Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

26 Construction The construction of the DriX is based on several different resins variously reinforced with fibres of glass, carbon and aramid. Eudeline is cagey about how and where they are used, and in what combinations, because their properties are key to suppressing the propagation of noise and vibration through the structure and therefore to the quality of the data the DriX can ultimately generate. That is especially true for the drop-keel, as the materials damp down vibrations to the extent that there are almost none at the gondola, he says. One of the composite construction processes iXblue uses is vacuum infusion moulding. This is a closed-mould process that uses only atmospheric air pressure to force the resin into the mould containing the fibre reinforcement. The flow of the resin is affected by its viscosity, the permeability of the fibre layers and the difference in pressure between the atmosphere and the evacuated mould. The method produces repeatable results so long as those three parameters are held constant each time. It is also considered a good way to make consistently strong parts, as it ensures a high fibre-to-resin ratio with few or no voids – spaces that the resin fails to reach. It is flexible as well, in that it can be used with two-sided moulds, single-sided moulds (with bagging film sealing the otherwise open side of the mould) and soft, envelope-style vacuum bags. The engine The propulsion system is centred on a Nanni N4.38 naturally aspirated marine diesel engine rated at 37.5 hp. Based on a Kubota engine modified for marine operation by Italian company Nanni, the N4.38 is a 1498 cc four-cylinder, four-stroke, liquid-cooled engine with mechanical indirect fuel injection and a dry weight of 153 kg. It draws fuel from a 250 litre tank at the stern. The iXblue team chose it because it is one of very few small engines designed for heavy-duty operation; most are intended for leisure craft. Eudeline says, “We were looking for something that could be used in a workboat, and this is the best compromise we found.” He explains that iXblue wanted a small engine because they generate less noise, and reducing noise at source means that less of the weight, volume and financial budget has to be spent on quietening measures downstream. “We almost don’t hear the engine at the gondola,” he says. The engine and driveline are mounted on vibration- and noise-absorbing silent blocks, an approach that’s widely used in the construction of submarines and the ships that hunt them. As well as quietness, the engine’s duty cycle is also critical. According to Nanni, the N4.38 is rated at up to 3000 operating hours per year with a load factor of up to 40%. It stipulates that the engine should run at full power for no more than one hour in every 12 operating hours, with the remaining time at or below cruising speed. Its rated speed is 3000 rpm, while it makes its 94.8 Nm peak torque figure at 2200 rpm and idles at 850 rpm. The engine drives a single propeller via a conventional propeller shaft. Although this can be regarded as a April/May 2019 | Unmanned Systems Technology The Nanni N4.38 diesel engine installed in an early DriX prototype. It was chosen for its low fuel consumption, quietness and ability to run workboat-like duty cycles (Courtesy of iXblue)