"The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in
message ...
On Wed, 27 Feb 2008 09:03:34 -0800, "Stuart & Kathryn Fields"
wrote:


I expect the Add Same on the tail rotor as I have checked it out and
found
a critical speed below the operational speed which will produce the
velocimeter being on the side opposite of the inbalance weight.
If anyone out there is interested in rotor balancing other than me, this
is
a follow up to the previous post. The next day I ran another check and
this
time I used "Add Opposite" and have the balance down to 0.1ips. I talked
to
Murray Sweet of Canadian Home Rotors and he told me to disconnect the
battery of the balancer and re connect it and it often cures the 180
degree
phase flip. On the DSS balancer, I'm going to add a battery disconnect
switch. Hopefully this will eliminate the funny phase data and save me
one
run up.

I'd be interested if I knew WTF "Add Opposite" etc was.


Ok a little discussion of balancing. If you have a shaft rotating at a
speed below it's "Critical speed" and it is out of balance, and you put a
pencil up near the shaft, it will mark the heavy side and if you are going
to correct for the out of balance condition, you need to put a weight on the
"Oppisite" side of the shaft. Hence "Add Opposite". When running a balance
check on my helicopter, the balancer reads rpm, ips and phase angle. I
interpret the phase angle measurement to mean the position of the rotor with
respect to a reflective tape where the max vibration point occurred. I
position the rotor at that angle and look across the shaft from the
velocimeter and Voila I "Add Opposite" and I have a balanced rotor after
about three to 4 runs. However, the tail rotor is spinning at a speed that
is above the "Critica Speed" and there is a 180 degree phase shift
encountered. Back to the pencil it now marks a spot on the side opposite
the heavy side so that corrective weights must be located by "Add Same".
This techniqu has gotten me balancer readings down below 0.1 ips. (Military
says anything below 0.4 is ok)

Note if you run at the "Critical Speed" and it doesn't come apart, the
pencil makes a mark 90 degrees behind the heavy spot. So if you are close
to the "Critical Speed" your pencil is going to mark somewhere and if you
try to "Add Opposite" or " Add Same" you are going to be chasing the little
dots around your polar chart if you use one.

Gawd I love helicopters they are an unending source of questions.

Stu Fields