Chassis rigidity

[Tim7139]

Guys, with all due respect, however interesting this may be, it's got little to do with the initial post. I am very familiar with what's possible and theoretically what's desirable. I was more curious about what's out there on a more less relative bassis.
It sounds like nothing in the way of any testing and / or ratings have ever been done, lots of "seat of the pants" type stuff.

[mrmustang]

Originally Posted by Tim7139

It sounds like nothing in the way of any testing and / or ratings have ever been done, lots of "seat of the pants" type stuff.

Plenty of computer modeling has been done, but no, there has not been a comprehensive set of tests done by a third party company. Would be interesting to see each (current) manufacturer donate a bare chassis for such testing, but I'm in doubt of getting many of them to do so.

So, with that said, how about you purchase a bare chassis from say the big five (ERA, SPF, Backdraft, FFR, and SAI), and then find a third party company to test each one against itself. You could then publish a small book on your findings and perhaps recoup 1/5th of your up front costs


Bill S.


Bill S.

[Richard Hudgins]

Tim7139,

I hope the below information is what you are asking for.

Bill. S,

We did do some third party testing and below are the results. (I must say that I was disappointed in the numbers as my computer FEA sims showed better numbers, but as they say, "Bob's your uncle" and there it is.)

The original 95 inch chassis was tested by Spectrum Technologies of Livonia Michigan in the mid 90's.

The results were as follows.

Elastic mode 1: Bare chassis (no skin) 4580 lbs per degree torsional-natural frequency 24.7 Hz
Elastic mode 2:Skinned chassis 8400 lbs per degree torsional-natural frequency 57.1 Hz
Elastic mode 3:Chassis with stressed engine. (302 bare block, front and rear plates) 10960 lbs per degree torsional-natural frequency 89.78 Hz

The inclusion of a 6 point roll cage changed the mode 3 numbers to 12680 lbs per degree torsional- natural frequency to 101 Hz.

The tests were done in both static mode (per degree notation, shaker rig) and dynamic mode (Hz notation, piezo transducers and hammer, Labview DAQ)

And of course all this talk of chassis rigidity really means very little as long as you are above the range of 3500 lbs per degree. You will probably be very happy with the chassis from a structural standpoint with that number.

Few Cobra folks will ever input wheel loads that impose a force sufficient to displace the pickup points enough to affect the tyre contact patch.

[mrmustang]

Originally Posted by Richard Hudgins

Tim7139,

I hope the below information is what you are asking for.

Bill. S,

We did do some third party testing and below are the results. (I must say that I was disappointed in the numbers as my computer FEA sims showed better numbers, but as they say, "Bob's your uncle" and there it is.)

The original 95 inch chassis was tested by Spectrum Technologies of Livonia Michigan in the mid 90's.

The results were as follows.

Elastic mode 1: Bare chassis (no skin) 4580 lbs per degree torsional-natural frequency 24.7 Hz
Elastic mode 2:Skinned chassis 8400 lbs per degree torsional-natural frequency 57.1 Hz
Elastic mode 3:Chassis with stressed engine. (302 bare block, front and rear plates) 10960 lbs per degree torsional-natural frequency 89.78 Hz

The inclusion of a 6 point roll cage changed the mode 3 numbers to 12680 lbs per degree torsional- natural frequency to 101 Hz.

The tests were done in both static mode (per degree notation, shaker rig) and dynamic mode (Hz notation, piezo transducers and hammer, Labview DAQ)

And of course all this talk of chassis rigidity really means very little as long as you are above the range of 3500 lbs per degree. You will probably be very happy with the chassis from a structural standpoint with that number.

Few Cobra folks will ever input wheel loads that impose a force sufficient to displace the pickup points enough to affect the tyre contact patch.

Richard,

Thanks for chiming in, as always, you are a class act, as was Bob from ERA for posting up a link to the article, explaining such things.


Bill S.

[Cobra #3170]

Originally Posted by Richard Hudgins

Tim7139,

I hope the below information is what you are asking for.

Bill. S,

We did do some third party testing and below are the results. (I must say that I was disappointed in the numbers as my computer FEA sims showed better numbers, but as they say, "Bob's your uncle" and there it is.)

The original 95 inch chassis was tested by Spectrum Technologies of Livonia Michigan in the mid 90's.

The results were as follows.

Elastic mode 1: Bare chassis (no skin) 4580 lbs per degree torsional-natural frequency 24.7 Hz
Elastic mode 2:Skinned chassis 8400 lbs per degree torsional-natural frequency 57.1 Hz
Elastic mode 3:Chassis with stressed engine. (302 bare block, front and rear plates) 10960 lbs per degree torsional-natural frequency 89.78 Hz

The inclusion of a 6 point roll cage changed the mode 3 numbers to 12680 lbs per degree torsional- natural frequency to 101 Hz.

The tests were done in both static mode (per degree notation, shaker rig) and dynamic mode (Hz notation, piezo transducers and hammer, Labview DAQ)

And of course all this talk of chassis rigidity really means very little as long as you are above the range of 3500 lbs per degree. You will probably be very happy with the chassis from a structural standpoint with that number.

Few Cobra folks will ever input wheel loads that impose a force sufficient to displace the pickup points enough to affect the tyre contact patch.

That is a damn good chassis.... if only mine were half that good I would be like the veritable pig in shi$$

[mdross1]

How about real world experience, a lot of Cobra's have been around 20 yrs. and more. What does the glass look like on cars that are truly put to the test.