Unmanned Systems Technology 036

76 Dossier | Hirth 3507-01M control of all oil pumps (via PWM), and communication with the flight control system via CAN. “When selecting our ECU hardware, the biggest consideration was how to tackle communication and control with our direct injection equipment effectively,” Bitter recounts. “This isn’t a common requirement, so there’s no ‘standard’ ECU for an engine or injection system like this. That therefore, along with successfully storing and using all the mappings for fuel injection, ignition timing, air pressure compensation and so on were really key.” Peter Lietz, director at Hirth adds, “The ECU records engine performance data so that if a customer is chasing a problem, they can share their data files with us so that our support technicians can analyse the data and get a really good idea of what’s going on with the engine. It really helps inform our understanding of what can go wrong over the engine’s lifetime, enabling us to give much faster and more effective support. “We are currently offering CAN bus as well as RS-485 bus, depending on what customers prefer, and we’re definitely seeing that CAN is of more and more interest, but that it’s sometimes tricky for them to use. One customer a few years back had changed one side of their CAN communication protocol, which caused the engine to behave strangely, and it took some back-and-forth to resolve those issues.” Future plans As discussed, Hirth has a number of projects running in tandem to enhance its growing portfolio of heavy-fuel engines, aiming at hybridisation, cooling, power-to- weight ratios and other qualities. In the long term, it plans to continue the work it began with the 3507 and 4202 – that is, to develop heavy-fuel versions of every gasoline model currently being produced (with prototyping and testing to follow, pending sufficient customer demand). It also plans to steadily reintroduce its i-power system across its production portfolio, using CFD analysis and ground testing to precisely reconfigure the technology for every Hirth engine, and bring in its improvements in gas mixing and combustion across the board. “In the future we’ll scale our r&d processes for conceptual HF versions of our other engines, and we intend to work on some concepts for bigger, more powerful engines in the meantime,” Lietz adds. February/March 2021 | Unmanned Systems Technology Diagram of the oil distribution system used in the 3507. Note the scavenge oil redistributed from the air compressor to the crankcase Each cylinder has a water inlet below the exhaust (top right), two side ports to the exhaust (middle), and a fifth transfer port is to be implemented in the future (bottom)