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58 I nsitu is a Boeing subsidiary that specialises in UAVs; its three current platforms are the ScanEagle, the Integrator and the RQ-21 Blackjack. The latter was developed for the US Navy as a spin-off from the Integrator project. The ScanEagle has been deployed by the US military since 2004. The ScanEagle has a 10 ft wingspan and is currently powered by a naturally aspirated, small-displacement, spark- ignited two-stroke engine built to Insitu’s prints by a third-party manufacturer. Insitu manufactures the ScanEagle and operates it on behalf of certain customers. Recently it decided to put all its UAV expertise and experience into developing an Insitu dedicated-UAS engine in the quest for superior reliability and performance. This bespoke engine, internally designated the N20, was devised by a special Propulsion Engineering group within Insitu. Headed by Kevin Beloy, the group started by defining the requirements for a clean-sheet-of-paper propulsion system – “and there were hundreds of high-level requirements”, Beloy notes. A procurement competition was then held to select the source of design and manufacture. Of the proposals received, “Orbital had the strongest technology, with the best design and manufacturing expertise,” remarks Beloy. Of particular interest was its unique direct injection (DI) technology. “We could find no better provider of fuelling technology for a small two-stroke running on heavy fuel,” he adds. “The Orbital compressed-air assisted direct injection technology that our new N20 incorporates is compatible with multiple fuel types, provides resilience to variations in fuel properties, is reliable and no glow plug is required,” he says. “Normally a spark-ignited engine runs hot to burn jet fuel properly, but the Orbital technology allows the N20 to run much cooler, increasing the time between overhauls by at least three times compared with other heavy fuel engines. It also requires only minimum scheduled maintenance such as air filter and spark plug changes, and no de-carboning or reconditioning procedures are required.” Beloy explains that the target was to increase reliability tenfold by controlling engine design and manufacture. “We When Insitu wanted a bespoke engine for its small unmanned aerial systems family it chose Orbital to provide the solution. Ian Bamsey reports Double act The Insitu/Orbital N20 two-stroke features advanced direct injection June/July 2016 | Unmanned Systems Technology