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

UAV,” remarks Sampson. “All the sensors, including the inertial sensors for the autopilot, are very sensitive to vibration. The turbine doesn’t need engine cooling, aside from some cooling for the oil. That’s the beauty of it: all the waste heat goes out of the exhaust pipe.” It is worth noting that the turbine in question is of the turboshaft type, meaning it is optimised to provide power to an integrated output shaft rather than jet thrust. Sampson emphasises that in any turboshaft unit, as much of the energy of the hot gas as possible is extracted as useful shaft power. “A jet engine extracts only sufficient energy out of the turbine wheel to power the [charge] air compressor; the rest is nozzled and blown out of the back to create thrust for propulsion. In a turboshaft engine we extract as much of the energy of that exhaust stream as we can as torque to drive the rotor. It comes out as rotation of a mechanically linked shaft. As much energy as we can get is extracted using that output shaft, and there is not much thrust left in the exhaust.” The lack of cooling requirement 21 The engine One of the attractions of the Helicycle for Scion was its use of a turbine rather than a reciprocating or rotary engine. Given the operational requirements of the NRL and the fact that the craft would need to use Navy-specification, kerosene- based JP5/JP8/Jet-A heavy fuel (which is very difficult to ignite compared with other liquid fuels) the engine options, given what was available on the market, narrowed down to four-stroke compression-ignition (CI) or turbine. Of those the turbine was the lighter solution – indeed, Sampson reckons that a CI engine of comparable power output would weigh at least twice as much. “In choosing to use a turbine we gave up some fuel efficiency,” Sampson admits, “but what we gained is that in the turbine all the parts are moving in the same direction – they just spin, they aren’t trying to beat themselves to death, like they do in a reciprocating engine. In a turbine there is a lot less stress, there is a very low part count and most of the parts don’t touch, aside from a couple of bearings. That helps make a turbine extremely reliable, and it requires little servicing relative to a reciprocating engine.” Clearly a turbine also runs inherently smoother than any reciprocating engine. “Smooth running is really important for a Unmanned Systems Technology | Spring 2015 During proving trials the SA-400 took off and landed from a towed platform while in autonomous mode In a turbine there is a lot less stress and a very low part count, which helps make it extremely reliable and it requires little servicing