Scissors

Actually, the C5 chassis is touted as being 4.5 times stiffer (torsionally) than the C4. At approximately 23 Hz for the C5, this means that the C4 was at approximately 11 Hz--above average for open top cars in the early 80s.

WhiteDiamond

Scissors,

Thank you for the comments, but you are wrong again. I have looked up information on the natural frequency and there are numerous ways to set up measurements and test platforms for this. Simply positioning the input acutator(s) for this experiement differently, or using the wrong input for the structure, will give you different readings.
Todd




[Modified by BLK 98WS6, 5:02 PM 2/20/2004]

WhiteDiamond

Duke,

Since the weight of the frame grows tremedously in an SUV application, say the mentioned VW example and the added weight will affect this test, how do the automakers get a 40Hz rating for such a large frame? I dropped by the VW dealership on the way home from school this afternoon and looked under a Toureg(sp?). I don't see anything dramatically different from other SUV frames(at least for big SUV's). I haven't put an effort into an equation for the frame, but it appears 40Hz is saying the VW frame is over 4 times stiffer yet than the Corvette C5's frame.

Todd

SWCDuke

I think the Toureg is a unibody design, and unibodies are stiffer than traditional body on frame construction. Also, I think they weight nearly 5000 pounds, so I'll believe the structural stiffness numbers, but wouldn't want to pay the fuel bill.

Modern structural analysis techniques, using multiple interations, enable designs with high stiffness to weight ratios. Overall stiffness can be highly affected by local weak spots, which may not be easily recognizable by even very experienced structural engineers, but the FEM/analysis programs find them. Then local stiffening is applied as required, and you continue to iterate until the target stiffness to weight ratio is achieved. The result is higher stiffness to weight ratios than anyone could have imagined 20 or 30 years ago, even 10 years ago.

Duke


[Modified by SWCDuke, 6:30 PM 2/20/2004]

WhiteDiamond

Duke,

Thank you for the info, again. I was under our Escalade for a little bit checking out the frame. I am curious what GM lists the natural resonance for the Tahoe/Escalade/Yukon frame. It looks like it is pretty stout, but as you mention it isn't readily evident.

So, has anyone seen specs for the C6 yet? Nothing came up in my search and re-read of C6 spec release material....

Todd

lateapex

According to Hib Halverson, I hope it’s OK to use his name here, “the convertible’s first torsional frequency is 20hz. Coupes with the roof out are at 20.5hz and, with the roof on, jump to 22hz. The Z06 is a stout, 24hz.” http://www.idavette.net/hibz06/page2.htm

I was considering buying the ’99 FRC, and I called the “concept vehicle” feedback line that Chevy had open during the summer of ’98. The only question I had for them was if there was ANY type of metalwork between the A pillar and the halo bar (B pillar) on this new lightweight model. The lady who answered the phone said she would go ask one of the CSV engineers. I could hear them talking in the background and he said that the only thing tying the A and B pillars together was the SMC bodywork, but that it offered significant stiffening. I thought that was a cheap solution, and am still waiting for a real fixed roof Vette.

The SSR's torsional frequency with the top up is approximately 16 Hz; with the top down, it is approximately 13.8 Hz. And that thing weighs 4800 lbs.
Carroll Shelby claimed that his Series 1 convertible was, “The most advanced production chassis in the world features extruded tubular and honeycomb aluminum construction for light weight and unparalleled strength and stiffness -- at 52 hertz…torsional rigidity”. That may be the truth; I doubt it.

Ferrari lies about the weight of their cars. Lbs are the same in Italy and the US; Ferrari simply lies, as do some other manufacturers.

SWCDuke

With the kind of structural adhesives available today, SMC panels bonded to a metal structure offer significant improvement in structural rigidity with very little increase in weight. In the case of bonding the FRC roof panel to the top of the windshield frame and door lock pillars, it becomes a truly closed structure, and the improvement in first mode proves the increased rigidity.

I'd call it a clever solution - a true composite structure.

My choice for the upcoming Z06 is the new coupe with a fixed roof panel and a flip up/removal sunroof option - increased rigidity, better rollover protection, and the option of semi-open air motoring.

Duke





[Modified by SWCDuke, 9:28 PM 2/20/2004]

Scissors

Sorry, but you're confusing "readings" and "results." Yes, the readings can be different, but they are then corrected for errors in measurement.

Do you honestly believe that any manufacturer would use a method of measurement different from the competition's which results in lower numbers and not correct for the difference? That would be very naive.

Scissors

Thanks. I couldn't remember the Coupe's numbers off the top of my head. :cheers:

WhiteDiamond

That also sorta leads to my point that as the frame structure grows in size AND mass that it becomes more difficult to get the stiffness numbers. I agree that there are many solutions to these various issues, but I also find it hard to believe that something as large and with the mass of the VW (Toureg)frame, unibody or not, that it would be difficult to achieve the numbers printed. Either way, the VW dealership here has a bunch of A-holes working today and I was trying to get a test drive in one to see if it felt any different than our Escalade(there are some extremely poor roads around the area of the dealerships). No luck, though.

Todd

ivan111

I was reading an article about GM Sigma platform use in the Caddy CTS and the rigidity levels of this structure are very impressive.....

26 hertz for bending
34 hertz for torsional

I would imagine that the CTS-V structure would be even stiffer than that mainly because of its cradle reinforments and the front tower brace..

This has to be GM stiffest structure......

:rolleyes:

F1freak

Then wouldn't open wheel race cars be even more torsionaly rigid and also more aerodynamic if they closed the tops? Why are open wheel race cars "open"?

ivan111

In case of the C6 it will be intresting to see how much they have improve the rigidity......

Is the C6 rigidity 10% or 20% stiffer than the C5?

Will have to wait until Hill makes that info available.......

I would expect something between a 10 to 20 percent improvement, with the C6 Z06 at or over the 30 hertz mark....... :chevy