How about a Kevlar Monocoque?????

Hi all

How about a Kevlar monocoque?
I am looking at the possibility of making a kevlar monocoque for track use.
The tub would closely follow the original lines of the steel tub, Kevlar is stronger than steel and as long as the load is spread at the attachment points by the use of sandwich plates then I think a Kevlar monocoque would be superior in every way.
The Mclaren F1 has a composite monocoque and so do most of the modern GT1 cars.
I think the rear suspension should still be hung from a U shaped steel or alloy cradle
but the cradle itself would spread the load and be attached to the Kevlar monocoque.
Do you think that Ford should have gone for a composit monocoque for the new GT40?
I would like to here your views and I am aware that we have had discussions on
monocoques before.

Regards

Chris

[ May 16, 2002: Message edited by: Chris Melia ]

 

[Guest]

If you could get detailed information on Jim halls #66 car(chapparal) from Midland Texas, that might be a good place to start.

 

[Jim Glickenhaus]

Jim Hall's tubs were fiberglass not kevlar.
Cost is a factor with Kevlar as is sanctioning bodies view for track use. Repair is also a factor as would be engineering. I think cost detered Ford with their new GT43. The Mk-IV has a composit tub which is lighter and stronger that MKI-MKII tubs.
Best
Jim

 

[Bob Putnam]

Kevlar has very poor compressive strength, so it is seldom used in a composite by itself. Tensile strength is good, elongation to breakage high, and the density is fairly low, so it's used to "toughen" laminates against catastrophic failure. If you want a stiff structure, graphite is actually cheaper than kevlar - which doesn't say to much about kevlar...

 

Hi Bob

when you say graphite do you mean carbon fiber?
I thought that carbon fiber although strong and stiff has a tendency to shatter on
impact. Would you say that a laminate of carbon and kevlar would be a better material
for the project?
What material would you recommend for a composite monocoque GT40 tub?.
Regards

Chris.

 

[Guest]

Jim,
Did you not notice that I said it would be a good place to start, I know they were fiberglass. I saw these cars many times when I worked in the pits at Laguna Seca.

 

Hi Malcolm

At the Stoneleigh kit car show last month was the Cox GT company and their kit car is based on a fiberglass monocque. All the suspension components were bolted through the fiberglass tub.
I asked if they had ever had a failure and was told that they had built fiberglass monocoques for 21 years and had never had a problem with the tub.
The galss was 1/4" thick at the suspension mounts and had a plate to spread the load.

Chris

[ May 16, 2002: Message edited by: Chris Melia ]

 

[Jim Glickenhaus]

Dear Malcolm
You're very lucky to have gotten the chance to have seen these cars run in anger. One of the greatest days of my life was at Goodwood where I met Jim Hall, saw his cars, and followed him up the hill in my MK-IV. He was driving the "sucker car" and I could see it suck down as he revved the snomobile engines around the turns.
Best
Jim

 

Chris,

Sounds as though you'd better get cracking. No time like the present.. BTW, for better or worse, I picked up a new Porsche 6 speed box from their 968 turbo rs factory racecar spares, allegedly the last one. All of the Porscheaholics say that it takes over 750 hp to break this one. Had any experience with it?

Regards,

Roger D.

 

[Jim Rosenthal]

Hi Chris:
Kevlar is seldom used by itself except in bulletproof vests and the like. It is usually used in combination with E glass or S glass. It doesn't wet out as well as other fibers. Whoever said carbon/graphite is better, I agree with them.
You can make composites stronger by using epoxy or vinylester resin instead of polyester. There are also fireproofing additives you can add to either which might come in handy. Look at the West System manual
(Gougeon Brothers).
Another option, which no one has explored that I know of, is to use preformed composite structurals and build the tub from them. You would need sheet, bar, beam shapes to suit and then glass them together. For low-volume production this would be better than having to build a set of molds.
It is also possible to use a combination of metal and composite parts which are glued together. I don't think, though, that you could simply start with the original drawings for the tub and make it out of composites. You would need the help of a materials scientist to figure out how to adapt the design to composites.
Good luck. I think it is a great idea, and after years in boating I have a lot of respect for FRP construction. I hope you are able to do it.

 

[Bob Putnam]

Jim's hints are excellent. If I were to do a monocoque with what I thought was the best cost/performance ratio (and that's strictly a personal decision), I would use a combination of materials. Mostly glass and kevlar, but using graphite in areas that were most critical to flex. There is a definite structural advantage to epoxy, but vinylester isn't bad either. In "production mode" I would vacuum-bag or used matched dies, but that makes the molds very complicated.

Building the tub from flat sections is an intriguing idea - I am not familiar with what's available. Perhaps you could get away with only molding the outside of the rockers. Connecting the panels could get pretty complicated and messy.

 

Chris,

I have had quite a bit of experience with kevlar & carbon. About 10 years ago I was involved in the manufacture of high performance windsurfing boards. They were designed to be built as strong as possible and as light as possible. We went through just about every combination of modern materials. Here is my slant:

1) Kevlar is an absolute pig to work with, and as already mentioned it has no compressive strength, however it has incredible tensile strength.

2) Carbon fibre has very good compressive forces, and is easier to work with.

3) Always work out what type of forces you are dealing with. e.g a windusrf board require compressive strength on the bottom and tensile strength on the top. There are also lateral forces involved.

4) We always used a combination of both kevlar and carbon - top and bottom.

5) Sandwich construction makes everything much, much stronger & lighter. A high density foam is sandwiched either side with kevlar/carbon and vacuum bagged with expoxy resin. This is roughly how the panels of the new McLaren Mercedes are made.

6) Consider very carefully the weave of the material. A twill is best used if complicated shapes are involved, ordinary woven will be much harder to use.

7) Bloody Good Luck !!! I have a friend who works for McLaren, and even they have problems using these materials. You will need some serious cash to do something like this. It is very unlikely that you would get it right first time. It's often trial and error, and when you are talking about high performance cars it's serious stuff.

8) I used to get a lot of info from Lotus's composites division, they have a wealth of experience and would probably be able to give some names of suppliers for kevlar and carbon etc.

I hope that gives you some food for thought. I would just go for a carbon kevlar skin, and replace some parts with titanium. An easier option without any headaches.

Sincerely,


James

 

James,

I too was vaguely involved in board construction. but 2 or 3 years prior to you...

My view is that not only was the material choice critical, but also a huge amount of emphasis had to be placed on the relative composite positioning.... different materials used in diferent ways to provide various combinations of stiffness, low weight etc and this was the complex part of the design... 3 dimensions made life tough...

Also, we had a lot of problems with very stiff sections joining to less stiff sections cause stresses in undesirable places... eg shock loads transmitted through very stiff areas and caused fractures. This would be a particular problem in any build up of fillers and resins to make panels line up, and in thick paint... eg your paint would probably suffer around the joins between carbons and polyesters etc etc..

Think hard about taking this approach!

Neil

 

[Ian K]

Roger D,

Aren't the 968's part of the 924/944 line?
If they used similar setups, then the
transaxle would have used a torque tube,
and thus will not work in a 40. Perhaps the
race version doesn't, but it would be
interesting to know either way.

ALso, HP is not the problem as much as torque.
In the GT40 Engine thread, you mention
looking at 600/600. I'd be more concerned
with the 600 lbs/ft of torque than 600 HP.
Getting 400 lbs/ft to hook up is hard
enough apparently.

Ian

 

[Jim Rosenthal]

Regarding preformed composite structurals:
the company that I know of offhand is Strongwell, which makes a variety of PCS shapes by molding methods such as pultrusion and moltrusion. (I am not making this up, honest). Usually resin and fiber are drawn through heated dies and cured in molds or something to stabilize the shape as it cures. Some of the big yacht manufacturers are using these items as it is frequently cheaper to just buy what you need rather than tool up for it. I found out about this type of materials from an article in Professional Boatbuilder magazine.
There are a variety of resins used and also fibers. The advantage is that you have all of their technology without the tooling cost. Of course, you pay for it.
You would still have to glass all this toether and figure out how to spec out the materials for the different parts of the tub.
If you look critically at the design of a GT40, the basic setup- a selfcontained tub with all the drive equipment in it, which could actually I suppose be motored around without either the front or rear clips fitted- may not be all that suited to the type of construction we're discussing. Maybe a better question, and food for more thought, is could you build a car that looked like a GT40 using a composite tub and would you necessarily have hinged front and rear sections that don't stiffen the car, or would you accomplish the passenger, driver and service access a different way so as to use those sections to contribute to the rigidity of the whole vehicle.
Don't mean to drift along, it's just a very interesting idea...

 

Ian, yes, the 968 is a front engine rear transaxle setu. A look at the 968 tranny, though, makes it appear that it could be used in a '40 configuration. I have one in a box to open tomorrow, along with the name of a fellow in GA who supposedly makes an adapter to ford block. It should all be a most interesting experience, but what on a '40 replica is not? Yes, I know the Gurney 427 will be a bit much, but I'll run that risk...

Roger

 

[Ian K]

Roger,

The problem with the torque tube transaxles
is converting them to use a standard clutch.
Robert Logan has looked into this for the
RF40, and that is why he went with the Audi
box. In essence, the Audi box and the 924/944/968
boxes are the same, except the Audi is
front wheel drive with a standard bellhousing,
and the Porsche uses the torque tube.

However, I'd be interested to hear if you get
it to work, since that would be another source
to consider.

Ian

 

I have a small amount of experience with carbon graphite structures in racing applications having done the finite element analysis work on the Mazda GTP car about 10 years ago. I believe that carbon graphite is commonly used in structural applications like this. It allows the design engineer to orient the layers in a manner that best addresses the design criteria, and it withstands engine compartment temperatures quite well. Usually a structure like this has a core of honeycomb or foam (various types are available) to move the carbon plies away from the centerline to increase the moment of inertia. You can do quite a lot by changing the angles of the plies, adding plies, and generally tuning the structure to do exactly what you want it to do. None of this is cheap or easy. The complexity involved in properly engineering a composite structure isn't trivial, and the equipment to properly manufacture a tub is expensive.

Racing is a life and death sport, and this should be kept in mind when developing a race car. The Mazda GTP car was the first car of its kind that used a composite rollover structure instead of a metal roll bar. We spent quite a bit of time making sure that the rollover structure would not fail. Sure enough, the first race for the Mazda GTP car was at Road Atlanta and somehow the car got upside down and landed on its roof at 160 MPH. Other than a few scratches on the roof, no damage was done to the car or the driver. If the composite structure hadn't been properly engineered the outcome could have been quite different and possibly very unpleasant for the driver.

I'm sure a composite GT40 is very doable, but it would take some time, money, and skill to do it properly. I imagine that the U.K. is loaded with firms that could easily handle a project like this. Talking to them would help define the challenges you would face in trying to do this yourself.

There are quite a few SAE papers on this subject. It might be worth taking a look at them if you want to learn more about what is involved in designing and engineering this sort of structure.

John Crawford

 

[Guest]

Jim,

I watched the '65 Sebring race ... where a Chaqppy 2D and a 2F fought a Mark II as well as a red Mark IV and a yellow Mark IV.

Several hours into the race the 2D started to release just a little smoke on shifts. Wasn't long before he was out. The Mark IVs fought the 2F for another two hours. As I rermember it, the red Mark IV and the white chappy 2F alternated lap records for the better part of an hour. The Mark IV would just out run Jim Hall on the North-South runway. By the time they made it around to the water tower, the Chappy was on the Mark IV's ass trying to find away around.

Was an absolutely amazing race! Four speed against variable vane torque convertor (and handling versus top end).

Soon the 2F started to smoke and it too retired. Left the Fords to tour out the rest of the race.

I still remember a scene after the race, when the driver of the red Mark IV had to stop on the way to the review stand to get all of the folks where were sitting on the car to get off ... he was afraid of toasting the already fragile clutch and not being able to make it to the ceremony ;>)

Wonderful race ... wonderful sounds ... lovely day!

Any chance J6 is one of the cars involved in that conflict?

 

[Jim Glickenhaus]

Dear Mike
MK-IV's didn't exist until 1967. The first race one entered was Sebring March 1967 (J4). It won driven by Andretti. The only other time a MK-IV raced was the four that ran at LeMans in June 67. I think the cars you saw in 1965 were MKII's. J4 is yellow as is J6. J5 is red. J7 is Bronze. J8 is Blue.
My car J6 finished fourth overall at LeMans driven by Donohue and McLaren. It's sister car J5 driven by Gurney and Foyt finished first. The other MK-IV's didn't finish. Andretti crashed and Ruby drove the other one into a sand bank.
Best
Jim

[ May 22, 2002: Message edited by: MK -IV J6 ]