Uncrewed Systems Technology 051 l Primoco One 150 l Power management l Ocius Bluebottle USV l Steel E-Motive robotaxi l UAVs insight l Xponential 2023 p Issue 51 Aug/Sept 2023 art 2 l Aant Farm TPR72 l Servos l Tampa Deep Sea Barracuda AUV

The Primoco 340 engine The Primoco 340 is a four-stroke, fourcylinder boxer, producing 25 bhp at a maximum speed of 5000 rpm, and consuming between 3 and 4 litres/hour depending on the UAV’s carried weight. It features dual EFI controls, dual spark plugs per cylinder, and dual injectors per row of cylinders. For added safety, the starter/ generator is designed and programmed to perform in-flight emergency restarts, and electrical power for onboard systems is generated by an alternator mounted on the rear of the crankshaft. “The alternator outputs 750-1000 W continuously and feeds into the accumulator, which consists mostly of LFP cells, which as far as we’re concerned is the best chemistry for safe and stable energy storage,” Fojtik explains. “But the accumulator isn’t just a battery pack, it also buffers and balances the power going between systems, including storing AC power from the alternator or powering emergency restarts from the starter/generator.” The accumulator is connected directly to the power distribution box, which integrates DC-DC converters to step the output voltage to 24, 12 and 7.5 V to cover the various requirements of the One 150’s electrical and electronic systems. Plans for the engine began as soon as the One 150 started flying, as the company quickly realised that there were some safety issues with two-strokes that could not be overcome. For instance, the very exposed exhaust system could be a source of ruptures and hence compression ratio losses, which in a two-stroke means rapid loss of altitude. A four-stroke though can suffer exhaust ruptures and keep on flying, albeit with greater noise emissions and fuel consumption. The company notes that the Primoco 500 had a superior power-to-weight ratio than the present 340, and that two-strokes in general will typically outperform four-strokes in this respect. However, this advantage was offset in practical terms by the 500’s much higher SFC, and the fact that it ran more optimally on heavy twin carburettors than on EFI, which brought risks of freezing (even without flying at particularly high altitudes) or vulnerability to gusts. While the two-stroke’s development was outsourced to Czech subcontractors VM Motor and Motordesign, the fourstroke was developed from a blank sheet by a crew consisting of in-house, subcontracted and part-time specialists, with all the design, manufacturing, testing and tuning taking place under Primoco’s roof and brand. The 340 is still being flight tested to validate key performance specs such as its TBO (which is estimated at between 200 and 400 hours for now, depending on fuel quality). STANAG 4703 compliance tests are also being run to increase its guaranteed service life, with the eventual plan of redesigning it as a two-cylinder with greater displacement than 340 cc to increase power. At present, however, allup weight comes to about 15 kg, and the system typically runs on widely available 95-100 octane unleaded gasoline. “The ECU monitors performance and controls parameters electronically, so if there are discrepancies between any temperature, speed or voltage readings from the sensors and what we want them to be, the ECU implements whatever the mapping or embedded programming suggests is best to mitigate the issue,” Fojtik adds. “As per STANAG 4703’s recommendations, the fuel lines are made from a special fuel-resistant, thermally resistant plastic that is nonflammable, and for further fire protection we’ve used specific aluminiums and other alloys around the engine bay for thermal distribution, compensating for the engine’s small size and the fact that it’s ram air-cooled. Also, the cables are all EM-shielded, as there’s huge potential for interference with data readings, especially if the SIGINT and ELINT-type payloads are installed.” Data links For stealth purposes, Primoco does not use omnidirectional antennas on the UAV during defence missions, instead opting for beamforming antennas. 35 Uncrewed Systems Technology | August/September 2023 Primoco’s 340 engine is a four-stroke, four-cylinder boxer, running on gasoline and producing 25 bhp at a maximum shaft speed of 5000 rpm