The power system of eVTOL (Electric Vertical Takeoff and Landing) aircraft essentially addresses a challenge unprecedented in aviation history: meeting the instantaneous high power required for vertical takeoff and landing, the long-duration efficiency needed for cruise, and safety redundancy no less than civil aviation standards, all under extreme weight constraints. The electric propulsion system is both the core of this challenge and one of the current major bottlenecks for industrialization. This article analyzes four aspects: system architecture, key technologies, airworthiness thresholds, and the competitive landscape.
I. Architecture Choice: Distributed Electric Propulsion and High-Voltage Bus
The underlying architecture of eVTOL electric propulsion is distributed electric propulsion: multiple small electric propulsion units are arranged on the wings or fuselage to generate thrust separately. The value of this architecture lies not only in redundancy—wherein if a single propulsion unit fails, the remaining units can maintain control through differential thrust—but also in its ability to utilize aerodynamic-propulsive coupling effects such as boundary layer ingestion and wake filling to improve aerodynamic efficiency. Furthermore, it achieves vectoring and differential control through independent precise thrust control, partially replacing traditional control surface functions.
Distributed architectures impose stringent requirements on energy transmission. On traditional low-voltage platforms, the weight and losses caused by complex cabling are difficult to tolerate. A topological optimization study targeting ducted fan eVTOLs indicates that adopting a high-voltage bus architecture reduces the weight of the power transmission system by 80.3% and cable power loss by 86.1%. High-voltage DC buses at 800V and even higher voltage levels are becoming standard configurations for next-generation eVTOL electric propulsion systems, which directly drives the penetration of silicon carbide (SiC) power devices in onboard inverters.
Another notable trend is the rise of hybrid architectures. Since 2026, solutions following "generator → electric bus → distributed electric propulsion" have begun to emerge: fuel engines or gas turbines drive generators, supplying power to distributed motors via high-voltage buses, while batteries primarily handle peak power during vertical takeoff/landing and acceleration. This approach attempts to balance the high energy density of liquid fuels with the distribution flexibility of electric propulsion, suitable for scenarios requiring longer ranges. The DF3000 "Youlong" 3-ton prototype, participated in by Tsinghua University's School of Aerospace Engineering, adopts a "distributed electric propulsion + series range-extending generation" architecture. However, hybrid routes involve significantly higher system complexity, so pure electric solutions remain the mainstream choice for manned eVTOLs in the short term.
II. Technical Analysis: Fourfold Constraints of Motors, Control, Thermal Management, and Redundancy
#Motors: Power Density is the Core Contradiction, Technology Routes Have Not Converged
eVTOL propulsion motors almost exclusively use Permanent Magnet Synchronous Motors (PMSM), but topological structures are highly diverse: radial flux vs. axial flux, inner rotor vs. outer rotor, direct drive vs. geared drive coexist. The core competitive metric is power density.
The industry currently exhibits a clear three-tier gap between "benchmark," "mainstream," and "ideal." Joby S4's self-developed electric drive system (motor + controller) achieves a peak power density of 8.4 kW/kg, with peak power of 236 kW, torque of 1800 N·m, and a total system mass of only 28 kg, representing the highest level among publicly available data. Archer Midnight has a continuous power density of 5 kW/kg, using a geared solution with motor speeds of 12,000 r/min. While the rated power density of the aviation propulsion motor body itself is considered to exceed 5 kW/kg in broader industry baselines, there remains a gap from the ideal target for eVTOLs of 5–7 kW/kg (system level) or higher. This gap is identified as the primary focus for breakthroughs over the next 3–5 years.
The axial flux route deserves special attention. Its disc-shaped structure offers inherent advantages in power density and torque density for applications with small length-to-diameter ratios, allowing axial dimensions to be compressed to one-half to one-third of traditional motors. Evolito (the aviation team spun off from YASA) in the UK claims its D250 axial flux motor reaches a peak power density of 28 kW/kg, and the D500 reaches 12 kW/kg, having accumulated over 1,000 hours of flight testing. However, it is necessary to distinguish between the metrics of the "motor body" and the "motor + controller system," as the latter represents the true constraint at the installation level.
#Electronic Control: Silicon Carbide is the Deterministic Direction, Integration Determines System Weight
The efficiency and weight of motor controllers (inverters) directly impact system-level power density. SiC MOSFETs offer significantly lower switching losses and reverse recovery charges compared to silicon-based devices, providing distinct advantages on 800V high-voltage platforms. They are already the deterministic technical direction for main eVTOL propulsion inverters. Domestic supplier J-Link Electronics has showcased products such as 400V SiC controllers and 800V SiC dual-redundancy controllers, establishing collaborations with OEMs like Vertax Aviation and GAC HiDong.
A deeper trend is the deep integration of motor-controller-reducer. Reducing system interfaces and harness volume is a key path to lowering overall integration weight and shortening engineering cycles. Joby's outstanding system-level 8.4 kW/kg is due to it being an integrated system performance metric rather than an isolated indicator of the motor body.
#Thermal Management: The "Invisible Ceiling" for High Power Density
The higher the power density, the more concentrated the heat generation per unit volume; cooling capacity directly determines whether the motor can sustain output under peak conditions without derating. eVTOL thermal management solutions evolve progressively from air cooling and liquid cooling to direct stator oil cooling. Direct oil cooling involves designing dedicated oil channels near the stator windings to remove heat via immersion or spray, which is currently a key research direction for high-power-density motors. A study on a 3,200 r/min, 270 N·m outer rotor PMSM showed that optimizing oil channel geometry can reduce maximum winding temperature and improve thermal uniformity at a constant flow rate of 10 L/min. CRRC Zhuzhou Motor's "Yufeng" T-series axial flux system also employs efficient oil cooling, achieving 95% motor efficiency and 98% controller efficiency. Thermal management is no longer a subsidiary system but a constraint as critical as electromagnetic design.
#Redundancy and Fault Tolerance: Architectural Design, Not Just "Backup"
eVTOLs have extremely low tolerance for single-point failures; redundancy must be embedded in the electric propulsion architecture itself rather than added post-hoc. Dual-winding design is the current mainstream engineering solution: each motor contains two physically isolated winding sets, powered by independent inverters and batteries. Vertax Aviation AE200's electric engine uses dual windings and cross-supply logic on opposite sides; even if two battery packs on the same side fail, the remaining batteries can still ensure the operation of all 8 engines. Joby's solution also uses dual-winding direct drive, with each inverter powered by two independent batteries to prevent fault propagation between battery packs. Enpower's eVTOL electronic control solution combines dual windings with dual electronic control processes, emphasizing sealing and environmental adaptability. Academically, dual-three-phase fault-tolerant IPMSMs and reconfigurable winding strategies provide topological foundations for higher degrees of fault tolerance.
III. Airworthiness: The True Gate for Commercialization of Electric Propulsion
No matter how impressive the technical specifications, commercial operation is impossible without airworthiness certification. The airworthiness pathways for eVTOL electric propulsion in Europe and the US follow different institutional logics.
EASA follows the "Special Conditions" route. In February 2025, Safran's ENGINeUS 100 received a Type Certificate (TC) from EASA, becoming the world's first independently certified electric propulsion system—certified as a standalone product rather than dependent on a specific aircraft model. Based on SC-E19 "Special Conditions for Electric/Hybrid Propulsion Systems," the certification took less than two years, completing 1,500 hours of motor certification tests and over 100 hours of flight tests in real aircraft environments. SC-E19 specifically redefines safety test requirements for worst-case scenarios involving high-voltage arcs and fire risks, setting a paradigm for subsequent electric propulsion system certifications.
The FAA categorizes eVTOLs under the "Powered Lift" special class, certifying them via Part 21.17(b). AC 21.17-4, released in July 2025, set baseline standards including a maximum takeoff weight of 12,500 lbs (approx. 5,670 kg), no more than 6 passengers, and battery-electric power systems. By replacing traditional minimum speed requirements with "flight profiles," it provided actionable compliance paths for OEMs like Joby and Archer.
The Civil Aviation Administration of China (CAAC) has not yet released independent technical standards for eVTOL electric propulsion systems. Domestic suppliers mostly follow the path of "binding with OEMs and obtaining certification alongside the aircraft." EHang's EH216-S took nearly three years from TC application submission to approval; this cycle itself constitutes a significant first-mover barrier. Airworthiness certification for electric propulsion systems is not a one-time product test but a systematic engineering process deeply coupled with OEMs from early design stages, spanning several years.
IV. Player Landscape: Coexistence of Self-Development and Third Parties, Scarce Domestic Supply
The competitive landscape for eVTOL electric propulsion differs sharply from new energy vehicles: higher safety standards, longer airworthiness cycles, and deeper customer bindings result in far fewer participants than in the automotive electric drive sector. The current landscape can be summarized into three forces.
First Category: OEM self-development aiming for system optimization. Joby and Archer are typical representatives. Joby relies on an engineering team from military, Tesla, and Apple backgrounds to fully self-develop motors and controls. Its system-level power density of 8.4 kW/kg is built on deep whole-aircraft coupling, making external solutions difficult to replicate. EHang Intelligence also self-develops brushless DC motors, using coaxial double-propeller designs to save space and weight. The advantage of the self-development model is high system integration and iteration speed, but the cost is extremely high demands on the OEM's design and manufacturing capabilities.
Second Category: Traditional aviation and industrial giants, represented by Safran, Rolls-Royce, and Honeywell. Safran's ENGINeUS series covers three power levels: 50 kW, 100 kW, and 500 kW. It obtained the first independent EASA TC for an electric propulsion system and supplies EHang's E20. Rolls-Royce previously provided electric propulsion systems for Vertical Aerospace and Airbus (though its electric propulsion division was sold in 2023). Honeywell entered via collaboration with DENSO, providing motors for Lilium and others. The core assets of these players are airworthiness experience and aviation supply chains, but their product metrics do not always lead in the high-power-density race specific to eVTOLs—Safran ENGINeUS 100's peak power density is approximately 5 kW/kg, showing a generational gap with Joby's 8.4 kW/kg.
Third Category: Emerging specialized aviation electric drive companies entering via axial flux and integration. Representatives include Evolito (spun off from YASA) in the UK, H3X in the US, MagniX in Australia, and EMRAX in Spain. H3X's HPDM-250 integrates motor, inverter, and reducer, weighing 18.7 kg with a continuous power density of 13 kW/kg, featuring 3D-printed cooling systems and SiC control technology. Evolito's axial flux route has been selected for Vertical Aerospace's Valo model. These companies possess high technical sharpness, but their airworthiness track records and scalable delivery capabilities still require time for validation.
Domestic Landscape: Scarce but with First-Mover Positioning. There are limited domestic suppliers truly capable of delivering aviation-grade electric propulsion systems. Wolong Electric adopts a "3+1" layout (small/medium/high power + airworthiness standards), with medium power (50–175 kW) targeting 4-seat manned eVTOLs, deeply bound with COMAC and Vertax Aviation. In 2025, they established a joint venture, Longfei Electric Drive, with Vertax Aviation, focusing on electric propulsion systems for airworthiness-certified aircraft weighing 750–5,700 kg. Enpower builds on flat-wire oil-cooled and SiC technologies from new energy vehicle electric drives, using dual-winding/dual-control solutions. They have a strategic partnership with EHang Intelligence and achieved small-batch deliveries of EH216-S motors and ESCs. In 2025, they further became the development service provider for Volocopter's XPro electric propulsion system. CRRC Zhuzhou Motor extends high-reliability experience from high-speed rail traction systems to aviation; its "Yufeng" T-series axial flux system has a continuous power density of 10 N·m/kg and peak of 20 N·m/kg, passing DO-160G electromagnetic compatibility verification. Additionally, Tianjin Songzheng, J-Link Electronics, NoEE, and others have formed differentiated positions in electronic control or specific power segments.
An easily overlooked structural fact is that competition among domestic electric propulsion suppliers is largely not about "whose technical metrics are higher," but rather "who can embed themselves earlier into the OEM's airworthiness certification chain." Wolong binding with Vertax AE200 and Enpower binding with EHang EH216-S are essentially locking in channels for joint certification through equity or deep cooperation agreements. In this sense, customer structure defines competitive positioning better than product parameters.
Technical competition in eVTOL electric propulsion is shifting from a "single-metric race" to a dual comparison of "system-level engineering capability + depth of airworthiness embedding." Approaching Joby's 8.4 kW/kg from the mainstream 5 kW/kg requires simultaneous breakthroughs in electromagnetic design, thermal management, and integrated architecture. SiC electronic control and direct stator cooling are deterministic engineering directions. Meanwhile, the pace of airworthiness certification will ultimately determine which players move from the prototype stage to large-scale commercial operation. The landscape of coexisting OEM self-development and third-party supply will not change in the short term, but a clear trend is emerging: electric propulsion systems are evolving from "onboard components" to core systems determining eVTOL product competitiveness, and their weight in the whole-aircraft value chain will only increase, never decrease.
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