"Richard Harrison" wrote

Jack Painter wrote:
"Scientists have now shown that blunt-tipped air terminals are attached
by lightning significantly higher frequency than sharp rods are."

I would have expected that sharp-pointed rods would be struck more
often.

Hi Richard, yes, you and Ben Franklin agreed on that. Modeling examples you
cited below appear to be incorrect for lightning, similar to how modeling
for ocean waves cannot be done in a bathtub, and even a swimming pool does
not closely replicate the action of waves in a large body of water. The
experiments and the conclusions offered by the blunt-tip lightning rod tests
were peer reviewed, are repeatable, and are being further studied. Their
conclusions describe behavior that was not expected or explainable by
current modeling. However it is easy to rocket-trigger lightning and this is
being done on a daily basis, so a few thousand repeatable findings should
soon arrive at a more permanent conclusion. Whether or not that is
explainable in terms that classroom scientists can model remains to be seen.
An awful lot of engineers have accepted the findings already, and specify
blunt-tip rods on new construction. The same cannot be said about other
questionable and unrepeatable theory such as charge transfer systems and
lightning charge dissipators. Their popularity relies soley on the ability
of snake-oil salesman conning a confused public.

73,
Jack Painter
Virginia Beach, Virginia



My CRC "Handbook of Chemistry and Physics" starts its coverage of
"Electricity and Magneyism with a page on Spark Gap Voltages. In every
case for a given breakdown voltage, the gap must be substantially wider
when the electrodes are needle-points than when they are spheres. For
example: With a voltage across the electrodes of 5 KV, the gap space
between needle-points needed to prevent a spark is 0.42 cm. The gap
between 5-cm sphheres is 0.15 cm under the same conditions. Much closer
before sparking points obviously means sharp points engourage breakdown
of the air between the points, while spherical (blunt) spark-gap
electrodes discourage the spark.

It`s been said that if the chsrges dont pile op at the pointed end of a
conductor, it would not have an equipotential surface as is required by
the conductivity ("College Physics" by Franklin Miller, Jr.

Best regards, Richard Harrison, KB5WZI