10 June/July 2023 | Uncrewed Systems Technology A UK company has developed an electric ducted fan (EDF) motor with a specialist blade geometry for low-noise UAV operation while maintaining high efficiency (writes Nick Flaherty). Greenjets is a spin-off of consultancy Blue Bear Systems Research, and is part of a UK project called InCEPTion to develop a quiet electric motor for large aircraft. It is developing a range of motors based on a scalable architecture that is optimised for customisation. The first is a small EDF, the IPM5, which has an outer diameter of 200 mm and weighs 0.75 kg with 5 kgf of thrust using a commercial motor. The ducted design provides more energy efficiency than a rotor-based design, and the company is also developing an integrated inverter and battery pack to further improve the end-to-end efficiency. The motor can also be used with a hydrogen fuel cell or a hybrid gasoline engine that uses a generator to provide the electrical power. This is already being used by one utility customer for a monitoring UAV that can fly for up to 20 hours over urban areas. The ducted propulsor also avoids safety problems with the parachute that the aerodynamics of the EDF to the characteristics of the power supply.” “The ducted architecture enables us to harvest the heat generated by the engine’s internal components to boost the overall system efficiency,” said Dr Guido Monterzino, CTO and co-founder of Greenjets. “The net effect of this is that a portion of the heat rejection turns into thrust.” The company plans to make 500 of the IPM5 propulsors by the end of this year, using suppliers from the motorsport industry, and already has 2000 on order. It has been tested in flight trials on multiple Blue Bear airframes and on an eVTOL in Germany. “We are not doing the manufacturing in-house but we are doing some of the assembly and all the functional testing and QMS inspection on each unit,” said Manohar. “We have a range of partners [from the motorsport industry] for the composites, motors, inverters and other components, and one of them has taken on the assembly line while we still do the final sign-off.” The initial IPM5 is designed for fixedwing and hybrid platforms, but the company is developing a derivative model for multi-rotor designs. Airborne vehicles Low-noise ductedmotor is required for flying over urban areas. The company is also working on a 50 kgf thrust version, the IPM50, that weighs about 8 kg, for larger uncrewed aircraft. The modular design can be modified to provide 20-80 kgf of thrust with scalable components and accordingly different all-up weights. The EDF uses a proprietary modular multimotor design for redundancy, and has been designed to easily scale the size yet still use the same tooling. The blades of the ducted fan have been designed using psychoacoustic modelling, which is where their shape is optimised to reduce the particular frequencies that people find annoying. It has been tested in an anechoic chamber by the Salford Acoustics Lab in Manchester, UK, and wind tunnel tested by the Cambridge Whittle Lab, who are partners in the InCEPTion project that still has a year to run. “We use the term electric propulsor rather than electric jet engine, as that describes what we are all about – converting electricity to thrust,” said Anmol Manohar, CEO and cofounder of Greenjets. “The electricity can come from anywhere – battery, fuel cell or generator – and we match The first electric ducted fan fromGreenjets is the IPM5, which produces 5 kgf of thrust
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