I don't give 2 hoots and a holler about flying inside a helicopter...
Hovering AND talking
Join Date: Feb 2003
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Ohm my lawd; this is "currently" on Jet Blast as well!
Quite shocking what some people do for a living.
Cheers
Whirls
Quite shocking what some people do for a living.
Cheers
Whirls
Join Date: Feb 2004
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After spending my whole career trying to avoid wires like the plague, I now find myself doing this. If you fancy a challenge and want to know the true meaning of "focus", then this is it.
Love it!
Love it!
Join Date: May 2001
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A great clip - taken from the IMAX movie "Straight up: Helicopters in action"
http://www.shaftesbury.org/straightup/
RD
http://www.shaftesbury.org/straightup/
RD
If you ever get the chance to see the IMAX version, DON'T miss it. I thought I was out sitting on the platform with the wire-walker. Great illusion! It really gave me the creeps. As well as a huge amount of respect for those folks.
rf
rf
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i guess its because its the same polarity. there is so much power running through that it will want to go somewhere. So he initiates a zap through the wand he then clips the earth on which keeps it the same polarity. so it does not bridge through his body. then does it all in reverse when the chopper comes in to pick him up.
hope i have this right.
anyone...anyone...bulier...bulier..
hope i have this right.
anyone...anyone...bulier...bulier..
Join Date: Mar 2006
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Correct Bladepitch
The current will 'fill' every item that comes into contact with the wire, looking for an easier path. This is not the same as earthing/grounding, where it wants to get to the ground.
If the 'earth strap', for want of a better description, was not on, then the worker would get burnt as the current jumps/arcs.
The same gets done for helicopters when refuelling. What you want is easy current flow between the two and some times the helicopter and drum may be on trolleys and therefore not in contact with the earth. Remember if rubber can insulate, then so can car/truck tyres.
If the 'earth strap', for want of a better description, was not on, then the worker would get burnt as the current jumps/arcs.
The same gets done for helicopters when refuelling. What you want is easy current flow between the two and some times the helicopter and drum may be on trolleys and therefore not in contact with the earth. Remember if rubber can insulate, then so can car/truck tyres.
Join Date: Nov 2004
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Line is AC, so voltage is constantly swinging between +/- many kV. Heli voltage just trying to keep up. 
Definate respect for the guys that do that job, especially in less sunnier climates.
Mart
Definate respect for the guys that do that job, especially in less sunnier climates.
Mart
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bbbbzzzzzztttt....
Are there any deviations or alterations in instrument readings or performance when connecting or connected?
That's apart from the pilots hair standing on end...
Mc Hover
That's apart from the pilots hair standing on end...
Mc Hover
Last edited by McHover; 27th Apr 2007 at 14:58. Reason: Dodgy spelling
Thread Starter
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I think this is the correct explanation.
There is a potential difference (voltage) between the helicopter and the powerline. The powerline is negative, meaning it has more electrons than the helicopter, which is positive. Negative flows to positive meaning the electrons flow to the chopper through the wand to bring it up to the same potential as the line. Also, ground is relative. In one sense the helicopter is at ground potential in relation to the line since it has fewer electrons than the line. However, it has more than the earth below it. Helicopters in the air can pick up a huge static charge - I know from experience having hooked a cargo net on a hovering chopper a few times.
There is a potential difference (voltage) between the helicopter and the powerline. The powerline is negative, meaning it has more electrons than the helicopter, which is positive. Negative flows to positive meaning the electrons flow to the chopper through the wand to bring it up to the same potential as the line. Also, ground is relative. In one sense the helicopter is at ground potential in relation to the line since it has fewer electrons than the line. However, it has more than the earth below it. Helicopters in the air can pick up a huge static charge - I know from experience having hooked a cargo net on a hovering chopper a few times.
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Rotornut, line voltage cycles at 60Hz (US) so relative to helicopter it goes from +ve to -ve every 17 milli-seconds. The best way to explain what then happens is that experiment in high school phys where a copper sphere gets charged to high voltage - but takes a minute or so to get there. Basically the heli acts as a large sphere (or capacitance), so that it only responds very slowly to the constantly changing line which is constantly trying to alter the heli voltage. So the electrons constantly jump back and forth across the gap.
The effect where cloud causes static charge pickup is similar to when you rub a plastic rod on a wollen jumper. Electrons are transferred to accumulate a huge static (as in not moving) charge. Fixed wings have a pointy metallic stick at the wing tips, since the small diam tip causes high electrostatic stress which makes electrons jump back off again before much charge accumulates.
BTW you pros could blow me out of the water anyday with what you do for a living!
McHover, i wondered the same thing. It must be that the faraday effect which protects the line worker, with that 25% steel mesh 75% nomex suit, also protects the aircraft electrical system. The MD500 looked modified specifically for that application. Anyone care to do some extracurricular test pilot work at the Qinetic high voltage facility?
Mart
The effect where cloud causes static charge pickup is similar to when you rub a plastic rod on a wollen jumper. Electrons are transferred to accumulate a huge static (as in not moving) charge. Fixed wings have a pointy metallic stick at the wing tips, since the small diam tip causes high electrostatic stress which makes electrons jump back off again before much charge accumulates.
BTW you pros could blow me out of the water anyday with what you do for a living!
McHover, i wondered the same thing. It must be that the faraday effect which protects the line worker, with that 25% steel mesh 75% nomex suit, also protects the aircraft electrical system. The MD500 looked modified specifically for that application. Anyone care to do some extracurricular test pilot work at the Qinetic high voltage facility?
Mart
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Would there be a significant amount of alternating electromagnetic flux to induce an adverse current within the helicopters wiring harness. Or even the instrument panel. It is AC, therefore induction could take place. I guess those of you that do visual line inspection will have the contacts with all these answers.
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SMM, current would be induced in the airframe which would cancel original wire B-field, thus shielding the heli electrical system. Since 60Hz wavelength is ~500km (assuming electricity v=~0.1c), induced current is limited to neutralising B-field difference across airframe.
Induced currents are certainly a problem when welding steel frames, the requirement being to disconnect all electrical system components from harness. I imagine the MD500 riveted alumininium frame is closely inspected for arc damage from the charge currents though.
Mart
Induced currents are certainly a problem when welding steel frames, the requirement being to disconnect all electrical system components from harness. I imagine the MD500 riveted alumininium frame is closely inspected for arc damage from the charge currents though.
Mart
Last edited by Graviman; 28th Apr 2007 at 05:42. Reason: Added bit about wavelength, and quick tidy up.
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There are no special mods to the machine except some have a separate switch for the radio altimeter which tends to dislike it when going "live", therefore switch it off beforehand. Helicopter types are tested on a ground testing facility up to about a million volts before going "live" and some do not pass the test. Older types like the MD500 and Bell 206 work well with no adverse effects but the Bell 407 cannot be used since the current plays havoc with the bonding paint on the main blades. At least that is my experience. Great work, challenging and rewarding.
