Unmanned Systems Technology 002 | Scion SA-400 | Commercial UAV Show report | Vision sensors | Danielson Trident I Security and safety systems | MIRA MACE | Additive manufacturing | Marine UUVs

53 Danielson Aircraft Systems Trident 100 TD2 turbodiesel | Dossier pump serving its single injector. “The common rail system is a source of potential engine failure; here we have a fully mechanical system for each cylinder operating independently,” he says. In the turbodiesel engine, fuel pressure needs to be very high relative to SI to suit the combustion environment, and the higher it is the smaller the droplets of atomised fuel and the higher the efficiency of burn: a typical figure for a common rail road engine is 1800 bar. In the Trident system, fuel pressure peaks at just over 1000 bar, which is perhaps the only compromise with the mechanical system. In most respects, says Hubschwerlen, system performance matches that of an electronically controlled one. The individual fuel pump for each cylinder is driven by the single overhead camshaft that also operates its two inline valves. Inside the pump is a piston that, as it reciprocates under the action of the cam, opens and closes a port that feeds fuel to the injector. The injectors are not switched on and off but dispense slugs of fuel as dictated by piston motion. The pump piston has a helical delivery slot. Turning the piston axially, by altering the position of the slot relative to the port, varies the quantity of fuel delivered on each stroke. Rotation of the piston is achieved through a push- pull mechanism ultimately controlled by the autopilot. “This system is simple but effective, and removes points of potential failure,” Hubschwerlen says. Engine structure A turbodiesel calls for a rugged engine structure to contain the implicit combustion pressures. This dry-sump engine has an all-aluminium structure aside from the lower crankcase/sump and a front cover, both of which are magnesium. Of the relatively few outsourced items, the head gasket is stainless steel. The engine is linerless but the bores have a hard iron-based coating using the Oerlikon-Metco SumeBore plasma spray process. The bore coating is applied either by Oerlikon-Metco in Switzerland or by Capricorn in the UK, with Capricorn also honing the bores. The magnesium front cover houses the timing drive and forms a vertical oil tank. In addition to the carbon fibre top cover, a starter-generator at the rear of the crankshaft also has a carbon fibre cover. The 100 TD2 has its timing drive at the front and its propeller drive at the rear. On the tail of the crankshaft is the aforementioned torque-smoothing device, then behind that the lower of the two step-up gears that comprise a fixed-ratio gearbox taking the drive up to propeller shaft height. On the very rear of the crankshaft, underneath the propeller shaft, is the starter-generator unit, which provides power for the UAV’s various electrical systems. The nitrided steel crankshaft runs in five main bearings, a pair sandwiching each big end with the fifth ahead of the torque smoothing device, supporting the lower of the two gears in the step-up gearbox. Conventional tri-metal bearings are used for the main and big-end bearings, of which there are three, each cylinder having its own crankpin. The crankshaft is made in-house, as are the steel con rods, which are H-section. The con rod small end is bronze bushed and the piston pin running in it is an uncoated steel item, again made in-house. The three-ring piston is aluminium with a cast-iron reinforcement carrying the upper rings, as per conventional high- performance CI practice. Danielson is considering the alternative of a steel piston, as pioneered by Peugeot in its Le Mans-winning engine. The valve seats are sintered steel while the valves are solid steel; dual steel valve return valve springs are used. Unmanned Systems Technology | Spring 2015 The Trident 100 TD2 uses a clever mechanical injection system In most respects the performance of the Trident’s mechanical engine control system matches that of an electronically controlled one