[TowerTalk] Thrust bearing question

[Gene Fuller]

Correction to my previous re mast loading. I think my mind was on vacation. 
Clearly, 18 x 4 = 72, not 64. Therefore in the example shown there is room 
for another 8x worth of antenna.  e.g. 1 more sq ft on the tribander at 1 
foot up and 1 more sq ft on the 6 meter at 7 feet up, with still a little 
room for ice or whatever.  Sorry, again, about that.

The "Economy of space" may well be in not having to replace the mast and 
perhaps one or more of the antennas after the first medium wind storm. Being 
a bit conservative in the design sure helps you sleep a lot better on those 
windy nights.

Gene / W2LU

----- Original Message ----- 
From: "Jon Pearl - W4ABC" <jonpearl at tampabay.rr.com>
To: "K8RI" <K8RI-on-TowerTalk at tm.net>
Cc: <towertalk at contesting.com>
Sent: Thursday, February 07, 2013 12:10 PM
Subject: Re: [TowerTalk] Thrust bearing question


> Hi Roger and Mike.
>
>
> On 2/7/2013 10:44 AM, K8RI wrote:
>>
>>
>> 2 points with the first beingm John is correct, a 16' mast putting the 
>> antenna 16' above the top of the tower substantially derates the tower 
>> below the 18 sq ft original rating.
>
> I've yet to finalize the spacing between the HF, six and two meter 
> antennas but I may well find some economy of space, allowing me to drop 
> the rotator further down into the tower.  I can't make it lighter but I 
> can make it stiffer by shortening it's effective length above the top of 
> the tower.
>
>>
>> The other is, you already have a thrust bearing in the form of that 
>> sleeve.
>
> I guess that's the point I was trying to rationalize between my own two 
> ears.  I received another email privately that essentially said the same 
> thing.
>
>> It wont support vertical load, but that sleeve will substantially reduce 
>> any lateral/side load on the rotator produced by the leverage of the 
>> mast.
>
> The M2 OR2800 is rated at 1800# vertical load and it incorporates a Center 
> Guide (cone) for the mast to rest on.  It's been a while since I've looked 
> at the slop between the present mast that's on the tower and the sleeve. 
> If it's substantial then a thrust bearing might be of service, if only to 
> cut down on the lateral movement.
>
>> the sleeve will serve as a pivot point with 16' above it and 5' below it 
>> for a 16:5  ratio for lateral force on the rotator, or slightly less than 
>> 4:1 which is a big number.  Fortunately the sleeve limits the pivot 
>> ability with most of the load showing up as lateral load on the tower. 
>> Thats good for the rotator, but for the tower? Not so much.
>
> Yes, I've looked at the same ratio and it may change.
>
>>
>> Assuming you install an antenna of 18 sq ft which is the tower rating, 
>> with 18' of antenna 16' above the top of the tower that is 18' multiplied 
>> by a 16' arm.  So the tower is going to see much more than 18 sq ft of 
>> load..
>
> The actual numbers from bottom to top are 9.25 sq. ft., 2.5 sq. ft., & 2.7 
> sq.ft.
>
>>
>> The rotator was already designed to support a substantial vertical load 
>> so the bearing capable of supporting a vertical load is not necessary, 
>> but sure is handy if you need to work on the rotator without taking all 
>> the antennas down.  OTOH you can build a simple fixture to hold the mast 
>> in that case
>
> When it's all horizontal at waist level, it's all much more manageable.
>
>>
>> IE "to me" 16' sounds like a bit much.
>>
>> 73 and good luck
>>
>> Roger (K8RI)
>>
>>
>
> Thanks again and 73,
>
>
> Jon Pearl - W4ABC
>
>
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