Issue 45 | Uncrewed Systems Technology Aug/Sept 2022 Tidewie USV Tupan | Performance monitoring | Bayonet 350 | UAVs insight | Xponential 2022 | ULPower UL350i and UL350iHPS | Elroy Air Chaparral | Gimbals | Clogworks Dark Matter

90 Dossier | ULPower UL350i and UL350iHPS “The oil pump is fixed to the crankcase, and directly driven via a shaft that mounts using a split connection on the front of the camshaft,” he adds. “The fuel pumps, on the other hand, are electromechanical devices from Bosch, and are widely used in FADEC engines.” After passing through the pump, the oil typically runs through the oil cooler. However, to avoid long warm-up times a thermostat checks the oil temperature, and if it is below 80 C, the thermostat switches two valves to send the oil on through a channel that bypasses the cooler. The oil then runs through a fine filter before passing into the main oil gallery that sits on the engine’s left side. Near here is an empty port where end-users can install or have customised another oil sensor if they wish. “From the main gallery the oil is delivered to the cylinder head,” Defoer says. “Every cylinder head has its own oil supply line, which is held in place by banjo bolts, with each line running from the oil gallery to the top of the head. “The oil enters the head and is sprayed onto the tops of the rocker tappets and valve stamps to lubricate and cool those parts directly. The oil then drains into the tubes where the pushrods are located, so from there it lubricates the cam followers, before draining back into the sump. “There are other channels that directly lubricate the camshaft, crankshaft bearings and con rods – the crankshaft is drilled with holes for routing oil directly to the con rods. And even indirect lubrication and cooling is generated through the ambient fog of oil inside the crankcase, so there’s never a lack of oil anywhere, and it is all eventually recovered by wafting back down to the sump.” Future plans ULPower’s engineers are particularly interested in ways to make their engines greener. To that end, the company is working with several customers on new configurations of its engines. Some of these are fully hybridised versions with alternators that can convert around 90% or more of its shaft horsepower into electricity, and plans are also moving forward on versions with seals and combustion chambers redesigned to run on alternative fuels such as hydrogen. “Later this year we’ll start a theoretical study with one of our university partners into what kinds of alternative and sustainable aviation fuels could be viable for our customers to use,” Defoer says. “Based on our findings there, we’ll start putting some of our spare engines on test benches, running them on the sustainable fuel types and adapting our fuel maps to see what they yield in terms of running costs, safety, lifetime and so on. “Then, wherever necessary, we’ll cut new metal to optimise how the engine runs on those fuels, so that when the time comes we’ll be able to offer the UAV market something sustainable, reliable and efficient.” August/September 2022 | Uncrewed Systems Technology UL350i/UL350iHPS Four-stroke Opposed four-cylinder Gasoline (Mogas minimum 95 octane on UL350i, minimum 98 octane on the UL350iS or UL350iHPS) Spark ignition Naturally aspirated Air-cooled (forced-air cooling on the UL350iHPS) Displacement: 3503 cc Bore and stroke: 105.6 x 100 mm Weight: 78.4 kg (90.4 kg on the UL350iHPS) Maximum power output: 88.2 kW at 3300 rpm (106 kW at 3500 rpm on the UL350iHPS) DC output: 30 or 50 A Compression ratio: 8:1 (8.7:1 on the UL350iHPS and other UL350 engines) TBO: 1500 hours Specifications The crankshaft directly drives the oil pump, and the use of a wet sump ensures that in addition to highly targeted lubrication, a ‘cloud’ of oil inside the crankcase keeps all the moving parts well-lubricated