Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

65 crankcase is that the propeller can be kept further from the ground more easily while being directly driven, compared to a conventional (automotive) crankcase design (reducing damage from grit and gravel during take-off and landing). This inverted configuration means the pistons thrust up into the cylinders. Also, the uniflow scavenging system means there are air ports around each cylinder, which are opened and closed by the passage of the piston, and poppet valves at the bottom of each cylinder, actuated by a camshaft near the bottom of the engine, above the oil sump. As the name indicates, uniflow scavenging has gas flowing in one direction only – downwards. Charge air enters through the air ports, and exhaust gases are drawn out through the poppet valves at the end of the combustion stroke. Induction is forced via a turbocharger-supercharger combination, with an intercooler positioned between the two to cool and densify air going into the engine. “Its currently-rated top speed is 2750 rpm, with 167 hp [124 kW] as its maximum output power,” says Mike Newton, director of ATI. “There’s no gearbox or clutch needed to drive the propeller since it’s designed as a direct-drive system; we wanted to eliminate as many potential failure points as possible. “On a lot of engine designs, the clutch can slip a bit on each firing pulse, so there’s a real risk that something will wear out or break eventually, but that’s eliminated with a direct drive.” In addition to the mechanical simplicity this entails – Newton estimates four man-hours to strip the engine, and four more to reassemble it – having no transmission or gearbox parts also meant saving weight, another key objective over the original design. The engine assembly and main radiator together weigh 118 kg; another 30.4 kg in total can be added by extra cooling units, hoses, a propeller (and nuts and washers for it), fasteners and through-bolts, and a straight exhaust pipe. Oil and coolant add a further 5.6 kg and 4 kg respectively. Cast LM25 aluminium alloy is used for the engine block, before it is heat- treated and machined to the specified measurements. “We’ve succeeded in making this about 80 kg lighter than engines of similar power output out there, which gives any UAV using it another 80 kg of payload capacity or 80 kg of fuel,” notes Phil Franklin, chief engineer at ATI. The WAM-167BB measures 914 mm at its longest, 528 mm in width and is 657 mm tall, with the centre of gravity between about the third and fourth cylinders, in the upper-rear of the system. To further improve simplicity and lightness, every WAM engine has incorporated indirect injection (IDI) in its fuelling system. “We could certainly integrate direct injection if an end-user requested it, which would probably reduce fuel consumption by 5%, but you’d be carrying 20-30% extra weight when you account for the extra complexity and Apple Tree Innovation WAM-167BB | Dossier Unmanned Systems Technology | October/November 2019 Enough components have been produced for three WAM- 167BB engines. The company typically has one or two complete examples at any one time running on its test rigs