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Epic Crashes, Carbon Fibre and Car Chassis
When I stepped foot into the McLaren manufacturing facility (MTC) in Woking, I couldn’t help but think I may have stumbled onto the set of the 2005 science fiction thriller The Island starring Ewan McGregor and Scarlett Johansson. Both play characters set in a highly structured, sterile world within a compound, governed by a set of strict rules. In the movie, the residents of this compound believe the outer world has become uninhabitable for human life. Thus, they are confined to the island. This may not quite be the reality for those working at the MTC, but the ultra-modern facility designed by Foster and partners had a distinct, clinical feel to it. Inspired by the rear wing support struts on the Le Mans-winning F1 GTR, it’s an architectural triumph. Think stark white, cavernous walkways and glass walls showcasing a ripple free artificial lake. It almost feels as though its wraps around the kidney shaped building like a moat, further drawing parallels to The Island.
Aside from marvelling at the architecture I was there on a mission. I wanted asses the impact carbon fibre has had on an industry aside from watchmaking. And where better than McLaren – the guys that brought the carbon fibre chassis to the Formula 1 grid in 1981. They knew they were onto something, when this very chassis (the MP4/1) enabled their driver, John Watson to walk away unscathed from a high-speed crash at Monza that very year. It had brought new levels of rigidity and driver safety to Formula 1. In a similar way to how technology now renders entire industries obsolete over night, this material advance had ensured the world of motorsport would never be the same again.
There are two sides to this – Formula 1 (McLaren have won 20 World Championships and over 180 races) and McLaren Automotive (in 1980 McLaren merged with Ron Dennis’ Project 4 Racing team). Let’s start with Formula 1. It wouldn’t be possible to discuss the impact of carbon fibre on the motor industry and not mention John Barnard. In 1980, when the merger took place, it meant designer Mr Barnard was heading back to McLaren. It may sound bizarre, but It’s fair to say, he was fascinated by carbon fibre composite. Prior to 1980, carbon fibre had been the reserve of the aerospace industry. Never motorsport. Its advantages were clear. It was light weight, high strength and it provided torsional stiffness, safety and durability. The carbon chassis was literally hand made at a facility in Shalford, England. Every fibre was painstakingly laid by gloved hands, vacuum bagged and prepared for long baking cycles.
While on my visit to the MTC I had the pleasure of discussing all things carbon fiber with programme Director Paul Mackenzie. Paul is a composite engineer. Prior to working at McLaren had spent time in the aerospace and military industries. To Paul, ‘the advantages of carbon fiber are that you can lay up the material in such a way that you can orientate the performance. For those looking to maximize speed – this is key’. This was the driving force behind McLaren experimenting with carbon fibre in the 70’s and early 80’s. He goes on: ‘whereas metal is homogenous – it has equal properties in all directions – with composites, because its fibrous you can lay the fibres up to give you the performance in the direction you want.
In the same way any piece of clothing is woven, the same can be said for carbon fibre. There is a vast array of weight and styles of fabric depending on what the objective is. Engineers undertake analysis to establish what the optimum layup is to match the requirements for the component. For example on the wishbones on the Formula 1 cars – its continuous unidirectional fibres so it’s not woven at all, it’s just in one direction because on a wishbone you want the performance i.e the bending, to be restricted to one direction. So the real advantage of composites is the ability you have of tailoring the strength in exactly the right place. With a carbon fibre chassis you can use sandwich construction – you can have very lightweight cores with then you have the skins with carbon fibre and as a result you get massive bending strength but it weighs very, very little’.
When it comes to Formula 1, the carbon fibre application used is called “prepreg”. Basically, it’s a reinforcing fabric which has been pre-impregnated (this is key) with a resin system. It’s highly labor intensive and very expensive. And for that reason reserved solely for Formula 1 applications. In short – the benefit of Prepreg is its strength properties. Having seen the level of hand craftsmanship that goes into the whole process, it’s staggering. So what does the application process look like? Well, having been pre-impregnated with resin, the prepreg goes straight into the mould. In order for the laminate to cure, it is necessary to use a combination of pressure and heat. When I asked Paul, he said ‘this is very much like in the textile industry, the roller material goes into the resin bay, then through rollers that nip it and ensure you get the correct amount of resin application.
It then gets placed between paper layers which have a waxy property to ensure they don’t stick to together. You then freeze it – and by freezing it you take it to minus 18 degrees, which stops the chemical process. This means it can then be stored for an indefinite period of time. When you want to use it, you simply defrost it like you would poultry from your deep freeze, you then you lay it up’. Following the templating and cutting phase, the carbon fibre goes into a vacuum bag and put it into a pressure cooker. There are applications in Formula 1, such as the exhausts, where a ceramic resin rather than a elastomer resin is used and temperatures of 1000 degrees Celsius are required. Paul mentioned that ‘it probably takes a thousand man hours to layup a Formula 1 chassis’. A good thing that they only manufacture three a year!
Above is an example of a one-piece molding of the chassis, it’s made using a process called resin transfer molding. As you’ll see, the fabric isn’t aesthetically pleasing and that’s because it’s not visible. As opposed to the prepreg form where it’s held in the resin. Here McLaren lay the dry fabric in the mold tool and inject resin in. There are key benefits to this from a safety perspective. By manufacturing the chassis in one piece and in carbon fiber it acts a safety cell while on the road. There are aluminum pontoons in front which are the crash structure and the engine casting on the back. So if there a crash all of the loads are transferred through the pontoons. Everything on a McLaren road car is designed to ensure a crash at anything less than 56 kph will be held within the crash pontoon. So on impact the pontoons crush but the will not actually damage the chassis.
On the flip side, the automotive applications for carbon fibre are vastly different. The 12C, 650S and P1 models created by McLaren Automotive are all direct descendants of the Formula 1 research and development programme. When it comes to the carbon chassis on the McLaren Automotive side Paul tells me ‘we are looking to produce fifteen of these a day’. As a result, the layup process needs to be far quicker than for the Formula 1 application.Traditionally McLaren have only used prepreg, but because of the high volume requirements of carbon fibre in the automotive side of the business, the focus has been on optimising the variety of processes for laying the carbon fiber down. McLaren have been producing road cars since the 1990’s. Ever since, every car has been a carbon fiber chassis. Even the Mercedes SLR 2003-2009 and MP412C had carbon fibre chassis.
The key from a safety perspective is that it’s all about transferring the load and ensuring the chassis is a safe zone. Interestingly, McLaren have produced 2,500 12C models and have never had to sell an aftermarket chassis. Before the use of carbon fiber these structures were all steel and aluminum. Historically this was troublesome because theses are ductal materials and if they are exposed to major impact, they crush. Designed to absorb the energy of an impact by deforming. As opposed to carbon fiber where we see the deformation of the pontoon and transferring of the load through the structure. An example of this in action would be Alonso’s crash in the first race of the 2016 season which many onlookers found hard to believe he walked away from alive.
McLaren use carbon fibre for structural reasons. In 2011 when McLaren showed the MP4 C to dealerships, there wasn’t a single bit of carbon fiber visible on the car itself. So the first thing McLaren did was re-tool some of the exterior furniture to have visible carbon fiber. Despite the factional weight saving ‘maybe a 500g saving on the roof panel’ says Paul – it was all about the aesthetic. The consumer just wanted to see more carbon fibre. In a bizarre way, the mystical status carbon fibre has developed over the years for being light and super strong has resulted in manufacturers putting it everywhere. Paul even says ‘I was away in France last week and the hire car, a Citroen I believe, it even had fake carbon fibre’. This minor adjustment has seen a huge impact on sales. ‘I though carbon fibre had, had its day from a visual perspective, but in actual fact we are seeing increased demand for satin finish or matte finish. In the last two years there has been a trend towards tinted carbon, where the standard carbon is clear gloss, we have taken twenty orders for colors from green to amber’ says Paul. It’s important remember that carbon is black, so McLaren have to add a gloss to color it.
While strolling through the boulevard, I found it fascinating looking at some of the old motor racing vehicles. The advantages of composites is that you can design features and brackets for example the wheel arch liner is one component which Paul says ‘this component on the P1 did the job of thirty parts on MP4 12C as we had an injection molding and lots of metal bracketry – now it’s made it a very expensive part, but when you think we didn’t have to sub assemble it or tool up individual parts it actually becomes far more cost effective’.
To end my visit – I was taken to a hidden room behind the boulevard, through a series of hidden doors and tunnels to view the The P1 – McLaren’s ultimate series car. It stopped being produced last year but almost all carbon fibre – with a top speed of 217MPH and a 0-60MPH in 2.8 seconds. It’s a wonderful machine. It’s got a carbon fibre chassis, carbon fibre body and interior, it’s the most carbon fibre heavy car they have ever produced, the only thing not carbon are the crash structures (although Formula 1 cars do have carbon fiber crash structures). ‘Tooling is always an issue’ says Paul. When laying up the carbon fibre on a mold – the mold is actually carbon fiber itself – so that mold will successfully make circa 150 parts off it, so part of the decision making is ‘what is my tooling strategy?’. Interestingly, when examining the various carbon fibre weave used on the P1, McLaren chose to use multiple different styles both on the exterior furniture of the vehicle but also under the bonnet. When asked why Paul said ‘we just thought it was cool’.
As with every McLaren designed and developed for the road or track since 1981, the heart of the Sports Series is a lightweight carbon fibre chassis. The narrower front still, which is different to the Super Series and McLaren P1 structures, combined with an 80mm reduction in height offers improved ingress and egress from the cabin. The carbon fibre chassis is 25 percent stiffer than a comparable aluminium chassis and has an even greater margin of superiority over steel, yet still weighs less than 80kg. The benefits of its structural stiffness are improved handling, agility, comfort and passenger safety. One downside to carbon fiber body is a lack of flexibility in the production process. For instance a metallic chassis can be heated and straightened if it is slightly bent or cracked. When asked what the impact of the carbon chassis has had on the performance of road cars, Paul said ‘aside from the safety aspect – the weight saving from steel would certainly reduce the 0-60 time by a couple of seconds’. Carbon fiber will not bend, once the force of impact is large enough it will crack or break and repairing it in most cases is not an option. The carbon fiber chassis is now an integral part of supercar design and manufacturing and should continue to advance in the automotive industry.
