36 is used for the blades, with the resin and the method by which the composite is formed via the autoclave being key to the blades’ mechanical properties. “There has been a huge learning curve since we made our first blades in 2008. For instance, in our early days, we’d find after flying and landing in rainy conditions that the blades were pitted all over their leading edges, and the more we flew in rain, the faster we were going through rotor blades,” Hunter recounts. “So, Johannes’ team came up with the idea to fix a nickel leading edge made by a third-party on our rotor blades, including on the tail rotors, which effectively stopped that problem. We’ve continued using and adapting that design since, and it’s great for the longevity of our rotor blades.” A second output shaft on the main gearbox powers the carbon-fibre driveshaft running to the tail gearbox, as mentioned, and a third output shaft powering an alternator. As well as gears, the gearbox contains a lubricating oil bath and dampening shafts. The latter smooths vibrations from the engine’s peaks and troughs of torque, being the main source of what little vibration a Wankel produces. Body matters Weight and aesthetics were the priorities in hull design, with Hans Georg Schiebel personally working on making the S-100 look like something navies and similar professional outfits would want to fly. The first submission from a commissioned design house was favoured by himself and his company, with minor optimisations made for cooling and similar needs. “The Camcopter 5.1 was a cluster of modules, which together flew very smoothly, but didn’t look at all like a serious tool for professional organisations,” says Hecht. “Optimising for weight, aerodynamics and resonance were important, as was designing for efficient manufacture later on, but we quickly learned in our early days – as much as some might not want to believe it – that customers buy UAVs with their eyes as much as with the datasheet and flight tests.” Internally, the structure is engineered as a single monocoque part, which directly integrates the fuel tank as well as mounting brackets for the engine, the main gearbox and avionics modules, as well as bearing the torsional and vibratory loads of the main rotor. “A lot of simulations and strength analysis calculations went into making sure the structural materials and design would serve those purposes, although there weren’t too many CFD or CAD tools for aerodynamics 20 years ago,” Hecht adds. “So, a lot of test flying was key for measuring relevant forces, and all we had to compare that against was basic literature telling us what to expect. The early structures were maybe 1.5 times heavier than they really needed to be, but with time and experience, we reduced all weight down to the absolute minimum we could, with just little tunings here and there today.” Material world Carbon composite is the main structural material, although a few fixtures of fibreglass composite are also used, and fixtures in the drivetrain are machined from high-strength aluminium, which, like the titanium rotor head, provides tensile strength advantages over carbon. The electronics are largely housed in aluminium housings for their combination of EMC-shielding and strength-to-weight advantages (including for the main avionics box containing the autopilot, power supply, data links and so on). As well as all carbon-fibre production and autoclaves being kept in-house, Schiebel has acquired metal additive printers (from which the titanium rotor heads are printed), and the company’s r&d department uses these to examine how weight may be removed from even highly loaded parts, such as the main rotors and landing gears. “They are laser sintering machines, which we can also switch to print using aluminium, and so a big future step will be looking into how all the aluminium parts could be redesigned through additive printing. It will really bring a new dimension to getting weight out of the UAV,” Hecht says. The composite parts are modelled in CAD, with that data fed directly into the automated prepreg cutting machines, which Schiebel reports as being more accurate than past manual cuttings. The moulds are manufactured from aluminium by a third party owing to their size, although the designs are generated August/September 2024 | Uncrewed Systems Technology Composite manufacturing, additive printing, engine manufacturing and more takes place at Schiebel’s factory in Wiener-Neustadt, Austria
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