What is the best material for a space frame chassis?

Posted 18 March 2008 - 12:42

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Im just about to start building the spaceframe chassis for my new track, and ive poured everything ive got into it (its even a true spaceframe-feels good to be 5'6 and 10st ) But now im coming to the building point im looking at other options i didnt really consider before, probably due to cold feet and trying to delay it all :

so first off, has anyone heard of or seen a titanium spaceframe/ rollcage before? Im contemplating building the front and rear subframes from ti but there seems to be a distinct lack of it use in this area. It maybe because the teams with the money for use cf monocoques instead or ive missed something in its stats that makes none of its grades suitable for the job?? like i said im no materials engineer.

Secondly, ive got a supply through work of various carbon fiber honey comb panels with various different materials but mainly ally honeycombs. Ive seen a few top end cars now using these for their bulkhead panels and floor panels due to the superior stiffness off them. How ever all the materials i seem to find on them are sae style papers etc and to someone whos never come across them before quite baffling! So if anyone could fill me in on the details it would be much appreciated. i.e are they a design in material like a pre peg component with the fibers the right way etc or is it like and ally sheet that can just be bonded on, that sort of thing really as there more than a bit alien to me.

thirdly does anyone know of a reliable way to bond steel tubes to carbon fiber tubes? im looking at removing some of the smaller non critical triangulation pieces in chassis and replacing them with carbon tubing to help bring the weight down. However other than a mechanicall bracket (like those used in bolt in roll cages) i cant find a reliable way of doing it? perhaps a stressed sheet over the whole section would resolve the problem better?

Ohhhh why couldnt i just be happy with what i had lol now im all confused again!

The cars a closed top single seater btw est finished weight 690kg with a 49:51 f:r weight split.
Its subject to no regs and ideally the front and rear subframes will be removable and replaceable as 1 unit to facilitate complete fresh suspension/ engine changes etc as my crazy learning curve needs to test its theories on.
thanks, harry

Afternoon all, ive got a few idiot questions for you! ive been trying not to ask them but im no materials engineer and everywere else i look for info on this baffles me!Im just about to start building the spaceframe chassis for my new track, and ive poured everything ive got into it (its even a true spaceframe-feels good to be 5'6 and 10st) But now im coming to the building point im looking at other options i didnt really consider before, probably due to cold feet and trying to delay it all :so first off, has anyone heard of or seen a titanium spaceframe/ rollcage before? Im contemplating building the front and rear subframes from ti but there seems to be a distinct lack of it use in this area. It maybe because the teams with the money for use cf monocoques instead or ive missed something in its stats that makes none of its grades suitable for the job?? like i said im no materials engineer.Secondly, ive got a supply through work of various carbon fiber honey comb panels with various different materials but mainly ally honeycombs. Ive seen a few top end cars now using these for their bulkhead panels and floor panels due to the superior stiffness off them. How ever all the materials i seem to find on them are sae style papers etc and to someone whos never come across them before quite baffling! So if anyone could fill me in on the details it would be much appreciated. i.e are they a design in material like a pre peg component with the fibers the right way etc or is it like and ally sheet that can just be bonded on, that sort of thing really as there more than a bit alien to me.thirdly does anyone know of a reliable way to bond steel tubes to carbon fiber tubes? im looking at removing some of the smaller non critical triangulation pieces in chassis and replacing them with carbon tubing to help bring the weight down. However other than a mechanicall bracket (like those used in bolt in roll cages) i cant find a reliable way of doing it? perhaps a stressed sheet over the whole section would resolve the problem better?Ohhhh why couldnt i just be happy with what i had lol now im all confused again!The cars a closed top single seater btw est finished weight 690kg with a 49:51 f:r weight split.Its subject to no regs and ideally the front and rear subframes will be removable and replaceable as 1 unit to facilitate complete fresh suspension/ engine changes etc as my crazy learning curve needs to test its theories on.thanks, harry

enzo

Racer

Join Date: Mar 2000

Location:

Indy,IN,USA

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The airflow off of the front beam can be blended very well by utilizing a long, tapered "pontoon" trailing back from the beam (and its full width) alongside the cockpit. The top surface wants to be fairly flat - not downward sloping - and the bottomside wants to sweep up like the underside of a wing, and the side perfectly vertical. Depending on just how the British rules read, you can put a "sideplate" on it to make it more effective. Either way, they will generate downforce and minimise drag. We did some wind tunnel work about 15 years ago and found it to be a very good solution. They are also a handy place to put the battery and fire extinguisher.

Naturally, you will need to incorporate a well rounded nose in front of the beam to smooth the sirflow around it and onto the pontoons. Do yourself a big favor and make the nose into a good crash attenuater.

To help get airflow to the heads, try tapering in width the bottom of the chassis starting at the drivers butt. By using some small vortex generators along the side of the cockpit panels at the start of the taper, you can keep the sirflow attached and deliver a LOT of air to the shrouds around the heads.

The easy way to mount the engine is to build the frame to overhang the engine, with a detachable bulkhead that goes all the way around the gearbox at approximately the junction of the gearbox and engine, and a triangular subframe under the engine that attaches to the base of the main frame and to that rear bulkhead. The bulkhead attaches to the frame with 2 bolts, and to the subframe with 1 bolt. You will also want a rearward brace from the bulkhead to the hole in the top rib of the 'box to give vertical beam strength and stiffness. The front of the engine gets a mount to the subframe that has good lateral strenght, but little vertical. Making that mount too solid in all directions will stress the block enough for you to see a noticable power loss.

With this sort of layout, it then becomes fairly easy to lay out an exhaust system with the collector under the 'box ( sorry, I won't divulg the secret on how to make a flat 4-2-1 collector work!). Running the pipes down and out helps keep the engine cooler.

Sorry - I don't off hand know the best head temp for these cars. Each engine builder has different desires, so I leave it up to the customer to sort that out.

The reason behind not wanting rearward trailing arms is that under braking the axles will exert a huge amount of outward force on the sideplate flower, resulting in both a lot of wear and tear, and in a lot of fricton, nevermind the the toe out problems from all that flexing. You will also have the problem of tearing off the back of the box in a crash, and ......

A long forward trailing arm has the benefit of little toe change, and anti-lift characteristics can be easily tailored by allowing vertical mounting point adjustability. Braking stabiity is generally much better with a long arm.

Stick with the zero roll monoshock and pushrod setup. Ed Zink first came up with that design about 25 years ago, and nothing better has yet to be seen. The pushrods accept most of the conering loads, minimising the friction at the sideplate flower just when the suspension needs to be it's most free. Your pullrod design will aggravate that problem. Too much friction in the rear of these cars will cause an unsolvable loose condition. The anti-droop is needed to fine-tune corner entry characteristics.

The front beam arms undergo a lot of loading in corners. Have you ever noticed that both front wheels camber towards the OUTSIDE of the corner whn loaded? That's a lot of flex. The loads cause the barrel between the beam bearings to bend, in turn causing the barrel to try to cock sdeways within each bearing. Lots of friction. All that friction is why the front shocks are so soft. If that friction can be reduced, the front tires will develop more grip.

One way to combat the arm flex problem and reduce that friction is to use what we call a "Lilly Bar".It was first used about 25 years ago by a Kentuckian named Lilly, hence the name. It's nothing more than an external anti-roll bar that mounts in front of the beam, with lever arms that extend rearward between the beam tubes. The levers attach via short drop links to a triangular frame made up of small dia tubing. The frame itself attaches to either end of the kingpin. What happens is that the leverage exerted on the kingpin by the triangle counteracts the loads that the arms see during cornering, keeping the wheel more upright, and the tires grip better.

With more front grip available, you will then need to increase the front spring rate to the max possible to help control roll and ride heights better, and so then will need the small rear bar that I mentioned earlier.

If you really are ambitious, you can make the front bar a blade type, and that make it cockpit adjustable.

As well as the Lilly bar works, I'm amased that I haven't seen it on a car in 20 years, except one that we did for a customer a few years back, who promptly trashed it in the first race when he lost his brakes and stuffed it into a barrier!

Have fun!

Last edited by enzo; 18 Dec 2001 at

04:51

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