72 In the young world of uncrewed systems, propulsion systems inevitably draw primarily on established technology. At the same time, the industry’s lack of maturity means there are plenty of projects exploiting today’s high-tech design and development tools to explore out-of-the box concepts. While many will ultimately fall by the wayside, we feel it is our duty to inform readers of any that make it beyond the conceptual stage, to thereby promote discussion of technologies that might one day prove genuinely disruptive. One such project is INNengine’s naturally aspirated 125 or 288 cc fourcylinder two-stroke for the UAV market, which exploits the axial cam concept for a package that is notably light and compact. This is an old technological approach that has been successfully applied in secret military roles but is virtually unknown in the civilian world. It means that the four cylinders all run parallel with the output shaft, and they are arranged evenly around that shaft (at 90o intervals). The drive is then imparted from the pistons to the driveshaft via a disc integral with the shaft that carries a 3D sinusoidal cam track. The disc, cam track and the shaft are all machined together as a single component (visible in its position in the middle of the cylinders in the anatomical diagram on page 73, and in the photograph on page 78). It should be made clear that, driven directly by the four piston assemblies via rollers, the disc is an alternative to a swashplate that might otherwise be used in such an engine. Here the piston consists of upper and lower tiers, which are rigidly connected by a rod; the upper tier is a ‘head’ largely consistent in form with a conventional piston, while the lower tier is a ‘body’ carrying the roller mechanism that runs in the cam track to drive it. The 3D cam track’s sinusoidal shape features two crests and two troughs, Rory Jackson reveals how this camoperated two-stroke axial engine has been developed for the UAV market Cam capability INNengine’s Rex-B is currently in its second prototype, and is at the stage where it is ready for production (Images courtesy of INNengine) December/January 2024 | Uncrewed Systems Technology
RkJQdWJsaXNoZXIy MjI2Mzk4