Issue 54 Uncrewed Sytems Technology Feb/Mar 2024 uWare uOne UUV l Radio and telemetry l Rheinmetall Canada medevacs l UUVs insight DelltaHawk engine l IMU focus l Skygauge in operation l CES 2024 report l Blueflite l Hypersonic flight

68 moving,” Webb says. “Each cylinder has a glow plug, as with most diesel engines, which we normally turn on for 10 seconds before starting for preheating.” Much of what follows, however, is untraditional for modern UAV engines, as the DHK180 has no ECU for managing the fuel and air quantities going into the engine, for the simple reason that it does not need one. Instead, it has been designed to operate using uncomplicated mechanical systems, which feature a minimal number of potential failure points and significant failovers or redundancies compared with many other power units. Like the WAM-167BB two-stroke diesel from Apple Tree Innovations (ATI), featured in issue 28 (October/November 2019), the DHK180 is a lever-controlled engine, with just a single lever at the back for toggling the quantity of fuel delivered to (and hence power produced by) the engine. A fitting sits at the back of the DHK180, where a control cable or linear actuator can connect to the lever, through which the autopilot can interface with the engine in a simple, straightforward manner. Fuel delivery occurs via two main pumps: a low-pressure pump atop the engine draws fuel from the UAV’s tanks and feeds a high-pressure fuel pump (HPFP). The low-pressure system is a gear-type pump, driven directly via an internal gear set on the back of the engine. “In all aviation installations, you’re required to have an electric pump as well for redundancy, and I’m fairly sure you’d want the same in an uncrewed application for redundancy, so we can integrate one of those if needed,” Webb adds. The HPFP assembly is on the back of the engine, attached to an accessory cover that houses a plethora of gears for driving accessory devices (and the aforementioned control fitting is on the bottom of it for mechanically managing the HPFP), all mounted externally for ease of maintenance. Four steel lines run from the HPFP – one to each injector – through which fuel sprays directly into the cylinders, as in all diesel engines. Additionally, a considerable amount of fuel bypasses the injectors and returns to the tank (also typical in diesel engines), but rather than returning directly, as is conventional, the DHK180’s bypass fuel is routed to the injector heads to cool them first. That heated fuel can, if needed, be used to pre-heat the incoming fuel through a heat exchanger (if flying in cold regions or weather fronts, for example). “Inside the HPFP assembly, running into each steel line and hence each cylinder, is its own independent plungerbarrel system; those piston back and forth to govern fuel delivery to the injectors, and are managed via a very small and simple camshaft – not at all the big kind you’d see controlling the valves in a four-stroke – and that camshaft is driven via a spline running off the back of the crankshaft,” Webb explains. Mechanical control The aforementioned control lever connects through a mechanism to each of the four high-pressure unit pumps, which controls the effective stroke of the plungers, thus determining (completely mechanically) how much fuel is injected with each cycle. “In essence, we have four independent fuel-pumping systems, with no electronics needed,” Webb concludes. “ECU hardware, software and wiring harnesses are complex, and hard for technicians to fix in the field. We designed our engine so any aircraft mechanic can fix it with hand tools anywhere around the world. “There’s no widespread maintenance network out there for aviation ECUs. You can’t turn up at an aircraft mechanic and expect them to know what to do with an ECU-managed compression-ignition engine. They’re not going to have spare MAF or MAP [mass air pressure] sensors in their inventories; they’re not going to have the kind of training in software programming for that.” He adds that in many cases, the failure of an ECU, a high-pressure fuel rail or a key sensor results in the failure of the engine, and hence the UAV. But if one of the four high-pressure fuel pumps on this engine should mechanically fail, only 25% of power is lost (and tests show no additional vibration, thanks to the three remaining power pulses per rotation), enabling the UAV to either attempt to complete its mission or safely return to land. Lastly, the absence of an ECU and sensors reduces the electromagnetic February/March 2024 | Uncrewed Systems Technology Dossier | DeltaHawk DHK180 The fuel injectors are mechanical, with lever controls determining the stroke of the plungers and hence injection quantities