bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

Static Discharge Visible On The Windscreen?

Thu Nov 20, 2003 11:55 am

Hi everyone. I was lucky enough to visit the flightdeck while inflight on an MD-83 of my national carrier. It was during night time, and I saw a wonderful purple set of waving flashes along the center window frame. It looked just like the small dancing lightings seen on those metal spheres surrounded by a much larger crystal sphere. The pilot was the one that got me out of my perplexness and told me they were generated by the friction with the air. Has anyone seen this?

It got me thinking, why is this static not discharged by the static wicks on the wingtips? And one other thing, is this seen on other aircraft other than the DC9/MD80/90/717 series? I refer to these because they have a center window frame that strikes the air more directly than the others and probably that is why I only saw it on the center frame. Thanks in advance

-Alfredo
 
MxCtrlr
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Joined: Tue Nov 13, 2001 11:22 am

RE: Static Discharge Visible On The Windscreen?

Thu Nov 20, 2003 12:29 pm

That is more commonly referred to as "St. Elmo's Fire" and happens quite frequently (especially in clouds and storms). The static wicks can only dissipate so much static at one time so you see this on occasion. It's really quite harmless.

MxCtrlr  Smile/happy/getting dizzy
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goboeing
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Joined: Mon Jun 05, 2000 5:31 am

RE: Static Discharge Visible On The Windscreen?

Thu Nov 20, 2003 12:34 pm

Here is a good picture of St. Elmo's Fire:

View Large View Medium
Click here for bigger photo!

Photo © Jake



It's probably what you saw so that's why I put that picture up. I've never seen it, but the basic description I know is that it's an electrical discharge and usually occurs during thunderstorms. That must have been exciting to see!

Nick
 
CX Flyboy
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Joined: Sun Dec 26, 1999 6:10 pm

RE: Static Discharge Visible On The Windscreen?

Thu Nov 20, 2003 12:59 pm

It looks like those glass spheres you get in the novelty shops with the static discharge against tha glass. I see it every few months, but instead of being a continuous streak, it comes in flashes against the cockpit windscreen and is completely harmless.
 
broke
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Joined: Wed Apr 24, 2002 8:04 pm

RE: Static Discharge Visible On The Windscreen?

Thu Nov 20, 2003 10:14 pm

I've have the opportunity to see St. Elmo's Fire on the windshield twice, both times I was riding the jump seat on an airliner.
The first time (727-200), I was a little startled and asked the crew if that was St. Elmo's Fire and they said it was.
The second time was a little more humourous, I was on a DC-9 and I guess St. Elmo's Fire was something new to the F/O. He almost came out of his seat and would have had to climb over me to get out of the cockpit. The captain and I shared some grins. It's fun to be able to share an inside joke.
 
EALBuff
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Joined: Sun Jun 16, 2002 7:54 am

RE: Static Discharge Visible On The Windscreen?

Fri Nov 21, 2003 2:45 am

I've seen it several times over the years flying as crewmember in Navy P-3's. Typically, it occurs when flying in the vicinity of thunderstorms, in air that is colder and drier than normal. It can be quite spectacular, covering the nearly all of the cockpit windows. Even the props show signs of it, mostly around the spinners. Also, I heard of several stories where it got so bad that it formed a ball of static electricity that went through the window and entered the airplane. It then harmlessly floated down the cabin, either dissipating or exiting the rear of the aircraft.
 
bio15
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: Static Discharge Visible On The Windscreen?

Fri Nov 21, 2003 5:52 am

Thanks for the responses. The picture shows exactly what I saw, good to learn it's nickname  Smile Now that you mention it, I do recall seeing lighting around us so we were close to thunderstorms.

Funny story about the FO who hadn't seen it before. It must be creepy to se such thing in your aircraft when you think you've seen it all!

Good Luck
-Alfredo
 
mlsrar
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Joined: Thu Mar 09, 2000 7:41 am

RE: Static Discharge Visible On The Windscreen?

Fri Nov 21, 2003 7:30 am

It then harmlessly floated down the cabin, either dissipating or exiting the rear of the aircraft.

It floated? Wouldn't it move rather quickly? (Forgive me, as I know nothing of the dynamics of static electricity, though I figured it would have moved quite quickly)
I mean, for the right price I’ll fight a lion. - Mike Tyson
 
EALBuff
Posts: 27
Joined: Sun Jun 16, 2002 7:54 am

RE: Static Discharge Visible On The Windscreen?

Fri Nov 21, 2003 9:00 am

Mlsrar, Sorry I can't further define 'quickly', I can only presume it was an event that was over in less than minute. First time I heard this story, I was skeptical, thinking it was some kind of aviation folklore. But over the years, I heard similar stories from several sources, so while I am also no static electricity expert, I've come to believe this is a rare, but possible phenomenon.
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Static Discharge Visible On The Windscreen?

Fri Nov 21, 2003 1:17 pm

Electrical bonding and static wicks are designed to handle the static charges generated by any amount of buildup on the airframe. Unfortunately, the static wicks can't do their jobs if bonding of the airframe is compromised.

This phenomenom is typically limited to structures that aren't properly bonded. Glass is an excellent insulator and special procedures are required to maintain a conductive coating on the glass. The windscreen often gets neglected.

Some composite structures suffer the same types of discharges. Unfortunately, it damages composite material by creating microscopic damage. Glass doesn't usually get damaged.

[Edited 2003-11-21 05:20:15]
 
musang
Posts: 788
Joined: Sun Apr 08, 2001 4:11 am

Static Discharge

Fri Nov 21, 2003 11:36 pm

First time I saw it was in a Cessna 208 Caravan, and the Captain told me to put my finger close to the windshield so as to conduct it. The pink sparks jumped to my nervous finger from about three inches range.

Much later, we've seen it in ATRs and Avro RJs, where it was white. Maybe the composition of the transparencies affects the colour?

Regards - Musang
 
Vimanav
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Joined: Thu Jul 31, 2003 4:33 am

RE: Static Discharge Visible On The Windscreen?

Sun Nov 23, 2003 6:27 pm

St. Elmo's Fire is named after St. Elmo - the patron saint of sailors. It usually appeared around mast heads of ships during the fag end of a thunderstorm and was taken to indicate the coming of good weather and hence a good omen.

St. Elmo's Fire is caused by the air immediately above the point of discharge being excited by the electricity, St. Elmo's Fire is actually a kind of plasma. Plasma is a fourth state of matter, where the atoms of the gas are stripped of their electrons, creating a distinctive glow of certain precise wavelengths, and being able to conduct electricity to some extent. Since air is a very good insulator, a massive potential difference is required to start St. Elmo's Fire, which explains why the phenomenon is most commonly observed during thunderstorms. Sometimes, crackling and hissing sounds occur. St. Elmo's Fire can also cause radio disturbances.

They are spectacular and harmless.

rgds//Vimanav
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