian helicopters. This is however an application not investigated before at the level of detail presented. Therefore, this work serves as a design philosophy and guideline for the development of electrical main propulsion drives for rotary-wing aircraft with a MTOW of 3t or lower. It proposes a systematic approach to a solution, and initial considerations for high-power/low-weight machines with low to medium rotational speed. Furthermore, it highlights the importance of the mechanical and structural considerations for both the electromagnetic mass and the support structure.

More-Electric flight is one of the main objectives of the aerospace industry for the future. Foraerospace applications, electrical machines providing high torque density are paramount for theviability of direct-drive electrical propulsion of aircraft. Besides low-weight and high torquecapability, a candidate solution should also be inherently fault tolerant for it to be used in aerospace.For these reasons a first solution based on Flux-Switching Permanent Magnet (FSPM) machines for anexemplary application of a helicopter main rotor drive was investigated, since these machines haveshown high torque-to-weight ratios and high efficiency during research in the last decade. Despite this,the task of designing a machine appropriate for this application goes beyond the electromagneticdesign and into the area of mechanical design much deeper than for traditional designs: Thelightweight nature of such an iron-based machine makes the design of support structures and airgapcontrol challenging and requires unconventional approaches. This paper presents the main design stepsand first experimental results for such a machine.