Aircraft Construction

automobile manufacturing where the unibody is considered Monocoque standard in manufacturing. Bulkhead Semimonocoque Semimonocoque construction, partial or one-half, uses a substructure to which the airplane’s skin is attached. The substructure, which consists of bulkheads and/or formers of various sizes and stringers, reinforces the stressed skin Stressed skin by taking some of the bending stress from the fuselage. The main section of the fuselage also includes wing attachment Formers points and a firewall. On single-engine airplanes, the engine is usually attached to the front of the fuselage. There is a fireproof partition between the rear of the engine and the Semimonocoque flight deck or cabin to protect the pilot and passengers from accidental engine fires. This partition is called a firewall and Stringers Bulkhead is usually made of heat-resistant material such as stainless steel. However, a new emerging process of construction is the integration of composites or aircraft made entirely of composites. Skin Composite Construction Formers History The use of composites in aircraft construction can be dated to World War II aircraft when soft fiberglass insulation was Figure 3-14. Semimonocoque and monocoque fuselage design. used in B-29 fuselages. By the late 1950s, European high performance sailplane manufacturers were using fiberglass to deformation of the surface. For example, an aluminum as primary structures. In 1965, the FAA type certified the beverage can supports considerable forces at the ends of first all-fiberglass aircraft in the normal category, a Swiss the can, but if the side of the can is deformed slightly while sailplane called a Diamant HBV. Four years later, the FAA supporting a load, it collapses easily. certified a four-seat, single-engine Windecker Eagle in the normal category. By 2005, over 35 percent of new aircraft Because most twisting and bending stresses are carried by were constructed of composite materials. the external skin rather than by an open framework, the need for internal bracing was eliminated or reduced, saving weight Composite is a broad term and can mean materials such as and maximizing space. One of the notable and innovative fiberglass, carbon fiber cloth, Kevlar™ cloth, and mixtures methods for using monocoque construction was employed by of all of the above. Composite construction offers two Jack Northrop. In 1918, he devised a new way to construct advantages: extremely smooth skins and the ability to easily a monocoque fuselage used for the Lockheed S-1 Racer. form complex curved or streamlined structures. [Figure 3-15] The technique utilized two molded plywood half-shells that were glued together around wooden hoops or stringers. To Composite Materials in Aircraft construct the half shells, rather than gluing many strips of Composite materials are fiber-reinforced matrix systems. plywood over a form, three large sets of spruce strips were The matrix is the “glue” used to hold the fibers together soaked with glue and laid in a semi-circular concrete mold and, when cured, gives the part its shape, but the fibers carry that looked like a bathtub. Then, under a tightly clamped most of the load. There are many different types of fibers lid, a rubber balloon was inflated in the cavity to press and matrix systems. the plywood against the mold. Twenty-four hours later, the smooth half-shell was ready to be joined to another to In aircraft, the most common matrix is epoxy resin, which is create the fuselage. The two halves were each less than a a type of thermosetting plastic. Compared to other choices quarter inch thick. Although employed in the early aviation such as polyester resin, epoxy is stronger and has good high- period, monocoque construction would not reemerge for temperature properties. There are many different types of several decades due to the complexities involved. Every epoxies available with a wide range of structural properties, day examples of monocoque construction can be found in cure times and temperatures, and costs. 3-9