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

56 Dossier | RCV Engines DF70 UAV boxer twin traditional small-displacement four- strokes, we have a far larger valve area, and our intake porting is unrestricted. We can double the power of small four-strokes derived from the likes of handheld power tools; at the same time, our rotary valve engine overcomes the problem of detonation associated with running a conventional four-stroke on heavy fuel. “You might be able to optimise a poppet valve four-stroke to match our performance on gasoline but, using four valves per cylinder, that would be a bigger, heavier engine – and you wouldn’t get it to run on heavy fuel. A two-stroke can be even more compact and light for a given power output, but again running it on heavy fuel is a challenge.” DF70 performance The RCV combustion system is ideally suited to heavy-fuel operation. Lawes reports that, once it’s at running temperature, it runs identically on kerosene/JP8 or gasoline, producing similar power and running without misfire over the same range of air-to-fuel ratios. He notes that the VRV offers inherently good throttle response, and that the DF70 can run to at least 14,000 rpm without issue, but there has been no call to develop it to go beyond the current 8500 rpm peak power speed. That speed is in turn a function of the propeller speed requirement in a typical fixed-wing UAV application using direct drive. The DF70’s peak torque speed is 6500 rpm while running on JP8 heavy fuel; maximum power at 8500 rpm is 4.2 kW (5.6 bhp). From 71.251 cc that amounts to 79 bhp/litre. Peak power is normally used only for take-off and subsequent climbs with fixed-wing craft cruising at partial load, at about 4000-5000 rpm, for the best fuel efficiency. Clearly, fuel consumption is partly a function of the craft under propulsion – in particular the propeller it is using – but a representative figure from the dyno is 300 g/kW/h (0.54 lb/hp/h). Engine life between rebuilds is limited by the rating of the bearings, which is 400 hours at maximum load. The base engine is only 263 mm wide, 70 mm high and 120 mm long. It weighs 2.7 kg (5.95 lb) complete with management system and exhaust (excluding only the propeller, cowling and any generator). Producing 5.63 bhp, it is thus very close to the 1 bhp per lb target set by DARPA. To improve power density further, weight-saving materials can be used: magnesium for the crankcase and titanium for the fasteners, for example. So far, only a few lightweight-specification engines have been supplied. Currently RCV offers only port injected gasoline and kerosene engines, with Mason noting that the engine runs on diesel fuel, still using spark ignition, but with a 5% drop in power and higher fuel consumption. Practical diesel operation would call for a costly development programme that awaits a user prepared to fund it. Dec 2015/Jan 2016 | Unmanned Systems Technology RCV Engines (RCV) was established in 1997 and currently employs seven people, with Eric Hill the managing director, Keith Lawes the technical director and Dr Brian Mason the commercial director. It is located on the edge of the New Forest in Dorset, England, within the premises of Manutech Manufacturing. Manutech assists in the production of prototype engines. Airframe integration is handled on behalf of RCV by HFE in Arizona and NW UAV in Oregon, the latter acting as a dealer for these UAV engines. RCV Engines The DF70 produces commendable power for an engine of its size Once the DF70 is at running temperature it runs identically on kerosene/ JP8 or gasoline, producing similar power without misfiring