From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: sanity check - tension bolt issue
To: flyrotary
Date: Wed, 30 Oct 2002 07:32:16 -0500
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In-Reply-To: <20021030070114.84762.qmail@web20706.mail.yahoo.com>
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Posted for Mr dan ruggirello <dan_ruggirello@yahoo.com>:

I posted earlier (@ flyrotary) that I was skeptical
that the tension bolt issue was vibration since my gut
feel was the bolt was much stiffer than 110hz (6500
rpm).  Well, I just estimated the 1st mode natural
frequency and low and behold, I calculated a frequency
of 150hz.  Too close for comfort!!!


Specifics:
fixed at one end, pinned at the other
diameter: 10mm
length: 273mm-10mm ~263mm (10mm thread enguagement)
E: 30 msi
I: 1.18E-3 in^4
density: .30 lbs/in^3

Yup, very likely it's vibration/fatigue.  Now my
question is if the RTV or shrink wrap is effective and
reliable......

I will probably calculate a fatigue life on the stock
bolt, use the RTV and replace the bolts every so often
based on fatigue life or go to a higher strength bolt
(given it meets the fatigue life) for added margin of
safety.  (I think I saw a higher strength after market
bolt).  This seems like a case where the bolts were
engineered for an average automobile environment where
continuous/frequent high rpms are not a design
consideration.  

I am not that familar with the bolt, anyone know what
the stock bolt material is?  Is the bolt diameter
equal to or less than the minor thread diameter?  

Dan