On Mar 23, 8:48 pm, "gman" wrote:
Hi Folks,
Here's an interesting phenomenon I observed recently and I was
wondering if anybody else has seen anything like it.

About two weekends ago, I was doing a cross country in actual (IMC)
with one of my Instrument Rating students near Cheyenne, WY. We were
at 11,000ft for a while and the temperature was near freezing but
there was no precipitation in the area. All of a sudden, there was a
sound like a pebble hitting the windshield. I explained to my student
that it was either an isolated hail pebble or ice coming off the
propeller. About ten minutes later, I heard the same sound but this
time it sounded more like an electric discharge similar to the one you
hear when you touch the door knob after walking on the carpet. I
rechecked the fuses and the alternator but everything was working
fine. The sound was definitely coming from the outside. Then about
five minutes later, we heard the same sound. But this time, I was
trying to read the mag compass which is mounted up high on the
windshield. I'm pretty sure that I saw a flash of light this time near
the top center of the windshield where the Plexiglas meets the
aluminum . This made me wonder: When flying in IMC over an extended
geographic area (Cheyenne to West of Denver) is it possible for the
airplane to start discharging by arcing? Has anybody else seen
something similar to this? I should mention that the winds were not
especially fast that day (about 160 @ 30kts).

Don't know what the wind would have to do with it, unless you were on
a boat and getting it.
St Elmo's fire , it's called, and it even built up on ships masts (I'm
sure it still does) but it's very common on airplanes. With a plexi
windshield, you can draw the littl elightning bolts into the cockpit
with the tip of a graphite pencil! But it's not supposed to be good
for your windshield, though! In jets we get it all the time. It can be
little lightning bolts across your windscreens (pencil trick doesn't
work through that much glass) and you can also get long fingers of a
dull plasma-like glow coming from the wipers and other bits or even a
long (maybe 20 foot long) cone of light built up on the nose,
depending on conditions. If there's CB around, you're quite likely to
get a lightning strike as well. I don't know if the fire makes you
more atractive to lightning or it's just co-incidental, but I've been
hit about a dozen times and had St Elmo along for a few minutes just
before we got smacked. Not to say it's common to get hit by lightning,
BTW. But it's unusual to go for more than a month's flying without
seeing St Elmo's fire at least once or twice in that period. Gotta be
wet, of course..!


Bertie