Unmanned Systems Technology 042 | Mayflower Autonomous Ship | Embedded Computing | ElevonX Sierra VTOL | UUVs insight | Flygas Engineering GAS418S | Ocean Business 2021 report | Electric motors | Priva Kompano

76 that is typically belt- or chain-driven, but ‘mechanical’ (as in gear-driven) superchargers are rarely the sole choice nowadays. As he recounts, they were popular in aviation from 1925 and through World War II, but fell out of favour compared with turbochargers owing to cost considerations – much like elliptical wing planforms and similarly advantageous aeronautical innovations of the age. “While I was working with Victory Team, I gained an extensive understanding of forced induction systems from their supplier, Garrett Turbochargers,” Gamberini says. “And I’m still very enthusiastic about using turbochargers when appropriate – they’re often less costly and easier to install than mechanical superchargers. But my experiences of aviation engines by 2002 convinced me that gear-driven superchargers are better for aircraft, not least because of reliability.” Zucchini adds, “A turbocharged engine will suffer higher exhaust temperatures and back-pressure because of the turbine. That increase in back-pressure reduces efficiency and power output, and the typical countermeasure is to consume more fuel. Our engine by contrast has no back-pressure, exhaust temperatures are kept low, and we sustain our forced induction much more reliably than belt- driven or chain-driven superchargers. “As an example, Rotax’s 914 engine was carburetted and turbocharged, and needed to use a TCU [turbo control unit] to cut the turbo power under certain conditions, such as when the exhaust temperature would pass 920 C, because at that point it could induce knocking in the combustion chamber. “Without question we draw some losses by running off the crankshaft’s power, but the net efficiency and reliability with our system over the length of professional UAV missions is still higher than you’d get with a turbo.” In addition, the company is firm on its choice of centrifugal-type superchargers over Roots-type blowers, Lysholm twin screws and other ‘volumetric’ (positive displacement) superchargers. Numerous reasons are given, but most strongly emphasised is weight: Gamberini and his team see centrifugal blowers making for very light superchargers compared with most other types. “The supply of air you get from centrifugal blowers – that is, the pressure and flow – also closely matches what the engine needs, when it needs it,” Gamberini adds. “They are highly efficient in power consumption and thermal terms, which is especially important for aviation; there’s a gulf in power requirements between take-off and cruise speeds. February/March 2022 | Unmanned Systems Technology The gear-driven mechanical supercharger is intended to overcome numerous key drawbacks of using a turbocharger or other superchargers The GAS418S’s 70 mm- diameter throttle and barometric control unit If we want to use a small flywheel but maintain a smooth, stable torque, we first have to increase the cylinder count – four helps here