On Wed, 5 Jan 2005 12:03:37 -0800, "Joel Kolstad"
wrote:

"Ed Price" wrote in message
news:gAdBd.6143$yW5.2@fed1read02...
We spend a lot of time now arguing about how well the computer model
replicates reality, and whether the math has enough variables accounted
for. Working models seem so old fashioned.

That's because they're so expensive to build. You'd probably never finish
designing something like a modern RF IC if all you could do was design it on
paper, build it, probe around a little to figure out what it 'really' does,
and repeat.

Likewise, few companies can afford to design the autopilot for a jet without
a great deal of simulation first. :-)


Hi Guys,

Back when I designed the UFDR for the 757/767, they were the first
airplanes designed entirely in software (conventional drafting went
the way of the Dodo). Today's 7E7 was entirely modeled in software if
I'm not mistaken.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 5 Jan 2005 12:03:37 -0800, "Joel Kolstad"
wrote:

"Ed Price" wrote in message
news:gAdBd.6143$yW5.2@fed1read02...
We spend a lot of time now arguing about how well the computer model
replicates reality, and whether the math has enough variables accounted
for. Working models seem so old fashioned.

That's because they're so expensive to build. You'd probably never finish
designing something like a modern RF IC if all you could do was design it
on
paper, build it, probe around a little to figure out what it 'really'
does,
and repeat.

Likewise, few companies can afford to design the autopilot for a jet
without
a great deal of simulation first. :-)


Hi Guys,

Back when I designed the UFDR for the 757/767, they were the first
airplanes designed entirely in software (conventional drafting went
the way of the Dodo). Today's 7E7 was entirely modeled in software if
I'm not mistaken.

73's
Richard Clark, KB7QHC


There's nothing wrong with doing a lot of modeling. OTOH, Boeing didn't go
from the computer model directly to production. Computer models don't do
very well in predicting the unexpected; things like digital designers
discovering the concept of parasitics ("There's nothing in my design that
generates 832 MHz!") or mechanical designers exploring the wonders of RF
stray coupling paths ("The RF gets from this compartment to that compartment
through a BOLT?!"

My initial point was that wondrous and amazing things can be proven through
software being pushed to the outer edges of its parameters. Before you
invest in several years of modeling, someone needs to take a whack at a
brassboard model to calibrate the sanity of the software.

Ed
wb6wsn

On Thu, 6 Jan 2005 04:21:19 -0800, "Ed Price" wrote:

OTOH, Boeing didn't go from the computer model directly to production.

Hi Ed,

That is arguably the goal if not the actual reality:

"As computers have become faster and more powerful in recent years,
we have been able to do a better job in modeling the entire airplane and
predicting the three-dimensional effects of the airflow around it,"
Cogan said. "The codes we have developed allow us to look at more
potential design options faster than ever before."

Indeed, Cogan said the process for developing airplanes today begins
with the computer model. The coding is so accurate that designers can
evaluate miniscule changes in a design to determine impacts on
aerodynamic efficiency, he added.

In fact, the accuracy of the coding has also focused the application of
another aerodynamics tool: wind tunnel testing.

In the '80s, the Boeing 767 team took more than 50 wing designs into
the wind tunnel to verify their designs, Cogan said. In the '90s, the
Boeing 777 team took 18 designs into the tunnel. "We were really not
verifying the designs as much as we were verifying that our computation
tools were accurate and looking at performance at the extreme operating
conditions, which the coding couldn't do," Cogan said.

"With the 7E7, we will take fewer than 12 wings into the tunnel," Cogan said.
"We are still proving our coding and testing the extremes.
The tunnel is a great tool but it's not very cost-effective.
So, being able to really focus on a few designs to get the data we need
is helping us be more cost-effective."

73's from Jet City,
Richard Clark, KB7QHC

Jack Painter wrote:
"An awful lot of engineers have accepted the findings already, and
specify blunt-tipped rods on new construction.:

They should specify what works.

Suppose a charged cloud arrives overhead and no lightning immediately
flashes. If the charge is positive, it attracts electrons in the earth
ond other conductors nearby. These electrons strain to reach the cloud,
runnibg through conducting bodies to get closer to the positive charges
overhead. The blanket of air insulates between the charges of opposite
polarity. The field grows faster than these charges are neutralized.
Sooner or later, the air at a high point starts to ionize (form a
conductive plazma). Then, current flow starts with a flash and a bang.
Thunder rolls as air rushes in to fill the void left by burnt
atmosphere.

Suppose that a lightning rod is at a high point beneath the positively
charged cloud as it arrives. Electrons are pulled up to its sharp point
(electrons repel each other, ao they tend to concentrate on the outside
of the rod and find the least outside opposing forces at the tip of the
rod.

To avoid corona formation, some transmitting antennas are fitted with
"corona balls" on their tips. This reduces the strain from a pointed
tip.

On a lucky day, the cloud is discharged without lightning. On an ublucky
day, your lightning rod may get pitted.

Best regards, Richard Harrison, KB5WZI

On Thu, 6 Jan 2005 12:21:25 -0600, (Richard
Harrison) wrote:
On a lucky day, the cloud is discharged without lightning. On an ublucky
day, your lightning rod may get pitted.

Hi Richard,

So much of this breathless science of rounded tips alludes to the
legitimacy of rare publications equal in scope and stature to those
that announced the proofs of cold fusion.

Did Pons and Fleishman turn their hands to designing Lightning
protection systems to redeem their credentials?

73's
Richard Clark, KB7QHC

Richard Clark, KB7QHC wrote:
"So much of this breathless science of rounded tips alludes to the
legitimacy of publications equal in scope to those that announced the
proofs of cold fusion."

Well, I`ll give the rounded tips one advantage, less likely impalements
and resulting lawsuits. But, I don`t know of any such cases on the sharp
lightning rods.

As for cold fusion, I`ll believe it when I see it. I really hope it
happens. The price of fossil fuels and their cleanup is excessive.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote

Jack Painter wrote:
"An awful lot of engineers have accepted the findings already, and
specify blunt-tipped rods on new construction.:

They should specify what works.

Suppose a charged cloud arrives overhead and no lightning immediately
flashes. If the charge is positive, it attracts electrons in the earth
ond other conductors nearby. These electrons strain to reach the cloud,
runnibg through conducting bodies to get closer to the positive charges
overhead. The blanket of air insulates between the charges of opposite
polarity. The field grows faster than these charges are neutralized.
Sooner or later, the air at a high point starts to ionize (form a
conductive plazma). Then, current flow starts with a flash and a bang.
Thunder rolls as air rushes in to fill the void left by burnt
atmosphere.

Suppose that a lightning rod is at a high point beneath the positively
charged cloud as it arrives. Electrons are pulled up to its sharp point
(electrons repel each other, ao they tend to concentrate on the outside
of the rod and find the least outside opposing forces at the tip of the
rod.

To avoid corona formation, some transmitting antennas are fitted with
"corona balls" on their tips. This reduces the strain from a pointed
tip.

On a lucky day, the cloud is discharged without lightning. On an ublucky
day, your lightning rod may get pitted.

Best regards, Richard Harrison, KB5WZI


Hi Richard,

Your example of lightning was the opposite, and very rare, from the normal
occurrence of lightning which is not positive-charged. You can read about
the discovery of this rare form of positive-charged lightning at:
http://www.ee.nmt.edu/~thomas/nyt/ny...lightning.html

As a thunderstorm approaches, preceding its arrival there is a "wave" of
positively charged ions that roll over the landscape like a wave. Buildups
of these positive charged ions do gather on objects, and there is little
favoritism that describes their formation on pointy or rounded objects, they
attach to everything. Upward-flowing streamers are emitted from these
objects as a negatively charged cloud adds its powerful attraction to these
ions. This occurs from human heads, shoulders, lightning rods (of any shape)
and your so-called corona balls that offer no protection from positive-ion
streamer emission whatsoever. I would suggest that in this area, your
recollections of early lightning theory require major updating, since it
seems based in part on radio theory that never applied to lightning in the
first place, however well intentioned many engineers in that field may have
thought it so. Corona balls are examples of the antenna being in the bathtub
and not influencing lightning in the least bit. Some things persist because
people want them too, whether scientific support for them remains or not.
Now, once lightning has broken down and been divided, lessened, etc, then it
begins to take on a shape that fits in the bathtub. Be corona-ball happy
then if you like.

The junk-science of early-streamer-emission (and prevention of sufficient
formation of same to attract a stepped-leader) relies on theories that you
would find can work in the bathtub but have no relevance at all to
lightning, for you see my friend, there are indeed great differences in the
way electricity behaves when it has exponential power behind it. It would
take thousands of Charge-Transfer-Systems (the ESE models) in a single
location to effect a measurable favoritism of attracting or avoiding a
single lightning charge. Yet in the bathtub (which is a very accurate
example of how water does not behave the same as in the ocean) sized
experiments, pointed-tip objects do attract charges. Too bad lightning
doesn't actually behave that way, it would fit those classroom models so
nicely!

A good example of draining a pitifully weak thunderstorm cloud without
experiencing an actual strike, is the St Elmo's fire (and lesser but
physically noticeable yellow air-coloring and even wet skin hair standing
up) that happen on sailboats in a storm. I have experienced the latter
several times, and while lightning struck the water close around, did not
strike the mast by great luck we could say. It was NOT a grounded sail boat
(Morgan, Out Island-41) and the potential from chainplates to waterline
would have been explosive had we been struck. There is no model that I am
aware of in thirty years of reading about this, that explains why a 65'
aluminum (but ungrounded) mast alone on the water in the middle of a
thunderstorm is not struck. And the boat was never struck in countless
exposure to such storms. I add this just to allude to the fact that while we
have learned a lot more about lightning in the last twenty years than we
knew in all of history up to that time, much remains a mystery. I still
find myself out on the water in thunderstorms, and also operate a
communications station without securing during storms, so it is certainly a
field that I have a vested interest in learning more about. I probably
learned more from your brilliant explanations of lightning protection
experience than any fifty other people I have talked with. And although he
lives in a area practically void of lightning, I include Richard Clark in
this category also because he is so well versed in the annals of common
mode, transmission theory, and a very well read liberal indeed. ;-)

In case you're wondering, I have indeed added blunt-tipped lightning rods to
the roofs of my residence. But I am also quite sure that the safety factor
of impalement-avoidance is much more likely than the chances that my roof
will ever be struck, with or without lightning rods. As there are now only
four of the twelve pines which surround my home that have *not* been struck,
somehow the odds seem to be approaching me! Four HF antenna systems are
suspended or attached to three of those "virgin" trees ;-)

73,
Jack Painter
Virginia Beach Virginia

"Richard Clark" wrote

So much of this breathless science of rounded tips alludes to the
legitimacy of rare publications equal in scope and stature to those
that announced the proofs of cold fusion.

Did Pons and Fleishman turn their hands to designing Lightning
protection systems to redeem their credentials?

Interested in your comments *after* you have read the study.
http://lightning-protection-institut...-terminals.pdf

73,
Jack Painter
Virginia Beach, Virginia

On Fri, 7 Jan 2005 01:53:00 -0500, "Jack Painter"
wrote:
Interested in your comments *after* you have read the study.
http://lightning-protection-institut...-terminals.pdf

Hi Jack,

"It is quite obvious from these plots
that the experimentally determined electric field
strength is less than the "simple-minded" V/d value."

Interesting brush-off so early in the paper begs for real editorial
control. As very few would experience lighting sourced from a grid of
wire 5M overhead this paper seems an example of the "laboratory
factor" it set out to examine and yields a paper confined to
laboratory arcana. All fine and well, but what is the point?

"There is an urgent need for detailed theoretical
modelling which can quantify the space charge
effects around air terminals, particularly in
relation to upleader development."

Which seems at odds with your statement:
On Fri, 7 Jan 2005 01:17:07 -0500, "Jack Painter"
wrote:
The junk-science of early-streamer-emission
but I'm not terribly interested. I wasn't particularly intrigued by
Pons and Fleishman either, beyond the hubris of their closet drama.

It would seem some have a desperate need to topple Franklin from a
pedestal of their own building. (Theirs is called the fallacy of
"present mindedness.") I'm satisfied that contemporary Europeans held
him in high esteem for many noble achievements. Reductionists are
measured against their own few of baser metal.

Hope you found that interesting, but I doubt it - rather banal stuff.

73's
Richard Clark, KB7QHC

Jack Painter wrote:

"Richard Clark" wrote

So much of this breathless science of rounded tips alludes to the
legitimacy of rare publications equal in scope and stature to those
that announced the proofs of cold fusion.

Did Pons and Fleishman turn their hands to designing Lightning
protection systems to redeem their credentials?

Interested in your comments *after* you have read the study.
http://lightning-protection-institut...-terminals.pdf

Yes, let's have more technical discussion and less name-calling, please.

There seem to be three observations that need to be understood.

1. The electric field gradient near a sharp point is greater than the
field gradient near a blunt point. This is basic physics and should be
completely beyond dispute. But that is the field gradient IMMEDIATELY
LOCAL to the point... and that's not what lightning protection is about.

The whole point of lightning protection is to make a strike attach
specifically to the installed "terminal' and lightning conductor, and
not to any other part of the structure that the installation is aiming
to protect.

So what we want to know is: when a lightning probe leader (the column of
ionized air coming down from the cloud) approaches the structure, how
does the lightning protection terminal attract it from a distance of
many feet away? How does it say "Hey, come over here"?

2. According to Moore et al (the source of the USA Today story that Jack
quoted earlier) a very high field gradient immediately local to tip may
actually be counter-productive, because it can produce corona discharge
which *reduces* the field gradient at a greater distance; and this may
make the probe leader attach somewhere else where there isn't a corona.

At least, that's my reading of Moore's papers (following the trail of
references from the USA Today page, back to the institute in NM where
Moore and colleagues are based). They have a lightning observatory on
top of a mountain, but there only seem to be three short guyed masts
with a different type of terminal on each. Instruments in a small
underground lab collect the data from lightning strikes.

Going back through the paper trail, they have been operating this
facility for more than 10 years, and occasionally produce a paper to one
of the lightning-related journals accompanied by a press release (the
latest of which was picked up by USA Today). However, lightning only
strikes when it feels like it, so the statistical data only build up
very slowly... and if they change the setup on the mountain-top, they'd
effectively have to start again.

Moore's conjecture that you can make the tip of the terminal *too* sharp
is interesting, but his type of "live lightning" experiment doesn't
provide any specific backup for what he's saying. It only produces the
raw observations that he's trying to explain.

Then there is:
3. The paper that Jack quotes above, which reports experiments in a
large 'lightning lab'. The experimental setup is big enough to
investigate effects over a range of several feet, so controlled lab
experiments could bring us a lot closer to the basic physics.

Unfortunately these particular experiments don't seem to help. Same as
with Moore's work, the experiments are heavily biased towards
commercially available lightning terminals which (rather like TV
antennas) come in a variety of weird and wonderful shapes. The
performance of commercial off-the-shelf terminals may be what the
lightning protection industry wants to hear about, but these complex
shapes (with their faint odor of snake oil) make it impossible to
understand what's happening at a basic level.


So it's still wide open for speculation and experiments. Moore's
conjecture - that you *don't* want a corona discharge, so the optimum
tip radius is the one that produces the highest possible field gradient
but *without* inducing corona - looks attractive, but as yet it doesn't
have much theoretical or laboratory backup.

We have to be missing something here in this discussion. There has to be
a whole range of scientific papers, in much more respectable physics
journals that are far removed from the lightning industry, that we're
not aware of.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek