You may have noticed the increased mention of ‘design flexibility’ in car industry launches, brought about by the need to service vastly different models from the same core platform.
Volkswagen Group’s MQB platform is one such example, as is Aston Martin’s VH architecture, the new iQ[Al] platform introduced last week on Jaguar’s X-C17 SUV Concept and a host of other recent examples. What VW, Jaguar, BMW, McLaren and Alfa Romeo are all trying to achieve is limit the cost and complexity of producing a multi-model vehicle range while enabling their designers to ‘fill their boots’ with ever more appealing and innovative cars.
Now you might ask, “what’s this got to do with a small specialist sports car maker?”
Well, ironically the global car makers have begun to borrow from the same principles that companies such as Lotus have been working to for almost 20 years, and more often than not this involves the use of extruded aluminium or carbon fibre to form the chassis on which suspension and bodywork are mounted.
Form ‘used to’ follow function
Lightweight performance sports cars have traditionally adopted a space frame architecture for their chassis. Take a handful of steel tubes, a brazing torch or MIG welder and a large helping of craft skills and the result is a relatively low investment route for turning a chassis designer’s concept into reality.
“The problem with a spaceframe chassis like that used on the Caterham Seven is that the shape of the product becomes locked with the chassis design..”
One of the best known examples of this approach is the Caterham Seven which was purportedly dreamt up on the ‘back of a fag packet’ by Lotus’s Colin Chapman. Apart from a few changes to meet modern homologation requirements and to incorporate amended suspension layouts, the framework that underpins the Seven today is essentially the same design that Chapman came up with more than 50 years ago.
Until the late nineties, Caterham and the various Seven inspired variations dominated the British lightweight market. It was not until 1996 when a senior lecturer from Coventry University by the name of Simon Saunders took the space frame approach to a new level. By allowing the chassis tubes to be visible from the outside with his exo-skeleton design for the Ariel Atom he finally moved the space frame concept forwards.
Move forward another 10 years and two brothers from Cheshire have created the latest take on a space frame based sports car with the BAC Mono. Brigg’s street legal single-seater is essentially based on the frame from a Formula 3 race car, clad with a lightweight body structure courtesy of a set of beautifully designed carbon fibre panels.
What all of these iconic products have in common is that their frames ostensibly define their shape – ‘form follows function’. So why has Zenos diverted from the tried and tested route and adopted a new approach for their E-Series Platform?
We spoke with Mark Edwards, co-founder of Zenos Cars and former COO of Caterham Cars, who told us of the targets he and Ansar Ali set for their new platform from the outset.
Driven by cost, weight and mechanical performance the team spent several months exploring and benchmarking a myriad of concepts to meet their requirements.
Having spent 7 years alongside Ali at Caterham Cars, Edwards is no stranger to the purity and simplicity of the space frame. The problem with these cars, he told us, is that the shape of the product becomes locked with the chassis design and as a result it becomes very difficult to keep the style of the car contemporary.
The Seven is fortunate that its shape is iconic in part thanks to a loyal following of admirers – a design that harks back to the British sports car revolution of the 50’s and 60’s when many icons were born.
Edwards told us that he and Ali were approached on numerous occasions with projects and offers to put a new body on the Seven but it never made sense; they could never justify the argument to add complexity, weight and cost purely for vanity’s sake. Seven customers and those that understand the design would spot the contradiction immediately – the very purity of the design would be diluted regardless of any claims of aerodynamic benefit.
Based on these experiences Zenos ruled out the space frame route very early on. Edwards was looking for a fresh approach that would allow his team to create contemporary surfaces without adding material to the underlying chassis.
They looked at the KTM X-Bow (and forthcoming Alfa Romeo 4C), which had in part achieved this with a carbon based structure. Edwards loved the composite approach as it offered the prospect of producing more complex shapes which are very expensive to achieve with metallic structures.
But with stories circulating of insurers unwilling to provide cover for these products due to their high repair costs, the team decided to rule out a composite design until they met ex-Bentley R&D designer Anthony Dodworth.
Dodworth Design has developed and patented an innovative new material technology which sandwiches a thermoplastic core between two skins of recycled carbon. The material is formable, lightweight, more affordable than typical carbon and most importantly retains around 70% of the material properties of ‘virgin’ material.
When Edwards first spoke with Dodworth the material was still in final development, being used by a premium manufacturer who has since adopted it for use in the floor pan of one it its new product ranges.
In addition the Zenos team were also concerned by the prospect of mating a composite structure to front and rear sub-frames. Whilst the technology of bonded structures had been well proven by Lotus in the Elise architecture, the team had first-hand experience during their time at Lotus of the high repair complexity and therefore consumer cost of bonded structures. As a result they also investigated a parallel concept with their partners at Multimatic, for developing an extruded aluminium spine upon which they could directly mount the suspension.
Edwards remembers a wintery day earlier this year whilst reading a blog about the restoration of an original Lotus Elan when the penny finally dropped. Why not saddle the spine with a tub made from the Dodworth material and harness the benefits of both material technologies? The Zenos E-platorm was born.
The team quickly developed a concept design and in conjunction with their partners ran some initial Finite Element Analysis (FEA) simulations to establish the mechanical potential of the concept.
Early results were astonishing; both meeting their targets for the chassis whilst in parallel proving to be economically viable. Zenos had the basis to do organic and contemporary shapes without sacrificing the purity of a ‘form from function’ philosophy.
Full speed ahead
With their recent financial award from the Niche Vehicle Network, Zenos are honing their design to ensure they meet the design, mechanical, serviceability, commercial and safety prerequisites to maximise their chances of success.
Simon Keys of First Principle Design, an ex-MIRA Consultant Engineer with a background in Vehicle Safety Structures, is part of the development team and so the platform will almost certainly meet if not exceed the legislative requirements for safety – another refreshing piece of evidence that the Zenos team are taking this project very seriously.
As a result the team are developing a roll over protection system that also incorporates a high level of side impact protection for the occupants. Over the next few weeks further FEA analysis and development will hone the Zenos design prior to the team committing to the tooling required to produce the finished platform.
We’ll bring you more details on the development of the Zenos E10 prior to its first public appearance at the Autosport International Show in January.