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

72 temperatures. Outside airflow is always going to hit one face of the cylinder first. By the time that air flows around to the other side, it has been heated, sometimes with a delta of 2-3 C. “Add to that the further flow distance of an inline engine or a boxer with four or more cylinders, and you’ll find that aircooled engines experience extraordinary thermal management shocks, and need sloppy clearances to compensate for the metal expanding and contracting. It’s not unusual for high-performance air-cooled aviation engines to need cylinders replaced halfway to TBO.” As an FAA-certified engine, DeltaHawk is awaiting the FAA’s official declaration of an exact TBO for the DHK180. However, Webb notes: “Our design life based on observed wear rates is 3000 hours, possibly more, for three reasons: the liquid cooling keeping the piston and cylinder clearances stable; the lack of a valvetrain and all the tiny parts there that constantly get burnt or otherwise worn out; and all the remaining moving parts are thermally isolated things, like our supercharger, turbocharger and fuel pumps.” Lubrication DeltaHawk has designed the DHK180 as a dry sump engine for two reasons. First, as a wet sump must be open and largely conformal with the crankcase, and hence must mount under the crankcase in a vee-engine, using a wet sump would have made the inverted-vee orientation impossible (the cylinders occupying the underside of the crankcase). Second, designing a wet sump largely fixes the oil quantity (relative to the size of the oil pan), whereas the dry sump approach enables integrators to change the size of the oil tank, such as increasing or decreasing it for longer or shorter endurance missions by virtue of having an external oil tank instead of one integral to the engine. Another advantage closely associated with that is maintenance: when the time comes to check or replace the sump, rather than having to unscrew an oil pan from the engine (which often means extracting the entire engine from the UAV), technicians need only remove the external dry sump. It also makes it easier to check or replace oil pumps and filters, as they are also mounted externally as a result of the dry sump approach. Oil for the DHK180 is first drawn from the tank, through a filter, then through a cooler, and into the back of the engine. There, it runs into an oil gallery, which feeds the crank journal bearings, and by extension the gudgeon pin and piston rings via pressurelubrication up the con rod. February/March 2024 | Uncrewed Systems Technology Dossier | DeltaHawk DHK180 The crankshaft has two crankpin journals, each holding two con-rod big ends, the surfaces polished to prevent wear; more journals would have meant a heavier shaft The con-rod’s small end is U-shaped, instead of circular, and bolts on to the gudgeon pin, forcing articulation of the pin and enabling a full-length pin-to-piston bearing surface