#2 Chassis Design and Construction 1980’s To the Present Day (article written by Jack Halford)

Welcome to the second installment on Chassis Design and Construction, this month we shall be covering the 1980’s to the present day with the technologies and materials that are currently used in a modern F1 car.

The 1980’s started once again with Colin Chapman pioneering developments in Formula One, the technology and innovative creation that Chapman had started with ‘Ground Effect’ had moved on to such an extent that Lotus were now starting to lag behind their rivals. Teams such as Williams and Brabham had developed ‘Ground Effect’ technology to perfection, cars were sticking to the tarmac like glue, lap times were dropping as speeds increased, the G-forces placed on drivers when cornering were starting to have a physical effect on them and was becoming a cause for concern.

The FIA or FISA as it was known then had decided to ban the use of sliding skirts to try and control the high speeds that the cars were now reaching, at the same time Chapman and his engineers had been quietly working on another revolutionary idea which would as Chapman saw it ‘get around the ban and still keep within the rules’. The Lotus Type 86 was conceived; this concept carried two separate chassis and suspension systems, the Primary chassis was manufactured using Carbon Fibre, Kevlar and steel whilst the secondary chassis was constructed of Aluminium.

Breaking the chassis down; the primary chassis carried the bodywork, sidepods and wings together with the radiators and all other associated componentry for the cooling system and was designed with the intended use of soaking up any normal track surface lumps and bumps whilst keeping any changes in the aerodynamics to an absolute minimum. The secondary chassis was the monocoque and was constructed using aluminium honeycomb panels; it carried the engine, gearbox and main suspension units, the secondary chassis would fully optimize the mechanical handling of the car and would ensure a very smooth ride for the driver. The best way to visualize how this system works is to look closely at a heavy goods vehicle, the cab has its own independent suspension system and moves totally separate to the main chassis thus giving the occupants a very smooth and comfortable ride, and this is known as a ‘Sprung Cab’.
A derivative of the Type 86 was introduced for the 1981 season; the Type 88 was Chapman’s first attempt at a full carbon chassis, with the help of Dupont Chemicals a new monocoque (secondary chassis) was created using a single folded sheet of Carbon Fibre together with a Kevlar skinned Nomex honeycomb sandwich with machined aluminium bulkheads bolted to the monocoque for additional strength and to provide mounting points for all peripheral componentry such as the engine/gearbox and suspension units.

Chapman and his team had missed out on being the first F1 team to introduce an all Carbon Fibre chassis by just one week, that accolade fell to the Mclaren International Team led by Ron Dennis. Dennis was another visionary but in a completely different way to Chapman; he brought the professionalism to Formula One that we see in all the teams today and throughout motorsport in general. Mclaren introduced the MP4/1 chassis designed by John Barnard, the focus at the time was still very much on ‘Ground Effect’ and Barnard wanted to optimize the concept in everyway that he could. He was looking for the largest ‘Under-wing’ (the floor on today’s F1 car) that could possibly be used and this meant that the chassis had to be kept small ‘no bigger than the drivers bum’ he was quoted as saying and the only way to reduce the chassis section whilst retaining the torsional stiffness was to use an entirely new material; Carbon Fibre.

Barnard had discussed his new design with several companies within the UK with regards to manufacturing the new chassis but always came up blank everywhere he turned. Everyone he spoke to thought that it was a crazy idea; that it wouldn’t be strong enough and the chassis would completely disintegrate if the car crashed, all very negative comments from the UK’s main manufacturing companies; this was definitely what Barnard didn’t want to hear. A chance meeting with an old colleague from Barnards Indycar days pointed him in the direction of an American company; The Hercules Corporation. Hercules had a research and development facility that was created to specialize in ‘One Off’ projects, but even they didn’t have sufficient Knowledge or expertise to create such an item that required complex curves. It was decided that the first chassis assembled would comprise of flat carbon panels with an Aluminium bulkhead at the front to serve as a mount for the front suspension. Barnard still wasn’t satisfied with this and set out to create a much better way of manufacturing the chassis, he wanted to decrease the weight even further whilst keeping the torsional rigidity as high as possible.

What he proposed was that a series of ‘male’ mould tools be machined and that the carbon cloth should be laid over the mould in multiple layers, Unidirectional cloth was used or ‘UD’ as we call it, this is where the weave of the cloth is in one direction only, usually along the length of the roll when manufactured. The main concern when using UD on its own is that when the material is put under extreme amounts of stress its strength is in one plane only; which is the direction of the weave. To overcome this problem and to achieve maximum strength the UD cloth was laid at differing angles.
Perhaps the easiest way to understand this is if you imagine or if you can; look at the face of a compass. The first ply would be laid with the weave running in a North/South direction, the next ply would run from North East/South West and the next from East/West and then South East/North West and finally back to North/South again; you get the picture! The orientation of the plies would be shown as 0/90, +45, 0, -45, 0/90 on the lay-up drawing. The process that was used is commonly known as a ‘wet lay process’. This is achieved when the cloth is laid onto a mould and a thin layer of resin is brushed over the cloth followed by another ply then another thin layer of resin and so on, it is a time consuming and very messy method. Today’s materials have a specific resin content already impregnated into the carbon cloth and is known as ‘Prepreg’ which makes for a much quicker and far cleaner way to lay-up a component.

Once a certain number of plies had been laid over the mould to form the inner skin, sections of honeycomb were laid and then further plies of UD over that to form the outer skin to finish off the lay-up of the chassis, simple you may think but manufacturing the MP4/1 chassis in this way would have taken several hundred man hours to complete far more than it takes to build a modern F1 chassis and that still takes a few hundred man hours from beginning to end, the finished chassis was then vacuum bagged and placed in an Autoclave for curing. An Autoclave is a large oven that can cure components at very high temperatures and also extreme pressure. The higher the temperature and pressure; better the consolidation is achieved, the material and resin is squeezed into every corner and recess on the mould, this all has to be programmed and monitored very carefully, get this part of the process wrong and the chassis will be ruined. As mentioned previously; Barnard had used a series of ‘Male’ moulds with the lay-up on the outside of the mould and once cured each section of the moulds were removed from the component leaving a very smooth finish on the inside of the finished chassis and a very rough textured finish on the outside.

It wasn’t until 1983 if my research is correct that ‘Female’ mould tools were first used in the manufacture of an F1 chassis. Gustav Brunner who at the time was working for the small ATS F1 Team began using the female moulds and thus change the way all F1 teams would manufacture their chassis and are still using the same build process today. Lay-ups were now done on the inside of the moulds and would allow the carbon plies to follow the contours of the mould to improve aerodynamics and most importantly reducing the amount of additional body panels that would be placed over the chassis at a later stage, this would also assist in reducing the overall weight of the car and give a massive saving in production time.

This was now the way forward and over the year’s the chassis or survival cell as the FIA now like to call it have become almost bulletproof in its construction. Stringent FIA tests on the chassis are now mandatory; impact tests, static load tests are all carried out with one specific aim; the safety of the driver. As from 2012 no team can take part in any pre season testing until their chassis has passed all of the FIA crash tests, massive pressure now placed on teams to get everything done even earlier. Crash tests have now become so rigorous that the chassis has become heavier; by as much as 30kg since Barnards MP4/1. It has been reported that when Barnard and Hercules began to refine the MP4/1 chassis they brought the weight down to an impressive 36kg, it must be said thought that today’s chassis is longer and taller in its construction which also adds to its overall weight.

So, what of today’s modern F1 chassis! Most teams these days begin working on the following year’s car midway through a season. Team bosses and their various heads of departments will sit down and discuss when to shift focus onto the new car and once a project plan and timescales have been worked out its full steam ahead. When the design of the new chassis has been finalized production can begin with the manufacture and machining of the pattern block from which the moulds will be made. This basically is large epoxy sheets bonded together, vacuum bagged and placed in an Autoclave to be cured under pressure, usually at 100psi (Pounds per square inch). The next stage the pattern moves to the machine shop where a large 5 axis CNC (Computer Numerically Controlled) machine will cut away at the pattern block until a rough shape is achieved. The tooling used at this stage of the machining will be large heavy duty cutters which will plough through the pattern block with ease, once the roughing stage is complete the finishing stage now takes place with the cutters becoming more refined and the machining more delicate as the smoothest possible finish is paramount as any abnormalities in the pattern will show up in the finished mould. After machining the pattern will be finished by hand to remove any trace of the machine cutters, painted black and then polished to achieve an ultra high shine and finally a release agent is applied to the finished pattern.

The next step in the process is for the moulds to be manufactured from the pattern, F1 teams can manufacture their chassis moulds in different ways. The first of two most common ways are to make just an upper and lower mould and the second way is basically the same again but manufacturing the upper mould in two parts and then bond them together and the same for the lower mould. Once the moulds have been laminated and cured they will be taken to a department that we call the trim shop for final finishing, all sharp edges will be removed and any carbon or aluminium inserts that are required will be bonded into the moulds before component manufacture can begin. The finished moulds are handed back to the composite technicians in the clean-room who then prepare them ready for the lay-up process, once again the moulds are cleaned and a release agent is spread over the moulds. Accurate templates are taken from the moulds which represent the first full ply that will be laid into the moulds which are then passed onto to the cutting room. The kit cutters take the templates and the lay-up plan and study it inch by inch to work out the full lay-up of the chassis; the templates are attached to a large digitizing board and are copied onto the CAD software on the computer. When that has been done the kit cutters can now start to make all the necessary adjustments to the plies i.e. sizing, weave orientation, number of plies required etc. There is also a major problem that the kit cutters usually face when doing the kit cadwork for a chassis and that is that the main plies or ‘all over’ plies as we call them that has an orientation of +45/-45 degrees are to large for the width of the roll of carbon cloth. So, important decisions have to be made with regards to where that particular ply will be cut into two or possibly three pieces for it to fit onto the roll of material when the kit is finally nested with all the other plies. Now it is not just a simple case of putting a cut through the ply to make it fit; the kit cutter will check with the design engineer as to what sort of loads and stresses will be placed on the chassis if a cut and to the orientation of that cut were to be put in a particular place on the ply. This information is vitally important as it must be carried through to all the main plies with the same orientation in the lay-up process, the kit cutter must also take into consideration that every ply that has any additional cuts that those cuts must not be in the same place as the previous one as that will weaken the chassis. All very technical and hours and hours of head banging; believe me I know!

When the kit cutter is satisfied that all the necessary changes have been made the kit can be ‘nested’, the CAD software takes all of the information that has been created and places it into a nesting file. The plies are mapped out onto a specific sized sheet (the width of the roll x usable length of the bed on the cutting machine) that has been selected by the kit cutter and the software then works out the most economical way of cutting the plies, the kit cutter can also make changes to the nest manually if he so wishes, the aim is to have the least amount of waste material possible as carbon cloth is very expensive. Cutting the kit can now commence and will take several hours to cut a complete kit for a chassis and using as many as four different materials each having its own characteristics and benefits in the lay-up.

As previously mentioned the choice of carbon fibre material today is ‘Prepreg’ and comes with various different types of weave patterns; Plain weave, Twill weave, Satin weave And Uni-directional (UD) are all used in the manufacture of the chassis and all associated components on an F1 car. So what are the differences between the various weave patterns, firstly the carbon fibre threads are known as ‘Warp and Weft’ threads. The warp threads run along the length of the carbon cloth and the weft threads across the cloth and are woven into the warp threads.

Plain Weave
This is the simplest of carbon fabrics to understand, when woven the weft threads are carried over all the odd numbered warp threads and under all even numbered warp threads, sometimes the weft can be passed over and under two warp threads. Plain weave is ideal for flat areas or simple one way curves but when used on more complex moulds with multiple curvature the cloth will wrinkle and not lay neatly, darting or snipping the cloth will be required for it to drape over the curve for a neater finish.

Twill Weave
This has a better drape over more complex shapes, the twill is formed when the weft threads are passed over the first and second warp threads and then under the third and fourth warp threads and so on. There are many variations of twill weave, 1×2, 2×2, 1×3 etc but the most commonly used is the 2×2 twill and when manufactured the cloth appears to have diagonal lines running across the fabric from right to left or vice versa. Another advantage of using 2×2 twill over plain weave is that the threads go over and under each other fewer times than the plain weave thus placing less stress on the fibres that could possibly create a weakness.

Satin Weave
When Satin weave is manufactured the weft threads can pass over as many as 12 warp threads before being woven in, the most common is called a 5 harness cloth; this is where one weft thread passes over four warp threads. The 5 harness is ideal for chassis construction since the threads have less crimping than the plain or twill weaves and makes for the strongest use of the fibres.

Uni-Directional
UD threads/fibres all run in the warp direction and as mentioned before; is only strong in plain so cannot be used as a main ply where strength is needed in various planes but can be used with woven cloth for keeping weight to a minimum in certain areas.

The kit has now been cut with the various materials that are to be used and what we have is a very large jigsaw puzzle with every ply having its own very important place on the mould. The composite technicians now set about laying the plies in sequence as described in the lay-up manual making sure that every ply is an exact fit in the mould, trimming material here and there, ensuring that all overlaps and butt joints are in the correct place with no creases showing in the cloth as the smoothest possible finish is required. Debulks will be carried out at various stages of the process, the composite technicians will place the mould in a large vacuum bag for all the air to be removed squeezing the material into every nook and cranny on the mould, the lay-up plan may call for a warm debulk and the mould will be placed into the autoclave and warmed up gently under vacuum with pressure also being applied. The composite technicians can lay as many as eight all over plies plus the plies from the other materials being used, in total there could be up to three hundred or more individual plies laid in the first stage or ‘outer skin’. Once the outer skins stage is complete the mould will be vacuum bagged (very carefully) and placed in the autoclave for curing at a temperature of 135°C and the pressure set at 90psi, the reason why I say very carefully is that when the mould is placed in the vacuum bag; if the bag has not been pushed into every recess on the mould when 90psi of pressure is placed upon the bag there is a possibility that the bag will stretch and burst and the vacuum would be lost, if this happens an alarm will sound on the autoclave and the program can be turned off, the job can be removed and the problem sorted out; but if the job was curing overnight and the same thing happened there is a very strong possibility that the component could be ruined, most F1 teams work through the night these days so its never likely to happen.

The next stage once the outer skins have been cured is for the ‘Core Stage’ to take place; the moulds are removed from the vacuum bags and the outer skins prepared (when manufacturing a chassis it never leaves the moulds until the very end of the construction), this involves sanding the inside of the outer skins by hand to give the surface a very slight rough finish to aid in the adhesion of the core, again the skins are cleaned and glue film is applied to the inside followed by the core. The core used is an aluminium honeycomb that comes in various thicknesses and cell densities, templates are used once again for sizing purposes and then cut by hand. Aluminium honeycomb is used in chassis construction for added strength whilst keeping torsional rigidity, weight and costs to a minimum, you can imagine how heavy and costly a chassis would be if ply after ply of carbon cloth were laid to the specified thickness required. Whilst all this is going on back in the cutting room the kits for the ‘Inner skins ‘ are being prepared, the CAD work, nesting and cutting will all have been finished and made ready for handing over to the composite technicians for the final lay-up stage.
As with the outer skins the inners will comprise of several all over plies still amounting to several hundred individual plies but not as many as the outer skins stage. The inner skin plies will be slightly smaller in size which would have been taken into account in the cutting room; the kit cutters will have staggered all the plies correctly making sure that once again no two joins are in the same place. The composite technicians follow the same procedures as before in laying the inner skins and once completed; vacuum bagged and cured. The moulds are then be taken back into the trim shop after curing where they will be cleaned up before the bonding of the two halves takes place and then finally removed from the moulds. ‘Hurray’ I hear you shout; after several hundred man hours in various departments we now have a chassis, we all give ourselves a pat on the back for a job well done, turn around and start all over again with the next chassis.

The number of chassis constructed over a season varies from team to team, some will build four chassis to see them through an F1 season but others may build as many as seven. Accidents take place in races, chassis destroyed because of those accidents, although a chassis can be repaired the life expectancy of the repaired chassis may only be for another one or two races before the team remove it from service. Even if a chassis has never seen an accident the teams still like to phase their chassis use in a revolving fashion i.e. number one and two chassis maybe used for the first three races of the season, then the team will change and use number three and four chassis for the next three races before number one and two are brought back into service and so on, it is just to prolong the life expectancy of the chassis.

Well; that’s it on Chassis design and Construction, I hope you have enjoyed this small insight as to what has gone on over the years; I certainly have enjoyed writing it. In our next article we will have a look at the different types and configurations of Engines and Gearboxes in Formula One over the years, so keep reading.

Jack

‘All views expressed in this column are those of the author and not Caterham F1 Team’

Written by: Jack Halford

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