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Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
term for "single shell". First used for boats, a true monocoque carries both tensile and compressive forces within the skin and can be recognised by the absence of a load-carrying internal frame. Few metal aircraft other than those with milled skins can strictly be regarded as pure monocoques, as they use a metal shell or sheeting reinforced with frames riveted to the skin, but most wooden aircraft are described as monocoques, even though they also incorporate frames. By contrast, a semi-monocoque is a hybrid combining a tensile stressed skin and a compressive structure made up of longerons and ribs or frames. Other semi-monocoques, not to be confused with true monocoques, include vehicle unibodies, which tend to be composites, and inflatable shells or
balloon tank A balloon tank is a style of propellant tank used in the SM-65 Atlas intercontinental ballistic missile (ICBM) and Centaur upper stage that does not use an internal framework, but instead relies on a positive internal pressurization to keep i ...
s, both of which are pressure stabilised.


Aircraft

Early aircraft were constructed using frames, typically of
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...
or
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
tubing, which could then be covered (or ''skinned'') with fabric such as Irish linen or
cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...
.Robertson, 1996, pp.1–2 The fabric made a minor structural contribution in tension but none in compression and was there for aerodynamic reasons only. By considering the structure as a whole and not just the sum of its parts, monocoque construction integrated the skin and frame into a single load-bearing shell with significant improvements to strength and weight. To make the shell, thin strips of wood were laminated into a three dimensional shape; a technique adopted from boat hull construction. One of the earliest examples was the Deperdussin Monocoque racer in 1912, which used a laminated fuselage made up of three layers of glued poplar veneer, which provided both the external skin and the main load-bearing structure.Aeronautics, 1912, p.112 This also produced a smoother surface and reduced drag so effectively that it was able to win most of the races it was entered into. This style of construction was further developed in Germany by
LFG Roland Luft-Fahrzeug-Gesellschaft, also referred to as LFG, was a German aircraft manufacturer during World War I. They are best known for their various "Roland" designs, notably the Roland C.II ''Walfisch'' (whale), Roland D.II ''haifisch'' (Shark) an ...
using the patented ''Wickelrumpf'' (wrapped body) form later licensed by them to Pfalz Flugzeugwerke who used it on several fighter aircraft. Each half of the fuselage shell was formed over a male mold using two layers of plywood strips with fabric wrapping between them. The early plywood used was prone to damage from moisture and delamination. While all-metal aircraft such as the Junkers J 1 had appeared as early as 1915, these were not monocoques but added a metal skin to an underlying framework. The first metal monocoques were built by Claudius Dornier, while working for Zeppelin-Lindau.Terry, 1981, pp.97–117 He had to overcome a number of problems, not least was the quality of aluminium alloys strong enough to use as structural materials, which frequently formed layers instead of presenting a uniform material. After failed attempts with several large flying boats in which a few components were monocoques, he built the Zeppelin-Lindau V1 to test out a monocoque fuselage. Although it crashed, he learned a lot from its construction. The Dornier-Zeppelin D.I was built in 1918 and although too late for operational service during the war was the first all metal monocoque aircraft to enter production. In parallel to Dornier, Zeppelin also employed Adolf Rohrbach, who built the Zeppelin-Staaken E-4/20, which when it flew in 1920 became the first multi-engined monocoque airliner, before being destroyed under orders of the Inter-Allied Commission. At the end of WWI, the Inter-Allied Technical Commission published details of the last Zeppelin-Lindau flying boat showing its monocoque construction. In the UK, Oswald Short built a number of experimental aircraft with metal monocoque fuselages starting with the 1920 Short Silver Streak in an attempt to convince the air ministry of its superiority over wood. Despite advantages, aluminium alloy monocoques would not become common until the mid 1930s as a result of a number of factors, including design conservatism and production setup costs. Short would eventually prove the merits of the construction method with a series of flying boats, whose metal hulls didn't absorb water as the wooden hulls did, greatly improving performance. In the United States, Northrop was a major pioneer, introducing techniques used by his own company and Douglas with the Northrop Alpha.


Vehicles


Race cars

In motor racing, the safety of the driver depends on the car body, which must meet stringent regulations, and only a few cars have been built with monocoque structures. An
aluminum alloy An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two princip ...
monocoque
chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpar ...
was first used in the 1962 Lotus 25 Formula 1 race car and
McLaren McLaren Racing Limited is a British motor racing team based at the McLaren Technology Centre in Woking, Surrey, England. McLaren is best known as a Formula One constructor, the second oldest active team, and the second most successful Formu ...
was the first to use carbon-fiber-reinforced polymers to construct the monocoque of the 1981 McLaren MP4/1. In 1990 the Jaguar XJR-15 became the first production car with a carbon-fiber monocoque.


Road cars

The term ''monocoque'' is frequently misapplied to
unibody A vehicle frame, also historically known as its '' chassis'', is the main supporting structure of a motor vehicle to which all other components are attached, comparable to the skeleton of an organism. Until the 1930s, virtually every car ha ...
cars. Commercial car bodies are almost never true monocoques but instead use the unibody system (also referred to as unitary construction, unitary body–chassis or body–frame integral construction), which uses box sections, bulkheads and tubes to provide most of the strength of the vehicle, while the skin adds relatively little strength or stiffness.


Armoured vehicles

Some armoured fighting vehicles use a monocoque structure with a body shell built up from
armour Armour (British English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or f ...
plates, rather than attaching them to a frame. This reduces weight for a given amount of armour. Examples include the German TPz Fuchs and
RG-33 The RG-33 is a mine-resistant light armored vehicle initially designed by BAE Systems Land Systems South Africa (formerly Land Systems OMC), a South African subsidiary of BAE Systems. BAE Systems in the US extensively modified it with addition ...
.


Two-wheeled vehicles

French industrialist and engineer Georges Roy attempted in the 1920s to improve on the bicycle-inspired
motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle Steering, steered by a Motorcycle handlebar, handlebar. Motorcycle design varies greatly to suit a range of different purposes: Long-distance ...
frames of the day, which lacked rigidity. This limited their handling and therefore performance. He applied for a patent in 1926, and at the 1929 Paris Automotive Show unveiled his new motorcycle, the Art-Deco styled 1930 Majestic. Its new type of monocoque body solved the problems he had addressed, and along with better rigidity it did double-duty, as frame and bodywork provided some protection from the elements. Strictly considered, it was more of a semi-monocoque, as it used a box-section, pressed-steel frame with twin side rails riveted together via crossmembers, along with floor pans and rear and front bulkheads. A Piatti light scooter was produced in the 1950s using a monocoque hollow shell of sheet-steel pressings welded together, into which the engine and transmission were installed from underneath. The machine could be tipped onto its side, resting on the bolt-on footboards for mechanical access. A monocoque framed scooter was produced by Yamaha from 1960–1962. Model MF-1 was powered by a 50 cc engine with a three-speed transmission and a fuel tank incorporated into the frame. A monocoque-framed motorcycle was developed by Spanish manufacturer Ossa for the
1967 Grand Prix motorcycle racing season Events January * January 1 – Canada begins a year-long celebration of the 100th anniversary of Confederation, featuring the Expo 67 World's Fair. * January 5 ** Spain and Romania sign an agreement in Paris, establishing full consular an ...
. Although the single-cylinder Ossa had less than its rivals, it was lighter and its monocoque frame was much stiffer than conventional
motorcycle frame A motorcycle frame is a motorcycle's core structure. It supports the engine, provides a location for the steering and rear suspension, and supports the rider and any passenger or luggage. Also attached to the frame are the fuel tank and battery. ...
s, giving it superior agility on the racetrack. Ossa won four Grands Prix races with the monocoque bike before their rider died after a crash during the 250 cc event at the
1970 Isle of Man TT The 1970 Isle of Man TT, the fourth round of the 1970 Grand Prix motorcycle racing season, involved a number of races on the Mountain Course on the Isle of Man. For the third consecutive year, Giacomo Agostini won both the Junior and Senior races ...
, causing the Ossa factory to withdraw from
Grand Prix Grand Prix ( , meaning ''Grand Prize''; plural Grands Prix), is a name sometimes used for competitions or sport events, alluding to the winner receiving a prize, trophy or honour Grand Prix or grand prix may refer to: Arts and entertainment ...
competition. Notable designers such as Eric Offenstadt and Dan Hanebrink created unique monocoque designs for racing in the early 1970s. The F750 event at the
1973 Isle of Man TT The 1973 Isle of Man TT was a road racing event for motorcycles held in the Isle of Man on the 37-mile Snaefell Mountain Course. It was the fifth round of the 1973 Grand Prix motorcycle racing season (now known as MotoGP). The Australian rider J ...
races was won by Peter Williams on the monocoque-framed John Player Special that he helped to design based on Norton Commando.
Honda is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan. Honda has been the world's largest motorcycle manufacturer since 1959, reaching a producti ...
also experimented with the NR500, a monocoque Grand Prix racing motorcycle in 1979. The bike had 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 . An aluminium monocoque frame was used for the first time on a mass-produced motorcycle from 2000 on Kawasaki's
ZX-12R The Kawasaki Ninja ZX-12R is a motorcycle in the Ninja sport bike series made by Kawasaki from 2000 through 2006. The inline-four engine produced at low speed, and increased to at high speed due to its ram-air intake, making it the most powerf ...
, their flagship production sportbike aimed at being the
fastest production motorcycle The fastest production motorcycle for a given year is the unmodified motorcycle with the highest tested top speed that was manufactured in series and available for purchase by the general public. Modified or specially produced motorcycles are a dif ...
. It was described by ''
Cycle World ''Cycle World'' is a motorcycling magazine in the United States. It was founded in 1962 by Joe Parkhurst, who was inducted to the Motorcycle Hall of Fame as "the person responsible for bringing a new era of objective journalism" to the US. ''Cyc ...
'' in 2000 as a "monocoque backbone ... a single large diameter beam" and "Fabricated from a combination of castings and sheet-metal stampings". Single-piece
carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
bicycle frames are sometimes described as monocoques; however as most use components to form a frame structure (even if molded in a single piece), these are frames not monocoques, and the pedal-cycle industry continues to refer to them as framesets.


Rockets

Various
rocket A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entir ...
s have used pressure-stabilized monocoque designs, such as
Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
and Falcon 1. The Atlas was very light since a major portion of its structural support was provided by its single-wall steel balloon fuel tanks, which hold their shape while under acceleration by internal pressure. Balloon tanks are not true monocoques but act in the same way as inflatable shells. A balloon tank skin only handles tensile forces while compression is resisted by internal liquid pressure in a way similar to semi-monocoques braced by a solid frame. This becomes obvious when internal pressure is lost and the structure collapses.


See also

* Backbone chassis *
Body-on-frame Body-on-frame, also known as ladder frame construction, is a common motor vehicle construction method, whereby a separate body or coach is mounted on a strong and relatively rigid vehicle frame or chassis that carries the powertrain (the en ...
*
Coachbuilder A coachbuilder or body-maker is someone who manufactures bodies for passenger-carrying vehicles.Construction has always been a skilled trade requiring a relatively lightweight product with sufficient strength. The manufacture of necessarily ...
* List of carbon fiber monocoque cars *
Space frame In architecture and structural engineering, a space frame or space structure ( 3D truss) is a rigid, lightweight, truss-like structure constructed from interlocking struts in a geometric pattern. Space frames can be used to span large areas w ...
* Thin-shell structure * Vehicle frame


References


Citations


Bibliography

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