zeeoo,
I have been researching all ideas that can be used to build a sport vertical takeoff aircraft.(not just helo's).
I am more concerned with simplicity, low cost and safety rather than performance.Looking for a safe way to fly low and very slow.
Tip jets were considered but I do not see any way to make jets work with a low cost piston engine.
If it was easy, everybody would be doing it!
P.S. There is a book at my local library, I think the title is somthing like "Whirlybirds" that has a chapter about the Hiller Hornet and tip ram jets.