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

82 A capacitive discharge ignition system provides for combustion of charge. As mentioned, two spark plugs sit at the top of each combustion chamber, partly for redundancy. However, the ECU is programmed to have both plugs fire simultaneously in standard operation, with each sitting slightly spaced apart. This gives a more homogenous spread and wave of combustion across the compressed charge following ignition. Cooling is achieved via a high- pressure water circulation system. The water pump is typically installed on the front of the engine along with a cooling fan, and a gear on the crankshaft is dedicated to driving a gear and shaft for the pump at a 1:1 rotation ratio to ensure the desired circulation pressure. Crank gears By design, the crankshaft fits very tightly inside the crankcase, with the engine block having been designed to be as small as possible to reduce the engine’s footprint and ease its integration into UAVs. Unusually for UAV engines (in our experience), the GAS418S uses a monolithic crankshaft. This is a deliberate choice by Gamberini, who feels that higher engine powers require stronger ones to ensure a long engine life. “At lower power outputs, you can use a composite crankshaft,” he says. “But when you increase the power and torque, you will generally need to increase the flywheel mass to stabilise the crank, which adds weight and material cost, unless you just use a single-piece crankshaft, which is inherently stronger and more stable. “Exact figures would vary from engine to engine, but for ours we save a few kilos of primarily flywheel weight by using a single-piece crankshaft, along with our supercharger, although an engine of similar size and configuration could probably get away with using a multi-piece crankshaft if torque never exceeded 200 Nm.” Flygas is reluctant to give exact details of the crank, as its design and engineering are key to the reliability of the mechanical drives of the various February/March 2022 | Unmanned Systems Technology Dossier | Flygas Engineering GAS418S The crankshaft is constructed with up to 19 gears, including the system of starter gears pictured here Given how critical the mechanical drives are to the functioning and lifespan of the engine, we can’t leave any oiling aspects to chance One of the casings used for the GAS418S’s water coolant pumps