66 Dossier | DeltaHawk DHK180 documents for certification, DeltaHawk has verticalised its production via manufacturing facilities that are fully controlled through electronic monitoring systems. Up to 10,000 DHK180 engines can be supplied and maintained per year at its current facility, which also houses three different types of dynamometer and a quality lab with coordinate measuring machine (CMM) systems, optical comparators, laser measurement devices and other metrology machines. Why a two-stroke? DeltaHawk has chosen to produce this engine as a two-stroke, but also to not broadcast widely that it is a two-stroke (the term being notably absent from the company’s website). “When you say ‘two-stroke’, people think of horrible fuel-oil mixtures, terrible emissions, poor fuel efficiency and short TBOs. It isn’t always correct to think that, especially since most of those problems can be attributed to gasoline-fuelled, crankcase-scavenged, air-cooled twostrokes, but many still do,” Webb remarks. “But a compression-ignition, liquidcooled two-stroke is completely different. Virtually all large ships use diesel two-strokes, renowned for long life and fuel efficiency. Half of all US locomotive engines historically used diesel two-strokes, with similar reputations. Now, we’re in aviation; certainly, a very different application to both of those, but there’s still several aviation advantages that the two-stroke has over four-strokes that put DeltaHawk on the two-stroke path.” For one, if an aircraft suffers a flameout at high altitude owing to a primary tank running dry, it must relight, which is very difficult in typical, turbocharged aviation four-strokes. Cooling from the exhaust stroke following each combustion stroke, combined with pressure loss from the sudden absence of exhaust gas to drive the turbocharger, means there is insufficient heat and pressure for ignition. This limits such four-strokes’ relight altitudes to about 6000-7000 ft (1828.8-2133.6 m) – anything higher and the UAV will lose all engine power. But as two-strokes are constantly compressing and combusting, sufficient heat is created to relight the engine as soon as a backup tank kicks in. With its mechanical (gear-driven) supercharger to maintain the pressure and volume of air entering the cylinders, Webb estimates the DHK180 has a maximum relight altitude of “somewhere in the high ‘teens’ of thousands of feet” (15,000 to 20,000). He adds: “We want to test it further before publishing an official number, but likely at least 10,000 ft higher than a four-stroke.” Simplicity and compactness Other motivations included simplicity: two-strokes operate without the valvetrains or camshafts of four-strokes, resulting in fewer failure points and pieces to replace at intervals. On top of this, DeltaHawk also wanted the simplicity, compactness and light weight of a direct-drive system. “The most straightforward route for high power is making a four-stroke engine with four valves per cylinder, double overhead cams, EFI and a very high rpm. That’s how Formula One makes power and how most modern cars make power, but there’s always a transmission that follows,” Webb notes. “Similarly, all our compression-ignition February/March 2024 | Uncrewed Systems Technology Fuel delivery into the DHK180 starts from a low-pressure pump atop the engine (above), which draws fuel from the UAV’s tanks and sends it to a high-pressure fuel pump (right), which contains four independent plunger-barrel and steel line systems; one for pumping fuel to each cylinder
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