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

84 Also, the dual-exit design of the Hall sensor makes for straightforward integration of two ECUs if the end- user wants a dual-redundant engine management system. Downstream from the throttle is the air manifold. ULPower casts its manifolds for the UL350 from aluminium for structural strength, before milling the cast parts down to thinner, tighter tolerances (which is critical for saving weight) before welding them together to a base plate that sits at the bottom. The designs have been optimised to ensure an even balance of airflow to all four cylinders. Upstream from the throttle is the air filter, which tends to be mounted and located in a way that helps maintain a safe internal temperature in the airbox. “The UL260 and UL350 actually use the same airbox, but we add some aluminium extension tubes to the UL350’s manifolds to compensate for the extra 8 cm of cylinder stroke of the latter,” Defoer says. For fuel spray, the engines are designed with multi-point injection rather than a single-point injector behind the throttle. Injector holders are installed atop the air manifolds running into the cylinder heads, which are fixed to the injectors to spray at angles of 45 º into the inlet tubes, mixing with the air as it flows from airbox to valve. “Also, the ECU pulses all four injectors at once, rather than timing each spray for each cylinder at individual, specific crank angles,” adds Defoer. “That’s the simplest way to do it from a programming perspective, and our tests and customer reports indicate that it works just fine, and that there’s no significant performance or efficiency gain to be had from going with a more computationally complex timing approach.” Engine management Keeping ECU development in-house is critical for the company, as it allows for constant adjustments and improvements to its programming. Also, all the fuel-air mapping is managed electronically in real time using maps embedded in the onboard data storage. “Every new prototype engine runs on the test bench for weeks, sometimes months. During that time we’ll change injection quantities, ignition timings, throttle widths and more, to observe how the engine performs at all points across its envelope and to determine how we can maximise safety, fuel economy and so on,” Denorme says. The ECU controls the engine’s timing and fuel-air mixture from start-up to shutdown. As a result, the cockpit of any crewed aircraft running on a ULPower engine has only a single lever – the throttle. The management system is designed as a full authority digital engine control (FADEC) module, which was developed from a blank sheet originally for managing rally car engines before being redesigned for aviation by an unnamed partner with experience in inferring differences in engine management approaches between vehicle types. “The FADEC system automatically sets the fuel mixture and ignition timing multiple times per second,” Denorme explains. “It will even fine-tune the fuel flow to compensate for changes in barometric pressure as well as inlet air temperature in the inlet manifold. That brings a tangible bonus in terms of cold and hot starts.” August/September 2022 | Uncrewed Systems Technology The air manifold is cast from aluminium for structural strength before being milled to save weight and then welded ULPower’s ECUs use data on crank position and speed, throttle position, oil temperature, manifold air temperature and manifold air pressure to manage the engine