Monocoque

Monocoque
Deperdussin Monocoque, with wooden shell construction

Monocoque (/ˈmɒnɵkɒk/ or /ˈmɒnɵkoʊk/) is a structural approach whereby loads are supported through an object's external skin, similar to an egg shell. The technique may also be called structural skin. The word monocoque is a French term for "single shell" or (of boats) "single hull".^[1]

Semi-monocoque

Some structures have sub-components that are monocoques, but which form part of a composite frame structure. Alternative structures to "true" to monocoques 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.^[2]

Aircraft

View of the inside of the tail of a Murphy Moose homebuilt aircraft under construction, showing the semi-monocoque design

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] 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.^[5] This reduced drag so effectively it was able to win most of the races it was entered into.^[5] 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.^[6] 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.

Automobiles

The McLaren MP4/1, introduced in 1981, was the first Formula One car to use a carbon fiber composite monocoque instead of the standard aluminum alloy

Commercial car bodies are almost never monocoques; instead modern cars use unitary body / chassis, unitary construction. unibody, or Body Frame Integral construction,^[7] with box sections, bulkheads and tubes providing most of the strength of the vehicle, while the skin adds relatively little to the strength or stiffness. The term monocoque has often been misused when referring to unibody cars. ^[8]

In modern motor racing however, the safety of the driver depends on the extraordinary strength of the car body which must meet stringent design regulations and a small number of cars have been built with monocoque structures.^[9][10] McLaren was the first company to utilize carbon-fiber-reinforced polymers to construct the monocoque of the McLaren MP4/1, which debuted in 1981. The strong and lightweight construction technique has become essential in high-end motorsport, and in 1992 McLaren made the F1 the first production car to use a carbon-fiber monocoque.^[11]

Armored vehicles

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.

Two-wheeled vehicles

Ariel Arrow showing monocoque frame^[12]

Between 1958 and 1965 the UK firm Ariel Motorcycles manufactured two production monocoque motorcycle models, the Ariel Leader and its sibling, the Ariel Arrow.

A monocoque-framed motorcycle was developed by the Spanish motorcycle manufacturer, Ossa, for the 1967 Grand Prix motorcycle racing season.^[13]

1968 Ossa 250 cc Grand Prix racer

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.^[13] 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.^[13]

Notable designers such as Eric Offenstadt and Dan Hanebrink created unique monocoque designs in the early 1970s.^[14] The 1973 Isle of Man TT was won by Peter Williams on the monocoque-framed Norton John Player Special that he helped design.^[15] Honda also experimented with a monocoque Grand Prix racing motorcycle named the NR500 in 1979.^[16] 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.^[17] 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),^[18] these are frames and not monocoques, and the bike industry continues to refer to them as framesets.

Rockets

First-stage view of the Falcon I rocket

Various rockets have used pressure-stabilized monocoque designs, such as Atlas^[19] and Falcon I.^[20] 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.

See also

• Space frame
• Backbone chassis
• Vehicle frame
• Chassis
• Coachwork
• Body-on-frame
• Thin-shell structure

References

Bibliography

• Megson, T.H.G. (1972). Aircraft Structures for Engineering Students. London: Edward Arnold Publishers LTD. ISBN 0-7131-3393-7. 
• Robertson, Bruce (1996). WWI British Aeroplane Colours and Markings. Berkhampstead: Albatros Publications Inc. pp. 1–2. ISBN 0-948414-65-0. 
• Schatzberg, Eric (1999). Wings of Wood, Wings of Metal: Culture and Technical Choice in American Airplane Materials, 1914-1945. Princeton, N.J.: Princeton University Press. ISBN 978-0691087733. 
• Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair (Publication AC 43.13-1B). Washington, DC: US Department of Transportation Federal Aviation Administration Standards Division. 2001. p. 1.2. ISBN 0-16-036209-1. 
• Unknown (1912). Aeronautics (October): 112.  Missing or empty |title= (help)

Wikimedia Commons has media related to Monocoques.