Unmanned Systems Technology 017 | AAC HAMR UAV | Autopilots | Airborne surveillance | Primoco 500 two-stroke | Faro ScanBot UGV | Transponders | Intergeo, CUAV Expo and CUAV Show reports

explains, “There’s a hinge next to each inboard motor on the back. The outboard tubes fold in towards the centre, and then it fits nicely in the case.” Hinging the rear tube next to each inboard motor didn’t impose as much of a weight penalty in structural reinforcement as dividing it at the fuselage, because the bending loads near the motors are much lower than at the fuselage. The hinge is a 3D-printed aluminium component that allows the booms to fold from their flight position. It is made using selective laser sintering by US company ShapeWays, which also prints plastic components by this method. “It’s really nice. We design the part, upload the geometry and then they put it in a box and mail it back to us – that’s all we have to worry about,” Fredericks says. Reliability and smoothness Another challenge was ensuring the reliability of the propulsion system. “One of the more dramatic failures was almost a year ago. The whole generator machine short-circuited, started smoking and caught fire,” Fredericks recalls. Fortunately, AAC soon identified the cause. “We’d over-temped the rectifier, two of the phase legs lost their insulation, a short-circuit developed and then the high-amp situation set the resin on fire in the generator,” Fredericks says. “The different-phase wires in the rectifier board shorted together because we’d overheated the board. So we’ve redesigned the installation to ensure adequate cooling and make sure that doesn’t happen again.” Other reliability work has focused on smoothness. Fredericks says, “We’ve done a lot of work to isolate the vibration of the engine from the rest of the aircraft so as not to shake the payloads it carries. “All the parts in the moving reference frame of the engine are building up cycles like crazy, so we’ve had a number of fatigue cracks, or cracks propagate through different parts around the engine, because the engine is shaking the frame so much.