Hi,
This is my first post here... For those that are interested in all of the gritty details of Igor's vertical flight development efforts, go look for a book on it: "Heelicopter: Pioneering with Igor Sikorsky", by William Hunt. I managed to score a used copy via an Internet resource; the ISBN # is 1-85310-768-9, and was printed by Airlife Publishing Ltd in England (1998). It has lots of engineering and hand-drawn drawings, and goes into almost excruciating detail. I haven't read it yet (only had it a couple weeks) but IMO it's a required addition to any RW pilot's bookshelf.
cheers,
Dave Blevins
San Jose, CA