[TowerTalk] Phillystran and cable clamps
Dave D'Epagnier
DAVED@ctilidar.com
Thu, 17 Dec 1998 07:49:32 -0700
Bill,
the force due to wind on a surface is:
f = A*(0.5p)*V^2*Cd
where: f = force (lbs)
A = area of surface (ft^2)
0.5p = 0.001188 (slug/ft^3)
V^2 (V squared) = wind velocity (ft/sec)
Cd = drag coeficient = 1 to 1.28 (unitless)
have fun.
Dave
AB0GJ
> ----------
> From: WBH3@daimlerchrysler.com[SMTP:WBH3@daimlerchrysler.com]
> Sent: Thursday, December 17, 1998 7:05 AM
> To: k7lxc@aol.com
> Cc: towertalk@contesting.com
> Subject: [TowerTalk] Phillystran and cable clamps
>
>
>
>
> Steve:
>
> I am somewhat concerned over your comments, ref: item 5 below, where
> you
> say that "cable clamps and Phillystran do not mix"!!
>
> I recently put up a 15 foot Create tower on top of my house and have a
> KT34-XA on top of it. Gerald at Texas Towers told me that the
> smallest
> Phillystran (1200 lb. test) would be sufficient to hold this in 70
> mph
> wind. Further, Texas Towers' catalog says to use 4 cable clamps with
> the
> smallest Phillystran and preform grips with all other sizes.
>
> The "local tower guru" only used 3 clamps, and said I didn't need 4
> anyway
> when he helped me put up the antenna Steve, could you elaborate a
> little
> on your comment? Am I at risk with only 3 clamps, considering the
> square
> footage of tower and antenna? (Tower is rated at 23 sq. ft. @ 90
> mph).
> Also...I don't understand the statement 23 sq. ft. @ 90 mph......what
> does
> it mean? How do you calculate what the windload is at 70 mph if its
> 23 @
> 90 mph?
>
> To me a more definitive number is how many pounds of wind force are
> trying
> to push the antenna and tower over. If I know how many pounds of
> force are
> pushing then I can calculate the vector forces vertically and then
> determine how much strength I need for the guy material. (Assuming
> that
> the pounds of force are horizontally pushing on the assembly). I
> realize
> that this can get very complicated since we need to know the angles
> the guy
> wires make with the horizontal, etc. How do I calculate the force on
> my 9
> sq. ft. of antenna at 70 mph? Someone told me it was 9 times 70 =
> 630
> pounds.
>
> Although I am an Electrical Engineer, I don't want a detailed
> mathematical
> formula, just a rough rule of thumb. Well, I guess that is enough
> questions for now (I have lots more...hi).
>
> Thanks, Steve
>
> Bill Haselmire WX8S
> wbh3@daimlerchrysler.com
>
>
>
>
>
>
>
> K7LXC@aol.com on 12/15/98 09:33:56 AM
>
>
>
> To: mlowell@noclant.navy.mil, towertalk@contesting.com
>
> cc:
>
>
>
> Subject: Re: [TowerTalk] thimble size
>
>
>
>
>
>
>
>
>
> 5/16" EHS 1/2" thimble
> > >
> > >3) If 4000lb Phillystran is used with Preform Grips, the thimble
> is
> > >7/16".
>
> This is correct but you're not using Phillystran.
> > >
> > >4) If 6700lb Phillystran is used with Preformed Grips, the thimble
> is
> > >1/2".
>
> This is also correct but you're still not using Phillystran.
> > >
> > >5) If Phillystran is used with cable clamps (highly not
> recommended)
> use
> > >one size smaller than above.
>
> Cable clamps and Phillystran do not mix anymore.
> > >
> > >In all cases the heavy duty version of the thimble is used.
> Use the 1/2" ones as per above.
>
> Cheers, Steve K7LXC
> Tower Tech
> Champion Radio Products
>
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