Linc wrote:

If you search this group, you'll find a post by Nick Lappos, or Dan
Hollenbaugh or one of the other several notable and knowledgable
sharers of information, and others, discussing the cost and benefits of
NOTAR vs. Tailfan vs. tail rotor. There may actually be several of
those discussions. One of them, at least, mentions that the reason
NOTAR and Tailfans are generally quieter than tailrotor systems is the
sound generated by the tip vortices of the main rotor colliding with
the tip vortices of the tail rotor. Now, I'm not knowledgable enough to
regurgitate any specifics, like how blade rpm and blade chord affect
such a phenomenon, just lucky enough to regurgitate the fact that I
heard it here.

IIRC, the same discussion particularly mentioned the distinctive sound
of the huey.

Linc

My thanks to all who replied. I vaguely remember that discussion, and will
google for it.

Guy