Colin Chapman: chassis pioneer

This new year sees a big anniversary for mainstream racing car design in general – and for Lotus in particular. At this time of the year in 1962, Colin Chapman and his men were building the first truly successful monocoque-chassised Grand Prix car – their Lotus 25.

The early months of that year had seen mechanics Dick Scammell and Ted Woodley working closely with Mike Costin, Colin Chapman and the Cheshunt factory’s panel beaters – so often cursed by Colin as “those communists” – in a corner of the workshop.

At that time so-called ‘monocoque’ construction had been for 50 years the most significant structural element of aeronautical design. Credit for its introduction may go to Frederick Handley Page for his aircraft displayed at Olympia in 1911, or to Ruchonnet, in France, but it was another French engineer – Louis Béchereau – who produced the first streamlined fuselage employing a load-bearing skin in his 1912 Deperdussin racer.

Béchereau used a skin of three 1.5mm-thick tulip-wood veneer laminations glued together around a mould. When cured, the structure offered inherent rigidity without internal framing. Its similarity to an eggshell coined the nickname ‘monocoque’ – from the Greek mónos and Latin coccum – or ‘single-shell’.

In 1915 the futuristic Cornelian light car ran at Indianapolis, featuring both a monocoque body-chassis unit and all- independent suspension. In 1923 Gabriel Voisin produced a monocoque Grand Prix car at Tours for the French GP, and in Britain, around World War II, both Alec Issigonis and Lawrie Bond built monocoque hill-climb cars.

Tom Killeen worked for Jensen around the War during which, in Malta, he’d gained experience of repairing Spitfire fuselages, and recognised their high rigidity for little weight. In 1952 he was awarded British patent 735110 entitled Improvements in, or relating to, Motor Road and like Vehicles – proposing ‘frameless’ monocoque construction. His Killeen K1 sports car of 1953 and its successors demonstrated the principle. He broadcast his concept in The Motor magazine, but few listened – and several side-stepped the patent he could not afford to defend. Mid-1950s Jaguar D-types used monocoque centre-sections. From late-1955 to ’57 the early BRM Type 25 F1 cars used semi- monocoque centre section stiffening – until, for accessibility’s sake, a pure spaceframe with all-detachable body was adopted in 1958-59.

At Lotus, early tests with the Elan sports- car’s prototype backbone chassis showed how this type of construction could be immensely rigid for its weight. In planning lunches at a local restaurant, Colin Chapman literally sketched on a napkin his original scheme to apply a backbone chassis to a single-seater.

“None of us really knew what we were doing, but it all took shape”

Colin: “I thought ‘Why not space the sides of the backbone far enough apart for a driver to sit between them?’. At the same time we’d had years of trouble with wrapping aluminium fuel tanks around tubular spaceframes and trying to stop them chafing through. So if we made the sides of the backbone as box-sections we could carry fuel inside them in rubber bags… It was the first monocoque racing car as far as I was concerned… I had never seen one before, and we didn’t know if it would work”.

Lotus produced its conventional multi- tubular spaceframe-chassised Type 24 for sale to its F1 customers, because in Colin’s words: “The spaceframe was a known quantity… We couldn’t be expected to sell them a revolutionary car which might not work, and might need a long and expensive development programme. At that time the monocoque was really an unknown animal…”.

Team’s 1961 US GP-winning Type 21 spaceframe had a torsional stiffness of 700lb ft per degree deflection, for a bare weight of 82lb, rising to 130lb with brackets and separate fuel tanks added. The Lotus 25 monocoque weighed just 65lb, yet offered 1000ft/lb/degree stiffness – rising to 2400lb when the Climax V8 engine was installed. This improvement showed little advantage against half-as-stiff Brabhams and Ferraris in faster corners, but allowed Lotus more supple suspension, which paid off in slower, tighter turns.

The first Alan Styman-drawn chassis ‘R1’ was fabricated in secret. Ted Woodley recalled Colin sitting in the mock-up and complaining “this cockpit’s too wide, take an inch-and-a- half out of it!”. They tried again. Dick Scammell recalled: “None of us really knew what we were doing, but it all took shape and it looked right. Mike Costin was wielding a riveter because he had experience in the aircraft industry, so we all thought he must know what he was doing… It was that kind of project”. The result Colin described as “…the cleanest and nicest-looking car we’d ever made. There were no holes in the bodywork, the engine and the gearbox were beautifully cowled-in and it worked well”.

From its debut in the Dutch GP in 1962 the Lotus 25 was the car to beat. When it finished it won. For ’63 the cars were made more reliable, and Jim Clark dominated the Championship.

Henceforth, monocoque construction became the norm for serious-level single- seater racing cars. Single-skin sheet aluminium gave way to honeycomb, then to moulded carbon composites – but in essence single-shell racing car construction still reigns today. Colin Chapman and Team Lotus were not the first, but their work was decisive. Celebrate it.