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