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

71 O’Neill Power Systems NorEaster | Dossier distribution of the oil across the cams, all around the cam case, and to the bearings, piston rods and oil rings. The oil eventually settles at the bottom of the cam case, where it is then recirculated, with no losses as the system is fully closed.” In the NorEaster’s current iteration, cooling is provided by the downward thrust of air from the propellers, which flows over the outer surface of the cam case and across the cylinders. The number of lobes on the driving cams may be subject to change. The primary aim of the engine’s design is that the output shafts move at between 750 and 1250 rpm, as befitting a helicopter rotor system. As the cylinders and pistons were originally designed for four-stroke operations at 4000 rpm, the cam currently has four lobes to provide a four- to-one reduction ratio. Accomplishing this reduction without belts or gears means the engine avoids all the inherent maintenance issues and points of mechanical failure that helicopter transmission systems are prone to. “I designed all the cams using my own cam design program, Dynacam,” Norton explains. “The cam profile data from Dynacam was then imported into CAD programs to generate the cam surfaces.” Valve control As the current configuration of NorEaster uses a four-stroke power cycle, the cam-driven engine has been designed with a series of components to form a secondary cam system, which acts as the power system’s valvetrain. “The valve drive system is so simple on this engine, compared with what you’d usually find on an automotive or UAV four-stroke,” Norton comments. The heart of the valve control and timing is a valve cam. That is the effective ‘camshaft’ of the NorEaster, although it is much wider than it is long (and therefore more closely resembles a pair of coupled rings than a shaft), and does not need any timing belt or chain to operate the valves or keep accurate timing. That has allowed the overall valvetrain to be designed in line with O’Neill’s philosophy of avoiding belt-oriented transmissions. Its design features two cams, set on two tiers with two lobes each, each cam’s lobes being set opposite to each other. In this arrangement, one cam actuates the cylinders’ intake valves while the other is fixed to operate the exhaust valves. As each valve cam has two lobes, compared with the four on the drive cams, each valve is opened and closed in order as well as once per power cycle, with timing fixed by the fact that the upper drive cam is directly driving the valve cam. Put more simply, just as two power cycles (or eight strokes) are completed for every rotation of the drive cam, so each valve will be opened and closed twice for every revolution of the output shaft. To actuate an intake valve, the valve cam’s first upper lobe comes into contact with a roller lifter, eight of which are arranged about the path of each lobe (for a total of 16). The lobe pushes the roller lifter upwards, which lifts a 22 cm pushrod up against the input end of a rocker arm. The output end of the rocker arm thus rotates downwards, pushing down against the spring-loaded intake valve and opening the port to the carburettor’s fuel-air mixture. As the zenith of the valve cam lobe passes, the roller lifter and pushrod are lowered down again, and the valve lifts upwards to seal the intake port with the valve seat. After the combustion phase, the second valve cam comes around to set in motion a largely identical procedure to open and shut the exhaust valve. While each valve cam’s lobes are set 180 º apart, the exhaust valve cam is offset slightly so that each intake lobe’s corresponding exhaust lobe follows slightly faster, at about 144 º . The intake valve seat (and by extension, the intake port) is 2.6975 cm in diameter, while the exhaust valve is 2.22 cm across. Both ports are placed atop each cylinder, equidistant from the centre of the bore, with a flat valve angle (0 º ) between them. Unmanned Systems Technology | August/September 2019 Within the (blue) drive cam’s raceway, the large bearings (green) on the piston rod’s cross- member push down on the cam’s inner lobes, while the smaller bearings (grey) on the outer part of the cross-member are pushed up to run against the outer lobes