Monocoque

Monocoque (/ˈmɒnəˌkɒk, -ˌkoʊk/), also structural skin, is a structural system where loads are supported through an object's external skin, similar to an egg shell. The word monocoque is a French term for "single shell" or (of boats) "single hull". 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. 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 tanks, both of which are pressure stabilised.

Early aircraft were constructed using frames, typically of wood or steel tubing, which could then be covered (or skinned) with fabric such as irish linen or cotton. The skin added nothing to the structural strength of the airframe and was dead weight beyond providing a smooth sealed surface. By thinking of the airframe as a whole, and not just the sum of its parts, monocoque structures made sense and various companies soon adopted 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.

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