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

[Richard Thorne]

Jim,

Good info.

I don't have the #'s to back up my results as you do.

I only have empirical info that coincides with your data.  I replaced an 
M2 40mLLDD with a JK SR3040 due to a bent element from a wind event.

This past summer I installed a JK801, JK SR3040 and a pair of Mid-Tri's. 
Beefy is a understatement.

Time will tell....

Rich - N5ZC



On 10/31/2017 1:53 PM, Jim Thomson wrote:
>    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
>
>   
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