So, I was re-watching The Hunt For Red October, (in light of current Russian shenanigans with Sweden), and there was a scene in which a crew-member on the ground was electrocuted by making contact (and presumably grounding) the helicopter, which had picked up a charge in the stormy weather. Can anyone explain more of what is going on here?
In the same way than an aircraft will build static charge on the wings from friction with the air, the same thing can happen with helicopters from fast moving blades.
From a 1962 US Army document:
Any aircraft flying in the atmosphere can be considered as a conductive body located in a highly electrically insulated environment. In such a body, electrostatic charge is generated by three principal mechanisms:
- Charge transfer created by a triboelectric effect between the aircraft and the atmospheric particles, such as dust, water, water vapor, snow, etc.
- Unbalance of the ionic content of the exhaust gases produced by the aircraft engine(s).
- Induction charge due to high electrostatic field gradients which are found occasionally in the aircraft flight path.
Here's a more detailed photo of the US army discharging a helicopter while wearing insulating gloves:
SGT Nathan Rodeheaven uses a static probe to discharge static electricity from a UH-60 Black Hawk before his teammate, PV2 Danny Browning, hooks up the cargo to the helicopter. The safety measure prevents the hook-up man from being electrocuted in the event there is accumulated static electricity. Photo: Kristin Molinaro
I am a Naval Aviator and as part of my water survival training, I was deposited by boat off the coast of Florida and picked up by helicopter. It was a huge point of emphasis that we let the helicopter's rescue hook touch the water to discharge any built up static before we touched it.
No one in my class grabbed it before it hit the water, so I can't speak to how bad the shock would have been.
I work for a Christmas tree farm and we harvest our trees out of the field using a helicopter. I am the hook man and attach the bundle of trees to the heli, then he takes them to another location. In that breif trip during a rain storm, or even a foggy day static charge will build resulting in a very unpleasant shock. Sometimes bad enough it will contract the muscles in my hand and arm. I’ve been doing this for 3 years and finally invested in some 20,000Vac insulated gloves that are enough to keep this from happening.
Helicopters in normal weather will build up a static charge, just ask any ground crew for a logging helicopter. Normally the hook will be grounded by dropping it on the ground before the hooker will touch it.
Or a grounding rod will be used to neutralize the static charge.
Yes they do. I was involved in many HDSs (Helicopter Delivery Service) and would earth the Helo with a sheperds crook and trailing copper linkage - often getting a visible spark. I also took part in the rescue of a few dozen (memory fades on how many) crew from a bombed ship with no hook and earthed the helo myself - yes it hurt.
It sounds like the helicopter had no static dissipators/wicks fitted (or broken ones!), and this resulted in the normal in-flight charge buildup zapping the groundman on the submarine instead.
I'm surprised the helicopter pilots didn't notice that awful noise in their radios well before this became a problem, though!
See What are these things hanging off the trailing edge of the wing? for more details.