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Author Topic: Rg on Ultra Zone  (Read 3401 times)

1MechEng

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Rg on Ultra Zone
« on: January 15, 2008, 01:15:02 AM »
Everything I have seen for the new Ultra Zone shows the Rg to be 2.40.

This is lower than the USBC regulations, which state:
quote:
Radius of Gyration:
The radius of gyration of a 13.00 lb. or more bowling
ball, about any axis, shall not be less than 2.430 inches
nor more than 2.800 inches. In addition, the maximum
differential radius of gyration between any two axes of
the same ball shall not exceed 0.060 inches. These shall
be tested in accordance with an USBC approved test
procedure (see Appendix C).


Is Brunswick really putting out a ball that will not be certified by the USBC, or is the listed Rg incorrect?!
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Dan
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Engineering * Bowling = a fun and practical application of rotational kinematics.

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JMORRIS

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Re: Rg on Ultra Zone
« Reply #1 on: January 15, 2008, 09:23:23 AM »
I'm pretty sure it's a misprint.  The Ultra is using the updated Phantom core, which has an RG of around 2.50 in the Blast Zone.

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1MechEng

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Re: Rg on Ultra Zone
« Reply #2 on: January 15, 2008, 09:27:36 AM »
I found it ... some e-tailers have been advertising the average Rg value of 2.4.

From BowlersDream.com:
quote:
Coverstock: EnMotion Hybrid Reactive
Color: Black Solid/Blue Solid/Silver Pearl
Hardness: 76-78
Glow Engraving
Factory Finish Rough Buff
Core Dynamics
RG Max: 2.504
RG Int: 2.484
RG Min: 2.458
RG Diff: 0.046
RG Asy: 0.020
Average RG: 2.4
Performance
Hook Potential: 135
Length: 90
Typical Breakpoint Shape: 75
Comparison Chart Position = P10


Next question ... what is the definition of the average Rg value? I thought the USBC spec said that the Rg couldn't be less than 2.4 at ANY axis on the ball? For an average value to be less than 2.43 means that there are some axes less than the spec.  Am I missing something here?

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Dan
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Engineering * Bowling = a fun and practical application of rotational kinematics.

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dizzyfugu

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Re: Rg on Ultra Zone
« Reply #3 on: January 15, 2008, 09:28:59 AM »
I think they just swallowed the last 2 digits - if it is the Phantom-ish core, then its RG should be 2.484, and there's no comment that this ball has a specially lowered RG, just that it is a lower RG alternative to the TF?

"The Ultra Zone brings the new EnMotion reactive coverstock from the Twisted Fury into the Zone line and combines it with the updated Phantom core to create an ultra-low-RG alternative that complements the reaction of the Twisted Fury"
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purduepaul

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Re: Rg on Ultra Zone
« Reply #4 on: January 15, 2008, 09:28:59 AM »
The RG specification is the lowest RG can not go below 2.43, average RG is a brunswick term, we just measure the three axes x, y, and z.
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Dr Curve

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Re: Rg on Ultra Zone
« Reply #5 on: January 15, 2008, 11:39:26 AM »
2.4 is the average based on a 1-10 scale with 1 being 2.430 and 10 being 2.800. If you look on Brunswick's spec sheets or web page it will list RG Min, Max, Diff and also RG-ave. Bowlersdream.com has the correct specifications.
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1MechEng

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Re: Rg on Ultra Zone
« Reply #6 on: January 16, 2008, 08:11:15 AM »
PurduePaul -
When the USBC tests the new balls for legality, do you locate the axes based solely on the pin position?
In theory, couldn't a manufacturer design and implement a pin in a position other than the highest/lowest Rg areas on the ball, thus circumventing the rules?
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purduepaul

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Re: Rg on Ultra Zone
« Reply #7 on: January 16, 2008, 12:52:29 PM »
Dan-

No, we have actually learned by a process that we need to locate the three axes more precisely using a deTerminator by Jayhawk.  With the deTerminator, you can find the high RG spot (PSA on assymetricals) or high RG equator (symmetrical balls).  With this measurement you can find both the true low RG axis and the z axis of a non-drilled bowling ball. If you have any other questions about procedures on testing they can be found on bowl.com under equipment specification and certification.

Paul
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