Where is the electricity coming from ?

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."

http://groups.google.com/groups?q=fe...s.com&rnum= 1