St. Elmo's Fire

[emerydc8]

This might be an interesting feature to model in PSX if it's not too difficult. Sorry about the bumps. We were getting thrown around pretty good.

https://www.youtube.com/watch?v=PXRTA1OqUNQ

[cagarini]

Great!

Thx for sharing!

[Britjet]

Actually, (and I know I will take flak for this) that isn't quite the same thing as St Elmo's fire, although it seems to have drifted into common use.
Historically it was seen on anything pointed that was in a static environment, like church steeples, or telegraph poles. I believe it was seen on early sailing ships in the rigging in storms.
The static on the windshield is often seen and a product of the plastic and metallic elements in the windscreen coating, but it's certainly a pretty, if slightly unnerving sight.
I have only seen the "real" thing n a very few occasions. On one occasion it looked as though we had a light in the nose - with a ghostly light spreading out many yards ahead of the aircraft, and I have also seen it at the front of the engine intakes on one occasion.
Nice video!
Peter.

[emerydc8]

Thanks, Peter. I didn't know what else to call it. I've always thought it was some sort of electrical discharge generated by the moisture passing over the windshield. We were in icing conditions at the time. Are you suggesting that the lightening-type discharge is actually occurring inside the glass as opposed to occurring on the outer surface? If so, I'm glad I posted this because I learned something too.

[Britjet]

I'm not sure where it discharges. Maybe between the layers of glass. You can't "lead" it down with your fingers as you probably know...it's still static of some sort so there must be some sort of external interaction..
Peter.

[emerydc8]

It would have been interesting to see what the discharge wicks were doing at the time (if anything).

[torrence]

Fascinating stuff - thanks for posting video.  Atmospheric electrical phenomena have been studied since at least the time of Ben Franklin and it's still a complex and evolving scientific field (the American Geophysical Union has a special section just devoted this discipline!).  I'm no expert in this area myself but I think Peter is basically right that what's shown in the video is due to charge build-up in the glass-laminate layers discharging internally to the metallic framework.  The nose and engine intake glows mentioned may be related effects influenced by shocks in the air flow.

Cheers,
Torrence

Addition:  I'll have to see if I can show this to some of the guys at the lab who do material testing on spacecraft cables etc.  - they also do public education shows with things like huge Tesla coils (very impressive on a dark night).
T

[United744]

It's on the outside of the aircraft, at the interface between the oncoming air and aircraft skin surface. If you could step outside, it extends over the aircraft skin, as well as the windows, but you can only see it at the windows because they're unable to discharge via the static wicks, so they eventually discharge onto the window when the potential is great enough.

The aircraft skin is designed to dissipate the static electricity around the fuselage rather than conduct it, so it doesn't build and start arcing.

If you could see the electric field around the wicks at the time, it would look like a stream of smoke.

It occurs because the aircraft flying through the air acts like a huge flying vandagraph machine. The light you see is actually plasma discharge.

If you listen to the radios, you can sometimes hear it, too.   It sounds like a ringing sound. On HF you'll probably hear it as increased static.

[torrence]

Thanks for the detailed explanation.  I had assumed the diffuse outside glows were plasma phenomena of some sort, but wasn't sure what caused the more intense window discharges.

Cheers
Torrence

[emerydc8]

Thanks to all for the explanations.

[DougSnow]

This reminded me of the part in Bob Buck's "North Star Over my Shoulder", where he flew a modified B17 during WWII to research static discharges.

Great book!

[Hardy Heinlin]

Which parameters and what values need to be used to enable this (randomized) effect?

We have:

OAT on ground
OAT at aircraft
TAT
flight deck internal temperature
windshield heat on/off
in-cloud yes/no
below-cloud yes/no
above-cloud yes/no
between-clouds yes/no
aircraft altitude
icing status wings
icing status nacelles
IAS
EAS
TAS
lat/lon
etc.


|-|

[emerydc8]

Hi Hardy,

I don't see this too often, so I'm not sure what the optimum conditions would be for it. If you look at the radar, we were paralleling a line of weather about 30 miles to the west -- Not super-strong weather, but with a lot of moisture. The winds aloft were pretty strong. I think I see 300/95 and probably blowing a lot of that moisture in our direction. We were at M.76 and FL330. I don't remember the temperature but we had nacelle A/I on so we were definitely below +10 TAT. We were not in the "clouds" but there was definitely visible moisture and I think the temperature was well above ISA. I don't normally use wing A/I unless I do so per the CF6 AD (ice crystal icing), requiring the wings to be on if in icing conditions (even below -40SAT) when at FL220 or below.

I took the video on 11/3 at about 0500Z, between KDFW and KCVG. As you can see from the ND, we were approaching PXV. Maybe there's a way to go back to the weather charts for that period and get the data. I don't know.
Jon

[cagarini]

Another interesting thread on the same theme, and a nice conclusion at the end ( last post ).

http://www.airliners.net/forum/viewtopic.php?t=737177

[emerydc8]

Everyone concludes in that string that it is St. Elmo's fire. I think Peter is technically right here -- It's really not St. Elmo's, but easily and commonly mischaracterized as such. So what do we call it? Plasma?

[torrence]

Which parameters and what values need to be used to enable this (randomized) effect?

Given the comments and the various links, Hardy, you might be able to model this relatively realistically by just associating the window electrical display with the existing weather model.  Here's one possible list for a WXR page setting:

Static discharge on aircraft ("St. Elmo's Fire") possible [y/n]
Required conditions
    Thunderstorm activity in the vicinity
     Between cloud layers with visible moisture
Probability of occurrence (similar to other items like go around or holding probabilities - randomized)
     Low
    Medium
     High (for demo purposes)

I think that covers most of the characteristics of what pilots report.  I've only experienced one 'event' as a passenger.  We were descending to land at LAX going through turbulence and clouds with lighting flashes in the vicinity when there was loud BANG and a bright light outside the left windows.  I thought initially of some engine problem, but - after a long 10 secs or so, the pilot came on the speaker and said there was no problem, but we had had a 'static discharge' off the nose of the aircraft.  I don't know exactly what it looked like in the cockpit, but they sounded impressed. [Note added:  This may have been in the category of a lightning strike for all I know - wasn't able to inspect the aircraft after landing.]

Cheers,
Torrence

Note - I'm of the school that thinks that the existing weather model/radar/native scenery is already very realistic and immersive.  There's enough complexity and randomly varying parameters the overall effect is quite convincing (leaving aside debates about how you can set it to reproduce 'exactly' what you see outside your window for a given METAR report)
T



       

[Hardy Heinlin]

Thank you, Torrence.

I'd like to make this effect completely automatic, i.e. not user controlled by additional switches on the WX page. So the main parameters, as you're suggesting, are:

• Thunderstorm activity in the vicinity
• Between cloud layers with visible moisture

(I wouldn't call it "St. Elmo's Fire".)

Unfortunately, I'm now seeing a cosmetic problem: When thunderstorms are in the vicinity, PSX already simulates bright random zigzag lines on the windshield, appearing for just a fraction of a second. Now, if I add such windshield discharging effects like in the video, they will look very similar to regular lightning lines (like reversed tree branches), and within these fractions of a second the PSX users won't notice the difference between regular lightning effects and windshield discharging effects. So I fear my idea to implement this effect is not worth the effort ... I'm not sure yet ...


Cheers,

|-|ardy

[Holger Wende]

Hmmm, not being an expert here and being aware that PSX is primarily a trainer:

Thunderstorm in the vicinity:
Shouldn't this be rather very diffuse "flashes", i.e. the whole coulds illuminate for a fraction of a second.
E.g. like a more intense "flashing landing light" while being within the clouds.

Windshield dischgarge/St Elmo's fire:
From the videos this appears to be more sharp-edged tree-like "flashes".

Also colour could be used to differentiate between real "lighning in the vicinity" and "windhield discharges".

I was always wondering when to use the storm lights.
Are we discussing training scenarios for when to use storm lights in this thread?

Just some amateur thoughts.

Regards, Holger

[Jeroen Hoppenbrouwers]

Holy Heinlin fire  :-)

[Hardy Heinlin]

(I'm not holy, I'm evil.)


These are still just nuances, Holger. But I think lightning in PSX is only visible when you are below the clouds (unless it's lightning caused by volcanic ash). That's a good point. The plasma effects may then only be visible when you are at high altitudes.


Regards,

|-|ardy