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  #21  
Old 07-08-2011, 03:57 PM
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Isolated ground rods are actually pretty crappy low resistance grounds in a ton of situations....
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  #22  
Old 07-08-2011, 04:42 PM
xblueh2o xblueh2o is offline
 
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I was cruising down the Q routes between LA and FL one night in clear smooth air at 450 on top of a pretty good set of storms when we got nailed by lightning coming up from below. No obvious damage or issues as a result but we took the airplane to the manufacturer in KSAV for a lightning strike inspection. They found the entry and exit holes in the lower radome and top of the tail respectively. After repairing these small holes, checking all the filters etc we were on our way. I don't recall the interval or duration but for a period after that we did follow up filter checks at home for a while in accordance with the maintenance manual.
Fixing the obvious might not be your only damage. Look everything over very carefully and monitor your filters for a while.
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  #23  
Old 07-08-2011, 06:30 PM
mfshook62 mfshook62 is offline
 
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Default Entry or Exit Wound

Lightning usually starts on the ground and sends a streamer up into the atmosphere, so the melted metal on the VS most likely is an exit rather than an entry wound. There may be more damage where ever the plane came into close contact with the ground.
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  #24  
Old 07-08-2011, 08:57 PM
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http://wiki.answers.com/Q/Why_does_l..._a_jagged_path

As I recall there are more things that come into consideration with high voltage/low current discharges (ionization) which makes it not behave like a typical parallel circuit.

As a side note, aircraft plugs don't fire off of both electrodes no matter how closely matched they are.
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  #25  
Old 07-09-2011, 12:28 PM
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Wheel bearings can also suffer damage from a lightning strike. If a lightning bolt has just cruised thru 10,000 feet or more of the atmosphere, that couple inches of rubber tire does not make diddly squat of an insulator to stop it from going all the way down thru the landing gear.
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  #26  
Old 07-09-2011, 12:41 PM
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pierre smith pierre smith is offline
 
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Default Now that I think about it..

Quote:
Originally Posted by mfshook62 View Post
....Lightning usually starts on the ground and sends a streamer up into the clouds, so the melted metal on the VS most likely is an exit rather than an entry wound. .
I should have realized that lightning starts from the ground, since it's the negative pole, so the tiedowns (Roee) were the path of least resistance for starters, travelling upwards to the positive sky, exiting the highest of the three prop blades, in this case.

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  #27  
Old 07-09-2011, 03:04 PM
tikicarver tikicarver is offline
 
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Lightning can travel from ground to cloud or it can go the other way.
(negative lightning or positive lightning)

read the wikipedia page about lightning, you will see that it is more complex then a big spark from the sky.

bottom line is a large current flowed through the plane. even if you find the exit point you still don't know what it flowed through. lucky most of the time in a metal airplane the current flows in the skin, that is why an airliner can get hit and nothing happens on the inside.
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  #28  
Old 07-10-2011, 07:45 AM
Lupin Lupin is offline
 
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Interesting discussion.

I work as an aircraft maintenance engineer for a Canadian airline and I get to see aircraft that were hit by lightening almost every month. On Airliners, everything is bonded via bonding cables in order to dissipate static electricity and to give an easy alternate path to any static electricity that might otherwise travel through bearings.

Rarely do we ever find large damage. Usually an entry point is found with an exit point and in the worst cases, the electricity dances in and out along the fuselage giving us multiple entry and exit points. It is usually a matter of replacing a few rivets when damage is found but most strikes cause no harm at all due to the designs of the aircrafts.

?ric
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  #29  
Old 07-10-2011, 02:05 PM
Daniel Hooper Daniel Hooper is offline
 
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Quote:
Originally Posted by John Clark View Post
Some years ago we had a C-150 sustain a lightning strike on the rudder. The rudder was "welded" in position, stuck. Safe landing, but a tough thing to taxi.
Quote:
On Airliners, everything is bonded via bonding cables in order to dissipate static electricity and to give an easy alternate path to any static electricity that might otherwise travel through bearings.
Aha! I always wondered about the true purpose of the bonding braids on control surfaces!
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  #30  
Old 07-10-2011, 04:32 PM
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pierre smith pierre smith is offline
 
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Default We used bonding braids.

Years ago, when we dusted with sulphur, we had to bond our control surfaces to reduce static electricity generated by the ailerons, elevators and rudder, as the air flowed over them. There were reports of airplanes catching on fire as the sulphur fire followed the airplane in the field, all the way to the hopper

The hinges often didn't/don't provide a good current path because of paint, nylon bushings in Heim joints and so on.

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