Issue 45 | Uncrewed Systems Technology Aug/Sept 2022 Tidewie USV Tupan | Performance monitoring | Bayonet 350 | UAVs insight | Xponential 2022 | ULPower UL350i and UL350iHPS | Elroy Air Chaparral | Gimbals | Clogworks Dark Matter

81 costly or difficult to replace, while still seeking to push the performance of their engines as far as possible. In 2006, when Denorme was satisfied with the fruits of their r&d, ULPower was officially founded as a company and its first UAV engine, the UL260, was introduced. While ULPower now produces a number of engines, the UL350 is its best-seller in the UAV world, hence our focus on it here. The standard-issue UL350, styled the UL350i, is a four-stroke, spark-ignited gasoline engine that weighs 78.4 kg when fully built with all ancillaries. It is a flat-four boxer engine that displaces 3503 cc (from which it takes its name) and produces 118 bhp (86.8 kW) of peak power. In addition to investigating the UL350i, we will also investigate a novel forced-air cooling system featured on the company’s UL350iHPS (High Power System), a version intended particularly for rotor-wing applications where no oncoming rush of airflow is typically available to help cool the engine. In addition to aiding safe operations on helicopter and multi-rotor aircraft, the UL350iHPS produces up to 150 bhp thanks to a modified camshaft and manifold. Overview and philosophy The UL series has four key members, with variants within each one. In addition to the UL350, they are the UL260, the UL390 and the UL520, with their names corresponding approximately to their capacities, like the UL350. All the engines follow a very similar design style and engineering philosophy, not least in being flat-opposed four- stroke spark-ignited types, and while the UL260 is a four-cylinder the UL390 and UL520 are six-cylinder systems. Crankcases, cylinder heads, combustion chambers, crankshafts and other core parts are recognisable from one model to the next, with common specs such as a 105.6 mm bore and a peak crankshaft speed of around 3300-3500 rpm. Also, common operational features include electronic spark ignition for variable timing, electronic multi- point fuel injection for pressure and temperature compensation, and the possibility of integrating the forced-air cooling system for more power. As mentioned, ULPower’s first engine was the roughly 72 kg, 97 bhp UL260, completed and commercialised in 2006. New variations of this design across the displacement classes of the UL series have been regularly unveiled since then to serve customer requests such as for higher power and acrobatic flying. Its latest engine, the UL520T, was unveiled in 2021. This is a version of the UL520i featuring a custom turbocharger for improved power and high-altitude operations, weighing 108 kg when equipped with all the typical accessories and outputting up to 200-220 bhp depending on the exact configuration. ULPower comments that the UL520T could therefore also be ideal for the burgeoning generation of very large, heavy-lift UAVs for air freight operations. The UL350i itself was launched in 2009, with the UL350iHPS following in 2010. Around 80% of ULPower’s engine parts are produced in-house, with the company’s five-axis CNC milling machine and automated production lines for instance being key assets for cutting aluminium and other metals; steel parts are made by Ropa, one of ULPower’s shareholders. A few remaining treatments and parts come from some subcontractors in Belgium and the US. “Most parts in the engine are cut ULPower UL350i and UL350iHPS | Dossier Around 80% of ULPower’s engine parts are produced in-house, with its automated production lines for instance being one of its key assets Uncrewed Systems Technology | August/September 2022 ULPower makes numerous engines with similar designs and modular components. The largest and most powerful is the UL520T (pictured), recognisable for its six cylinders and turbocharger