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'Vibration and Balancing'
1999\06\27@123823 by Bill Kichman

RE:  Vibration Analysis
Has anybody done any work with an accelerometer for vibration metering
and/or analysis?   I am asking, as I am interested in building a blade
balancing tool for propellors and helicopter blades.  I am not a vibration
expert, but it seems to me that the 2 variables to be measured include the
vibration amplitude, as well as the measured phase angle at the peak
vibration instant.  Using an accelerometer and  something to indicate the
phase angle, such as a strobe light and/or a photo-optic sensor, seems to be
the way it has been done,
based on my very brief research. (ref: Chadwich Helmuth equipment).  Maybe
some of you can shed some light on this matter?  Is this a possible
endeavor, or just too complex a project to undertake?
Thanks in advance for any input.
Bill Kichman

1999\06\28@104049 by Adam Davis

I work for a machine balancer company ( and the method
you describe is how most balancing companies measure vibration.  However there
is greater difficulty in balancing items that are powered using gas engines, or
moving equipment - you really cannot get a good idea of the actuall balance of
the propellors because there are so many other thing providing envoironmental
vibration.  I imagine one could do so using multiple sensors (we also make dual
plane balancers for instance, used on machine which have to account for
imbalance on both ends of a single shaft) but I can only imagine the math
nightmare one would have to deal with in doing so.

However, I imagine that the blades don't change balance often, so it should not
be too difficult to make a balancing stand to run the blades on with an electric
motor for balancing, or perhaps adapt an electric motor to the helicoptor when
you need to rebalance.

There are engineers here which would probably be happy to speak with you briefly
about the subject (I'm doing windows programming here, so I'm familiar with the
process and processing of the data the sensors and embedded equipment give me,
but I do not have an intimate knowledge of the physics of balancing.  I'm
telling you what I was told when I inquired about balancing car engines- imagine
having *no* noise from under the hood...)  You might try emailing for a better description.

So, in a nutshell, yes, you can measure vibration the way you describe, but the
item you are trying to measure introduces too many variables that you can't
ignore if you want a reading any better than a few hundred ounce-inches, in
which case your methed would not be useful. (but if you figure the math or
method out for it, you'll make a chunk of money...)

I hope this helps!

-Adam Davis

Bill Kichman wrote:
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