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

82 Dossier | ULPower UL350i and UL350iHPS from billet,” Denorme says. “When we started 15 years ago, we sought to cast everything, but we wanted to get rid of the porosities we were getting in the cast parts because it led to too many weaknesses. “With high-quality billets we basically never get porosities. And as a side benefit, whenever we want to make or test modified engine parts – which is often – we don’t have to expend time or money on changing casting moulds; we just change the CNC machine’s programming. It’s so much quicker and easier that way.” Jakob Defoer, quality engineer at ULPower, says, “We also have extensive test benches, as practical experimenting and real-world results are much more central to our r&d than computer-based calculations and simulations. Having a five-axis milling machine means we can iterate new parts really quickly to test some new design idea or a customer’s request, then assemble it and throw it on the dynamometer to see what it turns up. “For the turbocharged UL520T for instance, we started with a basic turbocharger simulation, then did our calculations for the air densities the customer wanted to fly at. We then quickly went to testing in order to optimise the wastegate and adapt the mappings in the ECU, followed by some failure mode and effect analyses to make the system as safe as possible, before programming the safety modes into the ECU and going to test flights. “That’s a very component-specific example, but it’s representative of our overall engine development philosophy, and how differently we can modify each of our designs for different customers and operating environments. As a further example, the manifolds are fairly different for the UL520T versus our other engines: a naturally aspirated engine sucks air in, whereas a turbocharged engine has its air pushed in, so some very different fluid dynamics had to be accounted for when we developed the airbox for that system.” Starting and electric power The standard UL350 comes with a 1.2 kW starter. “It’s a Bendix-type generator with built-in solenoids,” Defoer says. “It has two connectors with some quite big AWG 4 cables, so the battery must be able to handle that, especially if the user wants to have enough current for cold-crank starting. “Also, the starter’s ring gear is bolted directly onto the crankshaft for direct drive, so the pilot or autopilot can start the engine right away without belts or chains to worry about. Once the ECU detects some rpm, it responds by starting to inject the fuel quantities for standard fuel-air mixtures, and the engine starts running.” The UL350 comes with a standard generator of 30 A, or a 50 A generator can be installed if preferred. For UAVs running one or more sensor payloads, GPUs, comms relay antennas or other electronics that require high power, an external alternator of up to 4.2 kW can be integrated. Throttle and fuel The throttle body and lever are laser-cut from aluminium before being welded together to precise tolerances in order to meet the airflow and weight targets. “Naturally it’s critical to our engines’ performance targets that we can always bring in the right quantity of air, so for our four-cylinder engines we use a 38 mm throttle, while on the six-cylinders we go with a 45 mm throttle,” Defoer says. “It’s a single-lever throttle, as that makes it very simple to control. Until 2 years ago we used a potentiometer for throttle position sensing on the four cylinder engines, but we have since switched to a Hall effect sensor. It’s brushless and hence suffers much less wear than the potentiometer, making it more reliable and long-lasting.” August/September 2022 | Uncrewed Systems Technology High-quality aluminium billet is used to cut most engine parts, enabling quick prototyping of new components and minimising porosities in the metal