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#11
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Static Discharge
Morgans wrote:
toecutter wrote Hawker 800's have plastic windscreens and a marginal ground path. BTW, you're usually standing on a stepladder when you get poked... You might need to explain that one, a little more. What are you doing up around a windshield at altitude on a stepladder? g Holding on for dear life! TheSmokingGnu |
#12
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Static Discharge
"Morgans" wrote:
toecutter wrote Hawker 800's have plastic windscreens and a marginal ground path. Think about cold, dry air at altitude. They will indeed light you up if you aren't careful. Snap, Crackle and Pop. BTW, you're usually standing on a stepladder when you get poked... You might need to explain that one, a little more. What are you doing up around a windshield at altitude on a stepladder? g He must be one of these people: http://www.youtube.com/watch?v=wBm8I5JRNlw ;-) |
#13
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Static Discharge
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 |
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