Unmanned Systems Technology 007 | UMEX 2016 report | Navya ARMA | Launch & recovery systems | AIE 225CS | AUVs | Electric motors | Lethal autonomous weapons

58 Dossier | AIE 225CS UAV rotary The throttle is electronically controlled, and the 225CS is run by a full engine management system. A twin, side-by- side spark plug arrangement provides not only redundancy but also improves efficiency, as evidenced by a drop of 50-100 rpm at WOT when one plug is disconnected. Thus the twin-plug arrangement is justified by reduced fuel consumption. 225CS performance Power output from the 225CS is 10 bhp at 3000 rpm, rising to 40 bhp at 8000 rpm with maximum torque of 27 lb-ft (36.6 Nm) made at 7000 rpm and with in excess of 25 lb-ft (33.9 Nm) from 5000 rpm right through to 8000 rpm. Offering the inherently low vibration of a rotary, the engine runs comfortably to 10,000 rpm; to go higher would be feasible but would require certain design changes. The 225CS was specifically designed for an 8000 rpm redline to match propeller requirements. Fuel consumption is quoted as 310-350 g/kWh (0.51-0.57 lb/hp/h), and the engine runs for more than 500 hours between rebuilds. The compression ratio is 9.6:1 on gasoline, reduced to 8.5:1 for heavy-fuel usage. The heavy-fuel version has its own injector specification, is fitted with a knock sensor and has its own ECU mapping. To assist cold starting on heavy fuel there is a heating element in the intake to warm the incoming charge. 225CS development The 225CS Generation One was the prototype, whereas Generation Two is the production version, improved in the light of testing. Generation Two increased the volume of coolant, adding a coolant flow within each endplate to address an issue of marginal cooling without it. The rotor housing liquid cooling passageways were modified to enable the introduction of endplate cooling, which improved overall engine cooling and thermal stability. In other improvements, Generation Two has wavy rather than straight fins in the SPARCS heat exchanger, which increases fin area by 12% and thus its effectiveness. Generation One had separate covers over the endplates, whereas with Generation Two those items are combined, lowering parts count and weight, and in the process increasing rigidity. At the same time, with Generation Two the trigger wheel was moved from the propeller drive hub to an internal location, where it is integrated with the SPARCS fan. This allows for more variety of output shaft interfaces. New inlet and outlet elbow designs were also introduced, to allow greater flexibility in cooling system configuration. Looking to the future of AIE’s rotary development path, Bailey agrees that direct injection is a route worth exploring. “The aim of a direct injection programme would be to enhance fuel efficiency, especially when using heavier fuel. Range extension is always a priority.” He adds that forced induction is also under consideration by AIE, especially the use of an electrical supercharger. There is still plenty of scope for development from AIE’s initial UAV offering, including larger and smaller displacement versions currently in the pipeline, but already it has clearly set a very high standard for engines of its type. April/May 2016 | Unmanned Systems Technology Working on Wankel rotary engine design at AIE Machining a 225 CS rotor housing at Tata Steel