REFLECTOR:Balancer

[Robin Ream]

    Only three parts Brian.  An accelerometer (vibration sensor,) a photo
sensor, and the computer.  A piece of highly reflective tape is attached to
some part of the rotating disc (prop) that the photo sensor reads and
indexes so the computer can measure a vibration pulse relative to that given
index point.  Really very simple.  The RPM must remain constant because the
computer is calculating a phase angle based upon timing relative to the
index point.  It does the calculation and displays an angle and a vibration
intensity measured in inches per second (ips).  You do a simple calculation
on a polar chart, add a correction weight to the calculated point on the
rotational disc, and re-run to see how it balanced.  Assuming the RPM stays
constant, the phase angle is very accurate; the balance weight to be applied
takes a little experience to guestimate.  Assuming your phase angle is
correct, if you grossly over estimate the counter weight to cancel the
vibration it will just shift past dead center to some point 180 degrees
opposite on the polar chart.  That's ok because you then have a known
distance of change based on the given weight, and you back off the
percentage you over-shot.  ..............  It's a neat little machine, and
after playing with it a while you develop a whole new respect for the guys
who do vibration analysis for a living :-)
    Propellers are typically fairly easy projects to balance if everything
is kept constant.  An automobile is something else...  You very quickly
realize that all parts are connected, and in vibration, the whole is not
exactly the sum of all the parts.  --  Funny things happen in vibrational
interference.  I have a late model pick-up truck I was playing with and
trying to smooth it out like a Lexus  (Wrong!) and when I looked under it
real hard after chasing my tail on a few vibrations, I saw that the factory
had even incorporated a harmonic damper on the drive shaft and I knew right
then I was in deep sh**!
    Back to your airplane though, balancing is very important.  Much more
important than most people give thought to.  There are no springs, shock
absorbers, or dampers on the average airplane.  Therefore all vibration
shakes every part of the airplane (and we wonder why our panel instruments
and radios don't last long...)  Believe me, a well balanced prop and engine
will most certainly make your airplane a more friendly machine that is bound
to have a longer lifespan.
    Norm Serrano, the guy who designed this instrument at Vibe Tech, wrote a
small book used at Embry Riddle called Basic Principles Of Dynamic
Balancing.  If you can track Norm down ask him how to get a copy.  I would
imagine he's got it on computer and could possibly email you a copy if
necessary.  There are a few typos, but it's fairly easy reading and a big
help if you want to chase the "shake, rattle, and roll."  :-)

Good luck,
Robin


----- Original Message ----- 
From: "Brian Michalk" <michalk@awpi.com>
To: <reflector@tvbf.org>
Sent: Tuesday, June 10, 2003 12:24 PM
Subject: RE: REFLECTOR:Balancer


> I checked out the site, and it's not clear what hardware is offered.
> Do you attach some sort of self contained accelerometer to the prop as it
> spins?
> How is the vibration data acquired?
>
> > -----Original Message-----
> > From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> > Behalf Of HYTEC45@aol.com
> > Sent: Tuesday, June 10, 2003 11:13 AM
> > To: reflector@tvbf.org
> > Subject: Re: REFLECTOR:Balancer
> >
> >
> > In a message dated 6/9/03 5:26:41 PM Pacific Daylight Time,
> > robinream@earthlink.net writes:
> >
> > << Number one culprit.  --  The sun >>
> > Tried it after sundown on a black prop with no luck.
> >
> > << Second:  --  Don't be stingy with the tape.>>
> > Went as far as a two inch long piece of tape with no luck.
> >
> > <<You might have to play around with it a bit to get the photo
> > sensor angled
> > just the right way to pick up optimal reflection.>>
> > Made a bracket for the sensor that can adjust to be perpendicular to the
> > blade angle and tape and get a strong peanut light statically
> > with no luck.
> >
> > <<The further out on the radius you have your reflective
> > tape the faster it's going by the photo sensor>>
> > The unit is advertized to be good to 8000rpm, I lost lock after 1300.
> >
> > << It does take some practice though.  I've spent plenty of time
> > putting trial balance weights in the wrong place because I didn't follow
> > directions to the letter,>>
> > I wish I could get a balancing solution even once, to try putting
> > weights on.
> >
> > I could be missing something though.
> > Thanks,
> > TEC
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