On Sat, 01 Sep 2012 22:36:52 +0300, KBa wrote:

Just thinking of how glass ceramics may behave under bending force...

Machinable glass ceramic insulators don't behave... they break.
They're great under compression but miserable in tension. So-so in
torsion. All you have to do is make the insulator stronger than the
element it supports. If there's excess force on the element, the
aluminum element will bend rather than the insulator will break.

Element center gap is under very small vibration (wind load) and element
static load stresses the insulator center... it bends slighly depending
how elastic is the material...

I don't expect wind vibration to be much of a problem. The forces are
rather small compared to a flock of overfed birds landing on the
elements or the wind blowing at hurricane force. With a brittle
insulator, an impact with a flying hard object is a real danger.

Fiberglass have some elasticity... it's not brittle... on the other hand
there could be support limiting the bar bending or the element halves
might have more than two clamping points... so the center gap would
be steady...

You haven't supplied any numbers or dimensions, can't do any
calculations.

I don't think you'll have much trouble with the static loads
(including the birds). The wind loading might be a problem depending
on design.

Required reading "The Physical Design of Yagi Antennas" by Dave
Leeson:
http://www.universal-radio.com/catalog/books/0995.html
http://www.realhamradio.com/Download.htm
Ugh... I dunno about these prices:
http://www.alibris.com/booksearch?qwork=5115496
Mo
http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm
http://www.rotorservice.com/antenna%20wind%20load.htm
http://www.arraysolutions.com/Products/windloads.htm
http://www.sinctech.com/antenna_wind_loading.aspx

Actually I had in mind using extra varnish layers on fiberglass after
processed to diameter and then boiling it in bee wax...
This is still the plan b or c.

Bees wax won't work on fiberglass.

tnx oh6io

Perhaps if you build something really disgusting errr... innovative,
which balances some of the tension on the insulator with a little
compression, try building the yagi elements using wires instead of
tubing using a "cage". The "cage" will increase the effective element
diameter (thus increasing the antenna bandwidth). The "cage" will
also supply some tension to the insulator, which will balance some of
the tension.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558