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

22 U AVs provide tremendous opportunities to explore the potential advantages of unusual airframe configurations. Hybrids that combine the characteristics of multicopters and fixed-wing aircraft are increasingly common, but the Hybrid Advanced Multi-Rotor (HAMR) being developed by the Advanced Aircraft Company (AAC) under NASA alumnus William ‘Bill’ Fredericks is unique. It uses passively pivoting fairings that automatically adjust themselves in airflow to reduce drag and augment lift in forward flight, and minimise drag in a hover, without the need for actuators. Although the HAMR remains in rotor- driven flight throughout its envelope, its configuration and lift augmentation system improve significantly on the range, speed, payload and endurance offered by comparable conventional multi-rotor UAVs, and provide a degree of failsafe operation thanks to a hybrid petrol-electric power system. When we interviewed Fredericks for UST issue 13 (April-May 2017), he explained that this vehicle was intended to pave the way for the more demanding hybrid multi-motor tilt-wing Greased Lightning UAV by providing the start-up company with a source of revenue and a track record of bringing an advanced product to market. These days AAC is focused on precision agriculture and survey/ mapping, not only because current regulations permit UAVs but because there is an established market for these services. “The same design of the HAMR serves both applications, the only difference being the sensors that would be installed,” Fredericks says. AAC also plans to expand into linear infrastructure inspection – power lines, pipelines and railway tracks – and package delivery as the regulatory framework opens up to permit commercial beyond-line-of-sight operations. For the government/military sector, he says, the HAMR spans the gap in size between Group 1 hand-launched and Group 2 catapult-launched UAVs, noting that it has the minimal logistical footprint associated with Group 1 craft, which are typically lightweight but with greater endurance and the ability to carry payloads closer to those of the larger Group 2 vehicles. Final configuration After experimenting with prototypes, of which four have been built and flown with a fifth now under construction, the HAMR has settled into a configuration with six electric motors – earlier prototypes had eight – with two mounted on the short- span forward boom and four on the longer main boom at the rear. The front boom also carries a pair of pivoting fairings, one between each motor and the fuselage, while the rear boom carries four fairings in unequal- length pairs on each side. The longer fairings are between the outer and inner motors, while the shorter ones are between the inner motors and the fuselage. The composite fuselage houses a Desert Aircraft DA-35 engine (examined in detail in UST 15, August/September 2017) as well as a generator, a fuel tank, a Thunder Power lithium-ion battery, an autopilot and comms electronics, and two payload bays, one in the nose and one in the centre of the fuselage. Quest for drag reduction The HAMR’s fairings – passively moving wing surfaces – emerged from efforts to improve multi-rotor aerodynamics, particularly the lift-to-drag (L/D) ratio. Multi-rotors typically have an effective lift-to-drag (eL/D) ratio of around 2, Fredericks explains, manned helicopters have a ratio of between 4 and 5, and small fixed-wing UAVs achieve ratios in the 10-14 range. By comparison, airliners typically have an eL/D of 14-18. For fixed-wing aircraft, the L/D ratio is simply the lift – which is the same as the weight in level flight – divided Peter Donaldson details the development of this hybrid multi- rotor craft, designed as the prelude to a more advanced system Shape of things to come December/January 2018 | Unmanned Systems Technology