Structural Reinforcement

[randywebb]

damn! I guess we are back to stamping the 911 unit bodies out of titanium sheets...

[timlooney]

Well... not to nit pick but titanium is about as strong as steel but not quite...

The other thing with CF is that to get any significant strength, you will need layers. The layers complete with matrix will add some significant weight, perhaps more than selective steel reinforcements. There are calculations that you can run to determine how different layers will respond to different types of stress but I have not run them for this.

This would make a great project for a local engineering college. They are always looking for projects for their students. If the students are good they have access to the FEA (Finite Element Analysis) systems and corporate sponsors for free materials and equipment (CF or other material).

[randywebb]

A lighter, stronger (and cheaper) early 911 tub would make a great MIT project...

how far North of Bosstown are you?

[AtomicDog]

Randy,

Dimensions please, sir.

I would love to build a semi-monocoque chassis as a transplant recipient... The tube/tub has the best modulus/dollar ratio for the home enthusiast, as far as I can tell.

Does anyone have good data on the chassis measurement specs? There's got to be a body shop representative with access to this kind of thing.

Please. If the chassis is a fully developed 3D solidworks model, so much the better...

Chris

[randywebb]

I don't have any dimensions. That was just a joke re keep on stamping them out of Ti sheet -- figured everybody would know nobody is doing that...

It would be great if someone would take on the task of a lighter, stronger chassis... (that still looks like an early 911, not a 993).

[911pcars]

Last time I checked, a 4x8' sheet of 22 ga., Grade 4 Ti was more than $1k. Whilie Ti can be welded or brazed to dissimilar metals, it requires shielded arc welding equipment and post heat treatment, blah, blah, blah - not that it can't be done though.

Sherwood

[TRE Cup]

Well.. to get the early look and a stiff chassis, I think the best way to go would be to build a 73 RSR look on a 964 shell. Do the reinforcements as outlined on that excellent 964 build elsewhere on this thread, and you will have an incredible car that does not weigh that much more than the early chassis (all strengthened to the same level as the 964 - perhaps less??)

I picked 73 RSR look due to the positive offset of the later chassis' suspension. The wheels have to have the right depth to look good !

[AtomicDog]

Randy,

I was serious about the possibility of a body shop having access to the dimensions. The tube/tub is a no-brainer, and has been done many times. As for the tub mods necessary to convert a 911 to a true semi-monocoque, that would take a bit of work to preserve the 'spirit' of the car...

I guess what I'm asking for is most like a kit car chassis that will accept Porsche components as a true bolt-on. Something that is visually identical to the original from the outside. It would sure make a cool one-design club racing platform, don't you think?

Chris

[JeremyD]

Originally posted by AtomicDog
Randy,

I was serious about the possibility of a body shop having access to the dimensions. The tube/tub is a no-brainer, and has been done many times. As for the tub mods necessary to convert a 911 to a true semi-monocoque, that would take a bit of work to preserve the 'spirit' of the car...

I guess what I'm asking for is most like a kit car chassis that will accept Porsche components as a true bolt-on. Something that is visually identical to the original from the outside. It would sure make a cool one-design club racing platform, don't you think?

Chris

Sort of like...

[jluetjen]

Originally posted by JanusCole
I was just re-reading this idea and I think it is brilliant. And I don't see why it could not be done in an aesthetically pleasing way. For instance, why not coat the entire inner tub from the rear package shelf to the pedal cluster with a strong structural epoxy - the same stuff they use to assemble airplanes. Then lay a dozen or so layers of carbon fiber on top - essentially creating a carbon fiber monocoque using the original unibody tub as a mold. Then you can cover it all with carpeting and the thing should be TOTALLY stiff...

Is this too simple? Am I missing something obvious?

Kind-of. Just because Carbon fiber makes strong tubs in F1 doesn't mean that it's a wonder material. Carbon fiber is quite strong in some situations (and directions), and not very strong in others. The reason that F1 tubs are so strong has to do with the following:

1) The tubs have very few if any openings in them excepting those required by the rules (such as the cockpit) and by serviceability requirements (such as access ports to the pedals). A convertable or Targa 911 tub is a completely different design.

2) As I said, CF is very strong in some dimensions, and not in others. Just slapping CF down like shredded Fiberglass will not by definition make a strong tub. In reality the tubs come out strong because some clever engineers have figured out subtle ways to align the individual plys, and combine them in certain ways to manage some very specific load paths, both from the suspension as well as in accident situations.

3) In many cases a honeycomb matrix is put between the CF layers in certain areas to increase the cross-sectional area and thus increase the regidity of the tub.

So the short form answer is that slapping CF down on the shell of a 911 will most likely not make it a whole lot stronger.

That being said, you did prompt a recollection of an old Formula Ford trick -- which is to squirt some two-part expanding foam into any enclosed cavities in the chassis. This trick was used to good affect in some spec classes (Formula Opel/Vauxhall comes to mind) where the spec chassis was somewhat less stiff then desired. Just as adding honeycomb can increase the stiffness of CF or FG panel, so can adding foam to an enclosed space. The downsides are:

1) A slight increase in weight.
2) Once it's in there, it's never coming out
3) Many of these foams turn into noxious gasses if heated or burned, so consider carefully where you decide to put them.

A clear opportunity for this trick would be in the rockers and frame rails of open 911's.

[randywebb]

OK, Jeremy -- details...


IIRC, there are examples of foamed aluminum between plates. Of course, the ultimate would be the interior of a bird bone -- a tubular strut, with internal curved braces _grown_ right at the points of greatest stress.

[timlooney]

Hi Randy,

I live in Tyngsboro, MA which is about 30 miles outside of Bosstown. We are on the NH border. Basically its where the yards are bigger and the houses are cheaper.

As far as MIT, I will probably offend a bunch of people on the list but... an MIT student could turn it into a great science project but if you want any real work done you will have to go to one of the other engineering schools. There is a Prof at UMass Lowell that specializes in composite design. He designed an all composite car chassis for Solectria (electric cars) that met all of the government standards before any of the big boys got it done. Just him and a few grad students. Every year they have a senior design project to design and build a device or system. I am sure there would be a draw if there was an actual race car chassis design available for them to work on...

[AtomicDog]

For that one, you should contact my alma mater...


www.rpi.edu


Carbon nanotubes AND a race team...

Randy wrote:

OK, Jeremy -- details...

+1

Chris

[JeremyD]

Sorry - here's the site -





He builds a GT-40 replica


and a P4 replica


He's currently working on a


How cool would this be with 911 running gear/upside down g-50?

I saw a review on his work - it looks pretty top notch... Check out some of his suspension work...

[randywebb]

WOW -- Zeke ... we just found your next project!

[Elombard]

Now I know where I am going to sign my lottery check over to...awesome!

[blue72s]

Hello

Are the chassis of latest generation Porshces (997, Cayman etc) spot welded or seam welded?

TIA

[Wrecked944]

Originally posted by Tyson Schmidt
....Then, I reinforced the front of the center tunnel, since it's very thin, and ran two diagonals down to meet the center tunnel. They don't end up being symmetrical, since you have to tuck the left side behind the gas pedal.That's why I never tried productionizing it, or even posting any how-to's. It's simply too ungraceful. I was simply doing it as an exercize. it gave me a lot of feedback on how to stiffen an open chassis, and demonstrated the potential handling benefits of doing so, and I'm glad I did it once, but I don't think I'd do it again unless it could be done more gracefully. I may one day work something out. probably in a boxed sheet-metal way, hidden or disguised as a center console.

I was talking to Shaun84Targa about this thread and we were fantasizing about ways to make your design more "graceful"...so here is a nutty idea: If you want to tie the front of the tub to the back, then, as you did, the center tunnel can be reinforced and/or enlarged. But rather than using sheet metal to fabricate a larger and stiffer center tunnel, why not use an existing center tunnel cut from, say, a 964C4 and welded in to a targa or cab tub? Porsche made cars like the C4 that had tall center tunnels that could maybe be used to provide a "backbone" reinforcement to an earlier car.

[randywebb]

So there would be a tunnel within a tunnel? Two layers of sheet metal near each other to stiffen and provide a "Lotus"-like backbone?

- Sounds interesting. I wonder how much stiffness it would add, given the design of the 911 unit body.

[911pcars]

Originally posted by randywebb
So there would be a tunnel within a tunnel? Two layers of sheet metal near each other to stiffen and provide a "Lotus"-like backbone?

- Sounds interesting. I wonder how much stiffness it would add, given the design of the 911 unit body.

Randy,
The 911 chassis is relatively flexible. Moreso with the earlier versions and less so with the latest ones. Review the beginning of the thread for some data. The thread got a little off-track after awhle.

Sherwood