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

65 of the considerable work that goes into helicopter drivetrain maintenance, and the cause of a great number of crashes. These flaws drove much of the motivation behind the NorEaster’s development. Related to the tail rotor are several other issues that the conventional helicopter powertrain is subject to, which O’Neill wanted to address. “On almost all helicopters, you start with an engine, typically a turbine engine for larger helicopters, the output for which has to go through a highly complex transmission system with a reduction in two directions – one for the lifting rotor, one for the tail rotor,” he says. Helicopters typically require rotor lifting speeds of between 500 and 1500 rpm, compared with the typical turbine speeds of 10,000-20,000 rpm. Norton says, “Those transmission reductions are one of the most problematic technologies in aviation, purely in terms of maintenance requirements. They require persistent care, they often fail, and when they do it’s often catastrophic, because you then have a helicopter in the air with no lift. Without a pilot well-versed in autorotation, that helicopter is going to hit the ground extremely hard.” The NorEaster effectively eliminates that transmission, because the cam-drive system gives an automatic, internalised reduction ratio, equal to the number of lobes on each cam. And since it has been designed with two counter-rotating output shafts, there is no need for a tail rotor to counter torque – each propeller cancels the other’s torque reaction, as well as almost the entirety of each other’s vibration. A conventional helicopter powertrain also takes up a significant proportion of aircraft weight. As indicated, it requires a number of dedicated structures and gearboxes, as well as gearing systems to keep the engine’s centre of gravity stable. “So we wanted something that was more like an outboard motor for helicopters,” O’Neill says. “It’s a single, fully integrated turnkey unit, with no need for a complex transmission system. You just bolt it on to whatever you want to fly, and it uses a fraction of the parts and weight of a conventional helicopter transmission, which is critical for the viability of UAVs in particular.” It was around 1999 that O’Neill first conceived the idea of a cam-driven engine. “I made a couple of crude prototypes,” he recalls. “Soon after, through a stroke of luck, I met Bob Norton, who had written several books, including one on cam design and had taught at WPI for more than 30 years. He examined the cams I had designed and tested, and became a key partner in the design and development of the NorEaster engine.” Their collaboration quickly led to a third prototype, which used a four-stroke power cycle and featured two counter- rotating output shafts, one extending from the top of the engine and the other from the bottom. After testing and demonstrating that model, development of the engine was moved to WPI. With the help of two teams of mechanical engineering students, a fourth prototype was designed. That two- stroke version had an improved cam drive design to provide the revs and reduction ratio that O’Neill and Norton were looking for. “Further improvements on that led us to the version we have right now – our fifth prototype, a four-stroke 80 hp engine, with some dyno testing done to validate that the design performs exactly as we’ve been aiming for,” O’Neill says. “The next step would be to do a lift test, and that will be the last step, pending further development with partners and end-users.” Development of the current version began two years ago, with the first dyno test following a year later. Significant input into it has also come from Bob Anderson, founder of OceanServer Technology, an AUV manufacturer also based in Massachusetts. The decision to revert to a four- stroke cycle came partially from O’Neill and Norton’s automotive engineering backgrounds, which made them more familiar with such technology, and O’Neill Power Systems NorEaster | Dossier Unmanned Systems Technology | August/September 2019 The engine Is currently in its fifth prototype, which initially entered dynamometer testing about a year ago, starting with a version featuring four cylinders