Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

36 H irth is one of the world’s leading suppliers of two- stroke engines – over the past 70 years it has delivered more than a million of them to customers globally. Not surprisingly then, this well established engineering company based near Stuttgart in Germany is a major player in the growing market for engines for small unmanned aerial vehicles. Here we investigate a state-of-the- art UAV engine from Hirth, its 183 cc twin-cylinder two-stroke, project S1218. It bristles with innovative technology, which allows it to burn all forms of kerosene-based fuel, however low the octane rating, making it invaluable for military deployments. The direct-injected Hirth flat-two is a flyweight power unit that provides 15 bhp and can operate missions of 14 hours’ or more duration. That is standard-setting performance. A comparable diesel engine would require a far stronger structure to contain the greater combustion pressures, which would add weight and there would be more vibration. The UAV market is heavily influenced by power-to-weight ratio – in simple terms, less weight is longer flight time. Hirth concentrates on two-stroke technology, which is ideal for the power density requirement of UAVs. “We can get 120 Nm per litre without turbocharging,” notes technical manager Dietrich Kehe. “We are totally focused on two-strokes, and are experts in the technology.” Launched at the Orlando AUVSI show in May 2014, the S1218 introduces Hirth’s innovative i-power system, the development of which began a couple of years ago. S1218 is based on project S1212, which has the same base engine and has been proven in combat use in Afghanistan and elsewhere. The key aspect of i-power is that it allows the engine to ignite all forms of kerosene (paraffin) based fuel. Often the basis of aviation jet fuel, kerosene is far less flammable than gasoline (petrol). In the distant past kerosene was used as an inexpensive fuel for tractors; in that application the engine was started on gasoline and would only switch over to Ian Bamsey visits Hirth to investigate a state-of- the-art UAV engine that genuinely provides for multi-fuel operation The Hirth S1218 boxer twin features ‘i-power’ direct injection November 2014 | Unmanned Systems Technology Fuelling freedom