Imagine getting one of those through your headsetdemon wrote:... i was getting electric shocks through the headset and my hands on the bar.....
Lightning Strike !
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Oddball
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Ectually, what Demon describes is probalbly not St. Elmos fire; this is normally a glow rather than sparks and is caused by ionisation of the air around grounded objects.
Just because it is an aircraft does not mean that it is not grounded, by the way, when considering what grounding actually is... though this may take a while to explain...
What most likely happened was that a nearby strike caused a strong atmospheric electric field in the surrounding area. As this interacts with objects, such as the trike, different parts of the trike have different voltages induced in them. The wing tip closest to the field may have 20 000V induced and the other end maybe 15 000V (yes, that much). Now you have a potential difference (PD) of 5 000V between these two points and this will cause a current to flow. Where the impedance (sort of like resistance) between parts (flying wire to bar) is high there will be a high potential difference again and sparks jump over the high impedance path- which is what Demon saw.
So how can Demon, or anyone else caught in this situation, not be shocked so badly as to be injured? The answer is that you are most likely fairly insulated from the frame and your point of connection is your hands. Since the distance between the hands is small the PD is small, hence the current flow is small. Also, since you are 'earthed' to the structure via your hands you are generally at the same potential as the structure, which your body can handle. Its potential difference, and the resultant current flow that is the problem.
In the engine the whole engine voltage increases to 20 000V or whatever, but the relative PD between the parts that require PD to work stays the same. Viz. a spark plug may require a PD of 15 000V between its points to create the spark. Now the live part is at 35 000V and the 'earthed' part is at 20 000V =>PD is still 15 000V.
This is why the larger aircraft deal with strikes quite well; everything should be 'bonded' to everything else, forming a 'ground' plane, which you can now see is simply a conductive network that is all at the same potential. 'Live' voltages are positive or negative with respect to this plane. This is why bonding all the metal parts of aircraft is important- so that you do not introduce unwanted potential differences. And incidently why lightning protection on composites is a problem.
The other reason that cylindrical metal aircaft handle lightning strikes well is that they form a Faraday cage (same reason why a car is safe in a thunderstorm- well, as long as you stay in the car and the car doesn't hit anything else... :D ). Faraday discovered that high frequency currents (which is what lightning is) tend to travel around the outside of a conductor. When the current is presented with a cage it travels around the outside of it, and you are safe inside.
Just because it is an aircraft does not mean that it is not grounded, by the way, when considering what grounding actually is... though this may take a while to explain...
What most likely happened was that a nearby strike caused a strong atmospheric electric field in the surrounding area. As this interacts with objects, such as the trike, different parts of the trike have different voltages induced in them. The wing tip closest to the field may have 20 000V induced and the other end maybe 15 000V (yes, that much). Now you have a potential difference (PD) of 5 000V between these two points and this will cause a current to flow. Where the impedance (sort of like resistance) between parts (flying wire to bar) is high there will be a high potential difference again and sparks jump over the high impedance path- which is what Demon saw.
So how can Demon, or anyone else caught in this situation, not be shocked so badly as to be injured? The answer is that you are most likely fairly insulated from the frame and your point of connection is your hands. Since the distance between the hands is small the PD is small, hence the current flow is small. Also, since you are 'earthed' to the structure via your hands you are generally at the same potential as the structure, which your body can handle. Its potential difference, and the resultant current flow that is the problem.
In the engine the whole engine voltage increases to 20 000V or whatever, but the relative PD between the parts that require PD to work stays the same. Viz. a spark plug may require a PD of 15 000V between its points to create the spark. Now the live part is at 35 000V and the 'earthed' part is at 20 000V =>PD is still 15 000V.
This is why the larger aircraft deal with strikes quite well; everything should be 'bonded' to everything else, forming a 'ground' plane, which you can now see is simply a conductive network that is all at the same potential. 'Live' voltages are positive or negative with respect to this plane. This is why bonding all the metal parts of aircraft is important- so that you do not introduce unwanted potential differences. And incidently why lightning protection on composites is a problem.
The other reason that cylindrical metal aircaft handle lightning strikes well is that they form a Faraday cage (same reason why a car is safe in a thunderstorm- well, as long as you stay in the car and the car doesn't hit anything else... :D ). Faraday discovered that high frequency currents (which is what lightning is) tend to travel around the outside of a conductor. When the current is presented with a cage it travels around the outside of it, and you are safe inside.
A lone impulse of delight drove to this tumult in the skies...
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Oddball
- Solo cross country
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- Joined: Wed Jul 27, 2005 4:17 pm
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The answer is: it depends :D
It depends on the strength of the field 'driving' the lightning strike, but we are talking of distances up to 100-200m possibly.
It is also likely that you may be struck directly and not even know it; the strike will use you as a convenient conductive path going straight through you/ the aircraft structure. You may not not notice this, in terms of a shock, as most of the current will travel through the more conductive metal structure. But you will certainly notice the audio and visual effects! It will most likely also weld or melt parts of the airframe, and, depending on where that happens, you may suddenly be doing a lot more noticing...
Sorry that I took a while to reply- for some reason I did not get the subject reply email...
It depends on the strength of the field 'driving' the lightning strike, but we are talking of distances up to 100-200m possibly.
It is also likely that you may be struck directly and not even know it; the strike will use you as a convenient conductive path going straight through you/ the aircraft structure. You may not not notice this, in terms of a shock, as most of the current will travel through the more conductive metal structure. But you will certainly notice the audio and visual effects! It will most likely also weld or melt parts of the airframe, and, depending on where that happens, you may suddenly be doing a lot more noticing...
Sorry that I took a while to reply- for some reason I did not get the subject reply email...
A lone impulse of delight drove to this tumult in the skies...
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