Electric Machines for Electrified Aircraft Propulsion

Dear Colleagues,

Aviation has a meaningful and accelerating impact on our climate and air quality. Aviation’s share of the total, human-caused CO₂ emissions has reached 2.5% and is expected to continue increasing unless bold actions are taken. Both changes in the energy source and reductions in the energy used by an aircraft are required to reach international climate goals. Electrified aircraft propulsion (EAP) enables moderate to significant energy reductions by greatly expanding the aircraft design space. However, EAP’s success depends on advancing the state of the art of electric machines in terms of efficiency, specific power, reliability/maintainability, and power density. In this pursuit, an emphasis must be placed on electric machines with power ratings of about 1 MW to 10+ MW, because such power is required for the propulsion systems of large transport aircraft (about 150+ passengers) which cause the large majority of the aviation sector’s impact on the climate. The relative importance of the aforementioned performance metrics depends on the EAP system, aircraft, and mission, but in all cases the rank ordering should be informed by aircraft-level metrics such as energy use (e.g., fuel burn) or climate impact.

This Special Issue of Aerospace targets electric machines, the subcomponents and materials that they rely on, as well as the relationships between machines and the EAP system and aircraft they are contained within. The applications of primary interest are commercial fixed-wing aircraft at the large transport and regional scales, but interest extends to smaller fixed- and rotary-wing aircraft (e.g., urban air mobility) as well.

Dr. Justin J. Scheidler
Dr. Parag Kshirsagar
Guest Editors

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• electric machine configuration, design, and performance
• effect of machines on aircraft-level performance
• interactions between machines and other EAP system components and their combined performance
• reliability, maintainability, and concept of operations
• conductor selection and design
• lightweighting
• materials and subcomponents of cryogenic machines
• thermal management

Title: Design Optimisation Approach of an Outer Rotor Multiphase PM Actuator for Multirotor Aerial Vehicule Applications
Authors: Saad Chahba; Guillaume Krebs; Cristina Morel; Rabia Sehab; Ahmad Akrad
Affiliation: ESTACA’Lab – Paris-Saclay
Abstract: The electric urban air mobility sector has gained significant traction in public debates, particularly with the proliferation of announcements demonstrating new aerial vehicles and the infrastructure that goes with. In this context, the development of new methodologies for design and sizing of actuation systems, ensuring high performances of these aerial vehicles, remains an important task in this process. This will allow better integration within this transport sector. In this paper, a robust design optimisation approache of multiphase fault-tolerant (FT) outer runner (OR) permanent magnets (PM) for multirotor aerial vehicle applications is proposed. In order to show the effectiveness and the robustness of of the proposed design methodology, the number of stator winding phases; with a fractional slot concentrated winding (FSCW) configuration; as well as the PM configuration are considered as variables. Thus, 4 cases for the number of phases are considered, namely 3,5,6 and 7 phases, where for each number of phases case, the PM takes 3 configurations, namely surface PM, interior V-shape PM and interior spoke PM. Frist, a pre-sizing step is carried out; consisting in selecting the optimal combinations slot/pole, designing the multiphase FSCW layout, and estimating the EM geometry using analytical computations; to obtain a preliminary validation of the design specifications. Second, constrained multiobjective optimisation is considered in order to optimise the EM performances, such as motor efficieny and weight, under constraints; where FEMM/Matlab based Finite Element Analysis (FEA) tool is used to perform this optimisation. Finally, results analysis and performances comparaison of different EM configurations are carried out in order to assess the design parameters, such as phases number, PM position, and harmonic currents n the EM design and consequently to selecte the best confguration for the considered application.

Title: Cooling of superconducting motors on aircraft
Authors: Alan Caughley; Grant Lumsden; Hubertus Weijers; Sangkwon Jeong; Rodney A Badcock
Affiliation: Robinson Research Institute, Victoria University of Wellington
Abstract: Superconducting electric motors are required in order to deliver lower carbon aviation. Critical to the success and viability of operating superconducting electric motors in aviation is keeping the superconducting coils at their operating temperature. This paper examines the challenges of keeping a superconducting motor cold if it were used on a single aisle passenger aircraft such as an Airbus A320. The cooling problem is defined, and different cooling scenarios are investigated to determine viability. The investigation has shown that for a motor with a superconducting rotor only (copper stator), a Stirling-type cryocooler would be sufficient. However, if the motor is to be fully superconducting, then the cooling loads of the stator, which are much higher, make mechanical refrigeration impractical and the only option is to cool the motor with the heat sink of a liquid hydrogen fuel.

Title: Multi-electric Aero Engine Control and Hardware-in-the-loop Verification with Starter Generator Coordination
Authors: Jun Fang; Tianhong Zhang; Zhaohui Cen; Elias Tsoutsanis
Affiliation: College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Abstract: The starter generator, characterized by controllable starting torque and disturbance in generator load torque, poses challenges for the multi-electric aero engine control. The key to addressing this issue lies in multi-electric aero engine control with the collaboration of starter generator. Firstly, a multi-electric aero engine model is established, comprising a full-state turbofan engine model to enhance low-speed simulation capability and an external characteristic model of a starter generator to improve real-time simulation capability. Subsequently, the control methods for multi-electric aero engine with starter generator coordination are proposed in three processes, including starting process, acceleration/deceleration process, and steady-state process. During starting process, the acceleration is controlled by coordinating the torque of starter generator and the fuel of aero engine. During acceleration/deceleration process, the fuel limit value is adjusted based on the electrical load of starter generator. During steady-state process, the fuel is compensated based on the q-axis current of starting generator in response to load torque disturbance. Finally, hardware-in-the-loop simulation experiments are conducted for the control of multi-electric aero engine. The results show that the coordination reduces the oscillation of the acceleration during the startup of multi-electric aero engine, enhancing its ability to resist disturbances from electrical load fluctuations during power generation.