Unmanned Systems Technology 013 | AutonomouStuff Lincoln MKZ | AI systems | Unmanned Underwater Vehicles | Cosworth AG2 UAV twin | AceCore Neo | Maintenance | IDEX 2017 Show report

54 single shared crankpin, the normal configuration is the boxer, having 180° phased individual pins. For the shared crankpin, the secondary forces cancel out but the primary forces add up, whereas for 180° phased crankpins, both the primary and secondary forces cancel out. However, since the pistons are not in line with each other, the equal and opposing forces generate a rocking couple on the crankshaft. Heath notes that the ‘big bang’ approach with the cylinders firing simultaneously is in the interest of engine balance. At the same time though, the high cylinder pressures cause “high tensile loads”. In view of this, he says, “We put a lot of FEA into the design of the engine structure, to ensure the best load path from the head/barrel studs on each side through the crankcase.” There is no vibration damping in the cranktrain. The rocking couple is modest since the con rod offset is low – most of the vibration caused by cylinder operation is rotational, around the crankshaft axis. Heath adds, “With the big bang configuration there is a large firing pulse on each revolution of the crankshaft, and the mounting system is designed to isolate the airframe from that pulsing.” The AG2 is attached to the airframe by four bosses on the front of the crankcase, with the engine cantilevered. Fuel system The AG2 has fuel delivered to its common injection rail by a custom- made, lightweight, mechanically driven plunger pump. The quantity of fuel supplied is a function of engine speed, while the supply pressure is controlled at the common rail. Heath is reluctant to specify the operating pressure, other than to say it is “several hundred bar” and to confirm that it is a three- rather than four-figure number. In the rail a pressure relief valve (PRV) maintains the required figure at the injectors. That pressure is constant under all operating conditions, hence the PRV is a passive ball and seat arrangement. There is a fuel return from the rail to the tank. How fuel is lifted from the tank is specific to the airframe: for rig testing Cosworth uses a gravity feed. Heath will not disclose the type of injector, other than to confirm that it is April/May 2017 | Unmanned Systems Technology The AG2’s air-cooled cylinder head The AG2’s brake-specific fuel consumption