Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

72 Dossier | O’Neill Power Systems NorEaster A round steel tube extends upwards from the exhaust chambers atop the cylinder heads, before turning 180 º to funnel the exhaust fumes down between the cylinders. “We’ve also equipped it with mufflers from Briggs & Stratton, to reduce the noise generated by that eight- cylinder system,” O’Neill points out. “Originally the cylinder heads had the exhaust directed to the top, but we didn’t want that flowing near the rotors, so we redesigned it to direct the fumes below where they’d be less harmful.” On the current prototype, fuel is stored in a gravity-set fuel tank, with separate hoses extending from it to the carburettors on each cylinder head. Each carburettor has its own throttle body for air intake control. Cam engine versus crank/ con rod engine As well as improving over helicopter turbine-and-belt arrangements, the NorEaster’s cam-based drive system is designed to provide certain advantages over the more conventional reciprocating engine’s crankshaft-based drive. In a crank engine, each con rod’s big end rotates with the motion of its crank pin, while the small end of the con rod, being fitted to the piston pin, generates a secondary ‘side-to-side’ harmonic. That can create friction and wear between the piston and its cylinder wall, by pulling to one side during its downward stroke and to the other during the upward stroke. The NorEaster’s pistons are not pulled side to side in this way, as the drive cams exert balanced forces on either side, and the guide plates hold the cross-members in place to prevent the pistons being ‘twirled’ in either direction. Also, as mentioned, the radial operation of the NorEaster with the cylinders firing in opposing pairs means all the harmonics of the inertial force generated by combustion cancel each other out. “The co-planarity of the cylinder distribution about the cam case also means there is no inertial shaking moment,” Norton says. “And again, the counter-rotation of the output shafts and propellers cancels the reaction torque, making for a minimally vibrating power output.” The future In addition to welcoming engineering input from future partners and end-users, O’Neill Power Systems envisages several other configurations of the NorEaster. One, designed for UUV propulsion, uses an electric motor as the main power source driving the lower cam, with the cylinders removed and the piston rods held in their slots to actuate the upper cam and its output shaft. This alternative use case for O’Neill’s drive transmission system is titled the VorTaq. “UUVs are mostly electrically powered, with one propeller, so they need control fins which are constantly adjusting to compensate for the dynamic roll the prop induces, to stay level and flat to generate quality sonar imagery,” says Anderson of OceanServer Technology. “The counter-rotating propellers would induce no roll, so you could reduce those control fins significantly, meaning fewer potential points of mechanical failure and much less drag on the vehicle.” A future version might also integrate a tertiary output drive shaft, driven by a timed gear intermeshing with teeth formed on one of the drive cams. That would extend perpendicularly from the NorEaster, to drive a pusher propeller. Whatever form the next engine takes though, it is undeniable that the technology at the heart of the NorEaster system has the potential to revolutionise the next wave of UAVs and their markets. August/September 2019 | Unmanned Systems Technology Each valve cam (pink) pushes up against the lifters (gold) to actuate either the eight intake valves or eight exhaust valves, via a linkage made up of pushrods, rocker arms and spring-stems The valve cams (yellow) are bolted around the outer driveshaft, atop the upper driving cam