NEW CAV MONOCOQUE VS OLDER ERA?

[Bill Bayard]

You guys are getting ahead of yourselves.
I think Frank was referring to the using stainless steel being a bad idea, not building monocoque chassis. Read his post again.

Bill

 

[Frank Catt]

Thanks Bill, you are right, IS STAINLESS THE BEST WAY TO GO? THINK ABOUT AND COMMENT!

 

[Guest]

Hello all,
after reading the recent posts I thought I might add a few notes relating to monocoque builds as I am in the process of building one myself - (see previous post with pictures)

I have built two GTD spaceframes thus far and the stiffness of the chassis is quoted at 2700lbs per degree deflection. The aluminium monocoque I'm building has been quoted at 3400lbs per degree deflection and it is expected that once the space between the fuel tanks and the side pods is foam filled, this figure will increase by 10 to 20%.

On another note - apart from being somewhat heavy, stainless is ok for monocoque build providing the correct grade is carefully selected. If not, it is likely that fatigue cracks will develop adjacent / along welds or areas affected by the heat of the weld process.

RoySmart
[email protected]

 

[Guest]

Regarding the (continuing) discussions
of monocoque vs space frame...

I assume the question is which makes for
the superior handling car WITH the ability to handle significant street duty (is anyone in the US building a "track only" GT40 at this time?).

If one is building a "40" for the expressed
purpose of being the quickest around a track, I'd think an aluminum tub, properly executed would win, being the lightest (ala MK IV).

However since aluminum tubs are questionable
for significant street use, it appears we are comparing STEEL tubs vs STEEL space frame. I suspect the weight of each (properly executed) would be very close.

I also suspect 99% of us lack the driving skill to take advantage of any difference in chassis strength to make a difference in lap times. I'd bet other issues (tires, suspension setup, etc) have FAR more affect.

FYI, Not all stainless steels are equal.
400 series stainless is significantly stronger than 300 series stainless, but
more difficult to weld. ERA's website
says they use 400 series. What did CAV use?

MikeD

 

[Guest]

Mike D
I think I read some where the CAV uses 304 stainless steel. You have to pick the right grade of metal for the application. All these metals are available and you can find them on the web, theres no mystery if you want to do a little research. ALL three aluminium, steel and stainless have different grades to suit the application. Its just a matter of choice which way you want to go.
In the past I have used stainless steel for indirect cylinders and boilers, and have had no trouble at all with welds and cracks. In this type of application they were subjected to exspansion, heat,and pressure twenty four hours a day. We never had a failure with the stainless steel we used.
Mike, I would agree on some of your comments.

 

Wayne,

This is the dropped floor model that was in Las Vegas. It had decent room in side, but my head was still sticking through the roof. Very nice car, though.

 

AN earlier post on this site (last year) commented that a cllision creates "regional" damage on a monocoque vs "global" damage on a space fram. Any comments on this?

Also, ERA has been using stainless monocoques since 1996. does this tell us anything about satinless and/or monocoques? Chip

 

[Guest]

Repairability is not high on my list of concerns. But then again I don't plan to race it. Repairability is probably a much bigger issue for our friends in the UK, with all the racing they do.

ERA building SS monocoques for (6) years tells us a few things...

a) ERA is run by savy businessmen
b) Properly executed monocoques (SS or not)
make for really neat GT40s!

I think we all look forward to seeing more
come on the market.

MikeD

 

[Jim Rosenthal]

I find this stainless versus mild steel question interesting. There are a lot of varieties of stainless steel out there, but generally speaking I think they are harder to weld, have less ductility and tensile strength per pound, and WILL rust if they are deprived of free oxygen to maintain their oxide coating which makes them stainless. Stainless fittings are good above the waterline on boats; below, ie in an area where free oxygen tends not to be available, especially in stagnant water, they are not good at all.
I don't see the advantage of stainless in an application like a race-car monocoque; I would rather have zinc-coated mild steel or Corten. If you build a chassis of mild steel which is zinc-coated, then prime it with zinc chromate and paint it with two-part urethane, it would last as long as a stainless chassis and be stronger in the bargain. AND cheaper- stainless stock is expensive and not available in as many shapes as mild steel.

NOW- what somebody really ought to build is a carbon-fiber/epoxy GT40 monocoque. Here are the advantages; MUCH lighter, repairable without welding, stronger than steel by far, and can be bonded to the body for additional rigidity. Disadvantages? Plenty- very expensive, not at all original (more like a Chaparral than anything else) and it requires running an entire set of return wiring for all the ground connections (earths to you fellows over there) because plastic composites don't conduct electricity. I'm surprised, though, that no one's tried it. There are race cars out there with carbon-fiber or Kevlar tubs, arent' there?
If anyone decides to do anything this crazy email me and I will put you on to some sources about laminating and structural resins and fibers.

 

Bob Putnam noted that the original steel monos trapped moisture and ad to have major rebuilds after just 10 years. That's wh ERA went to stainless. The tub by it's ature and design has pockets that can trap moisture. Just look at the Panteras.

 

Jim-What is powder coating? That's what ERA used on it's steel tubs and what many use on space frames. How does powder coating compare to the other coatings that you describe. cb

 

[Frank Catt]

Jim, thanks for looking at my question re. stainless objectively. I still feel that at 150+mph I do not want to be worrying about propogating cracks in the structure,and the need to check it thoroughly after each run. The variable imposed loadings on the structure at each extremity,ie. at the suspenion mountings, means that it must be considered in design very differently to that of,say, an aircraft monocoque or a static vessel.The selection of the correct material is vital.Frank

 

[Bob Putnam]

We have never had confidence in powdercoating our GT chassis to prevent rust. There are just too many "nooks and crannies" that will remain uncoated. For street cars, we recommended a wax-based coating sprayed into all the cavities. It made a mess, but did a good job of preventing the classic pinch-weld corrosion that the originals had. We still seal the most vunerable lap welds at the bottom of the chassis but feel confident that the stainless won't propagate rust along horizontal surfaces like mild steel (even coated) does.

We use 400 series stainless, rather than the slightly more corrosion-resistant 300. This stuff is incredibly tough and is more resistant to fatigue failure. Because of the high elongation before failure, it absorbs a great deal of energy on bending - which comes in handy if you hit an immovable object.

 

[Guest]

Is there anything that stainless steel can be used for? Boy, have I learned a lot about stainless steel, after all this Im sure they will stop making it.

 

[Frank Catt]

MikeD, Thanks Mike, I just wanted to get some technical discussion going on this subject because it has been in mind since manufacturers started to build monocoques with stainless steel. Anyone who has read the autobiography of Colin Chapman (Lotus) will know of his early work on monocoque design and the associated problems, and his thoughts on using various materials. I could not design a monocoque, do I trust those that do?

 

Well to take this discussion on why not build the monocoque out of mild steel then
immersion dip it into a galvanizing tank. I understand that many of the prestigious
manufacture’s such as Roll’s Royce and Bentley do this. Galvanizing is a common
process for fabricated steel items and from what I can see, has no real down side when it comes to weekness around the welded area’s.
When it comes to painting a galvanized chassis there are etch primer’s available.

Chris.

[ February 12, 2002: Message edited by: Chris Melia ]

[ February 12, 2002: Message edited by: Chris Melia ]

 

[Guest]

Chris,
I wonder if the heat would distort the chassis ?
If I can get around the wife to buy another car, I wont worry if its a stainless monocoque or space frame. The wife is a much bigger problem for me, I would like some serious comments on how to handle the wife.

 

[Ron Earp]

This has been an interesting thread - sort of like an abortion topic or gun control/ownership, no matter what one side won't convince the other. Me, I like em all - no better time to be after a 40.

As for the wife, now there I can help. What you have to do is barter. In my instance, I bartered my participation in procreation. See, my wife wanted a child, me I wasn't sure. So, I managed a deal where I got to build and car and we have a little girl. Unfortunately, she was finished with her project fairly quickly while I'm still building. But, then again I bet I get mine out of the house before she does.

All in all, Sydney was a better choice after all and was a lot easier to build.

Ron

 

[Guest]

Making a carbon steel tub and then galvanizing it would be a great idea.
I don't believe galvanizing generates enough heat to be a problem.
But finding a vendor willing and able to dip a few tubs may be a challenge. The EPA has strict control over that industry.

I assume one could make a tub out of galvanized steel sheet. But the weld affected zones would be subject to corrosion, and would have to be re-protected
somehow, which sounds like the issue ERA
dealt with by simply making the tub in SS.

MikeD

 

[Guest]

Interesting discussion.
There are obviously many well read folks on the forum. Let me toss a few more items out.

* Jim is absolutely correct about stainless
rusting in stagant seawater. However I
don't see this as a risk unless you plan
to immerse your car in seawater.
SS will not rust in stagnant fresh water.

* Frank is right on about SS cracking from
too much localized heat. However with
today's modern welding material/equipment,
that should not be an issue if properly
done.

His other concern about SS fatique failure
can be addressed by proper engineering
(ie sizing/shaping/reinforcing the pickup
points to handle the load. Alternately,
there's no reason an SS monocoque can't
use carbon steel pickup points if desired.
Weld procedures exist for this.

There are many ways to build a safe/
effective chassis...but you must know
what you are doing!

MikeD