Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

58 Performance The 110xi has a 13,000 rpm potential, reports Schudt, but routinely it is run to no more than 8500 rpm. Ignition timing varies from 35 to 20 º BTDC according to operating conditions. The accompanying graphs include power output as measured at sea level. Wintrich remarks that the power curve can be manipulated via compression ratio, transfer porting geometry and ignition timing. There is also potential to increase power by lengthening the exhaust pipes, but for packaging reasons most customers prefer a compromise on that parameter. Cylinder head temperature is constantly monitored in flight, and engine cruise speed is adjusted to keep it within the correct range of 180 to 220 C. If cylinder head temperature gets too high, rpm is reduced, and vice versa, with the adjustment made thorough ignition timing, injection pressure and timing and throttle position. Throttle position is adjusted to compensate for the adjustment in rpm, albeit at the cost of higher fuel consumption since the engine is no longer operating in the optimum rpm band for fuel efficiency. Schudt says, “If the cylinder temperature is kept within the correct range then the engine will be very clean burning, with little carbon build-up, and fuel consumption will be optimised. The cruising rpm is focused on low fuel consumption. The customer will, in conjunction with us, design a cooling air system for their UAV – including baffling around the cylinders – that optimises the engine operating temperature within that desired rpm band under normal conditions.” The 110xi is designed to run for 1200 hours between overhauls in normal circumstances, but to be on the safe side a customer will typically service within the 400-800 hours range. Time between overhauls (TBO) varies according to the environment in which the propulsion system is operated: for example, it will be less in the desert than elsewhere. 3W works with each customer to determine a maintenance schedule appropriate to their specific requirements. Between overhauls the only maintenance items are the air and fuel filters and the spark plugs. Spark plug life is about 75 hours, although the use of diesel valve cleaner in the fuel can add around 100 hours to that. In addition, the customer is advised to make regular precautionary checks of externally accessible fasteners. Keeping the intake air filter clean is of particular importance, whatever the environment. The main items changed during a routine overhaul are piston rings and gaskets. The fuel pump, the bearings and the piston will be carefully inspected and might be changed, according to the effect of operating conditions and the type of lubricant used. “We tested one of these engines by running it hard for 240 hours,” recalls Schudt, “then disassembled, cleaned and restarted it, and it continued August/September 2016 | Unmanned Systems Technology Dossier | 3W-110xi b2 TS HFE FI The performance of 3W’s110xib2 TS HFE FI as measured on the in-house dyno