Monocoque (pronounced /ˈmɒnɵkɒk/ or /ˈmɒnɵkoʊk/) is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork. The term is also used to indicate a form of vehicle construction in which the body and chassis form a single unit. The word monocoque comes from the Greek for single (mono) and French for shell (coque). [1] The technique may also be called structural skin, stressed skin, unit body, unibody, unitary construction, or Body Frame Integral. A semi-monocoque differs in having longerons and stringers.[2]
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Early aircraft were constructed using internal frames, typically of wood or steel tubing, which were then covered (or skinned) with fabric[3] such as irish linen or cotton.[4] Aircraft dope was then applied which tightened the fabric and provided a smooth sealed surface necessary to prevent excessive drag.[4]
In 1912 Deperdussin introduced their 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.[5] This reduced drag so effectively it was able to win most of the races it was entered into.[6] This style of construction was copied, with some variations, in Germany by Albatros and others however it was prone to damage from moisture.[7]
Tanks and other armored vehicles generally use a body or chassis which is built of the armor rather than attaching armor to a body-on-frame design. Though this generally produces a fairly heavy vehicle, it can reduce weight for a given amount of armor compared to soft-skinned vehicles to which armor has been added either as a modification or a kit. For example, the German Fuchs 2 [8] and RG-33 have monocoque hulls rather than a separate body and frame, while the truck-based M3 Half-track and up-armored humvee have separate bodies to which armor has been added.
A monocoque-framed motorcycle was developed by the Spanish motorcycle manufacturer, Ossa, for the 1967 Grand Prix motorcycle racing season.[9] Although the single-cylinder Ossa had 20 horsepower less than its rivals, it was 45 pounds lighter and its monocoque frame was much stiffer than conventional motorcycle frames, giving it superior agility on the racetrack.[9] Ossa would win four Grand Prix races with the monocoque bike before their rider was killed during the 1972 Isle of Man TT, causing the Ossa factory to withdraw from Grand Prix competition.[9]
Notable designers such as Eric Offenstadt and Dan Hanebrink created unique monocoque designs in the early 1970s.[10][11] The 1973 Isle of Man TT was won by Peter Williams on the monocoque-framed Norton John Player Special that he helped design.[12] Honda also experimented with a monocoque Grand Prix racing motorcycle named the NR500 in 1979.[13] 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 only weighed 12 kg.[14] In 2009, Ducati introduced the Desmosedici GP9 with a carbon fibre semi-monocoque chassis.
Traditional bicycles are not monocoques; they are classic framed structures. However, carbon fibre monocoque framesets are slowly emerging in high-end competitive bicycles, due to their stiffness and light weight. The American company Kestrel USA pioneered the use of carbon fibre monocoques in bike frame manufacture in the 1980s, and since then the technique has become increasingly widely used. Items such as seat-posts and other components are now employing the same technique.[15]
Various rockets have used pressure-stabilized monocoque designs, including Atlas[16] and Falcon I.[17] Atlas was very light weight since its sole structural support was provided by its single-wall steel "balloon" fuel tanks, which held their shape by internal pressure.
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