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Author Topic: Lightning strike  (Read 495 times)

sevenlayermuddle

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Lightning strike
« on: April 29, 2017, 11:43:30 PM »

Walking in countryside near a small regional airport the other day, I watched as a small but bulky looking transport aircraft (military?) overflew then turned, preparing to land, I assumed.  Weather was good, the odd rain shower, but otherwise calm, certainly not thundery.

Suddenly and with no warning I saw a single bolt of lightning from a raincloud strike the aircraft, pass through it, and strike to ground.   I exclaimed to my walking companions "he's been hit by lightning".   They'd not seen it and looked unconvinced until, a moment later, a loud thunderclap convinced them. :D

There were no further lightning strikes on my walk and unsurprisingly, the plane seemed oblivous to the strike.  Not entirely sure though, why the presence of an aircraft should provoke a lightning strike when not in an actual thunderstorm?   :-\
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burakkucat

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Re: Lightning strike
« Reply #1 on: April 29, 2017, 11:53:57 PM »

Think of the cloud and the ground as two plates of a charged capacitor, with air as the dielectric.

Now insert a metal object, the aeroplane, into that dielectric.

I suggest that the one charged capacitor has now been converted into two capacitors, connected in series. And those two charged capacitors, at the moment that they are formed, each have a smaller breakdown voltage than the one charged capacitor which was their origin.

The end result is the breakdown, a flash-over, of each of those two series connected capacitors. The lightning bolt.
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sevenlayermuddle

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Re: Lightning strike
« Reply #2 on: April 30, 2017, 12:04:17 AM »

You may well be right.

My recollection of detail is obviously vague, having had only a fraction of a second to take it in.   But I am fairly sure that the upper (cloud to aircaft) spark looked similar in length to the lower (aircraft to ground) spark.  That might well be consistent with your theory?
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burakkucat

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Re: Lightning strike
« Reply #3 on: April 30, 2017, 12:09:33 AM »

One other fact that I failed to "throw into the pot" is that the exhaust of the aircraft's engines will either be slightly ionised or composed of gases that are more easily ionised than the bulk, surrounding, air . . .  :-\
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JGO

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Re: Lightning strike
« Reply #4 on: April 30, 2017, 11:04:18 AM »

Another factor is that with the aircraft present, it is no longer a case of  two charged flat(ish) plates. A sharp bend in the aircraft structure, say rudder,  would reduce the breakdown voltage and maybe start things off.
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tickmike

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Re: Lightning strike
« Reply #5 on: April 30, 2017, 02:49:20 PM »

bolt of lightning from a raincloud strike the aircraft, pass through it.
The electrical charge travels along the outside of the metal of the plane not though it.
Many planes are struck each day with no effect.
The plane = a portable 'Faraday Cage' .
None metallic planes could be a problem  .

In the electrical research department where I once worked we had an High Voltage lab that we could make our own lightning to test insulators.
I have watched some great electrical discharges and some of the odd things the discharge path can take .  ;D

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sevenlayermuddle

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Re: Lightning strike
« Reply #6 on: April 30, 2017, 03:17:51 PM »

I was aware of the theory that metal bodied aircraft are safe from lighthing but must admit, seeing it right in front of me, spectacular as it was, it was hard not to expect the worst just for a fleeting moment.    :o

There was of course, no apparent ill effects.   In fact I'd be interested to know if the crew even noticed it, I suspect maybe not.  Since it was on a landing approach I assume ground staff probably saw it too, so would have probably mentioned it at some point.
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