balancing act

Bad blade dampers on articulated (main) heads cause fits too. The test
equipment will say to make such-and-such adjustments, the guys make
those adjustments, you run the test again thinking the numbers will be
in limits or at least closer, and instead the equipment comes back with
numbers that make no sense.

I know the maintenance guys _hate_ changing out a damper.

For the OP, are there accessories running off the shaft? (Oil cooling
fan maybe?) What about the basics, is everything torqued properly,
clean, nothing loose (gearbox oil cap, access panels, so on)?

Linc wrote:
Steve,

It's been a while since I did any aviation maintenance, but the bearing
thing was exactly my thought as she described an unattributed shift in
the ips and phase angles on the repeated runs.

Once upon a time (it was a Sikorsky product) a T/R paddle had debonded
at one end, but internally, and was causing the maintenance pilot fits
as he tried to balance it. He even accused me of putting it back
together incorrectly just prior to my departing for vacation. He was
wrong. When they swapped out the T/R paddle and it balanced out, they
removed the boots from the bad T/R component and found it had failed.
The only symptom that I remember was variable ips readings and changing
phase angles of successive readings.

Linc

Steve R wrote:
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