What is it about the GT40 monocoque chassis?

[Joe T]

This is a nice article on the development of the Mono http://www.ict.mistral.co.uk/racing/whomono.pdf

I have a had a link to this on my site for some time, I showed it to Peter Ross who worked with Colin Chapman in the Early days. His remark centred around car chassis are very basic compared to planes as he was an Ex De Havilland recruit to Lotus like F Costin etc.

 

[Lynn Larsen]

The mono IS significantly stronger and obviously more correct ....

Fran,

"Obviously, more correct" is undeniable, but to say a mono is "stronger" is a bit of a stretch IMHO. Who's mono, which mono as compared to who's space frame, which space frame? Speaking in generalities, I have always heard the assertion that space frames were stiffer than monos. But stiffness is only one aspect of strength, so (sort of like Bill Clinton's "that depends on what 'is' is") I guess it depends on what one means by strength. My gut always believed that the mono could provide the required rigidity and ability to hold the four corners together at a lower weight than a space frame. Looked at the other way round, a space frame of equivalent weight would have weaknesses at certain points or in certain planes that could be handled with properly designed monocoque.

One would think that adding sheet aluminum skins to a space frame would not add significant strength. Like how several kit GT40 mfg's do it, UNLESS both sides of the space frame were to be covered with say .025 sheet and aircraft grade blind rivets were located about every 1/2" on center. Better yet fit and drill all the panels, then assemble wet with a structural epoxy.

My space frame is skinned with zinc coated sheet steel with 5/16" steel blind rivets on 1" centers. The tunnel is made of the same material and fastening system which also ties to the front hoop (dash) via a center console. My car may weigh a bit more (2550lbs w/ ½ tanks and my fat butt), but it is very stiff. While there hasn't been a scientific torsional rigidity test done on these chassis, afaik, I can provide this empirical evidence: I can jack up any one of the four corners and lift the adjacent two corners off of the ground in relatively short order.

Lynn

 

[Fran Hall RCR]

Lynn,

I am not going to be drawn down the road of disagreement ...suffice to say..........I have my reasons and data for making such a comment.

Lots of people love their Cobra replicas and feel they drive/handle great.....single plane twin tube ladder chassis......described by Shelby as a wet noodle.....their lack of torsional strength does not diminsh the enjoyment they provide.

Buy em , Build em and Enjoy em.

 

[Scott Calabro]

Hi Lynn,

By 5/16, do you mean diameter or length ? (5/16 dia. seems huge for that purpose from my aircraft exp.)
Do the rivet shanks have lock collars ?
You say that the tunnel is the same, is you're car a "backbone" type chassis?

I think a very good example of a backbone monocoque can be seen at VSECOBRA, Matt Adams outfit.

Excellent discussion...

Regards,
Scott

 

[Fran Hall RCR]

Herb Adams (VSE designer and owner) is a very good friend of mine....we talk chassis and suspension often

 

[Lynn Larsen]

Perhaps, I should have reordered my first paragraph:

The promise and reason for monocoques was/is equivalent or greater strength over space frames with equal or less weight (why else would a racer go with a different design). Beyond this "promise," it is very hard to make generalizations about one technique vs the other. As in all things, it is in the implementation of a theory that the rubber meets the road. Given your design capablility, Fran, I have no doubt that your monos are stronger than some (maybe many) space frames. Without a doubt, they are stronger than a single plane ladder frame as used in your example. But, your example proves my point: one must compare design/implementation to design/implementation, not classification to classification. That's all I was saying.

That said, there is no doubt that monocoque has a unmistakable coolness associated with it. An inherent provenance that comes with the fact that the most advanced race cars, both metal and composite, have been constructed this way for quite a few years now. This has an allure to a great many people, and I must admit that I am one of them. On the other hand, I don't want the guy with a space frame car to think that he, automatically, has an inferior car: that just isn't necessarily the case.

Scott, 5/16" is the diameter. Body of rivet has closed end that is bonded to mandrel, which is designed to remain in the shank of the rivet. The tunnel is not formed around a three dimensional frame (it's a monocoque design, if you will), so, no my chassis is not a backbone design. But because of its height and the way it ties in, front and back, to the space frame, it acts very much like a backbone design where longitudinal rigidity is concerned. The tunnel, together with the way the sponsons are sheathed, do add to the torsional rigidity of the chassis also.

 

[Fran Hall RCR]

Lynn,

I agree that there is a place for every chassis design and type of manufacture.
I enjoy the scratch build threads as much as anyone, as I know what these guys are going through...most are which are of tubular design probably due to the cost/time constraints I mentioned previously.

Nobobdy that owns any GT40, regardless of construction, should ever feel inferior as they have their own piece of styling excellence with the timeless looks of a GT40.

I think we have a case of thread drift going on though......

 

[John Lowe]

Fran - there's nothing wrong with a bit of drift, specially when its stimulated by 400bhp+.

As (yet another!) engineer.

1. Given the right degree of design excellence a mono will always be a better solution for a high speed road car/race car chassis if cost is not an issue.
2. The right grade ally is an excellent material for a mono.
3. The RCR chassis looks a beautifull and elegant solution to an engineering requirement, which is a good enough reason in its own right.
4. Personally, given very similar costs in the UK, I would feel shortchanged if I did'nt fork out the extra $ for a mono.

All of, course, IMHO

Grow old disgracefully

 

[Scott Calabro]

Fran,
The very first thing I thought of when I first saw your chassis, were Herb's designs ! I purchased many of the suspension parts for my road race Camaro from his son Matt. Herb's book, "Chassis Engineering" along with "Competition Car Suspension" by Allan Staniforth, are amazing reading to have for building your own chassis, or researching a store bought one. I am impressed that you have conversed with Herb on the subject at hand.

I wish someone would sell a set of chassis plans, copyrighted of course, only really selling license rights to build 1. On this website so that those of us who are not in a position to purchase a kit could start off small and build 1 chassis ourselves out of any material we choose.

Maybe a new market ?

Sorry about the thread drift....

Regards,
Scott

 

[Fran Hall RCR]

Scott,
do you think that a manufacturer could generate enough revenue to reimburse the development costs.???I gaurantee not
The issue is that as soon as the first set of plans are made available IP is gone forever.....end of story.

You would not believe the amount of people that have tried to purchase from me ...only, to find after some digging to find they are affiliated with another company .."thinking about gt40's"...yeah right.

Regardless of how many pieces of paper are signed to prevent dilution....it happens....
Everyone is always looking for a deal and a less expensive way to reach their goal....me included.

 

[Scott Calabro]

Fran,

And any other mfg. listening.... let it be said for the record....I WOULD NEVER DO THAT ! I cant help but think that one of you mfg's couldn't put out spaceframe plans that are web based only by subscription, relitively cheap after 1 proof of concept. Selling serial numbered tags with the license agreement as proof of license to build.

Think of the profit margin... subscription only web based plans updated as you build with no aluminum or steel on sales end.

Why does the mfg actutally have to build the car ?

I bet hundreds of suscriptions could be sold.

If cars are going to be pirated..is that even a word ? ....anyway why not beat them to the punch and SELL the plans, or the whole car if thats the way they want to go, and then continue to profit by supporting the build with parts ?

S

 

[Fran Hall RCR]

OK. point taken..
but your brothers wifes uncle wants to build a chassis and cant afford a license......he may just sneek a peek at your plans while you are not looking and bang...one unaffiliated unlicensed chassis running around.

The other thing is liability of construction.....can everyone weld like the next guy.....??So someone decided to try and wire weld a chassis set up to be TIG welded....a prospective XYZ customer views the aforemtioned chassis at a car show...but ..its not fabricated to XYZ standards...yet the proud owner is showing his pride and joy and advertising that this is an XYZ car....see the dilemma?

Why not design a chassis yourself and build one that would be easy to fab. in a home based shop with minimal fixturing and tooling costs and sell the plans yourself.?
You obviously have the self professed knowledge and skills from your day job.
I am sure all the scratch build guys on this and any other forum, that have been around will tell you that even starting with a good game plan and prior knowledge of the process...it is not easy....or fast.

Now get cracking....

 

[Scott Calabro]

UGH !

 

[Fran Hall RCR]

?????????
We do sell the base chassis/body package for 24k......
Then you can then purchase all of the associated parts individually, but you must have purchased the base package first...rockonsmile..

Should my post be moved to the RCR forum????due to advertising rules??

Maybe one of the scratch builder would be prepared to sell plans...I think Kalun D was offering some a couple of years ago.
Russ...what about yours???
Active Power or Turn Ten are doing chassis kits also...maybe they would be receptive to selling plans

 

Great question! I remember the first real GT40 I saw up close and personal. It was 1978 at the Chico Concours where I was showing a 63 black fuelie splitwindow corvette........ which at the time I thought was the ultimate ride. Oh I new what a GT 40 was Hell sakes I was saving my allowance in third grade to buy Road and Track for crying out loud ..... so I am walking through the infield looking at all the other cars on display and I walk up to this red GT40..... The car was as it turns out to be the last abbey panels car produced.... owned by a Jerry Frebries of Oakland ,Calif. I am totally knocked out... then what does the owner do.... He fires this monster up and drives it out on the road and nails it over an overpass adjacent to the field.... I was 30 years old but I swear that was the day my testicles dropped ..... 14 years later I won ''peoples choice'' at that very same concours with a Lola T70 GT restoration I did ..... but I got to tell ya driving up to the podium to accept my trophy did'nt come close to the thrill I got watching that damn GT40 windout over that overpass in Chico ,Calif. in 1978.... lets face it a GT40 is with out question the most beautiful ''race car'' ever produced...... Except for the Ferrari P4 of course

 

[Russ Noble]

?????????


Maybe one of the scratch builder would be prepared to sell plans...I think Kalun D was offering some a couple of years ago.
Russ...what about yours???

Yeah Fran, it's a thought.

I've been asked about this by other forum members. But as I have posted before, and you will be well aware, chassis design is a compromise and I'm sure the things I have compromised on mine for gains elsewhere would not suit 95% of potential builders. Plus, apart from a few rough conceptual sketches, there are no plans, just a bit of K1W1 do-it -yourself, fly-by-wire, build-as-you-go hard yakka.

Maybe if in the future I was to design and build something for myself, a little more representative of general demand..............?

Cheers

 

[Keith]

If you have the skill to copy.....you also have the skill the develop your own.....

So sayeth the Man....rockonsmile

 

Some people must have the skill! I seem to be selling GT40 and T70 Coupe bodies to a number of scratch builders. They all say they are not going to go into the business of being GT40 Kit Car Manufacturer. They just want a body to make a chassis inside the body. I guess it works for some people. Fran and I talk about this subject all the time. If poeple only knew how much work goes into getting a manufacturing company going, they wouldn't ask for plans I would guess. Some day maybe, someone might make them avialable. Then to really make a semi- mono chassis is another story!

 

[Scott Calabro]

FRPGUY,

It does not hurt to ask.

S

 

[Bill D]

Boy, this thread sure has drifted. I only wanted to know why guys love the original mono so much? Personally, I think it's a work of art!

Bill D