36 Dossier | Insitu ScanEagle VTOL & Integrator VTOL As our long-time readers will know, the ScanEagle comes with a few engine options, including: a 28 cc single-cylinder, originally from 3W International, but heavily modified by both Insitu and NWUAV; the NW-44, designed and produced by NWUAV (detailed in Issue 6); and the N20, co-designed by Insitu and Orbital UAV (detailed in Issue 8). “Which engine is ‘better’ depends hugely on where and how the end-user is operating. As the gross takeoff weight on different ScanEagle configurations has increased, the N20 can provide a degree of higher value among customers with greater payload requirements, and significantly higher power generation than our traditional, 28 cc engine,” Hartley says. “We have a gasoline, carburetted version of the 28 cc engine and an EFI, heavy fuel version, which provides some versatility, although the N20 was designed to run especially efficiently on heavy fuel via its compressed-air, assisted direct-fuel injection. We also have specific customers who prefer the NW-44.” The NW-44 and N20 have been covered extensively in this publication, and were among the first UAV-specific engines designed with eventual FAA certification in mind. Both of these are sparkignited, naturally aspirated two-strokes, designed around single cylinders and using electronic fuel injection (EFI), which have been optimised to run on multiple different fuels, including gasolines, Jet-A, JP-5 and JP-8. The NW-44 is a 43.6 cc product with an all-up weight of 4.3 kg, a maximum power output of 3.5 hp (2.6 kW) at 7250 rpm and a TBO of up to 500 hours. The N20 is a direct-injection engine, displacing 49.9 cc, producing 2.95 kW with a total weight of 4.97 kg. The Integrator, by contrast, comes with just one power unit option, developed in-house and referred to as the Integrator PMU (Propulsion Module Unit), which is described by the company as being in its third version (V3). Details on this engine are kept tightly under wraps by Insitu’s flight sciences team, but the company tells us that like the ScanEagle’s engines, it is a spark-ignited, air-cooled two-stroke, specifically designed for heavy fuel operations (particularly JP-5 and JP-8). It is configured with two cylinders rather than one (arguably an inevitable consequence of needing more power to shift the far heavier of the two UAVs), and it has been optimised to fit within the specifications laid out in original STUAS competition that spawned the Integrator over a decade ago. “We started with a blank sheet design, initially configured for running on gas or avgas, just to speed up the prototyping process, and evolved that into a heavy fuel engine after the programme was awarded,” Todorov says. “The PMU V3 is a wholly original Insitu engine design, maintained and iteratively optimised over the last 15 years, with specific improvements in durability, reliability, shaft power, and ultimately electric power for payloads being key targets.” More power, more footprint Fuel runs to the PMU from carbonfibre tanks integral to the Integrator’s structure, with baffle designs to maintain centres of weight and balance during fuel drawdown during flight. Through the shaft power driving an alternator, a standard electricity supply of 350 W is provided from the PMU for payload use. “We’ve done a lot on both platforms to keep separate, segregated payload power buses from our flight control buses, so payload demands from a power standpoint do not impact either of the UAVs’ ability to constantly maintain normal flight,” Hartley says. Hartley, Todorov and Pearce note that customer demands for power continue to rise, which has contributed to the integration of more capable engines and generators over the years, and vindicated the choice to design Integrator’s airframe with structural margins, along which the fuel tanks could be expanded. “Payload power growth has always been on Insitu’s roadmap, and we approach Integrator’s engine development almost like car companies do – as soon as we finished V3, we almost immediately started work on its next variant, based on industry trends we were seeing, even though the need wasn’t explicitly out there yet,” Pearce adds. Insitu is now conducting development and tests of a 4th generation PMU in response to increased customer demand for payload power, in pursuit of missions with more sophisticated maritime patrol radars, signals intelligence payloads and so on. “Fortunately, while copper is copper, there have been great advances in material science that allow you to June/July 2024 | Uncrewed Systems Technology The ScanEagle can run on either the NWUAV NW-44, the Orbital UAV N20, or a highly modified 3 W 28 cc, all three being two-stroke, single-cylinder engines
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