USE Network launch I UAV Works VALAQ l Cable harnesses l USVs insight l Xponential 2020 update l MARIN AUV l Suter Industries TOA 288 l Vitirover l AI systems l Vtrus ABI

69 Kehe predominantly led and coordinated the team, but had extensive project management support from Suter’s project leader Thomas Berli. “It’s worth noting that the TOA 288 has considerable roots in the Suter 500 cc four-cylinder engine,” Kehe says. “For example, if you look at the shape and style of the 500 cc’s cylinders, and remove the cooling fins, you see precisely where we took inspiration from for the cylinders on the 288 cc.” Going forward, CAE and Suter are prepared to re-engineer the TOA 288 for the inevitable alterations needed by different end-users. “The nature of this industry is such that any given engine is more of a ‘base’ than a set-in-stone product,” Kehe notes. “You can take it to a customer but they’ll request all sorts of modifications: things like moving the mounting points perhaps, or wanting it to run quieter. “During customisation and integration, new potential flaws and failures can occur. That’s because sometimes the end-users aren’t engine technicians, and without our ongoing partnership and technical support mistakes will be made. “Since so many of the parts – the shafts, crankcase and cylinder heads, to name a few – are designed and machined in- house though, we have all the knowhow and tooling needed to modify the engine according to a customer’s requirements.” Engine operation While the exact speed and power when cruising will vary between users, the TOA 288 can produce 14 kW at 6000 rpm while consuming around 380 g/kWh of fuel; at 4500 rpm those figures are 8 kW and 301 g/kWh. It runs on gasoline and synthetic fuels of at least 95 octane. It is also naturally aspirated, with Suter and CAE having considered a few options for ensuring a controlled one- way flow of intake air. “One route was to use disc valves, which work great when you’re at maximum speed and power, but that’s not so ideal for our operational range,” Kehe explains. “A UAV needs to be at wide-open throttle for take-off, but then throttles quite a bit back for a fuel- economical cruising speed.” He and his team eventually went with a reed valve intake, to enable the intake port to open whenever needed and to account for how the engine is used by UAV operators. Only if there had been problems with integration, for example if a customer had no space for the top of the engine where the valve sits, would they have considered using a different set-up. “The port timing has been calculated carefully up to 6500 rpm, and we have a total of five transfer ports inside the engine block,” Kehe says. “There are two ports on either side [one as a main port and one as a support] and the fifth one is on the rear – a classic racing cylinder design. “And while we’re happy to run the engine at whatever load an end-user needs during flight, I’d personally recommend the TOA 288 should be used at somewhere close to the maximum power output, maybe around 14 or 15 kW. Like other engines, if you run it too gently for too long, the pressure becomes too low, the spark plugs cool too much, and so on.” To assist with port timing (along with other key aspects of engine operation) an internal crank position sensor is installed beneath the throttle, with the encoder ring inside the crankcase. This configuration was chosen to keep the sensor element protected by the engine block against impacts and dust, and also to have more open space on the crankshaft. This extra space means more hybridisation flexibility for end-users in terms of the size of generator they would like to install for direct-drive electricity production. “If we need to design the crankshaft or crankcase a little differently to accommodate a slightly larger generator, that’s fine,” Kehe explains. “It’s another reason why we so strongly prefer machining the block and shaft than casting it, because if they were cast we’d need to make whole new moulds.” Unlike its intake port, the engine’s exhaust port has no valves. Kehe notes, “That means we don’t have a wide acceleration range, and we’re largely restricted to the propeller curve in that respect. But we don’t need to install exhaust valves when we’re in our rpm range, because the gain in acceleration would not be worth the added complexity and weight.” Suter Industries TOA 288 | Dossier Unmanned Systems Technology | June/July 2020 Working with motorsport company Suter Industries enabled Kehe and his colleagues to use its extensive testing and machining equipment