[TowerTalk] Wind survival + load ratings... vs, reality.
Steve Baughn
baughn at centurylink.net
Wed Nov 1 12:35:53 EDT 2017
Excellent idea Jim..It would be nice to have all this information in one
place so one could compare apples to apples.
73, Steve, WD8NPL
-----Original Message-----
From: Jim Thomson
Sent: Wednesday, November 01, 2017 12:17 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Wind survival + load ratings... vs, reality.
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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