Wierd vibration -- Prop or engine, balance or not???

[Chuck]

Hi guys & gals,

I purchased an older Cherokee 180 with a Lycoming O-360A4A and
Sensitech propeller. Unfortunately, I'm not sure on of the prop model
as I haven't pulled the cone yet.

Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job.

But since then, another very experienced A&P has told me that
fixed-pitch props are never "balanced". This guy told me that balance
jobs are done on constant-speed props and not fixed-pitch.

So, does anyone have experience with a balance job on a fixed-pitch
prop? Or has anyone had a vibration problem that turned out to be a
fixed-pitch prop balance problem???

I ask because it would take a week to get the equipment in and of
course, cost several hundred for the prop balance. I'd hate to spend
that money and still have the vibration problem.

Thanks for any suggestions or information you guys can offer.



Chuck
N7398W

[nuke]

<< Since I purchased my Cherokee, there has been a slight vibration in it
while running and flying. The first mechanic I had went for a ride
with me and immediately said the prop needed a "balance" job. >><BR><BR>

A prop shop can static balance the prop out of the plane and most can dynamic
balance it once it is installed.

Second mechanic isn't correct.

However, there are limits to the level of balance to be acheived.


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.

[Nathan Young]

On Sun, 28 Nov 2004 03:36:25 GMT, Chuck > wrote:

>Hi guys & gals,
>
>I purchased an older Cherokee 180 with a Lycoming O-360A4A and
>Sensitech propeller. Unfortunately, I'm not sure on of the prop model
>as I haven't pulled the cone yet.
>
>Since I purchased my Cherokee, there has been a slight vibration in it
>while running and flying. The first mechanic I had went for a ride
>with me and immediately said the prop needed a "balance" job.
>
>But since then, another very experienced A&P has told me that
>fixed-pitch props are never "balanced". This guy told me that balance
>jobs are done on constant-speed props and not fixed-pitch.
>
>So, does anyone have experience with a balance job on a fixed-pitch
>prop? Or has anyone had a vibration problem that turned out to be a
>fixed-pitch prop balance problem???
>
>I ask because it would take a week to get the equipment in and of
>course, cost several hundred for the prop balance. I'd hate to spend
>that money and still have the vibration problem.
>
>Thanks for any suggestions or information you guys can offer.

A dynamic prop balance would probably smooth the ride. Another thing
to check is the engine mount dampeners - if they are shot, no amount
of dynamic prop balancing will fix the vibration.

[Dan Luke]

"Chuck" wrote:
> But since then, another very experienced A&P has told me that
> fixed-pitch props are never "balanced". This guy told me that balance
> jobs are done on constant-speed props and not fixed-pitch.

Are you sure you understood him correctly? If so, you need to stay away
from this guy.

[snip]

> I ask because it would take a week to get the equipment in and of
> course, cost several hundred for the prop balance. I'd hate to spend
> that money and still have the vibration problem.

Might happen, but the prop should be dynamically balanced, anyway. For
the money, it's one of the best things you can do for your airplane. An
out-of-balance prop can have all sorts of bad effects on the airframe,
engine, avionics, etc.
--
Dan
C172RG at BFM

[[email protected]]

On Sun, 28 Nov 2004 03:36:25 GMT, Chuck > wrote:

Below, interspersed

>Hi guys & gals,
>
>I purchased an older Cherokee 180 with a Lycoming O-360A4A and
>Sensitech propeller. Unfortunately, I'm not sure on of the prop model
>as I haven't pulled the cone yet.

It's either a 76EM8 or a 76EM8S5

>Since I purchased my Cherokee, there has been a slight vibration in it
>while running and flying. The first mechanic I had went for a ride
>with me and immediately said the prop needed a "balance" job.
>
>But since then, another very experienced A&P has told me that
>fixed-pitch props are never "balanced". This guy told me that balance
>jobs are done on constant-speed props and not fixed-pitch.
>
>So, does anyone have experience with a balance job on a fixed-pitch
>prop? Or has anyone had a vibration problem that turned out to be a
>fixed-pitch prop balance problem???

I've balanced quite a few of them. Honestly, if you have a vibration
problem, you should probably have the propeller removed and inspected
for condition/static balance by a prop shop.

I really don't want to be the one to tell you this, but anyone
purchasing any aircraft with this engine/prop combination should have
the prop inspected as part of the pre-buy inspection.

This engine/prop installation has zero tolerance for diameter
reduction. Unfortunately, it is quite common for the tips to be
re-worked and re-painted, if the prop has been "shortened" at all, it
is no longer airworthy.

>I ask because it would take a week to get the equipment in and of
>course, cost several hundred for the prop balance. I'd hate to spend
>that money and still have the vibration problem.

When I was in the dy-bal business, we often charged a reduced rate if
no "balancing" was needed. Can't you find someone in your area that
performs dy-bals on a regular basis?

TC

snip

[Fly]

Your 2nd A&P doesn't know what he is talking about.
85% chance yours can be helped. I have the records to prove it. I
have checked over a thousand.

Find somebody in your area to check it. $175-225 probably.
Savy technician can give you opinion on whther lord mounts are bad.

Kent Felkins
Tulsa

"Chuck" > wrote in message
...
> Hi guys & gals,
>
> I purchased an older Cherokee 180 with a Lycoming O-360A4A and
> Sensitech propeller. Unfortunately, I'm not sure on of the prop model
> as I haven't pulled the cone yet.
>
> Since I purchased my Cherokee, there has been a slight vibration in it
> while running and flying. The first mechanic I had went for a ride
> with me and immediately said the prop needed a "balance" job.
>
> But since then, another very experienced A&P has told me that
> fixed-pitch props are never "balanced". This guy told me that balance
> jobs are done on constant-speed props and not fixed-pitch.
>
> So, does anyone have experience with a balance job on a fixed-pitch
> prop? Or has anyone had a vibration problem that turned out to be a
> fixed-pitch prop balance problem???
>
> I ask because it would take a week to get the equipment in and of
> course, cost several hundred for the prop balance. I'd hate to spend
> that money and still have the vibration problem.
>
> Thanks for any suggestions or information you guys can offer.
>
>
>
> Chuck
> N7398W
>
>

[Doug]

Balancing a prop dynamically is like getting the alignment done on
your car. You do it, only way to know if it was out, is if it is
better after you do it.
Anyway, just do it, it will probably help.

(nuke) wrote in message >...
> << Since I purchased my Cherokee, there has been a slight vibration in it
> while running and flying. The first mechanic I had went for a ride
> with me and immediately said the prop needed a "balance" job. >><BR><BR>
>
> A prop shop can static balance the prop out of the plane and most can dynamic
> balance it once it is installed.
>
> Second mechanic isn't correct.
>
> However, there are limits to the level of balance to be acheived.

[G.R. Patterson III]

Chuck wrote:
>
> So, does anyone have experience with a balance job on a fixed-pitch
> prop? Or has anyone had a vibration problem that turned out to be a
> fixed-pitch prop balance problem???

I had a vibration problem with my old Cessna 150 that we couldn't track down.
I finally had the prop removed an sent out for inspection. Turned out that one
blade had a different pitch from the other. I think some amateur tried to turn
it into a cruise-pitch prop. A prop overhaul cured my problem.

In any case, there are shops out there that will balance fixed pitch props. A
dynamic balance job will make it run much more smoothly -- until the next time
someone files a nick out of the prop.

George Patterson

[[email protected]]

Chuck > wrote:
: Hi guys & gals,

: I purchased an older Cherokee 180 with a Lycoming O-360A4A and
: Sensitech propeller. Unfortunately, I'm not sure on of the prop model
: as I haven't pulled the cone yet.

: Since I purchased my Cherokee, there has been a slight vibration in it
: while running and flying. The first mechanic I had went for a ride
: with me and immediately said the prop needed a "balance" job.

I've got the same plane/engine/prop combination. I had to change the
alternator belt a few months ago and my mechanic and I decided that the prop wasn't
indexed properly. The prop has a 6-bolt pattern so it could be put on incorrectly at
60 degree increments. The compression stroke used to put TDC with the prop at 3-9
o'clock. Now, it's more like 1-7 o-clock. It significantly reduced the vibration on
mine.

I know that the prop is supposed to be on only one way. The really annoying
thing is that the service manual for the plane says TDC should be at 2-8 o-clock....
exactly halfway between the two possible positions. My mechanic and I puzzled over it
for awhile, but eventually decided (from the way other Cherokees' had their props
indexed) that it should be moved. I can see why the previous owner may have put it on
the other way, but since the vibration is much reduced now I believe this way is
correct. I've also heard rumors about pigs flying and a slight manifold pressure
increase from having the carb air induction in the correct position to get a bit of
propwash. Not sure I buy it, but the new position would seem to make that more
possible (fiberglass clamshell cowling on mine).

Seems stupid to make it possible to put the prop on wrong, but they did.
Pity, too... it was much easier (and safer) to pull the prop through the compression
stroke at the 3-9 o'clock position.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[[email protected]]

Chuck

In my life I've purchased two brand new fixed pitch props. The first
was a replacement for an overhauled O-300D and the second for my
present 1975 172M when it was new. Both were made by McCauley, both
were out of balance when new, and both were made to run smooth by
Kenny Maxwell (a local prop shop).

I don't know how he does it given the comparatively crude tools used,
but he did. They were not balanced on the engine afterwards either.

The second one I first verified by wrapping two layers of duct tape
around a randomly chosen blade near the hub. If it is off in static
balance, it either will run smoother or rougher. That tells you the
next step. I finished having to put several coats of paint on the
back side of the lighter blade to get it to run smooth, but thought it
a helluva way to make a new 172 run right. Cessna picked up the
repair under warranty. Those were the days.....

If course you could also have prop roughness from unequal blade pitch,
or from the blades not being directly opposite each other (i. e. bent
like a boomerang).

If you have a similar driveline as my 172, it is also possible that
your prop is indexed wrong with respect to the engine crank. The
proper orientation should be described in the aircraft service manual.
The proper orientation is specific and some mechanics may not know
that. On my 172 facing the front of the A/C, it is to be at TDC when
the prop axis is at the 1:30 - 7:30 orientation.

Find out what is causing your problem. You'll save a lot of long term
agony.

[tony roberts]

Hi Chuck

I suggest that the first thing you do is check alignment/tracking.
Why? Because it takes one minute and costs nothing, and if nothing else
it eliminates a probable cause.

So. Get yourself a cardboard box, and stand it on something that allows
the prop to touch the box.

Place the box so it is exactly touching the prop.
Rotate to the other blade.
Does that also touch the same?
If it does then it ain't tracking.
If it doesn't - get that checked first.

HTH

Tony

In article >,
Chuck > wrote:

> Hi guys & gals,
>
> I purchased an older Cherokee 180 with a Lycoming O-360A4A and
> Sensitech propeller. Unfortunately, I'm not sure on of the prop model
> as I haven't pulled the cone yet.
>
> Since I purchased my Cherokee, there has been a slight vibration in it
> while running and flying. The first mechanic I had went for a ride
> with me and immediately said the prop needed a "balance" job.
>
> But since then, another very experienced A&P has told me that
> fixed-pitch props are never "balanced". This guy told me that balance
> jobs are done on constant-speed props and not fixed-pitch.
>
> So, does anyone have experience with a balance job on a fixed-pitch
> prop? Or has anyone had a vibration problem that turned out to be a
> fixed-pitch prop balance problem???
>
> I ask because it would take a week to get the equipment in and of
> course, cost several hundred for the prop balance. I'd hate to spend
> that money and still have the vibration problem.
>
> Thanks for any suggestions or information you guys can offer.
>
>
>
> Chuck
> N7398W




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

[Fly]

Toecutter gave you good advice.

If your engine is running in tip top shape. the vibration cause
probabilities are 1, dynamic balance, 2, rubber isolation mounts (lord or
barry), 3, interference problems, exhaust hiting cowling.
Interference problems can be checked easily and cheaply!

Without other instructions, install the prop with the blades aligned with
the crank throws as close as possible. Most 4 cyl Lycomings and 4 cyl
Continentals have two blade prop installed on the bushings at 1:00 & 7:00
facing from the front looking aft. Or from the pilots seats 11:00t & 5:00.


Many fixed pitch props are never checked after new installations. And a
metal fixed pitch prop will take a different set after 3 or 4 thousand
hours. Theblade angle may not match closely and the static balance be
different.

My area, props shops charge a hundred bucks for a static balance check and
blade angle check. An overhaul is about $500.

Toecutter is right in that many Sensenich props models are not to be
shortened because the vibration characteristics change.


Since you asked, you are obligated to inform us of what solves you problem.

good luck
Kent Felkins

[[email protected]]

Kent - Do you by chance know why the prop blades should be in the same
plane as the crank throws? Your description (1 & 7 oclock) is at odds
with that).

In 4 cylinder engines, I think I can see a basis for a 45 degree
offset to prevent second harmonic engine yaw from coupling into the
airframe as first harmonic due to the different swinging inertia of a
two blade prop.

Does anyone else know why or have a different reason for prop
orientation to the crank throws? I know the orientation is critical
on a 4 cylinder 172. A local flying club almost tore their newly
majored engine apart chasing engine first harmonics before finding out
the mechanic had put the prop on incorrectly.

I'd like to believe the balance people would have caught that sort of
thing rather than hang compensating weights on the spinner.

[[email protected]]

Another cheap check is to trace one of the blades on a piece of
cardboard and put it against the other blade.
If they match, Great!
After years of nick dressing your blades may not even be close to the
same dimensions/weights.

Dave

wrote:

> Kent - Do you by chance know why the prop blades should be in the same
> plane as the crank throws? Your description (1 & 7 oclock) is at odds
> with that).
>
> In 4 cylinder engines, I think I can see a basis for a 45 degree
> offset to prevent second harmonic engine yaw from coupling into the
> airframe as first harmonic due to the different swinging inertia of a
> two blade prop.
>
> Does anyone else know why or have a different reason for prop
> orientation to the crank throws? I know the orientation is critical
> on a 4 cylinder 172. A local flying club almost tore their newly
> majored engine apart chasing engine first harmonics before finding out
> the mechanic had put the prop on incorrectly.
>
> I'd like to believe the balance people would have caught that sort of
> thing rather than hang compensating weights on the spinner.

[Fly]

in reply to:

- Kent, Do you by chance know why the prop blades should be in the same
> plane as the crank throws? Your description (1 & 7 oclock) is at odds
> with that).
>
> In 4 cylinder engines, I think I can see a basis for a 45 degree
> offset to prevent second harmonic engine yaw from coupling into the
> airframe as first harmonic due to the different swinging inertia of a
> two blade prop.

I'm not an engineer, I have not done a modal analysis and do not know how
the 2nd harmonic will act.
45 degrees? The position is 30 degrees after TDC or BDC which ever crank
throw you are watching.
I have no idea why Lycoming does not put a bushing exactly at TDC. Though I
do recall seeing one there in the lightweight flange models.
Perhaps a Commanche. Or maybe the crank shop installed the bushing in the
wrong hole after regrind!

A prop installed on the 90 degree bushing can display a very acceptable
dynamic balance reading on the front end of the engine. However the engine
and prop assembly as a whole can be roughly moving in a dynamic couple.
This couple will be apparent if a second vibration sensor is used on the
aft of the engine. A differential of 0.30 - 0.40 Inches per second
is not unusual.

The pros do not always get it right the first time either. Some examples:
The first 300 of the Mooney 201's have a service bulletin that moves the
index bushings in the crank flange. Changes the IO-360 A1xx to a
IO-360-A3xx. A Lycoming service bltn say about the same for some Aviat
Huskys. Grumman AA-5A service manual is different from the AA-5B. 5a is
before TDC, 5b is after.

Perhaps the timing of the combustion impulse in consideration with the prop
vibe survey is a factor. Faint rumour is that it will be difficult to
certify a metal prop on a 4 cyl Lyc with electronic ignition. Did Van's
aircraft get Hartzell to bless their's?

And finally in reply to


> I'd like to believe the balance people would have caught that sort of
> thing rather than hang compensating weights on the spinner.

Been around aviation long?

Besides, heck, if a flying club was smart enough to know they were chasing
1st order vibres, they should have been savy to suspect prop index.
And another besides...... a lot of balance technicians are barely
acquainted with theory and don't need more than minimum experience.
Their box tells them how to do it!

Kent Felkins

[Chuck]

>Since you asked, you are obligated to inform us of what solves you problem.
>
>good luck
>Kent Felkins
>

OK Kent, I'll let the group know how it comes out.

Since this prop only has ~700 hours since new, I don't think that its
been modified or severely filed down. But you never know...

Looks like my first checks are prop dimensions, blade shape
comparison, and indexing. Those should be fairly quick & easy to do.
And if one of those doesn't expose the problem -- its time to call the
experts for a dynamic balance.

Thanks for the suggestions Kent.


Chuck

[Aaron Coolidge]

Chuck > wrote:
: OK Kent, I'll let the group know how it comes out.

: Since this prop only has ~700 hours since new, I don't think that its
: been modified or severely filed down. But you never know...

: Looks like my first checks are prop dimensions, blade shape
: comparison, and indexing. Those should be fairly quick & easy to do.
: And if one of those doesn't expose the problem -- its time to call the
: experts for a dynamic balance.

Chuck, as an owner of an older Cherokee 180 as well, I'd also look at the
motor mount Lord isolators. There is very little clearance between the
green tubular bracket at the back of the carburettor (which holds the
throttle & mixture cable sheathes) an dthe motor mount tubes. If the lord
mounts sag even a little this green tubular bracket touches the motor mount
and makes a very impressive vibration.
--
Aaron Coolidge (N9376J)

[Fly]

"Aaron Coolidge" > wrote in message
...
> Chuck, as an owner of an older Cherokee 180 as well, I'd also look at the
> motor mount Lord isolators. There is very little clearance between the
> green tubular bracket at the back of the carburettor (which holds the
> throttle & mixture cable sheathes) an dthe motor mount tubes. If the lord
> mounts sag even a little this green tubular bracket touches the motor
mount
> and makes a very impressive vibration.
> --
> Aaron Coolidge (N9376J)


Thanks for the tip Aaron. I'll remember to look at the speciifc point.

Many people do not realize the amount an engine moves while running. It is
even pulled forward some.

Try to have at least 1/2 inch clearance or more.
Kent Felkins