Posted for Sky2high@aol.com:
Marv, et
al,
A little more interesting with a Lycoming....... Also, it is my
understanding that dynamic prop
balances should be done close to usual
operating RPM
or higher as rotational speed may alter
the balance.
In my case (IO 320, Hartzell 2 blade) all dynamic balancing is done
between 2600-2700
RPM (2640 was my low altitude race rpm). I have achieved
.001
ips. I am using a "motor" balancer that
only records ips vertically on the
engine center line as close to the front bearing as possible. Some more
sophisticated balancers use sensors at both the front and back of the engine
.
Washers
are bolted up to the appropriate 12 holes in the flywheel and,
because of the 30 degree spread of the holes, weights are often
split
between
two holes. After I had a re-seal job done on my current prop, the first
step of the
dynamic balance was greatly improved by moving all the static
balance weights located near where the blade exits the hub to
the other
side.
With the system I have a polar chart is used to locate a point
representing
the angle reported by the device and the distance representing
the ips.
Artistic interpretation is required to place
and size the next weight.
This process is repeated until <.05 ips. I.E. the last plotted
point is
very
close to the center of the chart. Oh well, the pricey sophisticated
balancers do all the
thinking for ya.
Every prop should be dynamically balanced - Think of the tune "There's a
whole
lotta shaking goin' on!"
Grayhawk
[We normallly balance the M601/V508 combo between 1850 & 1900 RPM (cruise)
as red-line is 2080 and we recommend staying below 2050 for takeoff anyway. The balancer we use _is_ one of those "pricey sophisticated" jobs
that not only does props but allows us to perform a spectrum analysis on the engine to insure that the rotating parts are also within balance limits.
(It'll also do helicopter rotor balance and blade tracking, but that's a bit beyond our purview.) The balance-weight holes on the V508 spinner
backplate are laid out in pairs and I've created a protractor that allows us to readily match those hole locations to the positions called out by the
balancer for weight addition. It is strictly by chance that a balance weight will be required at precisely the location of one of the holes, so
our machine allows us to "split" the weights and tells us how much to add at each of two points to equal the moment of the single weight
required. We then get to tell it exactly how much weight was added at each of the two points (it's tough to hit exactly the hundredths parts of
a gram all the time) and it uses that data during the subsequent run to adjust the real location. Within about 4 iterations it's usually between
.01 and .02 IPS. WIth the balance completed the Vibrex allows us to print the chart you described, showing how the path of imbalance worked its
way to the center of the bullseye. It's really quite the amazing device and process. Wish I'd thought of it.
<Marv> ]
In a message dated 2/17/2011 10:16:01 A.M. Central Standard
Time,
marv@lancair.net writes:
Posted for "Kent" <kent@tulsaconnect.com>:
I
wonder which brand of equipment was used?
Interesting the manual cites tolerance much tighter
than industry
standard.
Do people have any idea or appreciate how much weight difference or change
in
location affects the balance reading?
Is that reading a raw value or
averaged value?
An AN960-10 washer weighs one gram. I don't recall what the Walter
spinner's diameter is but it is a large one, about 14-15 inches I think.
Kent Felkins
Tulsa Oklahoma
[Spinner
diameter on a V508 is about 18.5". And Brian's absolutely
correct... balance that prop down to .01 or .02
IPS and there's no
detectable
vibration at normal operating speeds. Here at DIemech we use custom made
lightweight fasteners for the extra light weights... typical AN hardward
can't
get you below about
3-4 grams, and that's a real problem when getting down
to the fine tuning. Ain't technology
grand. <Marv> ]
----- Original Message ----- From: "Brian Alley"
<n320wt@yahoo.com>
To: <lml@lancaironline.net>
Sent: Thursday, February 17, 2011
7:04 AM
Subject: [LML] Prop Balance
> Working on David Weinsweigs IVPT this evening with a
dynamic prop
balancer we
>found the initial readings to be .22 ips (inches per second) at 1900 rpm.
>After several engine runs and weight placement we were able to achieve
>multiple readings of .01 and .02 ips at 1900 rpm.
The manual says
anything
>under .05 ips is acceptable. The Walter 601EX with Avia prop is a very
smooth
>installation but with the prop properly balanced it should be like an
electric
>motor. If anyone
is interested in this service, please feel free to
contact me
>by phone or email.
>
> BRIAN ALLEY
(N320WT)
> CARBON FIBER COMPOSITES
> 101 Caroline Circle
> Hurricane, WV
25526
> www.carbonfibercomposites.net
> 304-562-6800 home
> 304-395-4932 cell
>
> How are you
going to win by a nose if you don't stick out your neck?
>
> --
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