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system, or on a strategy that relied on a plethora of different engine sensors at all times, as in speed density or mass airflow strategies. As Kehe explains, “The control system will change to closed loop in certain contexts. For example, when the temperature readings from the EGT and CHT sensors become too high and one of the compensation strategies occurs, that’s when the system goes into closed- loop operation. “The ECU then reacts, changing timings and fuel quantities, and monitoring the two temperature sensors for the expected change. Once they measure normal heat readings again, the engine returns to its normal open-loop Alpha-N. We want to keep operations running as smoothly and simply as possible, without relying on too many sensors and the wiring harnesses running between them. “We also use sensors for air temperature and manifold air pressure to automatically adjust fuel and ignition for altitude, but we don’t rely on them for the basic mapping. Having all these additional sensors present but external to the main propulsion system means that if one of them fails or becomes disconnected, the UAV can still get home safely.” Fuel-oil mixing The TOA 288 uses mixed lubrication (with 2% of the fuel-oil mixture being synthetic two-stroke oil), rather than having an oil injection system. While Kehe’s team can install either option, research and experience have shown that most of Suter’s and CAE’s customers prefer the former. “I do wonder if this preference comes from the earlier generations of commercial UAVs using RC model engines, which were all based around pre-mix,” Kehe muses. “Both approaches have their advantages, but if the oil mixed in with the fuel then it’s safe – it’ll be delivered to the con rods, pistons and bearings, and there are no fears over the oil line or pump breaking. By taking all that out, the weight and mechanical complexity of the engine system are reduced. “I have seen many instances of UAV technicians getting the fuel-oil mixture wrong, or using a pre-mixture they made months ago and forgot about. That means the oil and fuel have started to separate again, but good, clear in-house regulations can minimise the chances of such mistakes. “Oil injection is required in some cases, however, such as for helicopters that are constantly running at very high revs and need persistent lubrication to prevent the engine from seizing. We like to keep an open mind though, and we would not sell an engine to a helicopter UAV integrator without installing an oil injection system.” Phone: +1 (810) 441-1457 Email: [email protected] … as well as these other solutions We are proud to offer the Suter TOA 288 to the USA market…