Prop Balance and Murphy

WIth 4 hours on the fresh top overhaul I decided it was time to
balance the prop as we removed the weights when sending the props out
for new studs...

I was delayed a bit at my monthly meeting down in Grand Blanc and got
back to the airport at a quarter to one... The Kid was chomping at the
bit... He immediately dove into pulling the top cowel and the top
plate of the air pressure box around the engine... He bolted the
accelerometer to the engine, taped the strobe to the side of the lower
cowl, and cleaned the back of the prop with butyrate thinner and put
reflective tape on it...
(I love the smell of bannana oil - it always makes me remember my dad
as one of my earliest memories is following him around a yellow J3 Cub
as he was patching the fabric)
We pushed back out onto the ramp and did the engine run... It was 24
IPS at 2400 RPM - not good... The engine definitely was putting
vibration into the airframe... Even more noticeable with the cowel off
when you can see the cylinders vibrating...
He then pulled a spinner screw and hung an external weight on the
spinner in the amount that the balancer machine calculated and we re-
ran the engine... Oops, we were 180 degrees off on placement (Murphy
hanging around)... Quickly reversed that and ran it again... Balance
was about 0.9 IPS - mucho better...

OK, now we are in the ball park... The Kid changed over to internal
weights.. He had to calculate the new weight based on the fact that
they were closer to the crank centerline than when external, and plus
the additional weight that the computer called for the 0.9IPS of
unbalance... After mounting the internal weight we put the spinner
back on, and did all the safety wire and screws, etc... Took it out
and ran it... About 0.7 IPS, acceptable but nothing to write home
about...

We pulled back in and discussed it... Decided to go to split
weights... Took the spinner off again, which is not a trivial job
recalculated the weights for the split condition, rehung them, put it
all back together (it is 33 degrees and blowing and even with the
plane part way in the shop, I am by now shivering)... Pushed back,
engine run. 0.6 IPS @ 2400, but we both can tell it is smoother with
the split weights at idle than it was with a single weight... Asked
the computer for the new (and hopefully final) weight...

Once more into the breach we, the light Brigade, go...Take it apart,
add one thin little weight, put it together, push it back, run it...
Holy shakes, Batman - 0.2 IPS!
HIgh fives all around... Two hours of freezing our butts off and
wearing the tips off our fingers with lebenty seben screws...

ME: Uhh, why is there a film of oil on the back side of the accessory
case?"
The Kid: "Well, I was hoping you wouldn't notice that."
ME: "In your dreams, Tonto."
We are both peering at the offending specks of oil (just a dusting
really)
Looks like the gasket for the oil filter adapter...
The Kid sighs, "Well, lets push it in the shop and I'll change the
gasket tomorrow. I've got another job I promised to do today."
Ah jeez, I wanted to go flying... Does that Murphy guy ever take a day
off?

denny

"Denny" wrote in message
...
WIth 4 hours on the fresh top overhaul I decided it was time to
balance the prop as we removed the weights when sending the props out
for new studs...


You should probably plan on doing this again in about 25 hours. With only
four hours on a top your cylinder pressures are nowhere near even; you
should expect some vibration.

--

*H. Allen Smith*
WACO - We are all here, because we are not all there.

On Mar 13, 6:21 am, "Allen" wrote:

You should probably plan on doing this again in about 25 hours. With only
four hours on a top your cylinder pressures are nowhere near even; you
should expect some vibration.

But that causes vibration torsionally, which the accelerometer
ignores. The accelerometer reads vertical movement of the engine,
normally as close as possible behind the prop. Uneven firings will
cause the engine to rotate around the crankshaft, with no vertical
component.

Dan

On Mar 13, 6:21*am, Denny wrote:
WIth 4 hours on the fresh top overhaul I decided it was time to
balance the prop as we removed the weights when sending the props out
for new studs...

I was delayed a bit at my monthly meeting down in Grand Blanc and got
back to the airport at a quarter to one... The Kid was chomping at the
bit... He immediately dove into pulling the top cowel and the top
plate of the air pressure box around the engine... *He bolted the
accelerometer to the engine, taped the strobe to the side of the lower
cowl, and cleaned the back of the prop with butyrate thinner and put
reflective tape on it...
(I love the smell of bannana oil - it always makes me remember my dad
as one of my earliest memories is following him around a yellow J3 Cub
as he was patching the fabric)
We pushed back out onto the ramp and did the engine run... It was 24
IPS at 2400 RPM - not good... The engine definitely was putting
vibration into the airframe... Even more noticeable with the cowel off
when you can see the cylinders vibrating...
He then pulled a spinner screw and hung an external weight on the
spinner in the amount that the balancer machine calculated and we re-
ran the engine... Oops, we were 180 degrees off on placement (Murphy
hanging around)... Quickly reversed that and ran it again... Balance
was about 0.9 IPS - mucho better...

OK, now we are in the ball park... The Kid changed over to internal
weights.. He had to calculate the new weight based on the fact that
they were closer to the crank centerline than when external, and plus
the additional weight that the computer called for the 0.9IPS of
unbalance... *After mounting the internal weight we put the spinner
back on, and did all the safety wire and screws, etc... Took it out
and ran it... About 0.7 IPS, acceptable but nothing to write home
about...

We pulled back in and discussed it... *Decided to go to split
weights... Took the spinner off again, which is not a trivial job
recalculated the weights for the split condition, rehung them, put it
all back together (it is 33 degrees and blowing and even with the
plane part way in the shop, I am by now shivering)... *Pushed back,
engine run. 0.6 IPS @ 2400, but we both can tell it is smoother with
the split weights at idle than it was with a single weight... Asked
the computer for the new (and hopefully final) weight...

Once more into the breach we, the light Brigade, go...Take it apart,
add one thin little weight, put it together, *push it back, run it...
Holy shakes, Batman - 0.2 IPS!
HIgh fives all around... Two hours of freezing our butts off and
wearing the tips off our fingers with lebenty seben screws...

ME: *Uhh, why is there a film of oil on the back side of the accessory
case?"
The Kid: *"Well, I was hoping you wouldn't notice that."
ME: "In your dreams, Tonto."
We are both peering at the offending specks of oil (just a dusting
really)
Looks like the gasket for the oil filter adapter...
The Kid sighs, "Well, lets push it in the shop and I'll change the
gasket tomorrow. I've got another job I promised to do today."
Ah jeez, I wanted to go flying... Does that Murphy guy ever take a day
off?

denny

If you are running a ACES balancer it has been my experience if there
is any more then a light breeze while running it up it will not settle
down and give a perfect reading. Those units are great and very
sensitive. I usually don't stop till I get into the .0 something
range.As you found out to dial it in perfectly you have to split
weight it. Hope the oil leak is a simple fix and hopefully that Murphy
guy is gone for good...

tailwinds
ben

On Mar 15, 6:32 am, Peter wrote:

What suprises me is how few people know about this process. It makes a
very noticeable difference to vibration and probably shows through the
avionics living longer.

Gyros, too.

Dan

"Denny" wrote:

Does that Murphy guy ever take a day off?

Hah!

Getting close to an airplane with a wrench is like handing a stripper a credit
card.

--
Dan

T-182T at 4R4

On Mar 15, 8:32 am, Peter wrote:

What also suprises me is how bad brand new props can be, despite
having been statically balanced *supposedly* very accurately.

In my life I've purchased two brand new McCauley fixed pitch props.
Both were substantially out-of-balance as they came out of the box,
and both were fixed by a local prop shop. I am amazed the prop shop
(Maxwell) could do better given their comparatively crude tools. Must
just be skill & attention to detail.

*Must
just be skill & attention to detail.

Exactly... Look at the fine cabinetry for the nobility made in the
1700-1800's.... No rulers, no micrometers, no lasers, no power tools,
only crude hand tools and skill...


denny

Denny wrote:
Must
just be skill & attention to detail.

Exactly... Look at the fine cabinetry for the nobility made in the
1700-1800's.... No rulers, no micrometers, no lasers, no power tools,
only crude hand tools and skill...

Waaaaait a minute! G

I'm a serious woodworker, and the guys who made stuff for nobility back
then most certainly did have good tools!

1.) Wooden hand planes, some with metal mechanisms, go back to the
Greeks and Romans, as does metallurgy for making cutting tools. There
were many fine tool examples made in the 17 and 1800's. Basic tools,
like squares, go back thousands of years, and are easily made by the
user and calibrated to themselves.

2.) They had rulers back then, but they weren't made by Starrett or
Brown & Sharpe. G A ruler is simply an arbitrary measuring device.
If you use the same measuring tool to make an item, the tool doesn't
need to be accurate to a specific standard.

Furniture fits people, items made for specific people (the King), were
made to that person's preferences. Parts like doors and drawers are
made slightly oversize and hand fitted to specific openings. This is
still done today, with fine, very high-quality work.

Specific measurements are not important until interchangeability of
parts (factory production) becomes a requirement. Much furniture and
cabinetry is built with a measuring device called a "story stick". A
modern example of a simple story stick are the red 16" and black 19.2"
stud spacing markers printed on measuring tapes for framing buildings.

3.) You don't need micrometers for woodworking. They get used for
setting up precision machinery, not for measuring the wood.

4.) Water powered machines were available at that time for such tasks as
heavy sawing.

5.) Low cost apprentices, and sometimes slaves, were plentiful. Who
needs machines when you have 100 helpers?

On Mar 17, 6:52*pm, nrp wrote:
On Mar 15, 8:32 am, Peter wrote:

What also suprises me is how bad brand new props can be, despite
having been statically balanced *supposedly* very accurately.

In my life I've purchased two brand new McCauley fixed pitch props.
Both were substantially out-of-balance as they came out of the box,
and both were fixed by a local prop shop. *I am amazed the prop shop
(Maxwell) could do better given their comparatively crude tools. *Must
just be skill & attention to detail.

This flys in the face of the "FAA certified parts are perfect" theory.
One would think after spending several thousand dollars on a piece of
forged aluminum that might cost 200 bucks in raw materials that the
remaining costs are for the manufacturer to deliver a high quality
product. The fact that a local prop shop with crud tools can balance
it better then the manufatcturer is laughable......... JMHO..

Ben