Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

84 Focus | Composites stability, toughness and very low moisture uptake. They also isolate well against fire, smoke and toxicity, which can be critical for high-end unmanned systems, particularly long-endurance electric aircraft or autonomous transport vehicles. Also, blends of cyanate esters and nanoparticulate additives (such as nanosilicates and core-shell rubbers) in other epoxies have successfully been used over the past 2-3 years to further increase composite toughness and fatigue life, as well as reducing thermal contractions. Design Historically, vehicle OEMs would approach composite suppliers with a part (or parts) made from a single plastic or metal, and request identical, drop- in replacements made from carbon or glass composite. Over the past decade though, it has become common for new composite parts to be modelled as original designs in CAD software, especially for unmanned vehicles. SolidWorks and Catia are examples of CAD software that have proven useful for designing new composite parts with acceptable fidelity to their real-world structural loading, thermal and dielectric behaviours, as well as exporting them over to composites manufacturers well enough for them to make those parts a reality. But while many older UAV engineers have extensive experience of working directly with composite materials, and younger engineers tend to be very skilled with CAD and knowledgeable about additively manufactured parts, neither typically have the experience needed to design a composite part with properties that will transfer over to the real world accurately. Thus even among well-designed composite CAD files, it is typical for high- end composites suppliers to ‘tweak’ the design based on their accumulated experience of materials science and which cannot always be faithfully modelled or represented in CAD. For example, over- reliance on right-angles – which most composites abhor – can be removed. Also, points labelled for drilling through-holes, to insert fasteners or wire harnesses for example, will pose a concern to experienced materials engineers as any drilling or cutting of finished composites risks delamination or other means of damage build-up. Through-holes can instead be included in the moulding design and cut into the fabric before layup or curing. In more extreme cases, larger-scale changes might be recommended, such as splitting a design into constituent parts to bring its geometric complexity within the bounds of what conventional manufacturing can achieve, or even pointing out entire sections that would be less costly to make from thin, CNC-machined aluminium. And at a micro-level, proprietary software rewrites and plug-ins at the supplier’s end are often fundamental for outputting even the most painstakingly designed CAD models into the code for machinery used to cut fibre ply or grind finished parts. These types of adjustments are often made with a single consideration on the composite maker’s mind: what is truly necessary to produce these parts to the quality and quantity required? What is known as ‘design for manufacture’ has accordingly become the foremost objective, as designing pieces of composite to be high quality and manufacturable early on gives better value for money down the line. Manufacturing approaches Manufacturing quantities vary more among unmanned systems than most vehicle types. An order of new UAVs and spare composite parts for them, for instance, could run up to bulk orders numbering tens of thousands or single- digit orders more akin to motorsport. And with companies such as Starship Technologies and Zipline rapidly going global with their autonomous delivery operations, orders for the millions of parts typical of automotive OEMs could soon be seen in the unmanned world. The size of the order will largely dictate the kinds of tooling and processes that are appropriate for forming the pre-preg material to the shapes and properties requested. If only three or four units of a requested design are needed, relying on a tooling board made from epoxy resin (good for up to five uses before degrading) might be sufficient for forming the desired shape and geometry. However, most composite parts nowadays – even for limited-production UAVs and other unmanned vehicles – are requested for supply and replacement on an ongoing basis. Tools of a higher grade must therefore be produced, and in greater numbers. December/January 2022 | Unmanned Systems Technology Use of extremely thin-ply and spread-tow technology enables very high fibre-versus-resin content, resulting in carbon composites with optimal strength-to-weight ratios (Courtesy of Oxeon)