Sorry, nurses came to poke and prod me. Anyway, I derived an answer using
calculus, the derivation of which I'll share later. It turns out to be 2
feet. In other words, let the pipe drop 2 feet, and the Ferris wheel have a
4-foot drop. The maximum power obtained ended up being about 80 watts, if I
recall correctly. The thing is, I've never seen this in a book, nor heard it
from a guy in a white coat, so my confidence is somewhat low. Hopefully
everyone will chime in and say, "Why, everyone knows that, Bill." In the
absence of other info, I guess I'll go with my solution.
I'm going home tomorrow, so lots of stuff is happening today.