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

[jimlux]

On 10/31/17 11:58 PM, Kurt Andress wrote:
> 
> 
> 
> Message: 5
> Date: Tue, 31 Oct 2017 11:53:01 -0700
> From: "Jim Thomson"<jim.thom at telus.net>
> To:<towertalk at contesting.com>
> Subject: [TowerTalk] Wind survival +  load ratings...  vs reality.
> Message-ID: <1A1BAFDA3D7F4F67B3F5A6C6AAE8716D at JimPC>
> Content-Type: text/plain;    charset="utf-8"
> 
>    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  $9935.95
> 
> I have also stuffed several other yagis, like 40m, and  20, and 
> multibanders  etc  through the software.  Eye opener,  but not as bad as
> the 80m yagis above.   I tried Mosley, Hy-gain, old telrexs,  KLM, and 
> anything else I could get exact dimensions for.
> 
> Back in the day, ant makers could get away  quoting BS  gain and FB 
> numbers...... until software came along.    They are still  doing it,
> but with BS wind load ratings, and max wind survival ratings.     The  
> mechanical software is readily available, so why isnt anybody holding 
> them accountable ?
> In a lot of cases, hams are being sold a... bill of goods.
> 
> Jim   VE7RF
> 
> 
> 
> ------------------------------
> 
> Message: 6
> Date: Tue, 31 Oct 2017 14:53:39 -0500
> From:<maflukey at gmail.com>
> To:<towertalk at contesting.com>
> Subject: [TowerTalk] FW:  Wind survival +  load ratings...  vs
>      reality.
> Message-ID:<00c101d35281$f34fd2f0$d9ef78d0$@gmail.com>
> Content-Type: text/plain;    charset="UTF-8"
> 
> 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. Paul Sergi, NO8D (Summit Racing & DX Engineering) and his 
> people bought my software and decoded it and made their own version, 
> that was bench marked against the work I had done...I cannot speak for 
> the voracity of what they have done!
> 
> 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!
> 


I would say that perhaps we're at about the same place where we were 
when amateur runnable NEC models started to be practical - and folks 
found that the gain in the model was *substantially* different from the 
gain in the ad - leading to ARRL banning claims of gain in QST without a 
published model or test data.

Overall, hams are probably more comfortable running and believing an 
electrical model than a mechanical one (more time to become familiar, 
etc.? or just because the ham tests ask you about electrical stuff, but 
don't ask you about mechanical stuff)


There's another pervasive factor - probability
For electrical performance, the ionosphere is the wild card in most ham 
experience - Put up your new model ABC antenna during a sunspot peak and 
it works gangbusters - the vast majority of ham experience is empirical 
with an N of 1: "I put up this antenna and did that with it"

For mechanical performance, the wild card is the weather - how many hams 
have towers that are overloaded according to the code, but survive, 
essentially because they've been lucky.  So performance becomes anecdote 
- I put up a ABC antenna, and they reported 70 mi/hr gusts in my city, 
so my antenna survives 70 (whatever the wind speed actually was at your 
antenna site)

Another factor in mechanical designs is "hidden safety margin" - 
typically in a design, you don't claim the actual expected yield 
strength, you design for a bit lower (or design for a bit higher loads) 
- that accounts for material properties variation, variation in 
structure strength from the assembly process, etc.

So you might have a design which "officially" calculates out at 70 
mi/hr, but which actually survive 100, sometimes, on a lucky day, with 
the wind from the right direction.  That 100 is what gets claimed as the 
survivability.