Monocoque

Monocoque (pronounced mon-uh-kohk or mon-oh-kok (non-U))

(1) A type of boat, aircraft, or rocket construction in which the shell carries most of the stresses.

(2) A type of automotive construction in which the body is combined with the chassis as a single unit.

(3) A unit of this type.

1911: An English borrowing from the French monocoque, the construct being mono + coque.  Mono is from the Ancient Greek μόνος (monos) (alone, only, sole, single), from the primitive Indo-European root men (small, isolated).  Coque is from the Old French coque (shell) and concha (conch, shell), from the Latin coccum (berry) and concha (conch, shell) from the Ancient Greek kokkos (berry, seed).  In the early twentieth century, it was the French who were most dominant in the development of aviation.  Words like monocoque, aileron, fuselage and empennage are of French origin and endure in English because it’s a vacuum-cleaner of a language which sucks in anything from anywhere which is handy and manageable.

Noted monocoques

Deperdussin Monocoque, 1912.

A monocoque (sometime referred to as structural skin) is a form of structural engineering where loads and stresses are distributed through an object's external skin rather than a frame; concept is most analogous with an egg shell. Early airplanes were built using wood or steel tubes covered with starched fabric, the fabric rendering contributing only a small part to rigidity.  A monocoque construction integrates skin and frame into a single load-bearing shell, reducing weight and adding strength.  Although examples flew as early as 1911, airframes built as aluminium-alloy monocoques would not become common until the mid 1930s.  In a pure design where only function matters, almost anything can be made a stressed component, even engine blocks and windscreens.

Lotus 25, 1962.

In automotive design, the word monocoque is often misused, treated as a descriptor for anything built without a separate chassis.  In fact, most road vehicles, apart from a handful of expensive exotics, are built either with a separate chassis (trucks and some SUVs) or are of unibody/unitary construction where box sections, bulkheads and tubes to provide most of the structural integrity, the outer-skin adding little or no strength or stiffness.  Monocoque construction was first seen in Formula one in 1962, rendered always in aluminium alloys until 1981 when McLaren adopted carbon-fibre.  A year later, the McLaren F1 followed the same principles, becoming the first road car built as a carbon-fibre monocoque.

BRM P83 (H16), 1966.

In 1966, there was nothing revolutionary about the BRM P83’s monocoque chassis.  Four years earlier, in the second season of the voiturette era, that revolution had been triggered by the Lotus 25, built with the first fully stressed monocoque chassis, an epoch still unfolding as materials engineering evolves; the carbon-fibre monocoques seen first in the 1981 McLaren MP4/1 becoming soon ubiquitous.  The P83 used a monocoque made from riveted Duralumin (the word a portmanteau of durable and aluminium), an orthodox construction for the time.  Its novelty was that the engine was a stressed part of the monocoque.

BRM Type 15 (V16), 1949.

The innovation was born of necessity.  Not discouraged by the glorious failure of the extraordinary V16 BRM had built, with much fanfare and little success, shortly after the war, the decision was taken again to join together two V8s in one sixteen cylinder unit.  Whereas in 1949, the V8s had been coupled at the centre to create a V16, for 1966, the engines were re-cast as 180^o flat 8s with one mounted atop another in an H configuration, a two-crankshaft arrangement not seen since the big Napier-Sabre H24 aero-engines used in the last days of the war.  The design yielded the advantage that it was short, affording designers some flexibility in lineal placement, but little else.  It was heavy and tall, exacerbating further the high centre of gravity already created by the need to raise the engine location so the lower exhaust systems would clear the ground.  Just as significantly, it was wide, too wide to fit into a monocoque socket and thus was taken the decision to make the engine an integral, load-bearing element of the chassis.  There was no other choice.

BRM H16 engine and gearbox, 1966.

 

Structurally, it worked, the monocoque was strong and stable and despite the weight and height, the P83 might have worked if the H16 had delivered the promised horsepower but the numbers were never realised.  The early power output was higher than the opposition but it wasn’t enough to compensate for the drawbacks inherent in the design and, these being so fundamental they couldn’t be corrected, the only hope was even more power.  The path to power was followed and modest increases were gained but it was never enough and time ran out before the plan to go from 32 to 64 valves could come to fruition, an endeavour some suggested would merely have “compounded the existing error on an even grander scale.”  Additionally, with every increase in power and weight, the already high fuel consumption worsened.

The H16 did win one grand prix, albeit in a Lotus rather than a BRM monocoque, but that was a rare success; of the forty times it started a race, twenty-seven ended prematurely.  The irony of the tale is that in the two seasons BRM ran the 440 horsepower H16 with its sixteen cylinders, two crankshafts, eight camshafts and thirty-two valves, the championship in both years was won by the Repco-Brabham, its engine with 320 horsepower, eight cylinders, one crankshaft, two camshafts and sixteen valves.  Adding insult to the exquisitely bespoke H16’s injury, the Repco engine was based on an old Oldsmobile block which General Motors had abandoned.  After two seasons the H16 venture was retired, replaced by a conventional V12.