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

30 “We’ve had to redesign some parts so that they don’t crack, and the cracks don’t propagate. That has meant using a thicker gauge metal, making a stronger part so it doesn’t crack in the first place.” The engine is held in the fuselage by a novel system of vibration-isolating mounts, whose design is affected by the hybrid nature of the power plant. “The engine is designed to spin a propeller,” Fredericks points out. “Since we are not spinning a propeller on the HAMR, the engine acts as a generator and we don’t have to react the thrust loads and other forces from our prop, so the way we designed the vibration isolation system is different.” As AAC intends to file for patent protection for the system, Fredericks declines to go into detail about the design, but he is excited about its performance. “When we fly the HAMR on battery power alone with the engine off and look at the vibration data, and then fly it with the engine running and look at the vibration data again, there is negligible difference. So I think we’ve clearly done a very good job isolating the vibration of the engine from the rest of the vehicle.” As a series hybrid, the HAMR’s propulsion system relies on the engine to spin a generator to keep the battery charged, while current is drawn from the battery by the loads, including the motors, flight control electronics, comms and payloads. To govern the power flow between the generator, the battery and loads, hybrid technology developer LaunchPoint Technologies developed a control loop to monitor the current going into and coming out of the battery, and adjust the engine’s throttle to bring the difference between the battery input and output currents to zero. The battery also has a role in emergencies, providing enough energy to bring the HAMR in for a safe landing in case of an engine failure. If the engine does fail in flight, Fredericks says, the vehicle recovers very quickly. “It sags a couple of feet in altitude as the battery starts taking the load, with no action required on the part of the operator, and is back to steady state in less than 1 s.” As a future option, the operator will be able to stop the engine in flight to reduce the aircraft’s acoustic signature, for example to make a stealthy approach to a surveillance target or when flying in a noise-sensitive area, and then restart it when that phase of the mission is complete. Control authority The combination of motors and propellers provides all the control forces as well as thrust for propulsion. Varying propeller rpm generates the pitch and roll forces, as with conventional multicopters, December/January 2018 | Unmanned Systems Technology Dossier | Advanced Aircraft Company HAMR UAV The HAMR in its 54.4 x 29.2 x 16 in transport and storage case, the fuselage and power plant in one section and booms, motors and props in the other (Courtesy of AAC) The aluminium alloy hinges about which the rear motor booms fold for transport and storage are 3D printed by ShapeWays using a selective laser sintering process (Courtesy of AAC)