84 Dossier | Electric Flytrain EFT-Hybrid-1x their UAV. The DC supply from that goes to a battery pack which is managed by a BMS. Lastly, a Hybrid Control Unit (HCU) developed by EFT acts as the master controller for the powertrain. “We are optimising the Hybrid-1x for UAVs with aMTOWranging from70 to 150 kg,” Kahnert adds. “Switching from batteries to our powertrainwith a prudently sized fuel tank should extend their flight times from20-30minutes tomultiple hours, making it possible for them to rival crewed helicopters in long-endurance applications such as aerial logistics, surveillance and search & rescue.” Powertrain concept The company chose a hybridised gasoline four-stroke boxer configuration, principally to ensure that only mature, tried-and-tested technologies were incorporated into its first product. The route of hydrogen for instance, be it a fuel cell or hybridised IC engine running on hydrogen gas, was not taken because not every component would have been matured enough and have the availability to satisfy EFT to allow the stability of production and maintenance of such power systems. “However, subsystems for hybridelectric IC powertrains are widely understood, and their supply chains are quite stable,” Kahnert says. “That was the first best guarantee that we could achieve our goal of putting together an efficient turnkey package that would integrate easily and work consistently. “We also researched powertrain configurations that were popular across the UAV market, and found four-strokes to generally offer a higher measure of durability than two-strokes. That was really important if we were to achieve a reasonable parity with all-electric powertrains in terms of reliability. “There will be some higher maintenance because it’s undoubtedly more mechanically complex than a straight battery-ESC-motor set-up, but we still wanted to limit the extent of that as much as possible.” After selecting HC-Concepts as the engine supplier, EFT proceeded to design its solution as a series hybrid, with as much of the shaft power as possible being turned into electrical power via a shaft-mounted alternator. This approach, as opposed to a parallel hybrid or others with an open protruding shaft, would allow EFT to produce a power unit that could serve multiple UAV configurations and save end-users the work of optimising their UAVs for the relative quantities of shaft and electrical output power (or vice versa). That would also be the ideal choice for EFT’s target customers. To further optimise its solution for these users, the EFT-Hybrid-1x is also designed with an active thermal management system, with a forced-air system for keeping the combustion and electrical components at safe temperatures in the absence of any rush of cooling air. “That takes the cooling burden off our end-users’ shoulders, which becomes especially important during extended hovering periods when the engine and alternator will experience high power demands for prolonged times,” Kahnert says. “The cooling system therefore took up a huge part of our testing and iteration focus to ensure the whole powertrain could be kept within a safe temperature range, even when running at full continuous power.” Development timeline The company’s first research into promising hybrid powertrain technologies started in January 2021. Around 5-6 months later, Kahnert and his colleagues had largely agreed on their preferred configuration and key partners, and the first proof-of-concept prototype was being tested on a workbench by autumn 2021. That produced copious data on ways to optimise the solution, particularly in terms of customising and improving the various components to work together as if they had all been designed by a single integrated powertrain OEM. “That pushed us into our next phase, for our second-generation prototype, for which we started working very closely with HC-Concepts,” Kahnert explains. “That helped us really improve the HCU.” The second prototype was ready for testing by April 2022, after which EFT began the packaging stage, in which all the powertrain components were integrated into a physical form that could conceivably be sold as a product, including fuel tanks and June/July 2023 | Uncrewed Systems Technology The EFT-HCU-1x, or Hybrid Control Unit, has been developed in-house as the master controller of the powertrain
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