rotor balance

Interesting balance job. New Safari and initial balance run. Blades rough
tracked at 300 rpm and a balance run made skids on concrete. Added some
washers using the "Add Opposite" rule but not much change and phase angle
stayed pretty much the same. For an interest, put the helicopter up on
rubber to cancel out any reflected vibrations. What do you think? The same
ips but 180 degree change in phase. Did the skids on concrete create a
reflection that gave the balancer a 180 phase shift?
Got a good set of vibration absorbing rubber pads with 3/4" plywood tops.
Will repeat the test. One thing about helicopters, I don't get bored.

Sti

"Stuart & Kathryn Fields" wrote in message
.. .
Interesting balance job. New Safari and initial balance run. Blades
rough tracked at 300 rpm and a balance run made skids on concrete. Added
some washers using the "Add Opposite" rule but not much change and phase
angle stayed pretty much the same. For an interest, put the helicopter up
on rubber to cancel out any reflected vibrations. What do you think? The
same ips but 180 degree change in phase. Did the skids on concrete create
a reflection that gave the balancer a 180 phase shift?
Got a good set of vibration absorbing rubber pads with 3/4" plywood tops.
Will repeat the test. One thing about helicopters, I don't get bored.

Sti

Repeated the previous balance runs with helicopter setting on vibration pads
with 3/4" plywood tops. Results: Balancing @ 300 main rotor rpm got
balance down to 0.04ips. The best I've ever seen on a Safari main rotor.
Tail rotor, @1600rpm, is always a problem when running on concrete, was
balanced down to 0.1ips.
Remains to final tune main to 500rpm and tail to 2750. Some 180 phase
flippining was noted on the DSS MicroVib balancer. While this phase change
can be a nuisance, if you know that it can happen, it usually only costs a
run or two.