Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

60 A composite is essentially a material or structure formed of two (possibly more) distinct elements, the principle being of course to counter the disadvantages of the one with the advantages of the other(s), and vice versa. In unmanned systems, the functional engineering objective is most typically to achieve the best possible mechanical properties for the least weight, balanced against other factors such as transparency to communication/ sensor frequencies, overall cost to manufacture/maintain, and durability. The use of composites to achieve these objectives is a natural solution, as they often provide superior specific properties – that is, the strength or stiffness per unit weight of material – compared to those of non-composites. The composites used in unmanned vehicles can be divided into two basic groups – metal matrix composites (MMCs) or polymer matrix composites (PMCs) – which are then reinforced with fibres or particles of another material that is typically more brittle but far stronger and stiffer than the matrix. In such a combination, the reinforcing material carries the loading, while the softer matrix serves to protect the fibres and transfer the load effectively as well as holding the required geometry. Of the two, PMCs are more widely used in unmanned systems, given their excellent strength-to-weight properties and perhaps easier manufacturing than MMCs. Polymer composites The most popularly known PMC is of course carbon fibre, or more properly carbon fibre reinforced polymer (CFRP). However, there are many alternative reinforcing fibres available, and each has its own advantages depending on the application. The most commonly available reinforcements besides carbon fibres are aramid-based, glass, quartz or thermoplastic fibres. The carbon fibres themselves can be manufactured from petroleum-derived pitch as a base material, or more often from a polyacrylonitrile (PAN) polymer. PAN fibres are heated (oxidised and carbonised) to burn off other elements and leave the desired carbon, after which further heat treatments can be applied to Matrix revolutions Composites are a natural fit for unmanned systems, writes David Cooper , who explains how the materials are made and used November 2014 | Unmanned Systems Technology