In the right conditions (night, dry, etc), you can actually see the static electricity build up on Blackhawks just before touchdown. A little St. Elmo's will develop in a ring on the outer edge of the blades. Usually, this dissipates when the PIC keys his mike. For sling loads, we usually had a grounding hook (attached to wooden pole) that we would touch the line with first... THEN, we'd attach the load.