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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 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 The term semi-monocoque or semimonocoque refers to a stressed shell structure that is similar to a true monocoque, but which derives at least some of its strength from conventional reinforcement. Semi-monocoque construction is used for, among ot ...
is a hybrid combining a tensile
stressed skin In mechanical engineering, stressed skin is a type of rigid construction, intermediate between monocoque and a rigid frame with a non-loaded covering. A stressed skin structure has its compression-taking elements localized and its tension-taking ...
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 tanks, 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 tubing, which could then be covered (or ''skinned'') with fabric such as
Irish linen Irish linen ( ga, Línéadach Éireannach) is the name given to linen produced in Ireland (including both the Republic of Ireland and Northern Ireland). Linen is cloth woven from, or yarn spun from, flax fibre, which was grown in Ireland for many ...
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 The Deperdussin Monocoque was an early racing aircraft built in 1912 by the Aéroplanes Deperdussin, a French aircraft manufacturer started in 1911 and reorganized as the Société Pour L'Aviation et ses Dérivés ( SPAD) in 1913. It is so nam ...
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 using the patented ''Wickelrumpf'' (wrapped body) form later licensed by them to
Pfalz Flugzeugwerke Pfalz Flugzeugwerke was a World War I German aircraft manufacturer, located at the Speyer airfield in the Palatinate (German: Pfalz). They are best known for their series of fighters, notably the Pfalz D.III and Pfalz D.XII. The company went ban ...
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 The Junkers J 1, nicknamed the ''Blechesel'' ("Tin Donkey" or "Sheet Metal Donkey"), was an experimental monoplane aircraft developed by Junkers & Co. It was the world's first all-metal aircraft. Manufactured early on in the First World War, ...
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 Claude (Claudius) Honoré Désiré Dornier (born in Kempten im Allgäu on 14 May 1884 – 5 December 1969) was a German-French airplane designer and founder of Dornier GmbH. His notable designs include the 12-engine Dornier Do X flying boa ...
, 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 Luftschiffbau Zeppelin GmbH is a German aircraft manufacturing company. It is perhaps best known for its leading role in the design and manufacture of rigid airships, commonly referred to as ''Zeppelins'' due to the company's prominence. The name ...
to test out a monocoque fuselage. Although it crashed, he learned a lot from its construction. The
Dornier-Zeppelin D.I The Zeppelin D.I, or Zeppelin-Lindau D.I or Zeppelin D.I (Do), as named in German documents, also sometimes referred to postwar as the Dornier D.I or Dornier-Zeppelin D.I, for the designer,Grosz, 1998, p.12 was a single-seat all-metal stressed s ...
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 Hugh Oswald Short, AFRAeS (16 January 1883 – 4 December 1969) was an English aeronautical engineer. Early life Oswald Short was born at Stanton by Dale, Ilkeston, Derbyshire, the son of mining engineer Samuel Short and his second wife Emma R ...
built a number of experimental aircraft with metal monocoque fuselages starting with the 1920
Short Silver Streak The Short Silver Streak was the first British all-metal aircraft.Jackson 1973, p. 297. It was designed and built by Short Brothers at Rochester, Kent, England. Although ''Flight'' magazine claimed that it was the first instance of stressed skin ...
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 The Northrop Alpha was an American single-engine, all-metal, seven-seat, low-wing monoplane fast mail/passenger transport aircraft used in the 1930s. Design work was done at the Avion Corporation, which in 1929, became the Northrop Aircraft Corpo ...
.


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 monocoque chassis was first used in the 1962
Lotus 25 The Lotus 25 was a racing car designed by Colin Chapman for the 1962 Formula One season. It was a revolutionary design, the first fully stressed monocoque chassis to appear in Formula One. In the hands of Jim Clark it took 14 World Championship ...
Formula 1 race car and McLaren was the first to use carbon-fiber-reinforced polymers to construct the monocoque of the 1981
McLaren MP4/1 The McLaren MP4/1 (initially known as the MP4) was a Formula One racing car produced by the McLaren team. It was used during the 1981, 1982 and 1983 seasons. It was the second Formula One car to use a monocoque chassis wholly manufactured fro ...
. 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 vehicle An armoured fighting vehicle (AFV) is an armed combat vehicle protected by armour, generally combining operational mobility with offensive and defensive capabilities. AFVs can be wheeled or tracked. Examples of AFVs are tanks, armoured cars, ...
s use a monocoque structure with a body shell built up from armour plates, rather than attaching them to a frame. This reduces weight for a given amount of armour. Examples include the German
TPz Fuchs The TPz Fuchs from Transportpanzer Fuchs is a German armoured personnel carrier originally developed by Daimler-Benz but manufactured and further developed by the now Rheinmetall MAN Military Vehicles (RMMV). Fuchs was the second wheeled armou ...
and RG-33.


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 steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...
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 Yamaha may refer to: * Yamaha Corporation, a Japanese company with a wide range of products and services, established in 1887. The company is the largest shareholder of Yamaha Motor Company (below). ** Yamaha Music Foundation, an organization estab ...
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. A ...
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 race ...
, causing the Ossa factory to withdraw from Grand Prix 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 races was won by Peter Williams on the monocoque-framed John Player Special that he helped to design based on
Norton Commando The Norton Commando is a British Norton-Villiers motorcycle with an OHV pre-unit parallel-twin engine, produced by the Norton Motorcycle company from 1967 until 1977. Initially having a nominal ''750 cc'' displacement, actually , in 19 ...
.
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 Events January * January 1 ** United Nations Secretary-General Kurt Waldheim heralds the start of the '' International Year of the Child''. Many musicians donate to the '' Music for UNICEF Concert'' fund, among them ABBA, who write the so ...
. 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, their flagship production sportbike aimed at being the fastest production motorcycle. It was described by '' Cycle World'' 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 frame A bicycle frame is the main component of a bicycle, onto which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles: a main triangl ...
s 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 entirely fr ...
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 geograp ...
and
Falcon 1 Falcon 1 was a small-lift launch vehicle that was operated from 2006 to 2009 by SpaceX, an American aerospace manufacturer. On 28 September 2008, Falcon 1 became the first private spaceflight, privately-developed fully liquid-fueled launch vehi ...
. 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 Backbone tube chassis is a type of automobile construction chassis that is similar to the body-on-frame design. Instead of a two-dimensional ladder-type structure, it consists of a strong tubular backbone (usually rectangular in cross section) ...
* Body-on-frame * Coachbuilder * List of carbon fiber monocoque cars * Space frame * Thin-shell structure *
Vehicle frame 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 had a ...


References


Citations


Bibliography

* * . * * * * * * * {{CarDesign nav Automotive chassis types Motorcycle frames Airship technology Structural engineering Aircraft components