Historical context

Understanding modern aerospace manufacturing processes requires that they be viewed in the context of the historical development of vehicle design. The spruce and fir frames of aircraft through World War I required skilled woodworkers and their equipment, coupled with crafters—often women transferring homemaking skills to the shop—who laced or sewed fabric to the frames. These “skins” for the wings and fuselages were painted with acetone-based lacquers or dopes to tighten and toughen surfaces; thus factories had large brush or spray areas with natural or induced air circulation to enhance drying and dissipation of fumes. At the same time, with the exception of the air-cooled engine designs developed by the Wright brothers and sold widely in Europe, aircraft engine manufacturing was an extension of the production of liquid-cooled automobile motors. Emphasized were refined machining techniques for the cylinder head fins, which provided the extensive cooling surfaces needed.

The advent of metal airframes changed both the character of manufacturing processes and the skills required of production workers. At first, only the wood framework of fuselages was replaced by tubular aluminum trusses connected with mechanical fasteners or welding; coverings were still sewn and glued fabric. In the mid 1930s, as thin rolled aluminum alloys became available, all-metal structures for fuselages and then wings became prevalent. Skilled craftsmen were required to operate the metalworking machines, and new emphasis was placed on flush riveting and welding and on hard tooling of fixtures to facilitate alignment and assembly. At the same time, the forging of landing-gear components and major structural fittings and the forming of sheet metal grew to resemble processes in the automobile industry. This affinity became particularly close as all-metal bombers and transports revolutionized manufacturing of all but small private planes. It was not surprising, therefore, that the mass producers of automobiles and related equipment became manufacturers of military aircraft during World War II.

After the war, jet propulsion and other technical advances led to further changes in manufacturing techniques and processes. The economics of high-speed transports resulted in increases in passenger capacity, which necessitated aircraft much larger than wartime bombers. This, in turn, required expanded facilities and fixtures such that by the start of the 21st century initial plant investment for modern airliners had reached as high as $2 billion, even with more than 50 percent of the work being done by suppliers to the prime contractor. Thus, a community of structural subassembly contractors building wings, sections of fuselages, and horizontal surfaces now relieve some of the space and tooling needs of prime contractors such as Boeing in the United States and Airbus Industrie in Europe. Russian companies, however, still operate in a more vertically integrated mode, keeping all aspects of component manufacture and assembly within one organization.

Modern aircraft manufacture has been described as “a craft process with a mass production mentality.” With the exception of experimental and very specialized airplanes, this has generally been true. Large aircraft consist of the assembly of one million to five million separate parts, and complex spacecraft of several hundred thousand parts. Each different type demands unique skills and manufacturing methods.

Because of the extensive range of skills and facilities required, no single company builds an entire flight vehicle. Manufacturing in the aerospace industry crosses nearly all construction boundaries—for example, conventional machine shops for mechanical components, clean rooms for electronic parts, and unusually large final-assembly facilities for multi-hundred-ton aircraft, space vehicles, and missiles. In every developed country of the world, major aerospace production programs incorporate a complete range of hardware and software from suppliers that operate as subcontractors to the prime contractor or systems integrator. Subcontracting covers not only the onboard equipment but also, in most large projects, major elements of the airframe itself. In Europe, where large developments occur in multinational cooperative efforts, the distribution of the production is especially broad.

Fabrication processes and materials

Fabrication involves the manufacture of individual components that make up larger assemblies or end products. This activity encompasses the working of metals and the incorporation of electrical and electronic devices into processors, circuit boards, and subassemblies for the components of navigation, communication, and control systems. Most of the basic metal-fabrication methods have been employed since World War II. Modern differences, such as tighter metal-cutting tolerances, are related to advances in the capabilities of machines and tools (see metallurgy: Metalworking). In electronic fabrication, changes have mirrored those of the semiconductor and computer industries. In past decades, electronic elements having single functions were linked with wiring to make up the multiple functions necessary for systems. In modern systems, hundreds of functions are performed by a single microchip or, in conjunction with microminiaturized elements, by printed circuit boards (see integrated circuit).