Thread: old days
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Old December 14th 06, 04:54 PM posted to rec.aviation.rotorcraft
Stuart & Kathryn Fields
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Default old days

boB. I believe that the 1/rev vertical is due to tracking, and on my ship,
I either stick track for a ground check or use tip lites. Note us
experimental guys have a blade tip mounted LED two different colors, and we
can use these tip lites in forward flite. One person tracking is possible.
I also check the vertical vibration by using an accelerometer mounted down
by the passengers pedals. You are right. My initial tracking adjustments
are done with the pitch links and if I needed more in forward flight, I
would have to put some trim tabs on the blades. So far my blades run good
in forward flite, that is to say I don't have a climbing or diving blade.
My ship runs smooth in the vertical 1/rev down in the 0.1ips regions all the
way to 90mph. Even when I do vertical 2/rev, measuring in the same spot, I
don't get any significant readings. However measuring the horizontal 2/rev
just below the swash plate, I can get some significant readings when my fuel
level gets below 1/2 tank and I can feel it in the seat and controls. It
seems that all of the Baby Belles exhibit this phenomena to some extent.
Measurements on the Rotorway Exec showed similar readings but for some
reason their vibrations don't enter the cockpit.
I'm curious as to the sources of 2/rev vibrations. The two mentioned with
Don W I know about and not a lot can be done to either of these two sources,
but are there more sources?

--
Stuart Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478
(760) 408-9747 general and layout cell
(760) 608-1299 technical and advertising cell

www.vkss.com
www.experimentalhelo.com


"boB" wrote in message
...
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.



Stuart, you are definitely more current than I on blade tracking so let
me try to remember. A 1 or 2 per rev vibration which is constant
throughout the rpm range should require PC link adjustments. I hope I
remember, I did a bunch of these, a vibration which increases as RPM is
increased should require a trim tab adjustment. A flag is the easiest
way to adjust the blade track although if you have a vibrex you can get
it fine tuned. Tomorrow I'll go find my -20s for the OH58, UH1 and AH1
and see if my memory is bad.

--

boB
copter.six

P
U.S. Army Aviation (retired)
Central Texas
5NM West of Gray Army/Killeen Regional (KGRK)