[TowerTalk] US TOWER HDX-89 / Tash DX86 Wind Rating Differences

Sat Jun 10 12:15:20 EDT 2017

R,R on all the points.

We had a wx event here Thursday evening that happened quickly and there 
was no way to plan for it.

We had a thunderstorm come out of know where and it was a slow mover.  I 
haven't seen it officially recorded yet but I've heard rumors of 
straight line winds of 80mph (we're in an 85mph county per 
http://www.championradio.com/county.windspeed.data.html) In addition 
we're hearing an F1 tornado touched down just to our west as it blew a 
steel barn apart.  It blew down the north section of my back yard fence 
which uses steel fence posts (the new posts will be thicker gauge as the 
nasty winds normally come out of the north).

We had so much hail it looked like it snowed.

The highest recorded wind gust in our area is 81mph and I'm sure that 
does not include any tornado activity.

That all being said.  The reason for the crank up is easy maintenance 
down the road when I don't feel like climbing anymore. If I know a bad 
storm is coming I'll crank it down.  But I have to plan on the tower 
staying cranked up and being able to handle 85 mph.

Rich - N5ZC

On 6/10/2017 10:55 AM, Bob Shohet, KQ2M wrote:
> I would also add that you need to be aware of the fact that local qth 
> conditions (microclimate) in sudden, violent storms can vary 
> ENORMOUSLY from your general area and what the NWS or FAA thinks is 
> representative of your area.  In fact the max wind speeds in your qth 
> “zone” may only bear a passing resemblance to the likelihood of what 
> you will actually experience.
> Ridge crest/Slope are some of the exacerbating factors, but so is the 
> direction of the winds at a given qth.  At my qth the most violent 
> storms by far are when they approach the NY/CT border (12 miles West 
> of me) at a particular angle and funnel between the hills on both 
> sides of I-84.  They are terrifying and have on three occasions become 
> tornadic (wind speed plus twisting winds – far more damaging that just 
> wind speed alone).   During hurricanes the same thing is true – except 
> the location of the storm and its path have a lot to do with what to 
> expect. Even a 10 mile shift or wobble in direction can have enormous 
> differences in impact – and the “tighter” and more violent the storm, 
> the greater the different in impact a few miles can make.  And then 
> there are the effects of elevation.  In hurricanes, your height above 
> sea level can subject you to a higher sustained level of extreme wind, 
> over and above whether or not you are on a ridge line or on a slope.  
> In major hurricanes, elevations as low as 800’ – 1500’ ASL can subject 
> you to winds 20 – 40 mph stronger than if you were at 300’ ASL, which 
> is what happened at my qth during Hurricane Sandy. And the difference 
> in force between 70 mph and 110 mph is equal to the square of the 
> ratio of velocities, so the force of 110 mph is not 1.57 times 70 mph, 
> it is 2.47 x!!  Which can easily induce a failure.  If you are 
> elevated enough AND you are on a ridge crest / slope, (as I am) then 
> you can be in even more trouble!
> Simply put, it is during the particularly vicious storms that you are 
> most likely to experience failure and the wind velocities experienced 
> during those storms are least likely to be predicted by your location 
> wind zone that is used for calculation purposes.  Please remember that 
> when planning for your qth.
> 73
> Bob  KQ2M
> *From:* Rob N1KEZ <mailto:rob at n1kez.net>
> *Sent:* Saturday, June 10, 2017 11:20 AM
> *To:* Richard Thorne <mailto:rthorne at rthorne.net> ; Towertalk 
> <mailto:towertalk at contesting.com>
> *Subject:* Re: [TowerTalk] US TOWER HDX-89 / Tash DX86 Wind Rating 
> Differences
> Make sure you know what the wind ratings are for your area before 
> getting excited about a particular tower. Manufacturers assume you 
> live in the most favorable place. Wind rating for my tower location 
> turned out not to be 90 Mph but 130Mph! (Ridge crest/Slope etc).
>
> 73!
> N1KEZ de Rob
>
> Sent from my mobile device.
> Pse excuse brevity and any errorz.
>
> On Jun 10, 2017, at 7:00 AM, Richard Thorne <rthorne at rthorne.net> wrote:
>
> This may not be comparing apples to apples but here's my question 
> after studying the two towers.
>
> US Tower HDX-89 claims 9.2 sq ft of max allowable antenna wind area 90 
> mph 3 second gust
> Tash DX86  claims 21 sq ft of max allowable antenna wind area 85 mph 3 
> sec gust
>
> After looking at both designs they both start with a lower section 
> that is 28.75" wide and a top section that is 13 7/8" (Tash) and 13 
> 15/16" (US Tower)
>
> So the designs appear to be the same, why are the allow able antenna 
> wind loads so different?  I realize that one is based on 90 mph the 
> other on 85 mph.  Does the 5 mph delta add up to a 11.8 sq ft difference?
>
> Thanks in advance.
>
> Rich - N5ZC
>
>
>
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