Chassis rigidity

[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$$

[twin turbo]

I noticed a definite difference in my chassis rigidity when I added side bars and a full width roll bar in my car. Those numbers seem to bear that out when you added the cage.

[mrmustang]

Originally Posted by Cobra #3170

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

Now that, coming from you, is damn funny

[twin turbo]

Originally Posted by mrmustang

Now that, coming from you, is damn funny

So true!

[Cobra #3170]

Originally Posted by mrmustang

Now that, coming from you, is damn funny

My car is a wet noodle compared to what Richard has, I only can wish.....

[mrmustang]

Originally Posted by Cobra #3170

My car is a wet noodle compared to what Richard has, I only can wish.....

So I'll buy Richards car, and the you and I can do an even swap