The selection of propeller diameter and blade count for eVTOLs (Electric Vertical Take-Off and Landing Aircraft) directly determines the aircraft's thrust efficiency, endurance, flight safety, and airworthiness compliance. Unlike traditional fixed-wing aircraft or helicopters, eVTOLs must balance the high thrust demand for vertical take-off and landing with the high efficiency required for cruise flight. Their propeller parameter design must be based on multi-condition adaptation and synergistic optimization with the power system to achieve a balance between performance and practicality. Therefore, scientifically planning the diameter range and blade count configuration for different application scenarios is a critical link in eVTOL R&D and design.

eVTOL Propeller Diameter Range and Classification

Propeller diameter is a core parameter affecting lift output. A larger diameter increases the disc area, allowing more air to be moved at the same rotational speed, generating stronger lift. It can also meet lift requirements at lower RPMs, helping to reduce noise and energy consumption. However, an excessively large diameter increases the aircraft's volume and weight, reduces maneuverability, and may cause interference with the airframe structure or surrounding obstacles during take-off, landing, or hovering.

Based on eVTOL flight modes and application scenarios, propeller diameters can be classified into three categories.

1. Small Diameter Propellers (Diameter < 0.8m)

The advantages of these propellers are high maneuverability and high RPM, making them suitable for scenarios with stringent agility requirements. The small blade inertia allows for rapid response to speed changes, enabling agile attitude adjustments. In terms of size, they allow for compact layouts, facilitating the installation of multiple propellers around the airframe to form a multi-rotor redundant power system. However, limited by disc area, small propellers have lower lift efficiency per unit. To meet high payload demands, higher RPM is needed, which increases noise and energy consumption.

These propellers are typically used for small multi-rotor eVTOLs, suited for urban short-distance commuting and low-altitude tourism where high flexibility and spatial adaptability are required.

2. Medium Diameter Propellers (Diameter 0.8m - 2.0m)

Medium diameter propellers balance lift efficiency and maneuverability and are currently the mainstream choice for most eVTOLs. Their disc area is moderate, providing considerable lift at medium RPMs, with balanced energy consumption and noise. This size is highly adaptable, suitable for both multi-rotor configurations for low-altitude short-distance flight and tilt-rotor configurations for medium-to-long-distance flight, by adjusting blade count and airfoil. Structurally, they do not excessively increase the aircraft's lateral dimensions, relaxing space requirements for take-off and landing.

These propellers are the mainstream choice in the eVTOL field, balancing lift and maneuverability for various scenarios like urban/suburban commuting and medium/small cargo transport. For example, YIVTOL an 8-axis 16-rotor design with propellers approximately RAYI 57-64 inch carbon fiber propeller.

3. Large Diameter Propellers (Diameter > 2.0m)

The core advantage of large diameter propellers is ultra-high lift efficiency, generating massive lift at low RPMs, significantly reducing energy consumption and noise per unit of lift. They are primarily suited for eVTOL scenarios requiring heavy payloads and long endurance. However, limitations are evident: firstly, their large size requires spacious take-off/landing areas, preventing agile movement between urban buildings; secondly, large blade inertia leads to slow RPM response, resulting in poor aircraft maneuverability; thirdly, high structural strength is required, needing lightweight, high-strength materials to withstand centrifugal forces, increasing manufacturing costs.

Constraints for Diameter Selection:

• Structural Compatibility: The airframe height, landing gear design, and folding mechanism (if any) directly determine the maximum diameter to avoid blade ground contact during taxiing or VTOL.

  
  

• Power Matching: Excessively large diameter increases rotational inertia, causing a surge in motor starting load. It must be precisely matched with motor torque and RPM range to avoid efficiency decay.

  
  

• Condition Adaptation Differences: Propellers for cruise need to balance high-speed performance. Excessively large diameters can cause wave drag. Therefore, lift-and-cruise configurations often use a dual-system design: "large diameter VTOL propellers + small diameter cruise propellers," with cruise propeller diameters typically controlled between 0.8-1.5 meters to optimize high-speed efficiency. For ducted tilt-rotor eVTOLs like Lilium, to adapt to safety requirements in dense urban areas, small blades (diameter < 0.3m) are used, amplifying thrust efficiency through the duct structure, theoretically increasing power demand by 41% compared to open propellers.

  
  

eVTOL Propeller Blade Count Selection and Adaptation Scenarios

Blade count is a core parameter that works in tandem with diameter. For the same diameter, changes in blade count directly affect lift characteristics, noise levels, and structural complexity. Different blade counts are suited for significantly different eVTOL applications.

1. Two-Blade Propellers: Preferred for Lightweight, Short-Distance Scenarios

Two-blade propellers are the simplest structurally, offering light weight, low drag, and high efficiency. At the same RPM, blade loading is relatively low, and airflow interference is minimal, generating lift with lower energy consumption. They are ideal for small multi-rotor eVTOLs focused on urban short-distance commuting, which typically have light payloads (1-2 people), a flight radius under 50km, and high requirements for flexibility and endurance efficiency.

2. Three-Blade Propellers: A Balanced Solution for Multiple Scenarios

Three-blade propellers are the most widely used type in the eVTOL field. Compared to two-blade propellers, they offer higher lift density; at the same diameter, three blades can output greater lift, meeting medium payload demands. They also provide stronger flight stability, with more uniform airflow distribution over the disc during hover and low-speed flight, effectively reducing aircraft attitude jitter. They are suitable for multi-purpose eVTOLs balancing passenger transport and small cargo, such as 3-5 seat regional short-distance aircraft or low-altitude cargo drones with 50-200kg payloads. Tilt-rotor eVTOLs also often use three-blade propellers to provide stable lift in rotor mode and reduce drag in fixed-wing mode. For example, for commuting between urban and suburban areas, three-blade propellers can balance payload requirements with performance needs for high-speed cruise and low-altitude hover. 

3. Four-Blade and Multi-Blade Propellers: Essential for Heavy-Lift, Long-Endurance Scenarios

Four-blade and higher multi-blade propellers offer powerful lift output and excellent stability. Pairing multi-blade design with large diameters further enhances air utilization of the disc, generating massive lift at low RPMs, significantly reducing noise and energy consumption. However, multi-blade propellers are structurally more complex, and increased interference between blades adds drag, requiring precise airfoil design and blade spacing optimization. They are mainly used for heavy-lift cargo eVTOLs and long-endurance intercity aircraft.

Conclusion

In summary, during selection, a balance between lift, energy consumption, and noise must be found based on the aircraft's payload, endurance, and maneuverability requirements. Multi-rotor configurations are more suitable for small/medium diameters with multiple propellers, while tilt-rotor configurations need to balance performance in both rotor and fixed-wing modes, prioritizing medium-diameter three-blade propellers.

With advancements in material technology and aerodynamic design, eVTOL propellers will develop towards lighter weight, higher efficiency, and lower noise. The selection of diameter and blade count will also more precisely match diverse low-altitude traffic needs, promoting the eVTOL industry's transition from experimental verification to commercial application.