Don: I think that that may be one of the sources for tailbooms like the
206s, Hueys etc. but the Bell 47 and my Baby Belle has an open tail boom so
I'm not sure that there is any interaction there. I have done some math and
it shows there is a velocity term that occurs in forward flite that creates
both a lifting and drag force that varies at twice the rotation rate.
However I'm thinking that there must be more than just these?

--
Kathy Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478
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"Don W" wrote in message
et...
Stu,

Stuart & Kathryn Fields wrote:
I'll try one: What are the sources of 2/rev vibration in a two bladed
helo?
I know that I don't have any significant 2/rev in hover, but do in
forward
flite.


A WAG says that its the due to the blades being
aligned with the airframe twice per revolution (at
0 and 180 degrees). As each advancing blade comes
out of that alignment and hits the airstream I'll
bet it gets a small quiver which you feel as 2/rev
vibration. That would explain why you don't see
it in hover, but do in forward flight.

Right??

Don W.