I have knocked up a web based calculator to assist in design of simple wire
spans given the design wind speed, mass per unit length of the wire, wire
diameter and Gross Breaking Strength of the wire.

The draft calculator is at http://www.vk1od.net/rigging/awcc.php .

Constructive comments appreciated.

Owen

Owen Duffy wrote in
:

An email correspondent suggested that there was no use for such a thing. If
your antenna didn't blow down last season, then it wasn't big enough!

Well, you could use the calculator to remove most of the uncertainty and be
quite confident it *will* blow down. To do so, use a safety factor well
less than 1, say 0.5 should be reliable, and use a low wind speed, so that
you don't need to wait long for the event.

Owen

On Mon, 12 Mar 2007 07:29:09 GMT, Owen Duffy wrote:

Owen Duffy wrote in
:

An email correspondent suggested that there was no use for such a thing. If
your antenna didn't blow down last season, then it wasn't big enough!

Well, you could use the calculator to remove most of the uncertainty and be
quite confident it *will* blow down. To do so, use a safety factor well
less than 1, say 0.5 should be reliable, and use a low wind speed, so that
you don't need to wait long for the event.

Owen

Hi Owen,

Classic work includes wind load, ice load, and temperature, with
comined loads usually expressed in pounds per foot lengths. It is a
tedious translation to check your page though. Try researching Pender
and Thomson.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Mon, 12 Mar 2007 07:29:09 GMT, Owen Duffy wrote:

Owen Duffy wrote in
:
....
Classic work includes wind load, ice load, and temperature, with
comined loads usually expressed in pounds per foot lengths. It is a
tedious translation to check your page though. Try researching Pender
and Thomson.
....

Ok, so it is not for you apparently.

Calculating wind loading of cylindrical wire is problem enough, ice
loading might be cylindrical in laboratory tests, but is isn't reliably
so in real life. The surface isn't necessarily smooth either (so the
assumptions about laminar flow vs turbulent flow are affected). There has
been much written on the effects of ice on HV power lines, where they can
develop shapes that give them lift, with serious consequences when
adjacent lines fly into each other. (Differently to antenna wire spans
where wind load dominates the tension, large HV power conductors are so
strong and heavy for their diameter, that high winds only marginaly
increase tension, ice loaded spans are more affected.)

However, if you want to model ice loading, just increase the weight per
unit length of your wire for your chosen ice scenario, and increase the
windage diameter, change the GBS if necessary for the lower temperature
and run the numbers. I wouldn't propose an example, as I think the
results are unreliable.

The calculator probably has its greatest value as a learning tool in
individuals exploring scenarios for themselves, they might come to the
view that 160m dipole spans made from #16 magnet winding wire are not
practical in high winds.

Its not that we design to fail, its that we often fail to design.

Owen

PS: the calculator is metric units only to avoid the complication of
comprehensively dealing with imperial units, eg dimensions in decimal
inches, fractions, wire diameter in several gauge systems, lbs/mile etc,
force in pounds, slugs etc.

On Mon, 12 Mar 2007 20:10:10 GMT, Owen Duffy wrote:

Ok, so it is not for you apparently.

Hi Owen,

So you found the comments and references unappealing. Does that
invalidate them being constructive? As you do not offer the
mathematics to appraise, only a calculator to work; what constructive
commentary did you expect when someone runs an example? The color of
the box or the size of the font?

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

On Mon, 12 Mar 2007 20:10:10 GMT, Owen Duffy wrote:

Ok, so it is not for you apparently.

Hi Owen,

So you found the comments and references unappealing. Does that
invalidate them being constructive? As you do not offer the
mathematics to appraise, only a calculator to work; what constructive
commentary did you expect when someone runs an example? The color of
the box or the size of the font?

I took your comments on board, and have made some changes. The mathematics
aren't original or challenging, and in fact the results do show the detail
of the model fitted to the data.

The comments are appreciated though, thanks.

73
Owen