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[TowerTalk] How High Can I Go Over a Thrust Bearing?

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Subject: [TowerTalk] How High Can I Go Over a Thrust Bearing?
From: (Eric Rosenberg)
Date: Sun, 01 Apr 2001 23:03:10 -0400
As regular TowerTalkers have seen, I've been working on ideas to 
replace my roof quadpod with something taller to get my F12 C3-SS 
higher than it's present 6 feet above the peak of the roof.

My reason is to eliminate any interactions with roof, attic and attic 
fan that likely exist.

The alternatives I've looked at are taller quadpods (9-10 footers, 
costing ~$400) that don't require guying, or a section of Rohn 25 (plus 
top and bottom pieces, totalling 11-12 ft) at a slightly lower price 
tag, but with guying.

As I have time until the weather and my finances improve, it dawned on 
me that there is a third possibility:  using a taller mast.

With the present quadpod. the distance between the rotor place and top 
of the thrust bearing is 4.5 ft.  The distance between the legs of the 
quadpod at the roof is 3 ft.  The system has survived 63 mph gusts 
(last month).

My question is this:  with a C-3SS (31 pounds, 4.4 sq feet windload), 
how tall can the mast safely go above the thrust bearing?  I have the 
MARC software, but it doesn't give me that sort of information (or at 
least I don't know how to extract it).  Are there 'standard' formulas 
for this.  Likewise calculating roof and rafter strength.

Any information is appreciated!


Eric W3DQ
Washington, DC 

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