[TowerTalk] Wind survival + load ratings... vs, reality.

Wed Nov 1 14:10:53 EDT 2017

JK Antennas come up "site not available" on all my attempts to reach 
them. Are they still in business? All my HY-Gain LJ 5 element beams for 
20-10 survived Cat 5 Hurricane Maria with it's 179 MPH sustained winds 
but they were all on the ground held down with large wooden pegs. ☺ MY 4 
element CUBEX QUAD up on the tower with the least W/L looks like 
scrambled eggs. As the man in the movie JAWS said  "We need to get a 
bigger boat."

Herb, KV4FZ

On 11/1/2017 12:17 PM, Jim Thomson wrote:
> Date: Tue, 31 Oct 2017 23:58:52 -0700
> From: Kurt Andress <andresskurt at gmail.com>
> To: towertalk at contesting.com, jim.thom at telus.net
> Subject: [TowerTalk]   Wind survival + load ratings... vs, reality.
>
>
>    
> Hi Jim,you wrote...
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Thomson
> Sent: Tuesday, October 31, 2017 1:53 PM
> To:towertalk at contesting.com
> Subject: [TowerTalk] Wind survival + load ratings... vs reality.
>
>     Has anybody tried stuffing yagi manufactures  ele dimensions into software  like  Yagi stress.....  and  or  Yagi max ????
>
> I have been doing just that on a bunch of them...and in several cases, Im not impressed with the results.
> And Im using the correct dimensions for exposed length tubing, and correct OD and wall thickness, and correct
> yield strength.    Im  using both the ... no spec..aka  wind tunnel spec.......and also the old  C spec.
>
> Some of these yagis that are rated at ...  100 mph are actually only good for a paltry  64 mph...and that?s  with NO ice,
> such is the case with the M2  80m yagis.   Their  3 el  80m yagi uses C specs for  wind area.  They rate it at 32 sq ft.
> Its actually 48 square foot of projected area.   Their combo truss  +  LL  does nothing for ice loading, and nothing for
> horizontal deflection.    The LL reduces some ele sag, thats it.   Both  YS + YM spit out 64 mph  using  no spec..and
> both spit out  69 mph, using C spec...and that?s with NO ice.
>
> Toss just .25 inch of ice into the mix, and it becomes   48 mph  using no spec....and    52 mph  using C spec.
>
> The optibeam 80m yagi doesnt fare much better.  Good for  72 mph, using C spec....and less using  no spec....and that?s with NO ice.
>
> I also tried the JK antennas   3 el 80m yagi in YM  + YS.   Using no spec, it comes in at  103 mph.  Using C spec, its good for  107 mph.
>
> Now that?s a helluva  big difference between  m2s  64 mph...and the JK?s  103 mph.   Considering the M2 is not cheap at  $9935.95
>
> I have also stuffed several other yagis, like 40m, and  20, and multibanders  etc  through the software.  Eye opener,  but not as bad as
> the 80m yagis above.   I tried Mosley, Hy-gain, old telrexs,  KLM, and anything else I could get exact dimensions for.
>
> Back in the day, ant makers could get away  quoting BS  gain and FB numbers...... until software came along.    They are still  doing it,
> but with BS wind load ratings, and max wind survival ratings.     The  mechanical software is readily available, so why isnt anybody holding them accountable ?
> In a lot of cases, hams are being sold a... bill of goods.
>
> Jim   VE7RF
>
>
> <W3JK, who uses my software,  put me onto this post...
> <Now you guys are catching up with me, from the work I did in the 1980's to spend about 8 years creating YagiStress, and getting it verified by one of my P.E. colleagues with $18k software, Yagistress is within ~ 1% (or rounding  errors) with the pro finite <element linear analyzing engines.
>
> <What you're seeing Jim is what I have seen for around 30 years, and I have made comments on this reflector many times about that, but they were greatly ignored! I got run off this platform by too many other jungle knowledge experts that want to rule the <roost with their ever present emperical expertise! So, that's why I no longer devote much of my time to this venue....it is frought with way more "Jungle Knowledge" than engineering expertise!
>
> <Have fun out there imagining how you wish it would be, but not how it is!
>
> <73, Kurt Andress, K7NV, author of the YagiStress software...and tower service provider
>
> <P.S. You should simply throw away the EIA/TIA 222-C spec, it is now about 28 years old and does no longer apply!
>
>
> ##  Points well taken.  What I still dont get is.... the effects of the element tips bending.    I call that...shedding wind.  I dont believe the software factors that effect into the equation.   I have seen F12 els, where the tips and inboard sections from the tips, are bent straight  back, and the even more inboard sections still dont break !   IE: when the ends bend way back, the wind is now hitting them at a shallow angle..and less force applied to the ele ends.  The cross flow principle, so to speak.   Having said all that, when m2 is good for  64 mph..and the JK is good for 103 mph, thats a HUGE disparity..... yet both are rated for...100 mph.   In actuality, the actual breaking mph is probably 20 % higher than what the software spits out.
>
> ##  M2,  F12, Mosely,  Hygain, STILL use the outdated  222-C spec.  You have to add exactly 50% to their square footage, to get the real  projected areas.  To find out what their yagis are really rated at,  you have to take their eles, typ the REF..and stuff the dimensions into either  YS  or  YM.... then judge for yourself.     I dont mess with the C spec, nor the   222-F spec,  nor the  UBC-97 – exposure B/C/D spec.  I use the... No spec, aka wind tunnel...and so do many others.
> Heres what YM spits out for the m2  80m REF  using various  standards.
>
> No wind spec  -                                64.802 mph
> EIA-222-C spec -                              69.759 mph
> EIA-222-F spec @ 100 ft -               50.397 mph
> UBC- 97  Exposure B  @ 100 ft   -   60.492 mph
> UBC- 97  Exposure C  @ 100 ft   -   50.093 mph
> UBC- 97  Exposure D  @ 100 ft   -   45.549 mph
>
> Use  a 200’ tower instead of a 100 ft tower....and they all drop aprx 5 mph.
>
> IMO, measure the speed at the top of your mast... using a wireless, accurate, peak reading, wind speed indicator.   Forget the fastest  mile..and 3 sec gust bs.   I want the actual peak wind speed, and if a gust comes along, its the gust speed that I use.  Its also the gusts that break stuff.   The sustained wind speed is nice to know.... but its the higher speed gusts that I want to know about.   I dont want a wind speed indicator on the side of a tower either, nor the side of a mast.   Depending upon wind direction, the tower ..or mast  could impede airflow, and result in a lower reading.   Taking the wind speed  from the 6 oclock news is a wasted effort.  Done on the far side of town, at a much lower elevation, typ  33 feet.
>
> I would suggest to  JK ants,  who actually builds the...real deal, to tabulate both his ants, and all his competitors using  YS +  YM....then post the results on his website... for all prospective clients to see for themselves.   Then if the competitors whine + complain... too bad so sad, either put up...or shut up.   Since his competitors use the C spec, I would suggest posting both the  C spec..and also the  NO spec...aka wind tunnel  results.   Then at least joe ham can compare  yagis...using the same spec.   M2 Stating their 80m yagi is 32 sq ft and good for 100 mph, when software sez its 48 sq ft and good for 64 mph is nothing short of reprehensible.    Then folks can use the correct info to make an informed decision as to  actual tower type required, and also rotational torque required....and if a given yagi meets their site dependent WX requirements for expected max windspeed and gusts..and any ice loading, or heavy wet snow.     While we are on a rant, lets minimize ant torque.   Easily done with either a small counterweight  and or a Torque compensation plate.
>
> If one of these large  200-500 lb  yagis ever cut loose...  and came crashing down....and sliced a phillystran guy wire, or a solid fiberglass  guy wire..... the entire tower  could easily come down.   Neither philly nor solid fiberglass has any shear strength.... only good tensile strength.   Thats a safety issue imo.
>
> Id be right pissed if my competitors were spewing BS numbers.   And no, a cross bar mounted above either an element or boom, with dual truss lines on either side,  doesnt increase the max wind speed.  Heck it doesnt even  reduce the horz deflection.
>
> end of rant.
>
> Jim   VE7RF
>
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