Deperdussin Monocoque, with wooden shell construction
Monocoque (// or //) is a structural approach that supports loads through an object's external skin, similar to an egg shell. The term is also used to indicate a structure in which the skin provides the main structural support, although this is rare and is usually confused with either semi-monocoque or a unibody. The word monocoque comes from the Greek for single (mono) and French for shell (coque). The technique may also be called structural skin. The term is often misused for sub-components that are superficially monocoques, but which are used as a part of a larger frame structure.
Alternatives to monocoque include trusses, unibodies, inflatable shells and semi-monocoque or stressed skin. The semi-monocoque is a hybrid combining a tensile shell and compressive structure made up of longerons and ribs or frames.
Early aircraft were constructed using internal frames, typically of wood or steel tubing, which were then covered (or skinned) with fabric such as irish linen or cotton. The skin added nothing to the structural strength of the airframe and was essentially dead weight beyond providing a smooth sealed surface. By thinking of the airframe as a whole, and not just the sum of its parts, it made sense to adopt a monocoque structure and it did not take long for various companies to adopt practices from the boat industry such as laminating thin strips of wood. In 1912, Deperdussin introduced a monocoque racer using a fuselage made up of three layers of laminated strips of glued poplar veneer, which provided both the external skin and the main load-bearing structure. This reduced drag so effectively it was able to win most of the races it was entered into. This style of construction was copied, with some variations, in Germany by LFG Roland — licensed by them to Pfalz Flugzeugwerke in the so-called, patented Wickelrumpf (wrapped body) form using two layers of plywood strips and fabric wrapping between them over a male mold for each half of the fuselage surface "shell"; while Albatros, Hannover and Siemens-Schuckert used four-sided panels of plywood instead, covering the light internal framework working forward from the tail, and upwards from the ventral side of the structure. However, it was prone to damage from moisture and delamination. Following the initial successes of all-metal aircraft from the Junkers firm as early as 1915 onwards, by the late 1930s, aluminum monocoque skin was used to form a pressurized cabin for high-altitude flight, such as in the Lockheed XC-35.
Commercial car bodies are almost never monocoques; instead modern cars use unitary construction or unit body, unibody, or Body Frame Integral construction, with box sections, bulkheads and tubes providing most of the strength of the vehicle, to which the skin adds relatively little to the strength or stiffness.
Tanks and other armored vehicles such as the German Fuchs 2 and RG-33 may use a body which is built of armor rather than attaching armor to a frame. This reduces weight for a given amount of armor compared to vehicles to which armor has been attached to an underlying frame.
A monocoque-framed motorcycle was developed by the Spanish motorcycle manufacturer, Ossa, for the 1967 Grand Prix motorcycle racing season. Although the single-cylinder Ossa had 20 horsepower (15 kW) less than its rivals, it was 45 pounds (20 kg) lighter and its monocoque frame was much stiffer than conventional motorcycle frames, giving it superior agility on the racetrack. Ossa would win four Grand Prix races with the monocoque bike before their rider was killed during the 1970 Isle of Man TT, causing the Ossa factory to withdraw from Grand Prix competition.
Notable designers such as Eric Offenstadt and Dan Hanebrink created unique monocoque designs in the early 1970s. The 1973 Isle of Man TT was won by Peter Williams on the monocoque-framed Norton John Player Special that he helped design. Honda also experimented with a monocoque Grand Prix racing motorcycle named the NR500 in 1979. However, the bike also featured other innovative features including an engine with oval shaped cylinders, and eventually succumbed to the problems associated with attempting to develop too many new technologies at once. In 1987 John Britten developed the Aero-D One, featuring a composite monocoque chassis that weighed only 12 kg. In 2009, Ducati introduced the Desmosedici GP9 with a carbon fibre semi-monocoque chassis.
Single-piece carbon fiber bicycle frames are sometimes described as monocoques however as most use the components to form a frame structure (even if molded in a single piece), these are frames and not monocoques, and the bike industry continues to refer to them as framesets.
Various rockets have used pressure-stabilized monocoque designs, such as Atlas and Falcon I. The Atlas was very light since a major portion of its structural support was provided by its single-wall steel "balloon" fuel tanks, which held their shape by internal pressure.
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