| Fuselage and construction |
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Let's have a look at an aircraft fuselage. Why does a conventional airplane look the way it does? Today's aircraft all seem to have the same basic principle, the most common aircraft fuselage is called a semi-monocoque (monocoque meaning single shell) construction wich is a construction technique that uses the external skin of an object to support some or most of the load on the structure. This is as opposed to using an internal framework (or truss frame) that is then covered with a non-load-bearing skin. The first aircraft that were build with a semi monocoque construction had a single cilinder shape but to create more room for baggage the 'double bubble' construction was used wich basically meant two integrated cilinders shown very well in this picture of the Boeing C-97 Stratofreighter to the right. In modern airplanes they mostly done away with double bubble due to the size of the aircraft today and the stresses that appear at the joints. See this Airbus A380 picture.
For civil aviation the semi monocoque single bubble is now most commonly used, in the old military aircraft there were still many large aircraft build with a framework for strength in battle and ofcourse aircraft that are supersonic have a different fuselage shape as opposed to subsonic aircraft,
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Aircraft are build up of stringers that run horizontally and ribs that run vertically. Sections of two of these stringers are called frames.
The skin of the aircraft is glued or machined to these ribs and stringers and forms an integral part with the aircraft structure.
The floorbeams are also part of the integrity of the aircraft structure, the wings, horizontal stabilizer and vertical stabiliser are also all build up of stringers, ribs and skin. The wing even has fuel tanks in them while still being able to stretch the wings due to the airloads.
In between the wings is a torsion box to withstand the forces that come together at this central point and where the gaping big holes are for the maingears is a keelbeam to maintain structural integrity.