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

59 Cosworth AG2 UAV twin | Dossier Each primary exhaust stub is formed integrally with its respective barrel, avoiding the need for a bolted flange. The combined exhaust system is connected to each stub by means of a push-on hose formed from high-temperature silicone rubber. The shared silencer, says Heath, “contains various noise control measures such as expansion and resonance chambers”. There is also a novel exhaust valve at the exit. “We have an active element in the exhaust that alters the geometry at different engine operating conditions to provide robust combustion at altitude as well as reducing noise,” Heath remarks. “That allows us to run a lower compression ratio for better durability and still get the combustion performance we need at high altitude.” Like the silencer system, it is a lightweight carbon fibre production. “That is taking advantage of our low-temperature exhaust,” observes Heath. Cooling and lubrication The barrels and head are finned, and the airframe will provide suitable ducting with EMS-controlled intake flaps governing cylinder head temperature. Since pre-mix can’t be used for lubrication, there is a total-loss system that draws from a small oil tank on the vehicle. Oil is sent to the front and centre main bearings, in each case via an electrically operated pump. That pump meters the oil a drip at a time, as dictated by an ECU map, which in turn refers to engine operating conditions as identified by selected sensors. Heath reports, “Inside the engine the parts are very carefully designed to ensure that oil is targeted at the critical areas for lubrication. The system has been designed to minimise the oil flow as this reduces the mass of oil required on a long mission.” Each electrically operated (but otherwise undisclosed type) oil pump meters lubricant at a rate that under conditions of low speed and low load can amount to only one drip every 10 s; under more demanding conditions the maximum rate is one drip every 1.5 s. Oil consumption is less than 50 cc per hour. Engine control With no throttling of the charge air, all engine output control is via injector operation. The ECU controls the timing of the injector opening as well as the duration of its delivery. It also controls the exhaust flap valve, the twin oil pumps and the cooling air control flaps. The key inputs to the ECU are crank position, fuel pressure, intake air temperature and pressure, cylinder head temperature, and the load demand as dictated by the vehicle’s overall control unit (which in turn is a request for a given propeller speed). Unmanned Systems Technology | April/May 2017 The AG2’s principal engineer, John Heath The AG2’s project manager, Dr Guido Monterzino The AG2 has been developed in a factory that until recently produced Formula One engines