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Old 04-06-2008, 16:12   #31
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Lightning Diversion Systems - Aircraft Lightning Diversion Strips

Here is a web site that can explain it. The radome(aerodynamics) radar(electronics) and all of the associated systems that could be damaged due to a lightning strike are protected by diverting the lightning, not trying to provide a path through the cabin, to ground. Imagine a metal pole sticking out of a radome with a 4 gauge cable attached to it strung down the center aisle of the plane. That is what all the "experts" are suggesting. You are sitting in the water screaming HIT ME HIT ME.
I'll take my chances trying to divert the lightning when it hits me. I will lose wind, VHF and possibly some running lights but hopefully not much else..
7.25 years until the Carib
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Old 04-06-2008, 17:07   #32
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Originally Posted by easterly View Post
Imagine a metal pole sticking out of a radome with a 4 gauge cable attached to it strung down the center aisle of the plane. That is what all the "experts" are suggesting. You are sitting in the water screaming HIT ME HIT ME.
On a sailboat with a keel stepped metal mast or with a deck stepped metal mast resting on a metal support column there is already a lightning path into the cabin. The purpose of the #4 Ga wire is to ensure that as direct and uninterrupted path as possible exists between the masthead and seawater ground. This is much better then letting the mast rise to tens of thousands of volts relative to other metal object in the cabin or to the surrounding seawater. This rise in potential would most likely result in a flashover event that could injure someone or blow a hole in the hull. The goal is to ensure that flashover events don't occur by keeping all metal objects at the same electrical potential. And to do this it is necessary to bond every metal object together.

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Old 04-06-2008, 22:53   #33
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Let's make some sense here

Viking (and others) has it correct (IMO).

A fiberglass/wood/ferro boat has a big metal pole sticking up 30 to 60 feet in the air that if hit by lightning will try to conduct the charge to the sea water. Unfortunately the hull/decks/cabin of the boat trys to prevent this from happening. Usually the lightning wins and the hull/deck/cabin looses - so we try to protect the vessel by providing low resistance, high current carrying paths from the metal mast to the sea water (ie. the 4 GA wire etc).

How effective this is depends on the methods used and the size of the charge we are trying to conduct i.e. the number of joules contained in the lightning strike.

By the way, I fail to see how adding a 2 foot metal rod (with sharpened or rounded ends) on top of say a 40 foot metal mast will change the electrical aspects of the lightning discharge circuit. Of course it is different if the mast is timber!

Aircraft strikes are quite different except to say they are also very unpredicable. I have inspected at least a dozen aircraft after in flight lightning hits. Usually the damage is minor (but not always). Usually there is an obvious entry and exit point - burnt paint, holes in the airframe, propeller tips badly burnt, scorch marks etc. The avionics are usually (but not always) safe due to good shielding on wiring, bonding, farraday effect of airframe and general HIRF (high intensity RF) protection measures. Radomes are sometimes hit but not nearly as often as the rest of the airframe -due I guess to the lower resistance paths available by the airframe - but as is often noted, lightning is unpredicatable in where it strikes.

The LDS systems mentioned by Easterly have a place (and work to a degree) on radomes and other non-conductive airframe surfaces but they are NOT the whole answer and can't be transposed to other structures and be expected to work exactly the same. I think there is also a bit of spin associated with them but I might be wrong about that; however they certainly very effective in bleeding off "P" static build up which is a big problem with radomes.

The static wicks are solely provided to bleed off static build up on the airframe (especially precipitation static). If they weren't fitted, the charge on the airframe would build up until the charge is large enough to arc off to the surrrounding air (just like a mini lighting arc). They work by providing a high resistance path from the areas on the airframe where the static charge collects (usually the pointy bits of the trailing edges). The base on the static wick is bonded to the airframe with a resistance of less than 10 milliohms, while the resistance of the wick (i.e. the discharge end) is usually between 50 and 200 kilohms. Pull the static wicks off, fly through some wet cloud and the whole airframe becomes a mini platform of mini arcs and St Elmo's fire!

Best on water lightning protection in my mind is a steel boat with a metal mast - engage wind vane, go below, disconnect all antennas from radios and wiring to electronic systems, have a drink and enjoy the storm

My 2 cents worth.
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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