[TowerTalk] Antenna & Tower Wind Load Ratings

[Jim Thomson]

Date: Fri, 16 Jun 2017 23:40:50 -0700
From: Kurt Andress <andresskurt at gmail.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Antenna & Tower Wind Load Ratings



On 6/16/2017 11:34 PM, Kurt Andress wrote:
> Hi Jim,

> Rating rotators for the incorrect or correct antenna areas is totally 
> useless! Rotators only care about the torque developed by the antenna 
> system they need to control!

###  Correct.  Rating a rotor in sq feet is fubar.   All I want to know is how many FOOT 
lbs of tq it is capable of.   Rating a rotor in inch pounds is quasi  fubar.    Take the inch lb rating...
divide by 12, to get the foot lb rating.  Ok, now we have something we can relate to.   The 800
inch lb... Ham-V  rotor is actually just   67 ft lbs.   The T2X is 1000 inch lbs =  83 ft lbs.   My  2 ft
long torque wrench will out do both of them.   I envision the boom as 2 x back to back TQ wrenches.
I have measured the start up current on a lot of small AC motors and typ the start up current is triple
the running current.... which might explain why the start up TQ on some rotor specs is higher than the
running Tq...albeit it only last the 1st  1-3 secs.    BTW, I have 2 x OR-2800 rotors, one AC type..the
other is a DC type.   And also a K7NV small PP   + GH controller..which is now installed. 
VE6JY came up with a unique method of testing rotors....  by seeing how much weight they can lift.... before
they stall, and rpm drops to zero. Its an eye opener when comparing different rotors. 



>
> Jim, when you have developed the software to perform non-linear 
> analyses of antenna members continually inclined to different attack 
> angles in the increasing wind speeds, please let us know! Most of my 
> pro colleagues would like to have that capability, there is no 
> non-linear platform that can do it today....
> I know how I approach that, it takes many tons of time to even 
> approximate it, but it can be done if one is dedicated enough to spend 
> the time to approximate it! If you have finite element software and 
> are a capable practitioner with it, you can do this, it just takes 
> more time than following 222-G standards......

###  Points well taken.  However,   with the yagi pointed directly into the
wind..and all the eles  are bent back in an arc, they will shed wind...like branches on a willow tree. 
I highly suspect the actual wind survival under those conditions  will be much higher   vs   say eles that did not
deflect at all, dead straight, dont budge... which is what I believe  both YS + YM are based on.  If that is the case,
then perhaps the YS + YM software results are on the  conservative side of the actual V max breaking point. 
Too bad some of these yagis cant be tested in a wind tunnel...if they could fit.  Plan B might be ludicrous, like 
temp installing a single ele on top of a vehicle, with go-pro cameras, then take it for  multiple passes  down
a 10-15,000 ft long run way strip.   Then use the cameras to measure the deflection.   Increase speed...til 
something breaks.   




> On reflectors there are always people that say things, then there are 
> people that appear to know things, then there are people that actually 
> do the things they know......
> Nothing I have ever designed from scratch has ever failed, I've had 
> plenty of failures trying to make things delivered/built by others 
> survive!

##  I have not had one failure of any of my scratch built from the ground
up yagis that I designed. And they did not have excess weight.  Trying to
modify commercial built yagis  can be a pita.   40M KLMs  dont fare too well
in my town..and we hardly get any wind.  One 70 mph in the last 20 years. 
Buddy across town with his 150 ft rotating tower, chock full of KLMs  from
80-10m, has broken everything you can think of.   His 10 + 15m els have sheared
clean off.... just a few feet from the boom.   Another buddy with his 5 el 20m KLM
had the REF vanish off the boom... ended up in the Fraser river.  lexan insulators
were not strong enough.  Both DEs were dangling..with all tips facing downwards... 
held up only by the criss cross  phasing straps.   Lexan insulators survived, tubing sheared.
That was in a 70-80 mph windstorm.

##  The 20m 46 ft boom telrex  held up..for a bit.  Then the REF and last DIR wobbled about,
chewing up an enlarged hole in the boom.   Vortex shedding rips up the Hy gain yagis... unless
you rope the eles..then cap off the tips.  At which point the els fill with water..then freeze. 
I used to cap the ends of the booms.... until  I took down the 15m yagi...with the boom completely
full of water.   Now I dont cap anything..except the very top of the mast.    





>
> The linear analyses of EIA/TIA 222G do a pretty good job according to 
> the hordes of professional engineers that developed it, for us to use 
> as a guide to do what we do! I'm sure you have never ever even seen 
> it! But, you might learn something if you did........but, since this 
> is certified to be Amateur Experimental Radio, we all have free 
> license to just be Amateurs and experiment with what we think we know ;-)
> How the individual parts of antennas are designed and built is up to 
> the designer that is responsible for that, nothing I have designed 
> from scratch for any clients have ever failed, because I have fully 
> vetted them for the loads the were expected to encounter, for the 
> EIA-222-G rating I certified them for. I have no knowledge of what 
> others have done....

###   I have spent many hours trying to figure out the UBC-97
and their EXP B-C-D specs.   My  UST  HDX-689  uses UBC-97
exp-B.   Their  70 mph rating at the top of the tower works out
to just 56 mph at the 8.5 ft level..if I have done the maths right.  
Their exp-C spec assumes almost uniform wind speed top to bottom of the tower. 
Then the UBC spec sez that  eles  more than 2inch OD have more laminar flow 
vs  els that are  less than  2 inch.   UST then quotes  obscene wind load ratings
if the tubular members are  all greater than 2 inch OD.   Im trying to convert all that
into something that is closer to reality..and build in a safety factor.    



>
> There is one simple principle, that my first year engineering 
> professor drilled into our minds.....things only fail when they are 
> inadequate, there is always a reason for that, Our job is to 
> understand it and figure out how to not let that happen! What it takes 
> to do that is a bit more complicated.......
>
> 73, Kurt, K7NV

##  IMO, without a wireless wind speed indicating device at the very top of the mast, 
joe ham doesnt really know what he is dealing with.   Typ wind speed devices are located
25-50 ft off the ground, on the far side of town, which is what gets quoted on the 6 o clock news.  

##  Only good news is.... by plugging in all the data  into YS or YM, then you sorta end up with a 
baseline.   Then you get to play with adding doublers etc, to beef it up a bit.   Real hoot plugging in
numbers for all these older yagis... plus current ones.   M2s  light version of their 5 el 20M yagi  will  barely
handle 85 mph, using the 222-C spec, which is what they rated it at....and way less than that using any other spec. 
M2 still uses the obsolete  222-C spec....including their  125 mph..survivor series.  

## Jeff, AC0C wants a full sized  3 el  30M yagi.
After plugging in the numbers for his 40M telrex  eles,  I came to the conclusion that whoever designed the
40M telrex els  had his head up his #@%.  YM sez they break at low speeds like  54 mph using no spec...and
59 mph using the 222-C spec.   Even with the tips removed to shorten it for 30M, it was still  bad.  A bitch to add
doublers, then remove the oem loading wires at the boom.   I designed the 30M els from scratch, using YM.
Started at 1.75 inch od  x .120 wall.....then down to .375 at the tips.  Good for  110 mph using the basic wind speed loading
formulae..aka  no spec.   Comes out to 121 mph using the 222-C spec.  Handles 1 inch of ice + 40 mph.
Cost for tubing to build 3 x NEW full sized 30M els  was  $384.15  from DXE.  Then of course is all the other stuff, like boom, the oem
29 ft telrex boom was re-used in this case.   Then all the misc hardware,  like the 24 inch long x 4 inch wide channel aluminum for
each ele to boom bracket, stauff clamps, etc, etc...which all adds up. 

##  Point here is, one can  easily build any of these  yagis  from scratch..or beef up an existing oem yagi, with out spending a small
fortune.  Then you get to build it to any spec you want.   DXE is a superb choice for cheap tubing..+ they also carry .120 wall,
6061-T8 material in 1.5  1.75 2.0  2.25  2.50  2.75 and 3.0 inch OD.    That all slides together nicely.  The .125 wall material  requires machining
.005 off in a lathe..pita  for us HB back yard folks.   The .120 wall material is the best thing that has happened in a long time.  Makes fabricating
booms easy, with either inner splices, outer splices, or both... if you want say a 3 inch OD boom, built  in 6 ft long sections.    Or just reduce the
boom diameter in .25 inch OD increments.   DXE + others carry loads of stauff clamps.    DXE carries a variety of HD mast clamps,  SS U bolts with 
solid AL saddles....and also  aprx  1 inch wide clamps, which are a pair of textured solid saddles.  

##  Im not  a fan of optibeam yagis..due to their  huge shipping costs to western canada.  That plus their use of metric tubing....pita. 
JK antennas  are built right, both electrically and mechanically.   M2  doesnt offer any interlaced yagis at all...too bad.  LPDAs are out of the
equation for amateur use.  Better options out there.  

Jim   VE7RF