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74 Dossier | Flygas Engineering GAS418S well as naturally aspirated types. It was in 2008, while looking for valuable niches to apply their skills to, that Gamberini and his team first had the idea to draw from this broad area of technical experience to design an all- new UAV engine to suit what they saw as the biggest demands of the unmanned aviation market. He and his colleagues leaned particularly on lessons learned during the development of the GAS 252 engine, and from Gamberini’s experience of making race engines, not to mention some additional years he’d spent flying light sports aircraft as recreation. “Right from the start, we had a few key targets we wanted to tailor the engine to, given our specialisations across redundancy and reliability,” he recounts. “We knew the engine had to produce 180 bhp, and that it would need to run on gasoline, preferably 95 octane or higher – not diesel, JP5 or any kerosenes. If you’re not making a turbine engine, you shouldn’t be running on diesel or heavy fuels.” Davide Zucchini, engineer at Flygas, emphasises this point. “The freezing point of diesel [JP8] is just below -46 C, which is too high for the altitudes that UAVs fly at for wide-area surveillance, mapping or search & rescue. It’s unsafe and entails having to heat up your fuel. Using a heater wastes energy, and takes up weight and space that could be used for an additional payload or more fuel if you’d just gone with gasoline from the start, which freezes at -95 C.” Also, the company wanted the engine to be able to serve both fixed-wing and helicopter-type unmanned aircraft. To that end, the GAS418S can be mounted so that its crankshaft points horizontally or vertically, with the engine’s mounting points and oil sump changing depending on the type of craft it is for. Development of the engine proceeded gradually over the next decade, with Flygas using profits from its sales of components and engineering services to fund its r&d. The GAS418S first became commercially available around late 2019 after undergoing several hundred hours of bench and flight testing. Such is the company’s emphasis on reliability and longevity that the GAS418S has a TBO of 1200 hours – notably long for a gasoline engine. The various mechanical drives for ancillary components have all been incorporated into the engine to make this lifespan possible, along with various other key engineering features. Its maximum power is achieved at 5800 rpm, with its redline crank speed at 6200 rpm; its standard operating speed is 5000 rpm. Peak torque meanwhile is 224 Nm at 4200 rpm, and operating torque is 185 Nm at 5000 rpm. Gamberini notes, “These performance points were very deliberate choices for the markets we see the engine being used in. For instance, we’re confident that 4200 rpm is the limit of what’s optimal for helicopter blades in terms of speed and torque, and 5800 rpm is best for gasoline engine crankshafts to avoid drag-induced losses, to avoid the need for gearboxes for every single ancillary component, and to avoid other problems.” Gear-driven supercharger Gamberini notes that most forced induction systems in the aviation world (including in UAVs) rely on a turbocharger, sometimes with an accompanying supercharger February/March 2022 | Unmanned Systems Technology The company is well-known for its gear-driven superchargers, which are used in various engines in place of their alternative superchargers or natural aspiration We’re confident that 4200 rpm is the optimal speed and torque limit for helicopter blades, and 5800 rpm is best for gasoline engine crankshafts