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

24 Dossier | Scion UAS SA-400 optionally piloted helicopter taken off it, there is no conventional clutch in the transmission. Instead the engine is literally tilted down from a neutral start-up position so that its output shaft tensions the belts and thus creates drive to the transmission. This tilt mechanism operates at the front of the engine, and an over-centre approach allows it to lock into a position whereby once engaged there is constant tension on the belts. “The use of a conventional clutch would be heavier,” notes Scion UAS’ director of mechanical engineering Scott Lowry. “Since we have the [vertical] offset between the turbine output shaft and the transmission we can get two jobs done with the belts.” A small electric motor, which in the Helicycle is activated by a button pressed by the pilot, causes the engine to snap into its drive position. In the SA- 400 that function is integrated with the autonomous control system. “We have the computer check that the belt isn’t tensioned,” remarks Dr Phillip Jones, Scion UAS’ director of flight control and software development, “then it goes through all the process of starting the engine, then engages the belt drive and then revs up the engine to flight rpm: it is all automated. Then comes the next command, to take off.” An overrun clutch in the transmission allows the rotor to continue spinning if the power stops. This is purely an emergency device, to offer the chance of a safe touchdown in case of unplanned critical power loss. At the moment Scion is using the main rotor blades supplied with the Helicycle kit, which is formed as a bonded aluminium structure – in effect a folded sheet with a spar running inside the leading edge and other reinforcements. This is given special treatment to guard against corrosion and abrasion. Clearly, as a rotor spins, the airspeed as measured along the length of each blade increases with distance from the hub. As a consequence it can be advantageous to alter a blade’s profile along its length. That is not the case though with the SA-400’s off-the-shelf production, so Scion UAS is looking to develop a more sophisticated design that exploits such advanced tailoring as it moves in due course to a composite rotor blade that will be manufactured in-house. The stock tail rotor has already been replaced by Scion UAS’ own production. In effect, for a sideways flight requirement by the NRL it had to be beefed up – making the blade wider and more efficient – so both the rotor blades and the tail rotor hub mechanism were redesigned. For the time being, the production is still aluminium skins over steel spars, whereas in due course there will be a carbon fibre composite tail rotor. Spring 2015 | Unmanned Systems Technology Craft height: 82.1 in Craft width: 51.5 in Craft length: 232 in Rotor diameter: 250 in Empty weight: 700 lb Gross weight including full tank and payload: 1200 lb Turbine length: 33.4 in Turbine diameter: 21.4 in Turbine weight: 142 lb dry Maximum speed: 95 knots Cruising speed: 82 knots Mission duration: in excess of four hours. Some key component suppliers to the SA-400 Base helicopter, turbine & gears: Eagle R&D Autopilot: Adaptive Flight Servomotors: Moog Servomotors: Volz GPS: Novatel Alternators: B&C Specialty Products Battery: Odyssey Batteries Fuel pump: Facet Instrumentation: MGL Avionics Communications systems: Persistent Systems Navigation lights: Aeroleds Design software: CATIA Design software: SolidWorks CNC machines: Haas CNC machines: Zimmermann Pre-preg: Cytec Resin systems: MTM46 SA-400 general specification For the SA-400, Scion UAS designed its own tail rotor mechanism