Issue 39 Unmanned Systems Technology August/September 2021 Maritime Robotics Mariner l Simulation tools focus l MRS MR-10 and MR-20 l UAVs insight l HFE International GenPod l Exotec Skypod l Autopilots focus l Aquaai Mazu

66 Dossier | HFE International GenPod or clogged by sand and dust getting into the intakes,” West explains. “This arrangement also protects the plastic parts against direct solar heat or radiation damage.” The injector dispenses fuel at 35 psi, with the pressure regulated independently of the ECU. Fuel pump The fuel pump is a 12 V system that has been designed in-house, along with injection moulding of the housing and sensors for fuel pressure control. “Our pumps have evolved a lot over the years,” West says. “We started with a single pump, then went to a double- redundant pump, and then a double pump with a single motor.” The current system is a diaphragm pump rather than a gear, gerotor or other rotating pump type, as HFE views diaphragms as advantageous for handling dead-head pressure and self-priming. A fuel flow sensor is built into tubing at the pump’s mounting plate, with a pressure sensor installed above, in the tube feeding into the diaphragm housing. Fuel pressure readings are delivered to the ECU for operators to monitor and record. “Pressure fluctuations can be an issue with some diaphragm pumps though,” West notes. “Gear and other rotating pumps are great for preventing those, but they’re not good at dealing with damage caused by sand or other particles. “So handling debris was a major reason we chose a diaphragm pump, and we’ve put our fuel filter between the pump and the injector to keep the latter protected, along with its micron-sized orifice.” Mufflers The company is acutely aware that mounting and facing its mufflers downwards causes a lot more noise to be produced than is desirable. To that end, HFE is finalising work on a new muffler that will be available in the next couple of months. “We are collaborating with Slimline and Desert Aircraft for that, as well as with a company in Egypt called SidLab, which has a long track record in acoustic simulation as well as checking and validating others’ acoustic test results using some unique tools they developed in the 1980s for Volvo and Saab,” West says. These acoustic studies will be combined with specialist muffler manufacturing knowledge from Slimline, which is now a subsidiary of Desert Aircraft, to produce the new mufflers as cost-effectively as possible. West says the new muffler has been made as mechanically simple as possible, for ease of manufacturing, and it is lighter and quieter than HFE’s current versions. “We need to test them for performance though, as that might fall short of our current mufflers,” he adds. “Those are Cobra Aero mufflers – August/September 2021 | Unmanned Systems Technology Handling debris was a major reason we chose a diaphragm pump; we’ve put our fuel filter between the pump and injector to protect the latter The generator is a 500 W system co- developed between HFE and Sullivan UV