Steve: It is a Baby Belle. I recently repeated with just the engine
driving the main rotor and the tail rotor disconnected. I measured the
vibration at the tail rotor gear box to see if the engine vibration was
coupling thru the tail boom. Nope. I ran the engine up and took readings,
backed it to idle and went up again. Did not get repeatable readings. I
will try the balancer on a D.C. motor and flywheel I've rigged up and see
what it does.
I've been doing an article for our magazine on the comparison between the
Pro-Drive balancer and the DSS Micro Balancer and stumbled onto this
problem. In the past I've balanced mine and two other ships tail rotors
down to the 0.05 ips levels fairly easily. Now with the readings skipping
around, I don't have a chance.
BTW balancing the main rotor at it's 500 rpm does not have this problem. It
repeats nicely.

--
Kathryn Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478 ph
(760) 408-9747 publication cell
"Steve R" wrote in message
...
Hi Stuart & Kathryn,

What kind of helicopter are you talking about here?

Please excuse a wild guess from someone who has "very" little experience
in the experimental world but......... since you're not finding anything
overtly loose in the drive system or tail blades, I have to wonder about
something like a bearing going south on you? It might not be anything
you'll feel just moving a static system round but could start causing
problems when under load. Is there any kind of preload put on the system
during assembly? If so, is it even?

As I said, I'm just guessing here so if I'm totally out of line, please
excuse the reply! ;-)

Best of luck & fly safe,
Steve R.


"Stuart & Kathryn Fields" wrote in message
.. .
Here's one for the pros: I was balancing my tail rotor and had it down
to 0.27 ips and still had just a touch too much weight where I had added
it. So still needing to safety wire a bolt that is located in the center
of the tail rotor output shaft, I chose to safety it to a hole 180
degrees from the weight. The safety wire was small, 0.025, so I didn't
expect to see the ips go to zero, but I hoped they would decrease maybe
to 0.20. Well it didn't. All of a sudden I had 0.9ips, so I shut down and
removed the wire and ran again. This time I got 0.5 ips. The balancer
reading did not even come close to repeating. The phase angle was also
different. In an experiment, I would run up from idle to full chat and
take 4 averaged readings, come back to idle and go up to full chat again
for another 4 readings. Never repeats. Can't find anything loose in the
drive or on the blades. If I pull a set of readings at 2500, 2600 and
2700, all the readings pretty much agree with the exception of ips
increasing a bit with rpm. However if I take it to idle and come back
up, I get a different set.
Any ideas?
--
Stuart Fields
Experimental Helo magazine
P. O. Box 1585
Inyokern, CA 93527
(760) 377-4478 ph
(760) 408-9747 publication cell