Part 2: Chassis Design – Thinking Out of the Box
For some teams, chassis design was a low priority. The ViaRETRO reader will have noticed while viewing the Ferrari 156 video in Part 1 of The Long Read that the tubular chassis appears to have been built with leftover scaffolding and second-hand bicycle frames. Sometimes it is best not to meet your heroes…
The approach of Cooper, Lotus and BRM used finer tubes and the cars were perhaps lighter but despite the science and the effort, these were not as torsionally stiff as hoped.
At the time, the dedicated motoring enthusiast could also purchase for 30 shillings, the essential reading: “Racing and Sports Car Chassis Design” by Michael Costin and David Phipps. This book is very relevant to this Long Read as it sums up the different efforts of the time.
Michael Costin, joint founder of Cosworth, was also a full-time engineer at Lotus at the time. He was part of the “inner circle” and along with his brother Frank (aerodynamicist) he was a brilliant all-round engineer and a handy racing driver.
The following are quotes from the 1962 edition of the book. Admitted, some readers may find this rather dry unless heavily interested in the subject!
“The criterion of chassis design – and in fact the primary function of a high-performance chassis – is torsional rigidity… The best example of a space frame chassis from the point of view of torsional rigidity would be a square-section rectangular box, with ends, sides, top and bottom triangulated by diagonals through the centre to the opposite corner…it would be highly impractical for automotive applications.”
“Accessibility is almost as important a factor as chassis rigidity. Thus, a chassis has to be split into bays…”
“In the course of design, each panel or bay of a unitary construction chassis must be stabilised to carry out the function of transferring loads. The simplest way to achieve this would be to use a large, round section tube with the ends blanked off.”
“The use of this type of chassis would seem to offer many advantages, to judge from the developments carried out in recent years in aircraft manufacture. Such a structure can be made very stiff and extremely light – an essential feature of aircraft design – and in a car of this type 30-gauge material would probably be quite adequate.”
[30 gauge = 0.315mm]
“The load capacity of a unitary construction in bending should be extremely good, because bending loads are resolved in pure tension and compression in the undertray and roof, to which type of loads these areas are ideally suited…in practice everything depends on general and detail design around the apertures.”
“A unitary construction design should be stiffer than an equivalent tubular space frame and body for the same weight or lighter for a similar stiffness.”
The book provides a brilliant exposé of the thought process and the methods of calculation at the time: Even I can understand the maths! Hidden within the cryptic phrases above are allusions to what came next. Do read them twice.
Working from first principles and thinking outside the box.
Lotus’ poster pin-up, the type 14 Elite, was too costly to build which created sales problems, despite the beating meted out to rivals at Le Mans and the universal acclaim in the motoring press.
The remarkable part of the Elite’s design as launched back in 1957, was the conception of the car as a monocoque made from fibreglass (granted, with a few strengthening steel components).
[Obviously in 1934 the Citroën Traction Avant was the first steel production monocoque (a hybrid of experience with cold steel presses developed by Budd/Ledwinka (USA) and Citroën’s industrial designer, Flaminio Bertoni who would have been familiar with the 1923 Lancia Lambda, the first car to use much of the principle behind a unitary body design.]
Today’s Lotus Elite prices fairly reflect the genius of this design which owes very much to the hard work of many moonlighting enthusiasts. However, Lotus was losing money on every car and its finances at the time needed profits more than producing future treasures!
This is not unusual as not all classic car treasures have made money for their manufacturers. At the time, Ferrari also found it difficult to sell their 250 GTOs (already outdated in 1962), the original Mini was not profitable, the Jaguar XJR-15 (first monocoque carbon fibre car) and engineers’ foibles like the Audi A2 have not always caught the imagination of the public as they are expensive both to buy and to maintain.
In 1960, less than 3 years after production of this gem really started, the Elite was as much of a loss-leader as a race winner. The urgency was to develop a replacement that would be easier to manufacture and easier to sell to Californians and Europeans alike (two-seater convertible). Profitability was the priority over outright lap times.
But there was one major headache: How to build an open fibreglass monocoque with enough torsional rigidity? This problem was existential and not least a matter of engineering pride. The solution of using a chassis seemed vintage but was still common at the time and used by competitors such as the fibreglass Alpines:
The resulting design of a “spine chassis”, initially intended as a “mule” was a temporary fix that found its way into road going prototype form in June 1960.
According to Robert Reed: “The original concept included lightening holes skilfully place to facilitate assembly of the main components and spot welding of the chassis itself. The design team were suitably impressed by Chapman’s obvious command of constructional techniques in a medium (sheet steel) in which they had not seen him operate before”.
So, what was so special about this? What do Robert Stephenson’s Britannia Tubular
Railway Bridge and post-war aircraft have in common with this sports car chassis?
Answer: The torsion box.
“The properties of its thin surfaces to carry the imposed loads primarily through tension while the close proximity of the enclosed core material compensates for the tendency of the opposite side to buckle under compression.” (ref: Wikipedia)
Amusingly, many within the Lotus factory did not know that the prototype (the type 26 later revealed as the Elan at the end of 1962) indeed had a chassis. However, the innovative use of the torsion box gave plenty of other surprises: Costing just £10 per chassis to make, it was as light and torsionally stiffer than many racing cars of the time.
The photo below shows the Elan’s steel chassis. The nearest chassis to the camera is the S2 26R chassis (from November 1964) and the chassis behind is a S1 26R chassis. They weigh just 38 kilos each.
The design is elegantly simple, yet it incorperates complex flanges inside the central spine, the front cross member is also used as a vacuum tank used to operate the pop up head lamps and the design avoids additional heavy brackets or subframes.
Subsequently modified, the principle of the central spine was used on all roadgoing Lotuses (Europa, Elan +2, Esprit, Elite, Eclat, Excel, Esprit Turbo, Elan M100…) until the Lotus Elise.
So how did this road car design lead to the basis of modern F1 cars?
The answers come in Part 3. Essentially, when engineers spark ideas on each other and a few non-engineers recompose their findings, innovation happens. Once again, make sure to tune in next week…