To attach the main structural carbon fiber reinforced plastic (CFRP) booms and spars to our aircraft, we use clamping arrangements to avoid the need for drilling retaining holes in the parts. We find CFRP is not easily or cleanly drilled, so we avoid this where possible. Where the CFRP part is not meant for routine removal, we design such clamps to be closed with cap-screws, see Figure 18.19a. For clamps that retain wings or tailplanes, where these need to be repeatedly removed for storage and transport, we use quick-release systems so that the clamps can be undone without tools, see Figure 18.19b.
Conventional Bolts and Screws
To hold in parts that are not routinely being removed we make extensive use of stainless steel cap-screws and washers with nyloc nuts or plain nuts and thread-locking fluid. We often find it convenient to place the nuts in appropriately molded hexagonal holes in the SLS nylon and be retained there with cyanoacrylate glue so that only a cap-screw driver is needed to fix the bolt; it is often difficult to gain access to both ends of such screws to apply both driver and spanner, see Figure 18.20.
Figure 18.20 Cap-screws and embedded retained nuts, here on an undercarriage fixing point.
Figure 18.21 Transport and storage cases.
Storage and Transport Cases
Having assembled a new UAV that may represent a considerable investment in manufacturing cost and effort, we think it sensible to provide storage and transport cases, custom-sized to suit the airframe. Such cases are not very expensive and a number of companies around the world produce suitable items to supplied dimensions very rapidly. Ideally they should have armored corners and edges, locks, foam-lined interiors to match the airframe, and wheels and handles to facilitate handling. It is also convenient to have hinged lids with stays. Figure 18.21 shows two of our cases.