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Aerospace
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Electric Machines for Electrified Aircraft Propulsion
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Electric Machines for Electrified Aircraft Propulsion

A special issue of Aerospace (ISSN 2226-4310). This special issue belongs to the section "Aeronautics".

Deadline for manuscript submissions: closed (30 September 2024) | Viewed by 17712

Special Issue Editors

Dr. Justin J. Scheidler

E-Mail Website
Guest Editor
NASA Glenn Research Center, Rotating and Drive Systems Branch, 21000 Brookpark Road, Cleveland, OH 44135, USA
Interests: conventional, cryogenic, and superconducting electric machines; magnetic gears and magnetically-geared electric machines; electrified aircraft propulsion systems; extreme environment actuators for space mechanisms
Dr. Parag Kshirsagar

E-Mail Website
Guest Editor
Raytheon Technologies Research Center, East Hartford, CT 06118, USA
Interests: aircraft power systems; aerospace propulsion; electric aircraft

Special Issue Information

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

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Aerospace is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • 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

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Published Papers (7 papers)

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Research

12 pages, 959 KiB  
Article
Optimal Design of High Specific Power Electric Machines for Fully Electric Regional Aircraft: A Case Study of 1MW S-PMSM
by Taha El Hajji, Ahmed Hemeida, Antti Lehikoinen, Floran Martin and Anouar Belahcen
Aerospace 2024, 11(10), 820; https://doi.org/10.3390/aerospace11100820 - 8 Oct 2024
Viewed by 1847
Abstract
The aviation industry is undergoing electrification due to the increased global focus on reducing emissions in air traffic. Regarding the volatility of raw material prices, one main objective is the increase in the specific power of the motor. This matches the ambitious targets [...] Read more.
The aviation industry is undergoing electrification due to the increased global focus on reducing emissions in air traffic. Regarding the volatility of raw material prices, one main objective is the increase in the specific power of the motor. This matches the ambitious targets of the CoE project (Center of Excellence) in Finland on high-speed electric motors. The targeted specific power is 20 kW/kg. In this work, motors are designed and optimized for a fully electric regional aircraft. motors with different slot/pole configurations and rotational speed values are studied to determine the advantage of increasing speed in terms of weight reduction. As increasing speed requires the use of a gearbox, the overall weight of the motor and the gearbox is evaluated in post-processing, which allows for determining the impact of high speed on the overall weight. An optimization tool coupled with an electromagnetic and mechanical analysis is used to optimize 1 MW surface mounted permanent magnet synchronous motors (S-PMSMs) for given specifications of regional electric aircraft. Optimization results indicate that there is considerable gain in terms of overall weight only when increasing the speed to the range of 10,000–15,000 rpm. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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14 pages, 2235 KiB  
Article
An Endurance Equation for Hybrid-Electric Aircraft
by Aman Batra, Reiko Raute and Robert Camilleri
Aerospace 2024, 11(9), 698; https://doi.org/10.3390/aerospace11090698 - 26 Aug 2024
Cited by 1 | Viewed by 1259
Abstract
This paper introduces a new endurance equation for a hybrid-electric aircraft. This research follows the derivation of a range equation for a hybrid-electric aircraft case using constant power split that was carried out by authors in their earlier work. Thus, the derivation of [...] Read more.
This paper introduces a new endurance equation for a hybrid-electric aircraft. This research follows the derivation of a range equation for a hybrid-electric aircraft case using constant power split that was carried out by authors in their earlier work. Thus, the derivation of the endurance equation maintains the use of efficiency-based degree of hybridization (φ) used in the earlier research. For coherence, the paper also uses the same case study to assess endurance values over a range of battery energy density values and degree of hybridization (φ) values. Results show that any aircraft design has an Energy Density Threshold (EDT) value, before which the endurance of the aircraft reduces with an increase in the degree of hybridization values. Conversely, once EDT is exceeded, the endurance of the aircraft enhances with the increase in the degree of hybridization values. The EDT values are specific to the aircraft type, its specifications and key design parameters. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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31 pages, 18458 KiB  
Article
Cooling of 1 MW Electric Motors through Submerged Oil Impinging Jets for Aeronautical Applications
by Giuseppe Di Lorenzo, Diego Giuseppe Romano, Antonio Carozza and Antonio Pagano
Aerospace 2024, 11(7), 585; https://doi.org/10.3390/aerospace11070585 - 17 Jul 2024
Cited by 4 | Viewed by 2620
Abstract
Electrification of aircraft is a very challenging task as the demand for energy and power is high. While the storage and generation of electrical energy are widely studied due to the limited specific energy and specific power of batteries and fuel cells, electric [...] Read more.
Electrification of aircraft is a very challenging task as the demand for energy and power is high. While the storage and generation of electrical energy are widely studied due to the limited specific energy and specific power of batteries and fuel cells, electric machines (power electronics and motors) which have years of experience in many industrial fields must be improved when applied to aviation: they generally have a high efficiency but the increase in power levels determines significant thermal loads which, unlike internal combustion engines (ICE), cannot be rejected with the exhaust. There is therefore a need for thermal management systems (TMSs) with the main objective of maintaining operating temperatures below the maximum level required by electric machines. Turboprop aircraft, such as the ATR 72 or the Dash 8-Q400, are commonly used for regional transport and are equipped with two gas turbine engines whose combined power is in the order of 4 MW. Electric and hybrid propulsion systems for these aircraft are being studied by several leading commercial aviation industries and start-ups, and the 1MW motor size seems to be the main option as it could be used in different aircraft configurations, particularly those that exploit distributed electric propulsion. With reference to the topics mentioned above, the present work presents the design of a TMS for a high-power motor/generator whose electrical architecture is known. Once integrated with the electrical part, the TMS must allow a weight/power ratio of 14 kW/kg (or 20 kW/kg at peak power) while maintaining the temperature below the limit temperature with reasonable safety margins. Submerged jet oil is the cooling technique here applied with a focus on diathermic oil. Parameters affecting cooling, like rotor speed and filling factor, are analysed with advanced CFD. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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10 pages, 582 KiB  
Article
Cooling of Superconducting Motors on Aircraft
by Alan Caughley, Grant Lumsden, Hubertus Weijers, Sangkwon Jeong and Rodney A. Badcock
Aerospace 2024, 11(4), 317; https://doi.org/10.3390/aerospace11040317 - 18 Apr 2024
Cited by 4 | Viewed by 2590
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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23 pages, 8793 KiB  
Article
Multi-Electric Aero Engine Control and Hardware-in-the-Loop Verification with Starter Generator Coordination
by Jun Fang, Tianhong Zhang, Zhaohui Cen and Elias Tsoutsanis
Aerospace 2024, 11(4), 271; https://doi.org/10.3390/aerospace11040271 - 30 Mar 2024
Cited by 2 | Viewed by 1716
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 a starter generator. Firstly, a [...] Read more.
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 a 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 a multi-electric aero engine with starter generator coordination are proposed in three processes, including the starting process, acceleration/deceleration process, and steady-state process. During the starting process, the acceleration is controlled by coordinating the torque of the starter generator and the fuel of the aero engine. During the acceleration/deceleration process, the fuel limit value is adjusted based on the electrical load of the starter generator. During the steady-state process, the fuel is compensated based on the q-axis current of the starting generator in response to load torque disturbance. Finally, hardware-in-the-loop simulation experiments are conducted for the control of a multi-electric aero engine. The results show that the coordination reduces the oscillation of the acceleration during the startup of a multi-electric aero engine, enhancing its ability to resist disturbances from electrical load fluctuations during power generation. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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26 pages, 29417 KiB  
Article
Design Optimisation Approach of an Outer Rotor Multiphase PM Actuator for Multirotor Aerial Vehicle Applications
by Saad Chahba, Guillaume Krebs, Cristina Morel, Rabia Sehab and Ahmad Akrad
Aerospace 2024, 11(2), 150; https://doi.org/10.3390/aerospace11020150 - 13 Feb 2024
Cited by 1 | Viewed by 2213
Abstract
The electric urban air mobility sector has gained significant attraction in public debates, particularly with the proliferation of announcements demonstrating new aerial vehicles and the infrastructure that goes with them. In this context, the development of new methodologies for the design and sizing [...] Read more.
The electric urban air mobility sector has gained significant attraction in public debates, particularly with the proliferation of announcements demonstrating new aerial vehicles and the infrastructure that goes with them. In this context, the development of new methodologies for the design and sizing of actuation systems, ensuring high performances of these aerial vehicles, remains an important task in this process. This will allow for better integration within this transport sector. In this paper, a robust design optimisation approach of multiphase fault-tolerant (FT) outer rotor (OR) permanent magnets (PM) for multirotor aerial vehicle applications is proposed. In order to show the effectiveness and the robustness 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, four 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. First, a pre-sizing step is carried out, consisting of selecting the optimal combinations slot/pole, designing the multiphase FSCW layout, and estimating the electric motor (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 efficiency and weight, under constraints where the FEMM/Matlab based Finite Element Analysis (FEA) tool is used to perform this optimisation. Finally, results analysis and performance comparisons of different EM configurations are carried out in order to assess the design parameters, such as phases number, PM position, and harmonic currents in the EM design and consequently to select the best configuration for the considered application. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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14 pages, 1961 KiB  
Article
On the Range Equation for Hybrid-Electric Aircraft
by Aman Batra, Reiko Raute and Robert Camilleri
Aerospace 2023, 10(8), 687; https://doi.org/10.3390/aerospace10080687 - 31 Jul 2023
Cited by 7 | Viewed by 3855
Abstract
This paper proposes a new range equation for hybrid-electric aircraft. The paper revisits the theory of the range equation for a hybrid-electric aircraft with constant power split published earlier in the literature and proposes a new efficiency-based definition of the degree of hybridization [...] Read more.
This paper proposes a new range equation for hybrid-electric aircraft. The paper revisits the theory of the range equation for a hybrid-electric aircraft with constant power split published earlier in the literature and proposes a new efficiency-based definition of the degree of hybridization (φ), one which includes the efficiencies of the electric or fuel-powered drivetrain. The paper shows that the efficiencies of the respective drivetrains play a significant role in the range estimation of the hybrid-electric aircraft. The paper makes use of a case study to show the relationship between battery energy density, powertrain efficiency and modification in the definition of the degree of hybridization φ with aircraft range. We show that for every aircraft design, there is a battery energy density threshold, for which the aircraft range becomes independent of the degree of hybridization. Below this threshold, the range decreases with an increase in the degree of hybridization. Conversely, beyond this threshold, the aircraft range increases with the degree of hybridization. Our study finds that the new definition of φ has shifted this threshold significantly upwards compared to earlier publications in the literature. This makes the design of an aircraft with a high degree of hybridization less optimistic. Full article
(This article belongs to the Special Issue Electric Machines for Electrified Aircraft Propulsion)
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