Aluminium AC Cobra Chassis

sambo · #1 (**permalink**) 06-05-2009, 08:52 PM

Quote:

Originally Posted by 400TT

Your kidding right?

Craig, we're not all coach builders!

400TT · #2 (**permalink**) 06-06-2009, 01:22 AM

Fatigue testing is a good idea.

Then for good measure produce an incredibly stiff chassis. The chassis I posted above(without roll cage) is many multiples stiffer than registration requirements, even here in QLD.

Jac Mac · #3 (**permalink**) 06-06-2009, 05:50 AM

Quote:

Originally Posted by 400TT

Fatigue testing is a good idea.

Then for good measure produce an incredibly stiff chassis. The chassis I posted above(without roll cage) is many multiples stiffer than registration requirements, even here in QLD.

Not that any kit car is probably a good thing to have a major prang in, but I often look at chassis like this and try to visualise which way the panels would deflect in a serious head-on type road prang, the Cobra chassis in the first post has inner guards that could fold back like a guillotine if hit in the right spot, although it appears that the front X-member is going to be bolted in at multiple points. The GT40 chassis I would hope might deflect up & back into the dash area to act as an energy absorbing area rather than retaining its shape & giving the occupants a serious jolt. Might have some sore toes afterwards though.

albanycobra · #4 (**permalink**) 06-07-2009, 12:18 AM

Craig what is the torsional stiffness? we all know DRB and RF....

400TT · #5 (**permalink**) 06-07-2009, 02:29 AM

Jac Mac, safety is really important to me. We do have those bolt-on aluminium chassis extensions on the front of that chassis as well that should absorb some of the impact energy before it gets to the 1/4" aluminium plate used in that front tub section. You've also got to consider the strength on the welds as well. I certainly feel that the RCR designs are as safe as they can be given the restrictons. We've had a few RCR's involved in significant accidents now and all held up very well, kept the occupants safe and were easily repaired.

We all love our Cobra's, but you've also got to consider what is going to happen to that engine and transmission in a major frontal impact.

Albanycobra, I'm guessing you are chasing the RCR GT40 figures. The torsional stiffness is academic in an RCR GT40 as it is multiples more than what is required for registration or for performance reasons. They are stiff as a result of being built for longevity and strength. "Built like a tank" is a common phrase I hear from Fran Hall of RCR USA.

Due to other manufacturers using the NM/deg/M instead of NM/deg etc to significantly pump up their figures, we have decided to simply not publish them. I personally don't believe any figures I'm told unless I can view the chassis report. Past experience tells me the figures seem to get distorted by word of mouth.

I have copies of many, many chassis test reports at the factory. It makes for some very interesting reading as the higher 6000Nm/deg requirement in QLD really catches some manufacturers out. And that's 6000Nm/deg not 6000Nm/deg/M.

Hope that helps.

Does FFR Coupe make 6000Nm? The integrated full roll cage would really help it.

albanycobra · #6 (**permalink**) 06-07-2009, 05:49 AM

If the RCR is so stiff why not publish test results....it could only sell you more cars? I'm not having a go or trying to start sht just wondering why the secret if it blows the competition away.

I have tested many chassis over the years and have a bit of an interest in Torsion testing, I am also interested in the CAV chassis. I built a test rig years ago that is still being used today to confirm torsional figures for Locosts / Cobra's and one off jobs. These days it uses a load cell instead of weights.

[/IMG]

The only way to measure Torsion is through the wheels.

FFR will not publish Torsion test figures, beats me......

DRB seems to be the only Manufacture that lays it all on the table for everyone to read and I applaud Peter Ransom for it......

Jac Mac · #7 (**permalink**) 06-09-2009, 02:06 PM

Quote:

Originally Posted by albanycobra

If the RCR is so stiff why not publish test results....it could only sell you more cars? I'm not having a go or trying to start sht just wondering why the secret if it blows the competition away.

I have tested many chassis over the years and have a bit of an interest in Torsion testing, I am also interested in the CAV chassis. I built a test rig years ago that is still being used today to confirm torsional figures for Locosts / Cobra's and one off jobs. These days it uses a load cell instead of weights.

[/IMG]

The only way to measure Torsion is through the wheels.

FFR will not publish Torsion test figures, beats me......

DRB seems to be the only Manufacture that lays it all on the table for everyone to read and I applaud Peter Ransom for it......

Dave,
CAV claim 32000 NM/deg and have put out a report on that. I would point out that the test rig was bolted virtually flat plate style to front & rear of tub/mono & did not link thru suspension pickups as yours does so results are particular to their test rig, Just as yours are to your rig.

I would question your test rig in that the pivot point is below the chassis at front and therefore as you apply load that you are not going to get a true torsion only result. If you were to break down the chassis to simple form the lower plane of the chassis is simply being twisted as its at close to the pivot height, but the upper plane of the chassis is being subjected to a parallelogram type load. If you were to raise the front pivot point you might find you get even higher test results than your current readings as many chassis simply have heavier material in the lower frame rails which would now be subjected to the parallelogrm effect as well..

This is why most of these discussions go nowhere as data to be relevant needs to be collected from the same type test rig.