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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