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

49 Garside says, “The oil, supplied from a small metering pump, made only a single pass through the engine internals before being ejected into the eye of a pusher propeller. For the UAV application, this wet oil emission was not important, but it prevents use of the engines in tractor UAVs or for any ground application. To assist in minimising the rotor temperature problem, relatively high rates of oil usage (up to 5% or even 10% of the fuel flow) have been used. SPARCS uses a sealed rotor cooling circuit consisting of a circulating centrifugal fan and a heat exchanger to reject the heat. This is self-pressurised by capturing the blow-by past the rotor side gas seals from the working chambers. At high power (WOT) the pressure stabilises at around 5 bar (73 psi), this occurring when the inflow of gas from the high-pressure phases of the engine cycle is balanced by the outflow to the low- pressure phases. Garside says, “The resulting high- density gas circulating through the rotor provides much-improved cooling relative to previous systems using ambient- pressure air, despite the higher gas temperature. “Lubricating oil fed into the circuit now makes many passes through the rotor internals before eventually escaping past the rotor-side gas seals in a reverse manner into the working chambers, this being the only exit route for the oil. It lubricates all the gas seals and associated sliding surfaces before being either burnt or emitted through the exhaust port as a vaporised gas. The result is no wet oil emission and much- reduced oil consumption, and hence a take-off weight-saving.” AIE’s managing director Nathan Bailey says of rotary guru Garside, “I believe his new technology is a leap forward.” His company signed an initial limited licence to exploit Garside’s patents in September 2012, having been founded a few months earlier. First run in February 2014, the initial 225CS was the first application of what is known as Compact SPARCS (hence ‘CS’, as opposed to regular SPARCS), and its experience led to the further- refined 225CS Generation Two, first run in February 2015 and now in full production. Design philosophy The single-rotor 225 cc 225CS was designed from a clean sheet of paper by a team at AIE familiar with previous Norton- derived motorcycle engines and UAV power plants, in conjunction with Garside. “We didn’t reinvent what we knew already worked,” notes Bailey. “The basic engine geometry is a follow-on from Norton, which in turn was derived from the Fichtel & Sachs KM914 industrial 294 cc, 18 bhp rotary, first used in 1968 typically in snowmobiles, and later in the Hercules 1974 motorcycle.” In fact the 225CS has a wider rotor than the most directly comparable AIE 225CS UAV rotary | Dossier Unmanned Systems Technology | April/May 2016 SPARCS uses a sealed rotor cooling circuit consisting of a circulating centrifugal fan and a heat exchanger to reject the heat 225CS end plates