Carbon fibre moulding (chassis design update)

[kurtiejjj]

I was wondering how they made cars out of carbon fibre in 80s and early 90s, did they do hand lay-up or was technology already so advanced that they use pre-impregnated fibres and put it in on of these pressurised ovens?

I'm asking because I have this ridiculous idea of making a carbon fibre chassis myself but I'm not sure it would actually be strong enough with hand lay-up.

I have been researching into this subject for quite a while but I can't figure it out.

[Jersey Tom]

Why wouldn't it be strong enough with a hand lay up? I don't think it would be practical doing something that size in a wet layup, with that many layers of carbon and core and all.

The better way to do it, which would be tricky to set up but do-able, would be vacuum resin infusion.

I would agree its definately a ridiculous idea. I'd basically say.. don't do it.

What are the expected roll moments of the vehicle? How rigid does the chassis need to be in order to maintain suspension sensitivity? A good steel spaceframe can probably be done to 1500-2000 ft-lb/deg.

How would you do the design and analysis? What software do you have available that's capable of composite analysis with multiple layers of directional plies all over the place?

How would you make the tooling? If you were to have it machined out of tooling board (the right way of doing it IMO), expect to pay $10-15k. If you were to do it by hand expect to spend a month or two.

Carbon has been in short supply for the past couple years. It could be very hard to come by large quantities of carbon without a D-pass.

If doing vacuum resin infusion, expect to do a couple trial runs first with fiberglass to make it work right.

[Tom]

erm, what is the chassis to be used for? if its just display then I would just make a fiberglass or even wooden version, if its to race I'd get someone else to do it for you, if its a personnal prject to proove you can start with something smaller. I speak from experience, last year I had the crazy notion of designing a full le mans P1 car to the 2008 regs when I'd never designed anything more complex than a soldering iron before, this year I went for a wing and it's evolved to various parts now, start making a few parts out of Carbon Fibre (barge boards and wing endplates) and build from there if all is good.

[Carlos]

100's of aircraft have been homebuilt by wet CF layup using the foam plug method pioneered by Burt Rutan. For backround I would read " Composite Construction for Homebuilt Aircraft" by Jack Lambie and "Understanding Aircraft Composite Construction - Basics of Material and Techniques for the Non-Engineer" by Zeke Smith. The second book includes basic structural analysis. I have read that several FSAE teams are building in CF.

Burt Rutan's company - Scaled Composites - is hiring. See the Home Page. Gain experience and a paycheck. What could be better? Who knows - you may one day open your own company building CF monocoques. Look up Burt Rutan on Wikipedia for some backround before sending in an application.

What I am hoping to convey is that anything is possible. Don't be discouraged. Although I do agree that CF is in short supply.

http://www.scaled.com

There are a couple of things I would discourage you from doing - brain surgery and aircraft control. Almost anything else is possible, including CF fabrication.

Most small constructors are using space frames of 1020 steel tubing. Notch and Weld. Read " Racing & Sports Car Chassis Design" by M. Costin. He designed several F1 spaceframe cars for Lotus. His book might be useful. He did some notable work for a company called Cosworth. Acutally - he was the "Cos" in "Cosworth". Quite an accomplished gentleman.

Edit - Appendix 1 of RSCCD - Chassis Stress Calculations.

Appendix 111 of RSCCD - Suspension Calculations - aided by contributions from someone named Keith Duckworth - I suspect he was the "worth" in Cosworth. A111 deals with roll angles and cornering wheel load equations.

Besides CF - Fibre Glass - is a possibility - The Lotus Elite and Chaparral CanAm Group 7 cars all used fibre glass monocoques - a cheaper alternative to carbon fibre.

Vacuum Resin Infusion - I've seen it done with a plastic bag and a Shopvac vacuum cleaner. Primitive - also dangerous due to the possibility of sparking electric motor causing an explosion - don't try this at home - but it worked.

[AeroGT3]

Why wouldn't it be strong enough with a hand lay up? I don't think it would be practical doing something that size in a wet layup, with that many layers of carbon and core and all.

The better way to do it, which would be tricky to set up but do-able, would be vacuum resin infusion.

I would agree its definately a ridiculous idea. I'd basically say.. don't do it.

What are the expected roll moments of the vehicle? How rigid does the chassis need to be in order to maintain suspension sensitivity? A good steel spaceframe can probably be done to 1500-2000 ft-lb/deg.

How would you do the design and analysis? What software do you have available that's capable of composite analysis with multiple layers of directional plies all over the place?

How would you make the tooling? If you were to have it machined out of tooling board (the right way of doing it IMO), expect to pay $10-15k. If you were to do it by hand expect to spend a month or two.

Carbon has been in short supply for the past couple years. It could be very hard to come by large quantities of carbon without a D-pass.

If doing vacuum resin infusion, expect to do a couple trial runs first with fiberglass to make it work right.

I think a wet layup would be practical. Getting vacuum infusion down and getting the equipment would likely be MORE impractical due to the expertise and cost associated with it. A wet layup is quite easy.

It will take either a lot of time or a TON of money, but it could be done. I'd definitely suggest fiberglass though. E-glass is not that far off from carbon in terms of strength when you consider the price!

[BreezyRacer]

It's one thing to build some carbon bits like barge boards, etc and quite another to build a stessed monoquue. Even on F1 tubs chassis connections, etc are arranged where aluminum bulkheads are set into the tubs. If you were to emulate that type of layout and use something like a finnish plywood, then vaccum bag with carbon and E glass .. that might work out to a manageable project. In any case figure tubing for a roll hoop and study aluminum to carbon bonding. Have a plan to add tubing when it doesn't all work out. Get strength anywhere you can find it, including careful fab of the plywood structures. None of this is easy when you're trying to do a structural part.

All my work so far has been wet layup, no vaccum bag, non structural parts (ducts, body panels, etc). I wet in the carbon and epoxy on a glass sheet with a squeegie. Flip the carbon and squeegie again to make sure that there are no voids. Epoxy to carbon ratio should be equal weight carbon to epoxy. BTW, you can get a black dye to make E glass look a lot like carbon.

Good luck

[RH1300S]

You can buy pre-formed honeycomb boards with various thickness cores and thickness/types of skin.

Aluminium face - Carbon Face - GRP Face etc.

It seems to me that for critical parts - at least with these you know that they have been properly bonded and with the honeycomb core you will get tons of stiffness.

Is it worth considering a design with folded construction for the main members?

As Carlos says, there are many books around.

Also worth a read is Allan Staniforth's "Race and Rally Car Sourcebook"

Also Competition Car Composites by Simon McBeath

P.S. - A long time ago I fully intended to build a car (life got in the way - I got as far as a chassis mockup and a seat ).

I planned to use a folded construction for the main parts with space frames hung from each end to carry sub-assemblies. One advantage is that I was able to build mockup in balsa wood (don't laugh!) - that taught me a lot about where the chassis was flexing and where not.

Some of the appeal of the folded technique is that the construction of the important parts wouls have been relatively simple and almost idiot proof.

[kurtiejjj]

[quote="RH1300S"]
As Carlos says, there are many books around.

Also worth a read is Allan Staniforth's "Race and Rally Car Sourcebook"

Also Competition Car Composites by Simon McBeath
quote]

Yes I bought those books I will have them here in a few days, hopefully there is some interesting information that will help me further. I do intend to not only use carbon fibre in the chassis but also steel/alu for strength and easy mounting of the engine's.

I have drawn a lot of sketches of my ideas. Thing that buzzed me to build something myself is that I found an old book about racing car techniques of the 70s which looked not that difficult to actually make but then I thought: "Hang on a minute why can't I build a monocoque out of steel and carbon instead of steel with aluminium plating?" It should be stronger and have a bit more whif of technology about it.

For the engine I was thinking of a bike engine as these would suit such a car, light, powerfull.

Easiest thing would probaply be to buy a rolling F1 chassis and drop a bike engine in it, but that's not really a challenge, and I wouldn't be happy modifying it as I like original things.

[RH1300S]

Aha - the mists are beginning to clear - I think.........

Steel & Carbon chassis - does that suggest you are thinking of a tubular space-frame chassis, but using carbon sheet where you can't use diagonal tubes?

A bike engine is surely a good choice for this type of project.

My little design (for what it's worth) was sketched up in the late 1980's - it used a bike engine. I planned to use the front hubs from an MG Metro all round (small, available and with terrific brakes attached!). No roof, just two cockpit openings a bit like the D-Type Jag fairings. Engine from a GSXR1100 (they were just about the lightest and most powerful at the time). TBH - when I dreamt this up I don't think I had ever seen a bike engine in a car (Morgan 3-wheeler aside ) - it struck me that the power to weight would be terrific, also light engine could be hang with less weight in the chassis etc.

Amazingly when the first Radical came out it was almost identical to my sketches...........

Good luck -

[BreezyRacer]

Where are you located Kirtiejjj? Racing in many areas have classes like you are talking about. Might as well build to some rules so it's worth something after you're finished.

[Carlos]

Kurtiejjj - Goggle " NASA SP-8108 " It's old but useful. All the pioneering work.

The first G listing offers a list of papers written for NASA. SP-8108 is at the very bottom. There may be some material of interest. The pages on embedding metal-brackets and different profiles of
routered edges for foam sheeting are very good. The second book I recommended covered every area of discussion this thread has generated.

Epoxy and fabric matching systems. Where to buy vacuum bagging and vacuum pumps ect.

I agree with Aero. E-Glass is a good choice. The Chaparral 2A Gr7 car and the Chaparral 2D & 2F Le Mans Prototypes used E-Glass monocoques.

What were your sources of research?

Also find a good workplace that meets all local zoning codes. I had to abandon a similar home-built project because my neighbourhood is strictly zoned residential and complaints were filed.

[kurtiejjj]

Thanks for all the replies again, I really appreciate them. I read about that E-glass, bur it seems it's modulus Gpa rating is much lower than carbon, I don't exactly what it means but obviously it is an important factor otherwise race cars would have e-glass monocoques instead carbon monocoques? I believe this stuff was also used in the first Lotus elite in the late 50s but chapman apparently did not find it good enough and went back to steel chassis.

I was browsing on this website: http://www.azom.com/details.asp?ArticleID=769 and there is some interesting informationon on it about s-glass that is a stiffer version of E-glass which has an astonishing tensile strength of 4750!

However I am still awaiting the arrival of the 'race car composites' book, which is said to be very good.

What I also came up with was to use carbon fibre tubes and plates gleud together with a special glue to make a light and strong chassis without all the moulding. Lotus did it with their Elise chassis but then of course with aluminium. Would this be an interesting idea?

[kurtiejjj]

Allan Stanniforth book has arrived and already proved a great read! With info about suspension stuff etc. which is vital for a good handling car, I just found out that F1 cars in the 1980s practically had no suspension, especially at the front, apart from some friction. Great! [/img]

[zac510]

To answer the original question, most teams outsourced their chassis construction to aircraft companies.

[kurtiejjj]

Yes, I was getting a little off-topic. Now I will research things with my great new book and find out if there is a possibility of me building something that actually works

Well I'll let you all know.