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60 Digest | Quaternium HYBRiX 2.1 for aerial surveillance missions for first responders, security and public safety. And although the craft is rated to 4 hours of endurance, that is partially motivated to encourage safe and responsible use of the UAV. As mentioned, an experimental configuration of the HYBRiX 2.1 has been flown for more than 8 hours at a time in flight trials. “For surveillance flights we have also developed an EO/IR gimbal weighing 1.4 kg,” Fuentes says. “The HYBRiX 2.1 can fly for more than 3 hours with that sensor integrated, and we can install any other payload sensor so long as it is compatible with Ardupilot.” The company also sees cargo transportation, agricultural spraying and some other long-endurance, heavy-lift applications as potential uses for the quadcopter. A heavy-lift version is in the works, which will have an MTOW of 25 kg, and lift 10 kg instead of 5 kg, possibly with the same endurance. Hybrid powertrain At the core of the HYBRiX 2.1’s series hybrid range extender is a modified 32 cc two-stroke gasoline engine from Japanese company Zenoah. “Our modifications focused on increasing the power of the default version of the engine, in order to get a maximum continuous power output of 2.6 kW at a crank speed of 12,500 rpm, which is currently above any similar configuration available,” Cortes says. This power figure was made possible through a number of alterations, such as a custom-tuned exhaust – the standard exhaust was found to allow only around 1.8 kW of output. Quaternium experimented with COTS mufflers for a while before turning to customised shapes and more compact sizes, eventually resulting in the current, somewhat box-shaped muffler system. Fuentes adds, “Fuel consumption on the HYBRiX has also been reduced significantly over time – from 520 g/kWh to 350 – thanks to our work on the fuel injection system. We’ve tailored it to allow much finer adjustments and to eliminate potential hazards that can arise from imprecise injection and carburation.” The engine and its components have been repeatedly tested and improved using a chassis dynamometer, which Quaternium’s development team has used in order to measure the power and torque curves of the engine over hundreds of cycles. Overall, the HYBRIX 2.1’s range extender system weighs 3.5 kg, and during operations the engine is consistently active, on average providing all the power needed for flight and surveys. The battery is there mainly to provide sudden peaks in power demanded by the UAV (as well as a regulated DC voltage output of course) and is recharged by the range extender after such peaks. “The battery voltage is roughly the same before landing as it is after take- off, as it is constantly recharged by the engine. That slows the degradation of the battery capacity compared with all- electric UAVs,” Cortes says. “And of course, having that battery is also a useful source of power for emergency landing, in the unlikely event that the engine fails mid-flight. We use a pack of two 6S lithium-polymer batteries, which collectively weigh 1.6 kg and provide up to 6 minutes of flight in electric-only mode.” Control of the range extender system is handled autonomously, with an external management unit for monitoring and April/May 2020 | Unmanned Systems Technology A 32 cc two-stroke engine from Zenoah has been tested and modified to provide 2.6 kW of continuous power