Figure 15.13. Typical scheme of aircraft structural layout

Military Aircraft Design

For military aircraft design, the same philosophy about nonmetal (i.e., composites) components is maintained, with weights increased to 40% of the OEW. Typical nonmetal structures include the floorboards, control surfaces, complex fairings (e.g., intake ducting and wing–body junction), and empennage.

15.6 Aircraft Structural Considerations

Creating just the aircraft shell, satisfying only aerodynamic needs, has consequences during manufacture. It is simple to create the drawings but not as easy to produce the hardware. During the conceptual study phase, it is routine procedure in the industry to obtain the valued opinion of production engineers in an IPPD environment. Compromises may be made in shaping an aircraft if doing so facilitates manufacturability, which in turn saves cost – more so in the commercial aircraft business, where operational economic gains are more important than in pure aerodynamics.

Manufacturing philosophy is associated with the choice of materials, machining routine, forming, fabrication, and assembly-tool (i.e., jigs and fixtures) concepts (see Chapter 17). Typically, the aim is to shape components as simply as possible with fewer parts and faster assembly time. Attention is given to minimizing complex 3D curvatures; applying more circular shapes than complex, convoluted curves; maintaining commonality of geometry; and providing accessibility for maintenance.

Therefore, it is suggested that a second-term project be assigned to introduce the structural philosophy in harmony with the manufacturing philosophy, beginning with internal structural arrangements in simple line diagrams, as shown for an aftfuselage in Figure 15.13a. Similar line drawings for the wing and empennage are not shown herein. The advantages of using CAD are discussed in previous chapters of this book, which are apparent, as shown for a typical military aircraft fuselage in Figure 15.13b. If a basic aircraft configuration is created in CAD, then the external aircraft contour lines guide the shape of the internal arrangement, with the added benefit of being able to examine accessibility and production complexity to establish manufacturing philosophy.