Unmanned Systems Technology 013 | AutonomouStuff Lincoln MKZ | AI systems | Unmanned Underwater Vehicles | Cosworth AG2 UAV twin | AceCore Neo | Maintenance | IDEX 2017 Show report

63 Depending on the payload, it can hover in wind speeds of up to 18 m/s. The company quotes an operating temperature range of -10 to +45 C, and business development director Leon The says the Neo has flown in conditions ranging from cold, windy days in the Netherlands to the heat and sand of Dubai. Constructed from aerospace-grade materials, the airframe consists of a central hub surrounded by eight interchangeable arms in four vertically stacked and forked pairs. Most of the airframe (93% by weight) is carbon fibre- reinforced plastic, specifically 3K plain, twill and unidirectional carbon. The rest consists of 7075 aluminium alloy (6%) and 1% other materials such as titanium in some screws and elastomeric vibration damping material. Minimising drag Unusually for a multicopter, the arms are not simple tubes; instead they are shaped to minimise drag and moulded in upper and lower halves, giving the Neo a distinctively smooth look and creating a shell to contain and protect electrical and electronic components. Getting the shape and structure of the arms right was one of the main development challenges, according to design engineer Niek Groenendaal. He says the process involved close cooperation with the undisclosed partner company chosen for the composites work, which was developing its technologies to create complex shapes while AceCore was refining the shapes themselves. The 3K carbon, defined by the number of individual filaments per bundle or tow, is a relatively low-cost material with a coarse weave and not commonly associated with high-performance aerospace applications. However, it is light, relatively stiff, easy to work with and, in this case, comes in the form of a cloth pre-impregnated with aerospace-grade thermosetting epoxy resin. AceCore’s partner company uses a laser cutting machine to shape the cloth and ensure that, once cut, the tows in each part run in the correct directions to withstand the stresses imposed on them when they take up their final shapes after lay-up, moulding and curing. The shape of the arms is a compromise because of the need to balance the demands of reducing drag in a hover with minimising it in forward flight. All rotor craft experience parasite drag in a hover, which is caused by rotor wash impinging on the airframe from above. Exposed cables and other components also create drag, something that the Neo avoids by enclosing this equipment in the airframe. Much design effort also went into the means by which the arms are secured to the airframe centrepiece, with a particular focus on avoiding the stress concentrations typically associated with clamps and screws. Neo’s arms slide into place, creating a large area of contact between the carbon fibre surfaces to enable the lift and manoeuvring forces to be distributed throughout the entire airframe, Groenendaal says. Each is secured by a single titanium screw. A desire for compactness as well as drag reduction drove the ‘X8’ configuration, and the Neo has a much smaller overall span than a conventional octocopter with eight arms in the same horizontal plane. Each pair of arms resembles a tuning fork, a shape that also has a vibration management function for the benefit of the payload, according to Groenendaal. He explains, “The shape has a specific frequency at which vibrations are transferred into the centre frame. AceCore Neo | Digest Unmanned Systems Technology | April/May 2017 Each pair of arms resembles a tuning fork, a shape that also has a vibration management function for the payload’s benefit Detail of arm-to-centre body connection. The large contact area spreads flight loads