Avadi Engines | Engine dossier his team in how well they would integrate and run at the ends of the gear cranks. As a final point, Dardalis adds that past its rotary valving, the exhaust system is entirely conventional and will run with any choice of pipes or mufflers. Cooling down A forced air-cooling effect on the combustion chamber is created using the rotating cylinder. Two concentric sets of fins are installed near the top of the engine: one on the cylinder and one below the stator. As the cylinder and its fins rotate, their motion relative to the stationary stator fins acts as a blower, centrifugally pushing air outwards, radially from the stator fins. A series of ports running axially, up through the stator and directly above the fins, serve as inlets for air to be drawn in as the air pressure inside the stator fins drops. “The cylinder head is a different story,” Dardalis notes. “We currently have fins in the top of the cylinder head, which run shallow above the transfer port and deeper around it, and those inherently dissipate heat. “But, with some CFD and tuning for efficiency in subsequent iterations, it will also create a forced-air effect as the head rotates, likely via some ports we will cut into the side to serve as cooling air inlets and outlets once we’ve identified spots where leakage of oil from the transfer port to the outside won’t be an issue.” Looking ahead With the first few prototypes of the XMD-250 now complete, Avadi has several industry partners awaiting the results of its first testing runs (currently under way) such that trials in their UAS platforms can be discussed and arranged for applications ranging from military operations to commercial logistics. Avadi anticipates that it will pursue another funding round through Startengine.com before the end of this year, which is aimed at gathering sufficient runway to accelerate its optimisations. The company will then scale up production of its engine to meet its backlog of initial waiting list orders the following year. 77 Uncrewed Systems Technology | August/September 2024 XMD-250 Four-stroke Spark-ignited Single-cylinder Naturally aspirated Rotating cylinder valving Air-cooled Hard chrome liner Weight: 14.1 kg Bore: 7.8 cm Stroke: 5.2 cm Maximum continuous power output: 13 kW Maximum continuous torque: 31 Nm Maximum continuous speed: 4000 rpm Some key suppliers CNC machines: Haas Dynamometers: DYNOmite CAD software: Autodesk CAD software: Dassault CFD software: Convergent Science Various engine components: McMaster Carr Engine development support: NWUAV Pinion gears: Batom (AKA Great Taiwan Gear) Bearings: SKF Oil valves: Swagelok Starter-generator: ePropelled ECU & EFI: Wahlbro ECU & EFI: NWUAV Specifications Two sets of concentric fins create a forced-air blowing effect to cool around the combustion chamber
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