Unmanned Systems Technology 008 | Alti Transition UAS | Ground control systems | Xponential 2016 report | Insitu Orbital N20 | UAVs | Solar power | Oceanology International 2016 report

25 recovery at the wingtips, maximising efficiency for a given span and root bending moment. They are heavily raked to maintain attached flow through partial vortex lift at high wing loadings,” de Villiers says. Several aerofoil sections with different thickness-to-chord ratios at different positions along the span help to optimise the behaviour of the structure under aerodynamic loads. The aerofoil sections are drawn from a library and customised to form the final design, this detailed work having been carried out by D3 Applied Technologies, which Carbonix describes as a leading aero optimisation team. As standard, the winglets are integral with the wing, but they can be made as separate detachable parts as an option. Again as standard, they are made from carbon fibre-reinforced epoxy, but the customer can specify glass fibre reinforcement to make them transparent to radio signals so that they can house antennae. The transition to glass happens seamlessly at the lay-up stage, so that the structure remains continuous. The fuselage cross-section is essentially trapezoidal, a shape selected to maximise internal volume while keeping drag- inducing wetted area (skin exposed to the airflow) to a minimum. It has a flat bottom and vertical sides that taper inboard as they go up to meet the wing, while the fillet between bottom and sides is varied along the length of the fuselage. Tapering the fuselage cross-section below the wing helps to manage pressure distribution in a manner analogous to the area rule, although strictly that rule applies at much higher speeds. “This is an example of a detail that called for specialised expertise in tooling design, to allow the fuselage and wing roots to be moulded in one piece and still be released from the mould,” says Dario Valenza of Carbonix. Structural members The central fuselage and blended wing route moulding features a bonded-in tubular carry-through spar, while the outer wing sections each have a single spar that consists of a transverse foam sandwich panel with carbon shear webs and a foam core. “During development of the airframe we experimented with different solutions, such as a moulded I-beam spar laminated into the structure, and a Nomex honeycomb panel construction,” says de Villiers. “The current configuration reflects the best trade-off between structural efficiency, toughness and cost.” The central fuselage and wing root structure is a moulded stressed-skin monocoque with optimised fibre layout and patching, and the carry-through spar is bonded in while the fuselage skins are in the mould. Other integral structural components include the engine bulkhead, a ring frame to locate the motor controls and what de Villiers describes as a partial bulkhead that doubles as the front end of the fuel tank. The top of the tank also forms part of the payload shelf. Making every piece of structure serve more than one purpose in this way minimises weight and maximises structural efficiency, he says. Unmanned Systems Technology | June/July 2016 Transition sits on its fixed gear, the lack of wheels emphasising that it is a VTOL- only machine. The front two legs are shaped to help generate lift in forward flight