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

AAC chose brushless DC motors for the HAMR. The switch from eight motors to six saved a lot of weight but reduced the power margin. (Courtesy of T-Motor) 26 hover, the power required is dominated by induced power losses,” Fredericks says. “As the aircraft builds airspeed, the induced losses decrease and the parasite losses increase as a cubic function of velocity.” “At about 40 knots the total power required is back up to the hover power required. As speed builds further, the power required also increases as a cubic function of velocity.” Eight motors to six One of the main technical challenges in the HAMR’s development, he says, was to reduce its empty weight to improve its useful load, which involved a major change of configuration. “We couldn’t increase the gross weight because the current propulsion system produces 1.5 kW, and that limits the gross weight. To save weight, we therefore removed two of the motors and used the remaining six more effectively. “Our weight savings came from two areas. In the eight-motor configuration, the motors were kind of loafing along – they still had a lot of spare capacity in them. Now that we have gone down to six motors, we have also saved the weight of two propellers, two motor controllers, the wiring for two motors, as well as the motors themselves, and we have eaten up a lot of that surplus headroom,” he says. Also, in the eight-motor configuration the booms consisted of four individual tubes mounted at their inner ends to the fuselage sides, which is where the loading in the boom is highest. That meant the company had to include strong reinforcing brackets at the interface to attach them. Stronger, lighter boom “In the six-motor configuration though we made the tube continuous through the fuselage from one side to the other,” Fredericks says. “So we saved a lot of weight in the attachment brackets because the tube wasn’t cut where it had the highest bending moment. He adds, “The rear boom is actually made in three pieces. We have one tube that runs from an outer motor to an inner motor, another that runs from an inner motor continuously through the centreline of the fuselage to the other inner motor, and then the third tube runs from that inner motor to the outboard motor.” While a single continuous rear- motor support tube would be stronger and simpler, it would have been more than 10 ft long and hard to pack away conveniently for transport. So, Fredericks December/January 2018 | Unmanned Systems Technology Dossier | Advanced Aircraft Company HAMR UAV The motor booms now pass through the fuselage as continuous tubes, having previously separated at the fuselage sides. The new arrangement makes for a lighter structure (Courtesy of AAC)