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You will need a vibration range of about 0.03 to 2.0 IPS
(InchPerSecond) acceleration, whatever g-load that is.....
Anything above 0.7 IPS on a prop/engine combination is
considered "rough". If you get over 1.0 it is getting dangerous.
With new bearings and tolerances in spec you should be
able to balance down to 0.02 IPS. Most aircraft spec 0.2 IPS as
max.
Thomas J.
----- Original Message -----
Sent: Sunday, May 15, 2005 12:10 PM
Subject: [FlyRotary] Re: Prop
balancing?
Cheap man's way:
I'm sure you have access to an
oscilloscope.
Mount a position pickup (for prop) and connect to trigger
input.
Get an accelerometer (http://www.analog.com/en/prod/0,2877,ADXL105,00.html,
or similar - I bought mine from Newark many yers ago) and hook up to Y-input.
Mount on tip of PSRU (or remove PSRU and mount on engine to check its
balance).
You'll need some filtering circuit like a tunable notch
filter. Actually doen't have to be tunable - adjust RPM to hit the
notch.
I tried it with only the accelerometer and no filtering circuit
and couldn't read through it. Actually not sure if the G range doesn't have to
be bigger, like 20 Gs - seem to remember signal being clipped with the 5-G
sensor. Some of our physists on the list can undoubtledly answer
that.
Finn
Russell Duffy wrote:
I'm not familiar with the Chadwick unit, but it
probably operates on the same principle using a vibration sensor on the
engine and an optical sensor to pick up reflective tape on one prop blade.
No reason it shouldn't work.
Thanks for the info Perry. The Chadwick
was just as you describe, a vibration/optical sensor
that mounted to the redrive plate, and a piece of tape on the
prop. The guy who was running it admitted that it was probably
something he just didn't know how to set. The unit actually belongs to
his son, but he's working two jobs, and I never see him
anymore.
At least it's good to know that it should probably
work.
BTW, does anyone have any idea how much these
things cost? I assume "a lot".
Cheers,
Rusty
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