NEW CAV MONOCOQUE VS OLDER ERA?

[charles]

This bartering with the wife thing - I also have some experience. This is my story:

1. Yes I will marry you, but only if you buy me a Ducati 916 first.

2. Yes you can have a baby, but only if you buy me a GT40 first.

Got the bike in good time (now sold) but drove home the 40 on the day she found out she was pregnant. I would recommend a bigger safety margin than that!!

Charles

 

[Frank Catt]

Charles, can we guess at stage 3, maybe when you do your first competition - but what is she going to want in return? Frank

 

[Guest]

Lynn, Most of the semi-monocoques (for lack of a better word) I've seen are descendants of the first GT40 kit the KVA. Your Sabre in particular as KVA sold to Integrity which then sold to Sabre. Now with the RF photo gallery I can see that their tube design is pretty similar.

These tube frames alone without any cladding have almost zero torsional rigidity. If you haven't cladded yours yet test it and see, it's not that hard. With these designs the majority of torsional rigidity is obtained from the cladding.

The basic chassis theory is that rigidity is gained with triangles on six sides (a box with diagonals). Without any one of these sides you loose considerable rigidity. If you want to take it further the basic building block is a tetrahedron(three sided pyramid). Look at any of the kit chassis without cladding, how many tetrahedrons do you see?

The cladding adds most of the diagonals and thus a third leg of the triangle. This brings to mind a question I have for the RF guys (if any read this) The RF sheet rivet pattern is not a structural pattern so I'm guessing that the bond between the alum sheet and tubing relys on adhesive?

Is the tubing painted first and then the glue bonded to that paint? I was wondering because my project is near that stage. Reading a previous thread it was 3M 5200 marine adhesive correct?

And in regards to the term "semi-monocoque" I would call it a "shade tree engineer" term as marketing implies profit of which I have none ;> )

 

[Guest]

Lads,
I have a problem with the wife due to the passage of time, a lot of the barganing chips have gone. Its sometimes called past forty and the only cure is for the wife to think that younger women are taking an interest in you. This is also a very tricky road to go down, as there are lots of lawyers that want some quick money. I shall have to work slowly on this problem and it should be solved this year. One more thing I never call it a GT40 around the wife, women dont like the number 40. Now you know that stainless steel, mild steel, space frame etc are not a big issue for me.

 

[Ron Earp]

I'm not sure about what you mean by structural rivet pattern on the RF cars, but the panels are definitely held on by rivets. I'm using adhesive to bond as well, but the rivets secure the panels to the frame.

Genenerally I'm using 2" spacing on mine but sometimes less depending on the run. I'd call them structural for sure, at least for me they're part of holding the structure together. Overkill, maybe but if I sheet the entire chassis, bonded and riveted, it ought to be pretty strong. I don't know what the other folks are doing but rivets and drill bits are cheap and I'm only doing this once.

3M 5220 is about as good as it gets from the research I've done. I've got a bunch of tubes in black and with this and the black coated panels and frame it should look quite good.

Ron

 

[Hershal Byrd]

The RF car does use rivets to hold all the panels on the space frame. However, the material used that goes on between the panel and the frame rails is not a complete adhesive but an anti- chafing, sealant and sound deadener. There is some ahisve quality but not like the material you speak of.
I am no engineer but I have built my share of frames for various street rods. I believe
that if you could build the RF without the panels it would be almost as strong. In my opinion the frame does not rely on the panels for rigidity. The space frame is constructed to be stong on it's own. However
I do feel the panels offer some type of minimal support.
I was thoroughly impressed by the quietness
of the RF car at all speeds. It made no rattles or squeekes. There was no wind noise.

Hersh

 

Hi guys

bonding of the panels in addition to sound deadening and additional rigidity also helps
to prevent water ingress leading to dissimilar metal corrosion between the steel and aluminum. This can be a very serious topic to consider especially when you consider that the aluminum would become totally sacrificial to the steel. I have experienced this at first hand on the old BN100 4/6 Austin Healy’s. The Healy’s had steel wings (Fenders) bolted to an aluminum center paneling and boy can they corrode.

Chris

 

[Jim Rosenthal]

Right, when I am fortunate enough to own a GT40 I will not drive it in seawater. My point about stainless steel (which is a generic name covering a very large variety of iron-based nonrusting alloys) was that frequently to get the nonrusting quality you may trade off other metallurgical virtues more desirable when one doesn't plan to go swimming in the car...
Big auto manufacturers have the ability to hot-dip steel parts in molten zinc, which is hot-dip galvanizing. There is I think an electrolysis part to the process so the zinc coating stays on securely. Small builders use zinc coated panels, and then paint the whole assembly once it's welded together. I still think that works well, especially if you use one of the moisture-cured urethane paints like POR 15 which protects the metal really well against rusting.

 

[Guest]

Hersh and Ron

I hope I'm not belaboring a mute point but here goes.

Tubing in a triangle pattern is rigid. Tubing in a square pattern is not.

Tubing in a box pattern with diagonals on all six sides is rigid, a box pattern missing diagonals on any side is not.

this bare frame has diagonals on 2 at most 3 sides of the box

in order to achieve the rigidity required the sheeting becomes the diagonal structure.

----------------------------------

Structural Rivet Patterns Per Carroll Smith

the guy on the left is Carroll Smith

Mr. Smith has a 200 page book just about fasteners as relates to race cars. Including a 25 page chapter on rivets.

rivet diameter- 2-1/2x to 3x work thickness

edge distance- 2x rivet diameter

pitch distance- 8 to 10 times rivet diameter(minimum 3x dia) So that's about 1" max with 1/8" rivets.

In some instances double rows of rivets are called for.

this is not a structural pattern

this is a minimum structural pattern (3/16 rivets on 2" centers) but in some places is lacking notably the vertical at the firewall.

So without a structural rivet pattern the adhesive is key to bonding the panels to achieve torsional rigidity.


[ February 14, 2002: Message edited by: Kalun D ]

[ February 14, 2002: Message edited by: Kalun D ]

 

[Guest]

And here is a maximum structural rivet pattern, a "box" chassis, and Mr. Smith again.

and then we could talk about structural TYPE rivets <grin>

 

[Robert Logan]

Finally a thread with some "meat" in it. Please all excuse me with my lack of US names for things such as the 400 / 300 Series stainless steels. I do not know what they are , the alloying elements present and more importantly the precentages of these elements present. When I studied metallurgy in my degree the different stainless steels were refered to as Martensitic and Austenetic Stainless Steels and others and their applications were very varied as were their mechanical properties. A lot depended on the precentages of Chrome in particular. I have not looked into a stainless steel monocoque as it was not ORIGINAL and that is a good enough reason for me not to use it in the monocoque that we are having built. This does not say that it is not at least as good as steel or even better. I would not and will not coment as I have not studied this aplication for "stainless".

Now for the reason for my responce to this thread: "almost zero torsional rigidity" as stated by "Kalun D" .
In Australia there is a requirement to test all "individual construction vehicles" in over 50 (FIFTY) different areas such as side intrusion , seat belts, windscreen sweep, seat frame strength, as well as torsional and beam tests of the chassis. There are minimum levels that each car MUST attain for different engine sizes and the requirement for a V8 is 6000Nm/deg/m. This test can be conducted on complete cars ie. fully skinned or clad which ever you call it. I chose to do the chassis torsional and beam tests on bare chassis. Our tests "comfortabely exceeded" (the words used by my engineer) the requirements of Australian Design Rules (ADR's). My engineer is apointed by the Australian government to do such tests and I chose him because of his extensive race car experience and excellent recommendations. I have asked him to also respond to this thread !!!!
I totally agree with the "semi-monocoque" garbage, refered to by Kalun, and used by some manufacturers as a "smoke and mirrors" marketing ploy and I would like to confirm that Roaring Forties monocoque will be exactly that a monocoque but steel as the original.
On a lighter note I would like to wish both Malcolm King and Ron Earp continued success on the domestic front but I believe that the domestic arangements are best negociated a long time before marrage and training is best conducted on a daily basis to ensure compliance and my wife has given me full permission to say this.

Best wishes to all

Robert

 

[Guest]

Thank you Mr. Logan for your response, it's always nice to hear from the horses mouth so to speak. And kudos to your impressive operation and a visit from Carroll Smith!

I didn't mean to ruffle any feathers but based on my own experience with torsional rigidity testing it's hard to see how the bare frame would be that rigid. However I've been wrong before <grin>, maybe it's the photo not revealing everything being it's directly from the side.

Once again, thanks for you interest.

Oh and thanks for giving ERA some competition.

[ February 14, 2002: Message edited by: Kalun D ]

 

[Robert Logan]

Kalun,

To respond to some of your other questions , the chassis is FIRST powder coated and the aluminium is both bonded and riveted to the chassis. The bonding is mainly for sealing and it offeres limited strength and the material we use is Sikaflex 221. This is used a lot in the marine industry. The rivets are at 4 inch intervals and are not as structural as the monocoque you showed in the picture ( a Formula 5000 / Lola I think). The torsional testing was conducted without aluminium sheeting in place to allow for thinner sheeting to be used without retesting. I hope to do a full torsional test on a completed car one day but we are "flat out like a lizzard drinking" at present and the tests are not needed for any thing than interest!!!!
Keep up the quality of the thread.

Best wishes,

Robert

As regards to Carrol Smiths visit , I was indeed honoured and he drove my latest MkII and comented very favourably about the car. He is very well known here in Australia as he was in charge of the all winning Ford team in the early 70's. His contribution to the Cobra (wash out my mouth) and the GT40 domination is usually not appreciated as one Carroll Shelby takes most of the credit, but his ultra proffesional approach to the engineering of both thr GT40 and that other car was one of the major reasons for there success.
He still has a pencil and note pad at the ready and was constantly recording something. I was also very lucky to meet Phil Rimmington at the Knotts Berry Farm show last year and both these men are true ledgends and humble men.

 

[Guest]

Just a note on the SS monocoques. While there are some true monocoques being built as witnessed on this forum. The last time I checked many of these "monocoques" are actully panel clad space frames. Sometimes referred to as semi-monocoques, while they do gain rigidity from the cladding, they still rely on the space frame for their structural integrity. To my mind semi-monocoque is a marketing term, not an engineering term.

 

Hmmm...That Carroll Smith guy is fairly sharp, what's he doing hanging out with a lackey like you Robert???

Just kidding, Carroll Smith is one of the most prolific suspension/chassis design engineer writers around today and it doesn't surprise me a bit that Roaring Forties has had him by their shop to pick his brain. Robert continues to impress.

 

[Jim Rosenthal]

One more item about adhesives, apropos of a posting above; the aluminum panels should be bonded on with polyurethane adhesive (5200, Sikaflex, etc) BEFORE painting. This way you will bond metal-to-metal, not metal to paint. Again, this bond is very strong; I can't imagine that these panels bonded on would not contribute something in the way of torsional rigidity. And, you can paint or sand the adhesive once it's cured (days, by the way for a full cure)

 

[Robert Logan]

Wayne,

Did you ever get the sill stripes I sent you? I hope so and Happy Christmas (Bah humbug!!!!!!!).

Hope the CAV is going well.

Best wishes,

Robert

 

Robert, I did and thank you. I haven't put them on yet because they are both left side

 

[Guest]

Jim Rosenthal,
Back in nov 2001 you said you found the GT40 deal that was right for you. Did you buy this GT40 deal and what make is this car,kit ?.

 

[Robert Logan]

Wayne,

They all come that way, take the "GT40" bit out of the sticker and turn it upside down. Also please get a sticker guy to fit them as it is a much more difficult job than it looks.
Hope to see you soon and get another ride on the GO-ped (boy - what fun).

Best wishes,

Robert