Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

40 the ground during take-off or landing – could then throw off the ECU’s embedded maps and load lines, such as for rpm versus throttle. That can lead to major inaccuracies in the fuel feed, air feed, and spark timing of the engine. Differences between ECUs for reciprocating engines and rotaries tend to come down to their embedded software, particularly in terms of how the injection and ignition advances are synchronised, and how to estimate the required fuel for preparing the combustion mixture. For example, a speed density scheme can be used to calculate fuel injection in a two-stroke gasoline engine. That would be a sub-optimal approach though, owing to the difficulty of estimating air mass flow, as the manifold air pressure (MAP) of a two-stroke typically has a narrow range. On the other hand, the MAP in a four- stroke has a far wider range, enabling more precise air mass flow estimations, so speed density is much more applicable for this engine type than for two-strokes. The use of adaptive closed-loop control algorithms can confer several advantages on ECUs for engines that have slightly different calibrations. The algorithms can enable calibration maps to be quickly adapted to compensate for differences in performance specifications between engines, making the testing and mapping phase of a new engine much quicker. For heavy-fuel engines though, such algorithms may not be sufficient. While gasoline engines tend not to vary too much in the leanness of their air-fuel mixture, even at the ‘richer’ ends of their operating ranges, heavy fuel must be spark-ignited within a much more narrow range of mixtures. That means the calibration tools and methods must be far more precise. For example, cylinder head temperature sensors (and other temperature sensors) for heavy fuel two-strokes should be more accurate than those of gasoline in order to alter the air feed proportionally to how hot the engine is. Knocking In addition to the quality of fuel injection and calibration, the ignition on heavy-fuel engines can more easily trigger knocking when combined with a higher-than- average cylinder head temperature. It may therefore be important to program an ECU with temperature- correlated limits on when to advance the spark timing, or even an input interface for a knock sensor. The latter is particularly worth considering if the craft is to carry expensive payloads, experimental sensors or people (in the case of an autonomous urban air taxi), given that knocking can destroy an engine. To enable unmanned vehicle powertrains to be hybridised, control algorithms must account for how the engine will interact with the different components required for generating several kilowatts of electrical power from its crankshaft. Perhaps the simplest of these is how an ECU and motor controller will work together in response to load. If a UAV is flying at a gentle cruising speed, outputting 2 kW, and the starter/generator is supplying just a few hundred watts to the electrical systems, a sudden jump in the electrical load of just 100-200 W could trigger a critical error message in the ECU, or cause dramatic speed deviations or even stop the engine. Instead, the ECU should be designed to advance the throttle in proportion to the electrical load. As the generator can process and record measurements of that load within a few hundred milliseconds, the measurements should be sent to the ECU, so that the throttle October/November 2019 | Unmanned Systems Technology An ECU’s enclosure is often the heaviest part. Some are made from a carbon composite to save weight, which can also help protect against EMI from other avionics (Courtesy of Ecotrons) Control algorithms must be carefully updated for variations in the conditions, timings and componentry needed for heavy-fuel and hybrid-electric engines (Courtesy of Power4Flight)