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

75 is designed from a blank sheet in partnership with a third party,” Berli says. “It has a special [undisclosed] coating as well, chosen to further help the engine withstand insufficient lubrication.” In an unusual move for UAV engines, the team has installed a fully titanium muffler for the exhaust, for its high resistance to corrosion as well as strength-to-weight ratio. “Unlike UAVs, race teams almost always use titanium exhausts, and Suter supplying engineers with expertise on how to handle titanium was critical to manufacturing the high-temperature exhaust muffler we wanted,” Kehe says. “Having that [exhaust] also meant our combustion processes had to be engineered perfectly, because if our gas temperatures are allowed to run too high they’ll blow the titanium exhaust.” For the TOA 288’s size, air cooling by way of aluminium fins was determined as the best thermal management system. Liquid cooling can be designed in for users who want the engine customised for higher power, larger cylinders, helicopter integration or other factors that entail higher thermal management. “Considerable iterative work was performed in CAD software and testing to optimise the geometry of the fins atop the cylinder heads for the heat from combustion,” Berli adds. Future plans Suter and CAE are now focusing on ensuring series production of the TOA 288, after which Kehe and his team will look to their next project – for which they already have a few options in the works. The TOA 288’s design can be reconfigured and expanded modularly. As such, alternative versions of it – such as single-cylinder or inline two-cylinder – have been designed, as has a four- cylinder version that will have double the TOA 288’s power. “The TOA 288 was always intended to be the first in a family of new engines,” Kehe says “The four-cylinder is essentially the same machine, but we’ve doubled the length of the crankshaft and installed another 288 alongside it.” “We could have designed a 600 cc two-cylinder engine, but a four-cylinder 600 cc TOA will have far lower vibration. We won’t have to develop any radically different control strategies for the 600 cc four-cylinder version, do any extensive studies for engineering or port timing, or decide on a range of new ancillary parts, because it’s still the same series of cylinders, pistons and so on, which we already fully understand.” Alternatively, they might look at creating a heavy-fuel version of the TOA 288, if research determines that the ability to fly using kerosene is in higher demand among UAV operators than a 34 kW, 18 kg engine. Kehe notes, “That would take more r&d, more time and pose more of a risk in terms of cost, but we are putting our resources into whichever direction UAV manufacturers have the greatest need for.” Unmanned Systems Technology | June/July 2020 Specifications Suter TOA 288 Twin opposed cylinder Two-stroke Air-cooled Weight: 8.9 kg Dimensions: 460.13 x 333.04 x 320.60 mm Operating power output: 14 kW (19 hp) at 6000 rpm Maximum power output: 17.7 kW (24 hp) at 6500 rpm Maximum torque: 27.5 Nm at 5500 rpm Bore: 56 mm Stroke: 58.5 mm Displacement (per cylinder): 144 cc Displacement (total): 288 cc Compression ratio: 9.5:1 Naturally aspirated Fuels: Mogas, Avgas, and synthetic (with minimum 95 octane) Comms: CAN and RS-485 Top speed: 6700 rpm TBO: 250 hours at time of writing, 500 hours anticipated Some key suppliers Heads: in-house Block: in-house Crankshaft: in-house Pistons: undisclosed Con rods: undisclosed Big-end bearings: Koyo, FAG Main bearings: SKF, FAG, NSK Seals: Freudenberg Valves: Moto Tassinari Spark plugs: NGK Fuel injectors: Bosch Throttle servo: Volz Alternator: Plettenberg Exhaust: undisclosed Intake manifold: in-house Air filter: Hifi Filter (modified in-house) Fuel pump: undisclosed Oil: API TC Coatings: undisclosed Surface treatments: undisclosed Heat treatments: undisclosed Among the next prospective projects for Suter Aviation is a four-cylinder 600 cc version of the TOA 288