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

26 The ends of the carry-through spar in the fuselage and wing root structure mate with concentric stub spars bonded into the outer wings, while carbon studs locate the outer wing sections to prevent them from rotating about the spar ends. The pods containing the electric motors are moulded into the optimum aerodynamic shape, while the tail booms are simple carbon fibre tubes made with a 6k weave, which means there are 6000 filaments per tow or fibre bundle from which the part is woven. There are no mechanical hinges on the airframe due to integrating Kevlar hinges for all the control surfaces into the primary skin laminates. The primary benefit is toughness, as minor impacts – or bird strikes, says de Villiers – no longer threaten the loss of a control surface, while localised punctures or other field damage can be patched simply. No metal is used in the structure, so most fasteners tap into machined plastic tapping plates bonded to the inside of the structural skins, while the stub spars in the wings have a metal thread bonded in with epoxy resin to take the wing-retaining aluminium finger nut. The landing gear legs are also moulded in carbon fibre and are shaped to produce lift in forward flight. Pre-preg laminates To ensure a consistent ratio of epoxy resin matrix to reinforcing fibre, Carbonix uses a pre-impregnated (pre-preg) laminating system, while curing at high temperatures guarantees stability in hot operating environments, and a nano-toughened formulation improves resilience in bonding areas. De Villiers says Carbonix sources its carbon fibre from several suppliers. Specialised weaves come from SGL group in Germany, which also supplies Airbus and BMW, and from GMS in Australia. Surfacing pre-pregs, meanwhile, come from Lavender Composites, which for example offers a variant of ACG’s ZPREG range, as used by Ferrari. To form deeply curved parts such as fuselages, a plug or pattern is machined from plastic or tooling board, then a Gurit epoxy tooling system is used to make the mould from the same material as the final part to ensure consistent thermal expansion of tool and part at high cure temperatures. For prototype tooling, the company relaxes the tool specifications but adds an epoxy gel coat to give a hard, non- porous tool surface for production. With flatter parts such as wings and control surfaces, it mills the female mould directly from aluminium or steel using CNC machinery to provide an ideal hard and durable tool surface. In some cases matched moulds are used to give both sides of a part a smooth finish. Instead of using an autoclave, parts are cured in vacuum bags in an oven, because for thin parts excessive pressure can degrade structural performance by decreasing the moment of inertia of lightweight skins. Saito four-stroke single The thrust motor is a single-cylinder Saito FG21 spark ignition four-stroke engine with over-square bore and stroke dimensions of 32 x 26 mm for a capacity of 20.52 cc. The piston has a single ring for compression and oil control, and the valves are operated by pushrods driven by a cam geared to the crankshaft and rockers with valve clearance adjusters. The engine weighs about 620 g. With an operating speed range of 1800-9500 rpm, it runs on 91 octane unleaded petrol pre-mixed with high- quality synthetic two-stroke oil at a ratio of 20:1; Saito recommends Evolution Oil’s EVOX1001Q. This mixture is fed to the cylinder via a floatless carburettor supplied by a negative-pressure diaphragm pump. Saito provides its own ignition system consisting of the ignition box, earth, sensor and spark plug wiring and a switched cord for connection to the battery. The company also provides its own ¼ -32 spark plug designated SAIG20120. The Alti Transition has a three-blade propeller, and the FG21 is designed to drive units of 15 in in diameter with pitches between 7 and 9 in. (Pitch is a measure of how far the propeller would move forward in one revolution if it were a screw in a solid material.) Alti has made a number of modifications to the FG21 to suit it to its new home. The carburettor has been moved inside the fuselage, as has the ignition module, driving changes to the way it connects to the cylinder. There is also a new custom June/July 2016 | Unmanned Systems Technology Dossier | Alti Transition Transition’s electric lift motors also provide hover yaw control. In production versions, the rears will be integrated into the centre body/wing root section