What chance success?

[Guest]

I see from a number of posts that it is the ambition of a number of forum members to build their own authentic monocoque from scratch. A challenge indeed. I do not know the guys personally so these comments are not meant offensively. But what chance of success? Ceratinly a lot of time measured in years is going to be needed on an amateur basis. Skill definately and massive amounts of patience also required.

A space frame GT40 is a complicated kit compared to most self build cars. I know how much effort Ray had to put in to designing his GTD monocoque (CAV now?) and the problems encountered there.

Then there is the chap who wants to model and sculpt his own body as well!

Do these chaps want the engineering or the driving experience?

If/when they succeed and drive their cars for the first time, the sense of satisfaction will be enormous. It was great when I finished my GTD, so to finish a complete scratch build would be something else.

But will it or can it be acheived via a scratch monocoque build? What think you?

Good luck to the chaps giving it a go!

Malcolm

 

[Mike Dozier]

Malcolm

I know what you mean. To me, a long term project is anything longer than a week.
But some people have MUCH more patience than I will ever have.

I run into car guys that spend 10 YEARS or more restoring one car. They are in no rush,
seem to take more pleasure in the process, and usually do marvelous work. But the percentage of time they spend driving is
VERY low compared to the time spent building.

That's not for me. While I do enjoy the build, I enjoy driving equally. And the older I get, the less time I'm inclined to spend building.

So I guess it's just another instance of human individuality that makes the world
such a diverse and (unfortunately) sometimes
dangerous place.

MikeDD

 

Malcolm/Mike,

I guess I am one of those individuals that is seriously looking at building up a Monocoque... Yep.. We are all individuals!

I am doing it because....

1] This will be my 4th 'project' and I have found that the build up/construction is probably the bit I enjoy best

2] I have always promised myself a 'scratch' build at some point. I was looking at a spaceframe, but then decided that the effort might as well go into a monocoque instead. Especially as a couple of people currently buidling scratch spaceframes have commented that with hindsight, they would build a monocoque..

3] I am fanatical about GT40's, and what more satisfying than a car that is completely of your own making...

I fully expect my 40 to take a few years (7+)to get on the road...

What worries me a little, following some of the topics on this theme over the last few months is the underlying tone that these will be lower cost than buying a kit... for those thinking that this is the case... IT ISN'T... you have been warned... just wait till you price up the tooling....

Finally, I too am amazed at the guy that is looking to make up his own body... for me that is nigh on impossible... not just from a skills point of view, but space and facilities... if he is to use decent resin that won't cause him problems later on, then he is going to need all sorts of kit, right through to air extraction equipment and an oven!... but however, good luck to him... I hope he succeeds.

Me... I'm off to spend the next few months glued to a CAD screen drawing up a chassis!

Regards

Neil

 

Hey Guys,

I was wondering why my ears were burning.

You know it's funny but I'm fairly confident I can make the body. I've done this sort of thing before. Not to this scale but the principles are the same. I've got alot of experience making things like this. I've had more than one person tell me that something I was about to undertake is impossible. Believe me, nothing is impossible. Especially in this country. Anything is possible.

What scares the crud out of me is making the chassis. Cutting and welding 1/4" stainless steel. Bending it where it needs to be. Figuring out suspension and engine mounting points. And on and on. Neil, you have my respect sir.

I suppose it all depends on your background. If you are an engineer building the body seems crazy and impossible. If you have my sort of background building a chassis seems crazy and impossible. Yet, they are both very possible.

I don't think that making my own body is going to cost me any less in the long run, but it will in the short run.

Doug

p.s. if any one you guys that are building your own chassis would like to work on a deal for a set of body panels, let me know. Maybe, we can work something out.

D

 

[Bob Putnam]

If I recall correctly, I spent roughly 500 hours designing our monocoque. This, unfortunately, was pre-CAD for me. It would be roughly half that time now. That doesn't include designing suspension components or any jigs - another 100 hours for the jigs alone.

I had the luxury of working out the suspension geometry first, then designing the chassis to fit.

It's quite a project.

 

Thats good to hear Bob, because I have budgeted about 600 hours of CAD time for the design of chassis, and suspension.

I'm hoping to work from measurements from an original car, so its less a design task, particularly for the suspension mounting points/geometry, and more a verification task...

Although with Inventor etc nowadays, it'll be interesting to see how well the original geometry stacks up....

Regards

Neil

 

[Bob Putnam]

We all have our own philosophy of suspension geometry development. I tend to design for predictability rather than theoretical high cornering force, although with the GTs low CG it's hard to lose the latter.

The most important final consideration, IMHO, is bump steer/toe-change under load.

[ June 13, 2002: Message edited by: Bob Putnam -ERA- ]

 

[Mike Dozier]

Doug

I don't doubt that you can make body panels.
The question is how accurate can they be
without splashing off another body?

To my untrained eye, the compound curves
could not be accurately replicated unless you have an expensive coordinate measuring
machine.

And that doesn't even address the time and expense of constructing the molds!
All this for a 1-piece run???

Just curious.

MikeDD

 

Ah... now this is getting interesting...

I would agree with you Bob... and with the caveat that I have not yet had any chance to analyse GT40 suspension geometry, I would have had these initial thoughts running through my mind...

The '40 does indeed has very low CG, but I would have also thought that it has relatively limited suspension travel, and as such bump steer is, while to be avoided as much as poss, not likely to be the key factor?

I would also suspect that with the low CG, and relatively solid suspension setup, that things like roll centres would not move around that much...

accordingly, I would be looking to find a nice balance of ultimate grip in corners, and predictability through focusing attention on KP Inclination, anti-dive etc etc

I guess that unless you design a car around an event like Le Mans, then the predictability is more important from a safety/driveability point of view than 'ultimate cornering g-force'..... then again, the car WAS designed around an event like Le Mans!

I will enjoy the suspension analysis!

I also guess that one of the parties with an interesting contribution to make on this discussion will be the GTD guys who race regularly?... what do you guys focus upon in setup?

Neil

[ June 13, 2002: Message edited by: Neil Strenge ]

 

[Bob Putnam]

I designed our GT with the assumption that almost all of the cars would be used on the street, so we have over 6 inches of wheel travel and fairly soft (relative to a race car, anyway) springs and dampers. In Connecticut, we have some "interesting" road conditions, so I've always been biased toward a car that doesn't bottom out. The nice thing is if the bump steer is good at 3" jounce, it's even better at 1".

Still, the car rolls very little, so camber change is minimal. With some stiffer springs, the car can be track-friendly too, of course.

 

On that subject... has anyone used Performance trends suspension anlayser software available here ?

Regards

Neil

 

[Guest]

Neil, you asked about what the GTD competition guys do on priority on suspension? We have a different starting point to what you have. In principle our suspension mounts are pre determined fixed points on the chassis. We can't do the ideal and design a complete system for one thing or another. Also we do not necessarily design and manufacture, but instead predominantly use off the shelf parts, therefore being limited to someone elses point of view of what is correct. And as we all know, with suspension, there is no correct answer, just compromise.

I am currently half way through fitting the Gardner Douglas front uprights. These have a different KPI to the standard GTD (cortina) front upright, ie more KPI but less KPI than the racing uprights Ray Christopher designed and made. The ackerman angle will be neutral (if I make the connections right!) where as before it wasn't.

I beleive bump steer will be an issue for you to resolve. There is more suspension travel in a 40 than you initially guess at. On a GTD the rack is one of those fixed points although the best results were obtained from raising it by 7/16 inch and is a standard mod (add a spacer under the steering rack bolt on points).

The rear toe changes are critical to control as otherwise you have serious rear wheel steering.

CoG is just as low as you can get it. From what I have learnt recently (from one school of thought at least) is that Roll Centres should be about 2 inches above ground level and on an incline to match the attack angle of the car. From my basic software these centres move around massively when cornering. Add a bump in to a corner and they disappear over the horizon!

I aim (note the word aim) to change my car to something that makes it handle neutrally at speed, so I can throw it around in competition. I wish to emulate the proper race drivers who can drift their cars at well over 100 mph. I wonder if I ever will. With the hill climbing and sprints normally being on tighter venues than Le Mans(!) my car set up will differ from a pure track car or indeed a road going only car. What affects the handling most is in fact tyre pressures. A 1 - 2 lbs difference change can dramatically change the handling from oversteer to understeer or vice versa.

Yet recently I was told that a small change in ackerman combined with an increase in castor made one members car handle the best it ever had in 10 years.

There comes a point when you make changes but by then you have forgotton what starting point you actually had as you don't have F1 type data or a team to do the work for you. Or budget. I haven't driven a standard GTD now for about 7 years. Certainly I know my car is unique in its suspension set up (shall I call it a trade secret or confess it was a cock up that seems to have worked ok?)

Simple. When the other guys beat me (on a regular basis?) I shall do something about it!

From the comments above I would summarise that those chaps looking on to those who are going to build a scratch car think they are all barking mad! Those who intend to do it (at least those that commented above) are very confident in their own field of expertise. Proves there are many different chaps out there to make up this very varied world.

Malcolm

PS Neil, get to Goodwood on 6th July. We are all entered into an Aston Martin Owners Club sprint then. It is where FAV used to test the original cars. There will be about 6 GTD cars entered and I guarantee none will have the same set up, parts or even the same school of thought about what is correct. Come and take your pick.

 

[Brian]

Neil, if offered a ride, be wary of St Mary's ................

 

Mike,

I know it's a little weird. Ideally, I'd be able to pull molds from a real GT40. I would then be able to have the most accurate body possible. And, who knows? Maybe, have a tiny cottage industry.

My other alternative is to make my own panels from scratch. If this is the case I may decide to take a shot at doing something in between the original GT40 and the new one. I do like some of the things they did to the new one. If I did this I wouldn't need to make moulds.

Doug

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>Originally posted by MikeDD:
Doug

I don't doubt that you can make body panels.
The question is how accurate can they be
without splashing off another body?

To my untrained eye, the compound curves
could not be accurately replicated unless you have an expensive coordinate measuring
machine.

And that doesn't even address the time and expense of constructing the molds!
All this for a 1-piece run???

Just curious.

MikeDD<HR></BLOCKQUOTE>