Electricity question - helicopter rescue ???

[Conase]

I don't know another group to post to and have gotten answers on questions here in the past.

I was watch Electricity follows down the cable and as you get near the water you start grounding out and the shock hits you and feels like "twice the strength of sticking your finger in a light socket".

NEVER HEARD OF THIS !

Where is the electricity coming from ? Static from a cable going down a pulley ? If true, why can't they put some kind of INSULATOR between the hook and the cable ? Construction workers experience cranes and cables on pulleys everyday with no problem AFAIK. Where is the electricity coming from ?

We always see these rescues on TV, and no rescuer looks like s/he is shocked at

240 volts.

TIA

[Joseph Meehan]

Static. Rather high voltage and difficult to overcome with an insulator large enough to stop it and still suitable for the use. It would also likely require a grounding of the line to the local earth prior to pickup, not always possible.

Personally I think the description "twice the strength of sticking your finger in a light socket" was poorly chosen at best.

[David Martel]

Conase,

The cables and cranes used in construction are usually attached to the earth so if static electric charges are deposited on them by passing clouds et c. the electricity will flow to the ground. Air craft, on the other hand are not connected to the ground during flight. Static charges built up during flight will be discharged via the rescue cable as it nears the ground. If you are standing on the ground and reach for a cable that has not yet touched the ground the static electricity will discharge through you.

Dave M.

[m Ransley]

The electricity comes from the rotors developing a static charge it can be very high, the larger the blades , larger helicopters, and proper weather conditions can knock someone over . IR [i beleive] photography at night will show it visibly. Electricity could jump an insulator as well its strength would be a problem.

[Chris]

If you would like to see Hollywood's interpretation of this phenomenon; rent "The Hunt for Red October". In a scene, the character Jack Ryan (Alec Baldwin) is transferred from a carrier to a submarine. Due to the choppy water, a boat transfer was not advised, so they dropped him on the sub via helo. The seaman on the sub has an insulated shepherd's crook to catch their "electrically charged" passenger.

Not sure how accurate the scene is; but it is based on real facts/experience.

Chris

[R. Doornbosch]

Use to have the same problem when sand blasting, the new guys would often grab a plastic 5 gallon bucket, put a bunch of small pieces of metal in it and start blasting, they usually discovered very quickly that when the metal head from their blast hose got to close to the bucket and grounded it they would get knocked on their @$$ and we would hear a loud bang. If your smart you only did it once. Never under estimate static electricity.

[Eric Tonks]

I have a large deck surface covered with a composite (plastic) material. Walking across this generates static electricity. You often get a shock when you grab the door knob in the metal door, even though the door has no direct grounding. Static can be generated in many ways. Even dirt and air being sucked through a plastic vacuum hose will create a shock.

[m Ransley]

With the right weather and a big chopper death could result.

[m Ransley]

Taking a vacume cleaner to sensitive electronics can deliver a fatal blow to your unit, car fires are started at gas pumps from static electricity. Unloading a pickup with bed liner loaded with equipment can give a jolt.

[John‰]                      Â]

All aircraft generate large amounts of static electricity; it's caused by friction of the air moving over the wings and other surfaces. If you check the trailing edges of commercial airliners, you will see what look like small antennas or small ropes attached that allow these charges to dissipate. Helicopters are huge static generators; the larger the helicopter, the larger the charge. Cranes don't move through the air at high speed and hence to not build up a static charge.

Having been plucked from the ocean by Coast Guard helicopters a few times during water survival training, they caution you never to grab the "horse collar" attached to the cable as it approaches you. The pilot will dunk it in the water about five feet from you to discharge the static and then drag it through the water to you.

For a photo of how they discharge the static during sling operations, go to

scroll down to "13 March 2001".

For further, do a google search for "helicopters + "static electricity""

John

[R. Doornbosch]

IF you want to scientific about it you don't really generate static electricity as much as you attract it. So to be very basic everything in life is either giving electrons or taking them, even if you don't always notice. These electrons are just lazy, and very "Canadian" they like lots of open space around them so they are always looking for more space. So they jump onto big Rotor blades and then see some really big ground and it looks even better. Just make sure your not in the way of them getting there

[Richard J Kinch]

If there are high voltage power lines nearby, the field strength can be many volts/meter even at some distance, and a long conductive cable can induce a lot of voltage.

[Conase]

Holy static discharge, Batman !!!

Thanks for the intelligent discussion of a serious question.

Learned a lot about different forms of STATIC electricity that I never really thought of.

Never knew they make the HORSE COLLAR hit the water first to discharge potential electricity.

Thanks again.

[... ...]

The military has an interesting way of landing artillery from a helocopter. The ground crew has a long pole that is grounded at one end and has a hook on the other. They hook the piece first to ground it then they lower it so the ground crew can grab it and move it into position

[John‰]                      Â]

Everything you ever wanted to know about a HORSE COLLAR:

Do you think I made it up?

John

[Jeff Cochran]

Static generated by the rotor blades.

It's metal...

Static is both high voltage and tough to insulate.

Not if they've been flying the crane through the air. :)

Asked and answered.

Have you been hanging on the line?

I've seen it in person, and it won't kill you but it will let you know you're alive. Biggest danger is usually the reaction to the discharge.

Jeff

[ps]

This is also interesting, I found a long quote from Feynam on Google Groups. I remembered this from school days. I don't know if it applies to helicopters. The link has the full text:

"Here's the real scoop (source: The Feynman Lectures on Physics, Vol 2, chapter 9). Away from thunderclouds, the earth has a negative charge relative to "the sky." The potential difference is quite incredible: about 100 volts per meter. Why does this not electrocute you? Because your skin is so much better at conducting than air, your skin can be treated as a perfect conductor. Your head and your feet have the same potential as the earth. A foot from your nose, the air is at a potential of +200V."