Unmanned Systems Technology 005 | Selex ES Falco UAV | Sense and avoid systems | RCV Engines DF70 | DSEI show report | Fuel cells | CUAV Expo, InterDrone and CUAV Show reports | SLAM

48 Dec 2015/Jan 2016 | Unmanned Systems Technology Horizontally opposed twin 36.0 mm bore x 35.0 mm stroke = 71.25 cc Naturally aspirated Heavy fuel Aluminium crankcase and cylinders Linerless; nickel silicon carbide bore coating Three main bearings, ball Steel crankshaft, two pins Steel con rods Light alloy pistons, one ring Gear- and shaft-driven vertical rotary valves One rotary valve per cylinder, one plug Electronic ignition Sequential port injection Engine management system 8.5:1 compression ratio Maximum rpm, 14,000 (8500 rpm normal operating limit) The DF70’s crankshaft runs in three main bearings, two of which sandwich the pair of crankpins and the three webs that connect them, with the third outrigged to the front to support the output drive to the propeller. The propeller is intended to attach directly to the front of the crankshaft; as standard, there is no form of clutch. The crankshaft is built from five elements. The first is the front section of shaft (running through the front two main bearings) and the associated front web. The second is the front crankpin, the third the web connecting that to the rear crankpin, which is the fourth section of shaft. The fifth section forms the rear web and the rear section of shaft (running in the rear main bearing). The crankcase directly carries the three main bearings, which are steel deep-groove ball bearings running on journals 15 mm in diameter. The two crankpins are a push fit into the respective webs, using an interference fit. Both pins carry a needle roller bearing. Steel rather than ceramic bearings are used throughout the engine. The steel con rods are I-section, 55 mm from eye to eye and, thanks to the built-up crankshaft, are made in one piece, with needle roller bearings at both big and small ends. The piston pin is 8 mm in diameter. It runs in a simple, single-ring slipper- type aluminium piston, with one end blind and the other carrying a PTFE button to retain it. Neither the aluminium piston nor the steel pin is coated but the steel ring, which runs against a nickel silicon carbide bore, has a chrome plating. The crankcase splits into two halves, vertically along its main axis such that each half carries one of the two cylinders. Six bolts tie those two halves together. The assembly is completed by a back plate, likewise aluminium, which, attached by eight bolts, adds to the integrity of the overall structure. Four bolts attach the base of each cylinder assembly to the respective crankcase side. Liquid gasket is used for the sealing faces. The cylinders are machined from billet aluminium, with the cylinder bore and the bore within which the VRV rotates given a nickel silicon carbide coating. Atop each cylinder is a timing drive gearbox, which encloses the gears driving the VRV. Six bolts attach this to its cylinder. Concealed by the crankcase back plate is a bevel timing drive gear, keyed to the crankshaft behind the rear main bearing. Each VRV timing drive shaft has on its lower end a mating bevel, which is keyed to it. At the top of the shaft, within the timing drive gearbox, is a spur gear, again keyed to it. The spur gear on one side mates with the gear mounted atop the VRV. On the other side there is an intermediate idler gear to reverse the Anatomy of the DF70 Key elements of RCV Engines’ DF70 rotary valve boxer