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

49 RCV Engines DF70 UAV boxer twin | Dossier Unmanned Systems Technology | Dec 2015/Jan 2016 rotation, so that both VRVs run in the same direction. This allows the inlets and exhausts to be on the same side of the engine respectively. The shafts and gears are all steel. There is an aluminium housing for each shaft, which provides support for the shaft’s deep-groove roller bearings. This housing bolts to the crankcase and to the timing drive gearbox, with O-ring sealing. Removing the timing drive gearbox top cover allows access to the VRV and its overhead gear for ease of servicing. The VRV and its drive gear can quickly be re-assembled and timed. The VRV is hardened steel with an all-over DLC coating. It is plasma nitrided prior to the application of DLC. It runs in a ball race and is driven by a gear mounted atop it with a locating pin to determine the valve timing. In most applications each throttle body is fed through a tuned-length pipe with an independent air filter. The throttles are mechanically linked so as to be operated by a single servo. Four bolts attach the aluminium throttle body directly to the cylinder. The throttle body mounts the single injector downstream of the barrel (and pointing forwards down into the airflow). Opposite the injector is the throttle body cartridge heater. Each exhaust primary is attached to the cylinder by four bolts. The two steel primaries (one emerging from each cylinder) feed into an aluminium cross-pipe/muffler body. In turn there is a single central rearwards exhaust exit from that. The DF70 is run by an ECU that is custom made for RCV, while the software is based on a universal field-proven code. The engine is port fuel injected using a single injector per cylinder. The fuel injectors are conventional off- the-shelf components from a 49 cc four-stroke scooter engine. The ignition is distributorless using a double-ended ignition coil with a wasted spark system to fire both plugs at the same time. The ignition system is inductive, providing a higher spark energy and duration than a more conventional CDI system. The miniature fuel pump is electric. It pushes pressurised fuel through a pressure regulator and back to the fuel tank, and supplies both injectors at a pressure nominally set to between 2.5 and 3 bar (and there is no link between the two cylinder supplies). The engine management system controls only the ignition coils and the injectors – the throttle is operated by the wider craft control system, together with the louvres controlling the cooling airflow. Meanwhile, the electrically driven gear-type fuel pump operates at a constant speed, so only needs to be switched on and off. The engine management system, aside from speed and load sensors, monitors cylinder head temperature, manifold pressure and fuel pressure. To measure engine load, the system uses inlet manifold pressure, which is sampled over a specific period in the four-stroke cycle to give a more linear representation of the amount of air flowing into the cylinder. Fuelling is primarily governed by the main fuelling map. This is two-dimensional and adjusts the amount of fuel according to rpm and engine load. Fuelling is then further adjusted according to cylinder head temperature, inlet air temperature and barometric pressure. There is a facility to monitor fuel consumption when the engine is in use. Lubrication is by means of adding a tiny proportion of oil to the fuel, in typical two-stroke fashion; the lubricant is fully synthetic two-stroke oil. The engine is air-cooled and has glow plugs for cold start on heavy fuel. The DF70 can have a starter linked to the rear of the crankshaft or, for packaging reasons, either of the two VRV driveshafts. Some customers put an electrical generator between the propeller and the crankcase, and this can be operated in reverse as a starter motor. The propeller bolts to the front of the crankshaft with half-a-dozen bolts. Components of RCV Engines’ DF70 rotary valve boxer in the metal