Helix and Zoerkler develop compact eVTOL propulsion unit

A geared electric propulsion unit has reduced motor diameter by half while supporting demanding lift and cruise requirements.

Helix has collaborated with Zoerkler to develop and validate a geared Electric Propulsion Unit (EPU) for advanced air mobility applications, combining high-power-density electric motors with lightweight transmission technology.

Designed for lift, cruise and tiltrotor aircraft configurations, the EPU addresses one of the longstanding challenges of eVTOL propulsion. High-torque applications have traditionally required direct-drive systems, resulting in larger-diameter and heavier motors.

By integrating Helix's motor technology with Zoerkler's transmission, the partners have developed a 32.2kg propulsion package capable of delivering high torque in a unit measuring just half the diameter of an equivalent direct-drive system.

The initial EPU delivers 100kW and up to 1,600Nm of torque in lift applications, while providing 250kW continuous and 400kW peak power in cruise configurations.

With transmission efficiency reaching 98%, the motor can be significantly narrower and lighter than a direct-drive alternative. The resulting 26cm-diameter package offers aircraft designers greater flexibility while helping reduce nacelle size and aerodynamic drag, supporting improved payload and range performance.

“This new EPU shows that when brought together, best-in-class motors and transmissions can unlock a far lighter and more compact solution than direct drive systems,” says Derek Jordanou-Bailey, chief engineer for aerospace at Helix. “By combining the world-leading power density of Helix motors with Zoerkler's lightweight and precise transmissions, this EPU provides advanced air mobility applications with a compact, low-mass solution that meets and even exceeds their range and payload requirements.”