Alum or Steel Driveshaft ??

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Mike Peters
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#16 Post by Mike Peters » Wed Jan 16, 2008 11:37 am

Hey Craig. Thanks for the insight. I saw you post about this same subject on YB, didn't I? Webb City, MO. eh? How come you ain't racing in the MAKO series? Come on out.
"If winning was easy, losers would be doing it"

waterdog
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#17 Post by waterdog » Sat Jan 19, 2008 10:43 am

Got my carbon fiber shaft from PST in Clearwater fl. several years ago. Just had it serviced recently after a bunch of passes and 1400 miles on the powertour and they said it was still perfect. I don't know how heavy it is, but that sucker is lite. Hey Mike cool bike , Walt
1970 Nova SS 3580lb, Shafiroff 434 na, 9.94@135.8

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Craig W.
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#18 Post by Craig W. » Sat Jan 19, 2008 10:19 pm

One thing I haven't seen mentioned is moment of inertia. Sort of the combined effect of weight and diameter. While a steel shaft is heavier, the aluminum shaft is typically bigger in diameter to maintain strength. So the lower weight of aluminum is farther from centerline, which almost negates the weight loss.

I ran the numbers on this a couple years ago and decided to go with a Denny's Nitrous Ready 3.5" shaft instead of aluminum. The small reduction in moment of inertia wasn't worth the extra expense.
Craig Watson
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John_Heard
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#19 Post by John_Heard » Sun Jan 20, 2008 11:15 am

Craig I think that's a pretty good point. I'm wondering what everyone's thoughts are about driveshaft critical speed - which is also why the mfg's seem to want to make the diameters larger. In other forms of racing, specifically dirt late models/circle track it seems the smallest dia and lightest shaft is what's used without regard to any specific critical RPM's.

Has anyone had a situation say with a shaft that is supposed to be "critical" at a specific RPM and actually had problems operating through that RPM range? This is more like a resonant frequency that the driveline sweeps through vs a specific failure point isn't it?

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Craig W.
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#20 Post by Craig W. » Sun Jan 20, 2008 8:31 pm

I've never heard of anyone having a driveshaft failure due to exciting it at its resonance frequency. That makes me think that the resonance frequency is outside the typical range of usage. Could be wrong.

Most seem to fail right at the hit, so that would be a failure from loading and not harmonics.
Craig Watson
2QuickNovas Racing
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