Fuselage and Internal Structure
Having initially made fuselages and other complex structural components from pre-preg carbon fiber patches laid into molds or laser-cut plywood with various forms of covering, we have now switched almost exclusively to the use of 3D printed parts, either made from fused deposition modeling acrylonitrile butadiene styrene (FDM ABS) or, more commonly, SLS nylon. This approach allows for considerable structural sophistication, permitting various forms of stiffeners, hatches, bayonet joints, reinforcing in way of the main spars and landing gear, and so on. The parts thus produced represent the single biggest investment of design effort in the airframe, often involving hundreds of hours of computer-aided design (CAD) effort. However, once designed, they can be readily manufactured and offer many benefits, although they are somewhat heavier than equivalent fiber-reinforced molded structures. Perhaps the greatest advantage they offer is the rapid customization and modification that this approach lends to the design efforts. Each new part that is manufactured automatically reflects the latest design standard, and the turnaround time for any design change to having flight-ready parts is typically 48 h. Repeatability is very easily achieved, making replacement parts interchangeable with those on an airframe without further effort. Figure 2.5 shows a typical SLS structural
Figure 2.5 A typical SLS structural component.
component from the SPOTTER aircraft, illustrating the complexity that can be readily achieved by this approach to design.