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

Wed Nov 1 14:15:55 EDT 2017

Yes, was just on their site yesterday and bought from them earlier this
summer.

https://jkantennas.com/

73,
Mike ND9G

On Wed, Nov 1, 2017 at 1:10 PM, Herbert Schoenbohm <
herbert.schoenbohm at gmail.com> wrote:

> 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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>>
>>
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