Fuselage

Thefuselage(/ˈfjuːzəlɑːʒ/;from theFrenchfuselé"spindle-shaped" ) is anaircraft's main body section. It holdscrew,passengers, orcargo.In single-engine aircraft, it will usually contain anengineas well, although in someamphibious aircraftthe single engine is mounted on apylonattached to the fuselage, which in turn is used as a floatinghull.The fuselage also serves to position thecontrolandstabilization surfacesin specific relationships tolifting surfaces,which is required for aircraft stability and maneuverability.

Types of structures

Piper PA-18welded tube truss fuselage structure

Truss structure

Some older types of aircraft design utilized open truss structure constructed of wood, steel, or aluminum tubing.^[1]^: 3–3

This type of structure is still in use in many lightweight aircraft usingwelded steeltube trusses. A box truss fuselage structure can also be built out of wood—often covered with plywood. Simple box structures may be rounded by the addition of supported lightweight stringers, allowing the fabric covering to form a more aerodynamic shape, or one more pleasing to the eye.

Geodesic construction

Thegeodetic airframeof aVickers Wellington,visible as a result of damage sustained to the fuselage skin on the aircraft's tail

Geodesic structural elements were used byBarnes Wallisfor BritishVickersbetween the wars and intoWorld War IIto form the whole of the fuselage, including its aerodynamic shape. In this type of construction multiple flat strip stringers are wound about the formers in opposite spiral directions, forming a basket-like appearance. This proved to be light, strong, and rigid and had the advantage of being made almost entirely of wood. A similar construction using aluminum alloy was used in theVickers Warwickwith less material than would be required for other structural types. The geodesic structure is also redundant and so can survive localized damage without catastrophic failure. A fabric covering over the structure completed the aerodynamic shell (see theVickers Wellingtonfor an example of a large warplane which uses this process). The logical evolution of this is the creation of fuselages using molded plywood, in which several sheets are laid with the grain in differing directions to give the monocoque type below.

Monocoque shell

TheVan's Aircraft RV-7of semi-monocoque construction

In this method, the exterior surface of the fuselage is also the primary structure. A typical early form of this (see theLockheed Vega) was built using moldedplywood,where the layers of plywood are formed over a "plug" or within amold.A later form of this structure usesfiberglasscloth impregnated with polyester or epoxy resin as the skin, instead of plywood. A simple form of this used in some amateur-built aircraft uses rigid expanded foam plastic as the core, with a fiberglass covering, eliminating the necessity of fabricating molds, but requiring more effort in finishing (see theRutan VariEze). An example of a larger molded plywood aircraft is thede Havilland Mosquitofighter/light bomber ofWorld War II. No plywood-skin fuselage is trulymonocoque,since stiffening elements are incorporated into the structure to carry concentrated loads that would otherwise buckle the thin skin. The use of molded fiberglass using negative ( "female" ) molds (which give a nearly finished product) is prevalent in the series production of many modernsailplanes.The use of molded composites for fuselage structures is being extended to large passenger aircraft such as theBoeing 787Dreamliner(using pressure-molding on female molds).

Semi-monocoque

Monocoque and semi-monocoque design^[1]^: 3–9

Monocoque construction uses stressed skin to support almost all loads much like an aluminum beverage can.

Semi-monocoque construction, partial or one-half, uses a substructure to which the airplane's skin is attached.

Sectioned fuselage of aBoeing 747showing formers,stringersand skin all made ofaluminium

This is the preferred method of constructing an all-aluminumfuselage. First, a series offormersin the shape of the fuselage cross sections are held in position on arigid fixture.These formers are then joined with lightweight longitudinal elements calledstringers.These are in turn covered with a skin of sheet aluminum, attached byrivetingor by bonding with special adhesives. The fixture is then disassembled and removed from the completed fuselage shell, 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 withfastenersto 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 many identical aircraft are to be produced. Early examples of this type include the Douglas AircraftDC-2andDC-3civil aircraft and the BoeingB-17 Flying Fortress.Most metal light aircraft are constructed using this process.

Both monocoque and semi-monocoque are referred to as "stressed skin" structures as all or a portion of the external load (i.e. from wings and empennage, and from discrete masses such as the engine) is taken by the surface covering. In addition, all the load from internalpressurizationis carried (asskin tension) by the external skin.

The proportioning of loads between the components is a design choice dictated largely by the dimensions, strength, and elasticity of the components available for construction and whether or not a design is intended to be "self jigging", not requiring a complete fixture for alignment.

Materials

Inside view of the wooden, fabric-covered fuselage of aFisher FP-202.

Early aircraft were constructed of wood frames covered in fabric. As monoplanes became popular, metal frames improved the strength, which eventually led to all-metal-structure aircraft, with metal covering for all its exterior surfaces - this was firstpioneered in the second half of 1915.Some modern aircraft are constructed with composite materials for major control surfaces, wings, or the entire fuselage such as the Boeing 787. On the 787, it makes possible higher pressurization levels and larger windows for passenger comfort as well as lower weight to reduce operating costs. The Boeing 787 weighs 1,500 lb (680 kg) less than if it were an all-aluminum assembly.^{[citation needed]}

Windows

Cockpitwindshields on theAirbus A320must withstandbird strikesup to 350 kn (650 km/h) and are made ofchemically strengthened glass.They are usually composed of three layers or plies, of glass or plastic: the inner two are 8 mm (0.3 in.) thick each and are structural, while the outer ply, about 3 mm thick, is a barrier againstforeign object damageandabrasion,with often ahydrophobiccoating. It must preventfogginginside the cabin and de-ice from −50 °C (−58 °F). This was previously done with thin wires similar to a rear car window but is now accomplished with a transparent, nanometers-thickcoatingofindium tin oxidesitting between plies, electrically conductive and thus transmitting heat.Curvedglass improvesaerodynamicsbutsightcriteria also needs larger panes. A cockpit windshield is composed of 4–6 panels, 35 kg (77 lb) each on anAirbus A320.In its lifetime, an average aircraft goes through three or fourwindshields,and the market is shared evenly betweenOEMand higher marginsaftermarket.^[2]

Cabinwindows, made from much lighter than glass stretchedacrylic glass,consists of multiple panes: an outer one built to support four times the maximum cabin pressure, an inner one for redundancy and a scratch pane near the passenger. Acrylic is susceptible tocrazing:a network of fine cracks appears but can be polished to restoreoptical transparency,removal and polishing typically undergo every 2–3 years for uncoated windows.^[2]

Wing integration

"Flying wing"aircraft, such as theNorthrop YB-49 Flying Wingand theNorthrop B-2 Spirit bomberhave no separate fuselage; instead what would be the fuselage is a thickened portion of the wing structure.

Conversely, there have been a small number of aircraft designs which have no separate wing, but use the fuselage to generate lift. Examples includeNational Aeronautics and Space Administration's experimentallifting bodydesigns and theVought XF5U-1 Flying Flapjack.

Ablended wing bodycan be considered a mixture of the above. It carries the useful load in a fuselage producing lift. A modern example isBoeing X-48.One of the earliest aircraft using this design approach isBurnelli CBY-3,which fuselage was airfoil shaped to produce lift.

Gallery

Interior rear-end of the main passenger level on anAirbus A340,showing the rearbulkheadas well as a doorway opening
RoughBoeing 747interiorairframe
Fuselage of aCubCrafters Carbon Cub
The fuselage can be short, and seemingly unaerodynamic,as in this Christen Eagle
Gliderfuselage schematic