Most slow airplanes do not have static discharge wicks, but
in the correct conditions, they can build static which can
build to very high voltages. It is also possible that the
grounds [bonding] between components is not good and that
can lead to arcing across hinges and between ailerons and
wing, etc.

Snow and ice crystals cause the build up, the fix is proper
bonding and static wicks, even on a C172.


"gman" wrote in message
ups.com...
| 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).
|