In the context of the global shift toward green and electric aviation, the low altitude economy has emerged as a pivotal domain, driving innovations in aircraft propulsion systems. As nations push for carbon neutrality and urban air mobility (UAM) solutions, electric vertical take-off and landing (eVTOL) vehicles and unmanned aerial vehicles (UAVs) are becoming central to this transformation. The propulsion system, particularly the drive motor, serves as the core component determining efficiency, payload, and reliability. This article examines aircraft drive motor technologies from a patent perspective, analyzing global trends, key applicants, and comparative performance of motor types, with a focus on their role in advancing the low altitude economy. We integrate tables and mathematical models to summarize data and projections, emphasizing the criticality of motor innovations in achieving sustainable aviation goals.
The low altitude economy encompasses economic activities within airspace below 1,000 meters, including logistics, surveillance, and passenger transport via eVTOLs and drones. Drive motors, such as permanent magnet synchronous motors (PMSMs), induction motors (IMs), brushless DC motors (BLDCs), and reluctance motors (SRMs/SynRMs), are at the forefront of this revolution. Their development is fueled by the need for higher power density, efficiency, and fault tolerance. For instance, PMSM efficiency can be modeled using the equation for power loss minimization: $$P_{loss} = I^2 R + K_h f B_m^\alpha + K_e f^2 B_m^2$$ where \(I\) is current, \(R\) is resistance, \(K_h\) and \(K_e\) are hysteresis and eddy current constants, \(f\) is frequency, and \(B_m\) is magnetic flux density. This highlights the trade-offs in motor design for low altitude applications.
Global patent filings for aircraft drive motor technologies reveal a exponential growth trajectory, aligned with the expansion of the low altitude economy. The data can be summarized in Table 1, which outlines patent application trends from 1913 to 2024, segmented by technology phases. This growth is driven by policies like the European Clean Sky Initiative and China’s low-altitude economy pilot programs, which incentivize electric aircraft development.
| Period | Phase | Annual Applications | Key Drivers |
|---|---|---|---|
| 1913-1989 | Technology Embryonic | <10 | Basic electromagnetic theories, experimental prototypes |
| 1990-2009 | Slow Growth | 10-50 | Energy crises, initial electric propulsion research |
| 2010-2024 | Rapid Expansion | >200 (peak in 2022) | Green aviation policies, eVTOL commercialization, SiC devices |
The surge in patents underscores the strategic importance of the low altitude economy, with major applicants including U.S. and Japanese firms leading in innovation. For example, the power density of motors, a critical metric for eVTOLs, can be expressed as: $$P_d = \frac{T \cdot \omega}{V}$$ where \(P_d\) is power density, \(T\) is torque, \(\omega\) is angular velocity, and \(V\) is volume. This equation emphasizes the need for compact, high-output designs to support urban air mobility in the low altitude economy.
Permanent magnet synchronous motors (PMSMs) dominate the landscape due to their high efficiency and dynamic response. In the low altitude economy, PMSMs are preferred for main propulsion in eVTOLs, where weight and reliability are paramount. The torque equation for PMSMs is: $$T = \frac{3}{2} p [\lambda_m I_q + (L_d – L_q) I_d I_q]$$ where \(p\) is pole pairs, \(\lambda_m\) is flux linkage, \(I_d\) and \(I_q\) are direct and quadrature currents, and \(L_d\) and \(L_q\) are inductances. This model allows for optimization in fault-tolerant designs, crucial for safety in low-altitude operations. Table 2 compares PMSM subtypes used in aircraft, highlighting their applicability to the low altitude economy.
| Type | Structure | Efficiency (%) | Power Density (kW/kg) | Applications |
|---|---|---|---|---|
| Surface-Mounted PMSM | Magnets on rotor surface | 92-95 | 3-5 | Low-speed drones, precision control |
| Interior PMSM | Magnets embedded in rotor | 94-97 | 5-8 | High-speed eVTOLs, redundant systems |
| Axial Flux PMSM | Compact radial design | 95-98 | 8-12 | eVTOLs with space constraints |
Induction motors (IMs) offer robustness and cost-effectiveness, making them suitable for auxiliary systems in the low altitude economy. The slip-based torque equation for IMs is: $$T = \frac{3 V^2 R_r’ / s}{\omega_s [(R_s + R_r’ / s)^2 + (X_s + X_r’)^2]}$$ where \(V\) is voltage, \(R_r’\) and \(R_s\) are rotor and stator resistances, \(s\) is slip, \(\omega_s\) is synchronous speed, and \(X_s\) and \(X_r’\) are reactances. This simplicity enables IMs to handle extreme conditions in low-altitude environments, such as high vibrations in agricultural drones. However, their lower power density compared to PMSMs limits their use in primary propulsion. Patent analyses show that IMs are often integrated into hybrid systems for the low altitude economy, providing redundancy in case of motor failures.
Brushless DC motors (BLDCs) are widely adopted in small UAVs due to their high thrust-to-weight ratio and simplicity. In the low altitude economy, BLDCs power multi-rotor drones for delivery and surveillance. The back-EMF and torque equations are: $$E = K_e \omega$$ $$T = K_t I$$ where \(K_e\) and \(K_t\) are back-EMF and torque constants. These linear relationships facilitate control in dynamic low-altitude maneuvers. Table 3 summarizes BLDC performance metrics, emphasizing their role in cost-sensitive segments of the low altitude economy.
| Parameter | Value Range | Impact on Low Altitude Operations |
|---|---|---|
| Speed Range (rpm) | 5,000-50,000 | Enables rapid take-off and landing in urban areas |
| Efficiency (%) | 85-92 | Reduces energy consumption for extended missions |
| Cost (USD/unit) | 50-500 | Supports scalable deployment in logistics drones |
Reluctance motors, including switched reluctance (SRM) and synchronous reluctance (SynRM) types, are gaining traction in the low altitude economy for their rare-earth-free designs and high-speed capabilities. The torque production in SRMs relies on magnetic reluctance variation: $$T = \frac{1}{2} I^2 \frac{dL}{d\theta}$$ where \(L\) is inductance and \(\theta\) is rotor position. This makes them suitable for high-redundancy systems in eVTOLs, aligning with the safety demands of the low altitude economy. However, torque ripple remains a challenge, addressed through multi-phase topologies in recent patents. The power scalability of reluctance motors can be modeled as: $$P_{max} = k \cdot f \cdot B_{sat} \cdot A_c$$ where \(k\) is a constant, \(f\) is frequency, \(B_{sat}\) is saturation flux density, and \(A_c\) is cross-sectional area. This equation highlights their potential for high-power applications in emerging low-altitude transport networks.
Future trends in aircraft drive motors are closely tied to the evolution of the low altitude economy. Key directions include the adoption of rare-earth-free materials to reduce dependency on critical resources, which is vital for sustainable growth in the low altitude economy. For instance, the use of ferrite magnets in PMSMs can be optimized using the energy product equation: $$(BH)_{max} = \frac{B_r^2}{4 \mu_0}$$ where \(B_r\) is remanence and \(\mu_0\) is permeability. Additionally, digital twin technology and AI-based control algorithms, such as model predictive control (MPC), are enhancing motor reliability. The MPC objective function for motor control can be expressed as: $$J = \sum_{k=1}^{N} (x_k – x_{ref})^T Q (x_k – x_{ref}) + u_k^T R u_k$$ where \(x_k\) is the state vector, \(x_{ref}\) is the reference, \(u_k\) is control input, and \(Q\) and \(R\) are weighting matrices. This enables real-time optimization for low-altitude flight dynamics, reducing energy consumption by up to 15% in simulated eVTOL missions.
Thermal management is another critical area, as motors in the low altitude economy often operate under high loads. The heat dissipation equation: $$q = h A (T_s – T_\infty)$$ where \(q\) is heat flux, \(h\) is heat transfer coefficient, \(A\) is area, \(T_s\) is surface temperature, and \(T_\infty\) is ambient temperature, guides the design of cooling systems. Innovations in integrated cooling, such as direct liquid cooling, are emerging in patents to support continuous operation in urban air mobility scenarios. Moreover, the integration of wide-bandgap semiconductors like SiC and GaN into motor drives improves efficiency, as shown by the switching loss reduction: $$P_{sw} = \frac{1}{2} V I (t_{on} + t_{off}) f_{sw}$$ where \(t_{on}\) and \(t_{off}\) are switching times and \(f_{sw}\) is frequency. This advancement is crucial for the low altitude economy, where energy efficiency directly impacts operational costs and range.
In conclusion, the low altitude economy is catalyzing rapid advancements in aircraft drive motor technologies, with PMSMs leading in efficiency, BLDCs in affordability, and reluctance motors in sustainability. The patent landscape reflects a competitive race to overcome challenges like torque ripple and thermal limits, with future innovations focusing on material science, intelligent control, and cross-domain integration. As the low altitude economy expands, these motors will underpin the commercialization of eVTOLs and drones, enabling a new era of urban air mobility that aligns with global sustainability targets.