Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

68 As Franklin notes, however, “The actual power rating we’ll give a manufactured engine will very much depend on the user and how arduous their intended duty cycle is. In performance terms, we’ve proved that the cylinder architecture is well-capable of more than 150 bhp on the three-cylinder engine, so more than 50 bhp per cylinder. But it’s all going to depend on the structural durability required for that particular application. “Alongside that, there are some proprietary material changes that we can make which will give the higher power output, but they’re more expensive. If a user is willing to pay, we can put the more expensive material in to enable the engine to handle the higher loads of the higher power capability.” A mechanical control unit (MCU) provides a ‘power lever’ for controlling and stabilising engine fuelling (this being a diesel engine, the power output is almost directly proportional to the fuel input). As well as that lever/actuator, there is a ‘stop’ lever for (immediately) shutting down the engine if there’s a problem. Both levers are linked to a ‘rack’ control rod in the fuel pump, the power lever via a sprung link that also incorporates a linkage to a pneumatic actuator, giving an engine speed governing function for idling and low-speed operation. The stop lever is directly linked to the rack in the no-fuel direction. The rack itself is sprung in the ‘full-fuel’ direction so that failure in the system results in maximum power, with an override capability to reduce power and stop the engine being retained by the stop lever. As the standard configuration of the WAM-167BB comes without an ECU, all the key timing functions of the engine are factory (mechanically) set on build. The 840 mm crankshaft, for example, is CNC-machined, from EN40B nitriding steel, with 90° crank pin angles so that the first cylinder fires at one-quarter turn, the second at half-turn, and so on. The crankshaft notably features six multi- layer plain bearings – one between each cylinder, one either side, and one bearing further on the front for the propeller governor. The big-end bearings are also plain multi-layer shells running on the crankpins and held in the horizontally split big-end eyes. All the bearings are pressure-fed with oil. As mentioned, the fuel is injected into a pre-combustion chamber beneath each cylinder. Although injection timing is also factory-set, with injection pressure fixed at 300 bar, the company has declined to disclose an injection angle (or angles) for the chute or injection timing. The fuel flow valve on the fuel pump is entirely mechanical, and is controlled through a governor. The company is aware though that some commercial and most military UAV operators would probably want to control the fuel pump electronically to provide bespoke power bands, rates of response, optimise the SFC or other factors. And being a compression-ignition engine, no throttle is used of course. To that end, ATI has deliberately kept to relatively simple mechanical controls, leaving the architecture open for end- users and their engineers or preferred suppliers to design their ECUs according to their mission-specific requirements, or for them to request that of ATI. As Franklin says, “It’s relatively easy, if a customer requests it, for us to write an algorithm for an ECU that will swing the power lever or stop lever to reduce or stop the engine power when needed.” The air-fuel mixture during flight will typically vary between 18:1 and 50:1, from highest to lowest operating power output (and if no fuel is injected, the engine stops of course). Engine operation A 2.5 kW starter motor on the forward lower-right of the crankshaft provides initial power for turning the crank, via a ring gear on the forward counterbalance, with minimal counterbalancing designed along the shaft itself. A Roots-type twin- rotor supercharger provides initial air compression before the turbocharger can activate. On the back end of the crankshaft is a timing drive gear. As the crank turns, the gear interacts with a second gear of equal size and shape – 20 cm in diameter with 113 teeth – which controls the fuel pump. The gear October/November 2019 | Unmanned Systems Technology Dossier | Apple Tree Innovation WAM-167BB ATI has developed the WAM-167BB with the aim of a four-cylinder engine producing a more commercially desirable power output – currently 124 kW at maximum power rating