Antenna Wind Survival
Bryan Byers
what the best thing is to ensure the the survival of ground mounted
vertical antennas? I noticed that most antenna brands list a wind
survival rating of 80 mph
and I wonder why they pick that number?
Thanks, KA9KHD
Crazy George
It is an industry standard rating. Obtain a copy of the latest revision of
EIA Standard RS-222, "Structural Standards for Steel Antenna Towers and
Antenna Supporting Structures" for background and test information for
outdoor antenna structures. You will find a map of expected wind velocities
in the US, and the statistics used to develop a consensus survival standard.
--
Crazy George
Remove NO and SPAM from return address
Bryan Byers <bcb...@netusa1.net> wrote in message
news:3C71B396...@netusa1.net...
J. Harvey
> I noticed that most antenna brands list a wind
> survival rating of 80 mph and I wonder why
> they pick that number?
Most of the antennas that I have been looking at recently are rated for wind
speeds fairly close to Mach 1. Airplanes you see... :-)
Heinz W. Wiggeshoff
And do they factor in bird strikes?
J. Harvey
> Most of the antennas that I have been looking at
> recently are rated for wind speeds fairly close to
> Mach 1. Airplanes you see... :-)
"Heinz W. Wiggeshoff" asked:
> And do they factor in bird strikes?
Much, much, much more common are flightline crew 'head strikes' (<KLUNK>
"Owey! Uh oh...") on the bottom mounted antennas and other protrusions.
If an airplane antenna did hit a big goose in flight (for example), it would
probably tear off the larger part of the antenna. The fuselage and doublers
should survive, but might be bent. Better the antenna than the windscreen.
JLB
I have my guess.
In most cases if the wind was above 80 MPH you would be worrying about
other things besides your antenna, like your house.
J. McLaughlin
to account for gusts. (this is good) Some manufacturers use no such
factor.(this gives you a number that is unrealistically too high - bad)
In other words, the peak pressure, which is approximately proportional
to the square of the wind velocity, that an antenna element can
withstand without permanent deformation is the number you want, but will
not get. At least one good antenna that is for sale has elements that
all will bend at about the same pressure (good design), however the wind
velocity stated corresponds to the theoretical pressure of a smooth flow
of air. Without ice, it will hold together 'till about 55 mph (as
measured by the weather people), but will be long gone before reaching
the specified 80 mph.
Survival specifications of yagi/LPA type antennas should be given in
terms of pressure to cause deformation of the most weak part when the
wind is head on and again when normal to the boom. (It would also be
nice to have the same pair of numbers when the elements are encased in
0.5 inches of ice and to have the effective area in both directions)
One could then apply a safety factor appropriate to the material and to
the gustiness of the wind. The SF should also have a height factor and
a roughness factor. (Flat, rural, treeless land has quite a different
wind characteristic than that of a residential tract.) It is a pain to
have to calculate these numbers in order to know when an antenna is
likely to fail and in order to know the force loads on the supporting
tower.
So.... ask what equation is used to relate the specified wind
velocity to pressure.
<rant mode off.> 73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
Home: J...@Power-Net.Net
Office: J...@McLMcL.Com
"Crazy George" <muns...@attglobal.net.SPAM> wrote in message
news:3c71c...@news1.prserv.net...
Richard Harrison
"I noticed that most antenna brands list wind survival rating of 80 mph
and wonder why they pick that number?"
They need a standard for comparison. Winds exceeding 80 mph are
uncommon. The pounds per square inch produced by 80 mph depend on
surface shape and orientation.
Crazy George gave you a good answer by referring you to RS-222. Towers
are often built for higher wind velocities than 80 mph for areas subject
to higher winds.
Best regards, Richard Harrison, KB5WZI
Richard Harrison
"The pounds per square inch produced by 80 mph depend on surface shape
and orientation."
I`ve found the "conventional figures" used by some antenna manufacturers
for "normal" antenna installations:
60 mph---11 lbs/sq ft of antenna
70 mph---15 lbs/sq ft
80 mph---20 lbs/sq ft
90 mph---25 lbs/sq ft
100 mph--30 lbs/sq ft
Antenna manufacturers should give the effective area of their antennas
for windloading calculations and estimates.
Richard Harrison
"Better the antenna than the windscreen."
Reminds me of the storied loan by NASA of their "Chicken Cannon" to
British Aerospace for windscreen testing.
The Brits asked: "What`s wrong with this thing? It takes out the
windscreen, the pilot`s headrest, and knocks a hole in the bulkhead
behind!"
NASA replied: "Thaw the chicken."
Mark Keith
No doubt. A bird can do a lot of damage to a plane that is really
moving. Most airlines have speed skeds to reduce damage from possible
bird strikes. IE: Below 20,000, stay under 300 IAS. By the time they
get down to 14,000 or so, they slow quite a bit. Some is ATC induced
of course, but also partly is birdstrike damage avoidance. You have to
be down to 250 knots when passing through 10,000 anyway. MK
Mark Hall
polarized, as evidenced by a MicroBurst in my back yard that left 5 huge
Oak trees felled in random directions on top of each other, but 100' away
no damage at all. Vertically polarized wind spells death to Yagi's,
although Circularly polarized winds probably cause the most damage.
'73 KI4Z
Richard Clark
Hi Richard,
The Chicken Cannon now finds service in the Canadian TV program Royal
Canadian Air Farce.
73's
Richard Clark, KB7QHC
SAM
standard is a minimum recommended standard specified in ANSI/EIA 222-E and
widely accepted in the tower manufacturing industry. The standard
establishes a minimum windspeed and radial ice load that a tower should
withstand if it is to me safely erected. I can't remember, but I think that
80 MPH is a category two hurricane, something that is not out of the relm of
possibility anywhere in North America. Again, this may be incorrect. Just
going from vague memory. Try doing a search on EIA 222-E.
Scott M.
KA1MRO