Fuselage
In an aircraft, the fuselage is the main body section that holds crew and passengers or cargo. In single engine aircraft it will usually contain an engine, athough in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage. The fuselage also serves to position control and stabilization surfaces in specific relationships to lifting surfaces, required for aircraft stability and maneuverability.
Fuselages are constructed using three types of structures:
- A truss structure. The structural elements resemble those of a bridge, with emphasis on using linked trianglular elements. The aerodyamic shape is completed by additional elements called formers and stringers and is then covered with fabric and painted. Most early aircraft used this technique with wood and wire trusses and this type of structure is still in use in many lightweight aircraft using welded steel tube trusses. This method is especially suitable for amateur built aircraft kits, where a complete welded truss structure is delivered with the fitting of other components, covering, and finishing completed by the user, as it ensures that a robust, uniform load bearing structure is within the completed aircraft.
- A monocoque shell. In this, the exterior surface of the fuselage is also the primary structure. A typical early form of this was built using moulded plywood, where the layers of plywood are formed over a "plug" or within a mold, A later form of this structure uses fiberglass cloth impregnated with polyester or epoxy resin. A simple form of this used in some amateur built aircraft uses rigid expanded foam plastic with a fiberglass covering, eliminating the necessity of fabricating molds, but requiring more effort in finishing. An example of a moulded plywood aircraft is the De Havilland Mosquito light fighter/bomber of World War II. The use of molded fiberglass using negative molds (which give a nearly finished product) is prevalent in the series production of many modern sailplanes.
- Semi-monocoqe. This is the preferred method of constructing an all aluminum fuselage. First, a series of formers in the shape of the fuselage cross sections are held in position on a rigid fixture. These formers are then joined with lightweight longitudinal elements called stringers. These are in turn covered with a skin of sheet aluminum, attached by riveting or by bonding with special adhesives. The fixture is then disassembled and removed from the fuseleage, which is then fitted out with wiring, controls, and interior equipment such as seats and luggage bins. Most modern large aircraft are built using this technique, but use several large sections constructed in this fashion which are then joined with fasteners to form the complete fuselage. As the accuracy of the final product is determined largely by the costly fixture, this form is suitable for series production, where a large number of identical aircraft are to be produced. Early examples of this type include the Douglas Aircraft DC-2 and DC-3 civil aircraft and the Boeing B-17 Flying Fortress.
Both monocoque and semi-monocoque are referred to as "stressed skin" structures as all or a portion of the load is taken by the surface covering.