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

72 camshaft, the cam is easily lubricated by indirect splashing or misting from the pool below, without the need for galleries or pipes running across it. A wet sump has been used because it generally requires fewer pipes, joints and other components than a dry sump, making the engine simpler. “If required, however, it would also be relatively simple to fit a dry-sump system, by using a low-profile collector tray at the bottom of the cylinder head, just below the camshaft and pumping oil to an external tank,” Newton adds. The main oil gallery for the engine also feeds oil to the propeller governor through drillings on its mounting flange, for lubrication and for users looking to integrate a hydraulic variable-pitch propeller. The gallery then runs along the left side of the engine and is tapped to provide oil for the turbocharger, with a temperature sensor and pressure sensor inside. Wherever possible, ATI has sought to use COTS turbo parts, but chose to design and manufacture its own turbine housing after it had determined that there was more weight on the turbine than was optimal for an aircraft engine. “That housing is integral with the manifold, and is made from thin stainless steel to be both lightweight and strong, whereas a typical COTS turbocharger will use cast iron for that,” Franklin notes. “The bearing system, and the middle and rear section, are COTS. As commercial turbines are designed to last the lifetime of a commercial diesel truck, which is a million miles at an average of 50 mph, it lasts a long time, consistent with our TBO goal.” The supercharger is a bespoke design and incorporates a low-stiffness drive system to enable it to be driven by one of the timing gears. It was created by the ATI design team specifically for this engine, as commercially available units of correct flow capacity were too heavy to allow weight targets to be met. Although no muffler is provided, the turbocharger takes a lot of noise out of the exhaust on its own, with the expansion path through the turbine suppressing exhaust noise significantly. “We’ve had a couple of customers who decided to use straight-through pipes and have had no noise issues whatsoever,” Franklin says. Cooling A number of different configurations and components have been designed into the WAM-167BB in order to dissipate heat. As mentioned, the exhaust valves at the bottom of each cylinder have been moved further apart than in the previous generations for better cooling, and the oil injected onto the pistons also serves a cooling purpose. The engine is liquid-cooled throughout, typically using premixed Cool-Elf-Supra (a standard aerospace grade antifreeze). On the front of the engine, mounted beneath the propeller governor, is a water radiator. The radiator has a broad surface area with a honeycomb matrix of vanes about a network of flow passages, to maximise the area across which the heated water-antifreeze fluid can cool down. The velocity of a fixed-wing UAV, once airborne, provides sufficient airflow over the radiator to cool the fluid, before it is piped back towards the main areas that need cooling. Of perhaps greatest concern are the fuel injectors, as they are mission- critical components sitting directly next to the area of combustion. A coolant jacket is therefore fitted around each pre-combustion chamber to provide cooling for the injectors. Given the proximity of the pre- chambers and cylinder heads, coolant pipes run from each jacket between each exhaust valve to provide cooling. Another set of fluid jackets run up and around each cylinder to mitigate heat build-up through the crankcase. Coolant pressure is provided by a water pump at the rear-base of the engine, which injects the water-antifreeze mixture into the jackets surrounding the pre-chambers and cylinder heads before it runs up into the cylinder jackets. After cooling the engine block, the fluid comes out of a flange and into a wax thermostat that regulates the flow, sending it to the radiator if it’s too hot or back to the pump if not. Should a customer require more sophisticated coolant control, an external inline thermostat can be used. “Each cylinder’s jacket is essentially a tube, which we’ve designed to be fairly narrow in order to get a high flow velocity, because that greater velocity improves the heat transfer coefficient,” Franklin says. “So you get more heat out of the same area.” As mentioned, the engine integrates an intercooler that sits between the turbocharger and supercharger to cool the air from the turbocharger’s compressor. October/November 2019 | Unmanned Systems Technology Dossier | Apple Tree Innovation WAM-167BB In the WAM-167BB the air and exhaust gases flow in a single direction, towards the exhaust poppet valves, which are actuated by this exhaust camshaft