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tc1917(at)bellsouth.net
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 Posted: Wed Feb 03, 2010 3:35 am Post subject: rum rum |
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I have synchronized the carbs four times. I tied it down and ran it until
it made the harmonics and carefully opened just one carb. stalled and
skipped, did not stop it. I pulled the filter on both and carefully lifted
one barrel at a time and still no good effect. I do not believe it is the
carbs. I was always wondering if the timing on one side is somehow
different but that is not how the timing works. It would have to be
different on each set of plugs but I dont think that would do it either.
Wondered if I had one piston not doing its job or lagging but compression
check says they are all pretty much the same. Had to pretty much just suck
it up and live with it. Friend has a plane coming up here with a Hurth.
Says if I fly with him I wont be able to HEAR my plane. Talked to Ronny
Smith and he says to just live with it. (same answer I got two years ago).
Says it is a combination of airframe, engine, set-up, exhaust and blades. I
dont really buy that. I think that any sound can be changed, no matter
where it comes from. Besides, I have went from no prop spacer to four inch,
three inch and now a two inch and that works about best for flying. SAME
NOISE. I guess I am going to see about a muffler from the exhaust people.
May not stop the rum rum but mayb, just maybe it will be less audible. What
the heck, only another six to eight hundred bucks. No big thing, right?
Sorry for the longoo. my bad. Thanks everyone. Ted Cowan oh yeah, not
really going to squirt that foam in my wings, just thinking out loud.
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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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| Posted: Wed Feb 03, 2010 4:37 am Post subject: rum rum |
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Ted, Perhaps TNK can tell you who supplies the engine mount dampers. You could see if they have different hardnesses of the rubber. You also might try making up some small bags of lead shot and lay them on various frame components to damp out any possible source of the vibration. How do the strut and wing mount holes look and fit?
Rick Girard
On Wed, Feb 3, 2010 at 5:12 AM, Ted Cowan <tc1917(at)bellsouth.net (tc1917(at)bellsouth.net)> wrote:
[quote] --> Kolb-List message posted by: "Ted Cowan" <tc1917(at)bellsouth.net (tc1917(at)bellsouth.net)>
I have synchronized the carbs four times. I tied it down and ran it until it made the harmonics and carefully opened just one carb. stalled and skipped, did not stop it. I pulled the filter on both and carefully lifted one barrel at a time and still no good effect. I do not believe it is the carbs. I was always wondering if the timing on one side is somehow different but that is not how the timing works. It would have to be different on each set of plugs but I dont think that would do it either. Wondered if I had one piston not doing its job or lagging but compression check says they are all pretty much the same. Had to pretty much just suck it up and live with it. Friend has a plane coming up here with a Hurth. Says if I fly with him I wont be able to HEAR my plane. Talked to Ronny Smith and he says to just live with it. (same answer I got two years ago). Says it is a combination of airframe, engine, set-up, exhaust and blades. I dont really buy that. I think that any sound can be changed, no matter where it comes from. Besides, I have went from no prop spacer to four inch, three inch and now a two inch and that works about best for flying. SAME NOISE. I guess I am going to see about a muffler from the exhaust people. May not stop the rum rum but mayb, just maybe it will be less audible. What the heck, only another six to eight hundred bucks. No big thing, right? Sorry for the longoo. my bad. Thanks everyone. Ted Cowan oh yeah, not really going to squirt that foam in my wings, just thinking out loud.
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by0ung(at)brigham.net
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| Posted: Wed Feb 03, 2010 7:58 am Post subject: rum rum |
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I have synchronized the carbs four times. I tied it down and ran it until
it made the harmonics and carefully opened just one carb.
Just thinking out loud here... could it be a possibility that it is the
positioning of the prop blades in relation to the pulse from the exhaust?
The gear box having a 2.27 to 1 reduction will put the prop blades at a
slightly different position every time it fires. Cyl 1 for example will
fire every 2 turns of the engine,,,,, and the .27 will be quite close to
the .333 of a turn for the next blade to be in position, multiply this by
4 with all four cylinders firing, and rum rum.... if an exhaust pulse is
echoed off a blade as it is going past, then no echo when no blade is not
present. Maybe if you could terminate the exhaust further away from the
prop arc.
Just a thought.
Boyd Young
mkiii
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Wed Feb 03, 2010 9:07 am Post subject: rum rum |
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> Just thinking out loud here... could it be a possibility that it is
the
| Quote: | positioning of the prop blades in relation to the pulse from the exhaust?
The gear box having a 2.27 to 1 reduction will put the prop blades at a
slightly different position every time it fires. Cyl 1 for example will
fire every 2 turns of the engine,,,,, and the .27 will be quite close to
the .333 of a turn for the next blade to be in position, multiply this
by
4 with all four cylinders firing, and rum rum.... if an exhaust pulse is
echoed off a blade as it is going past, then no echo when no blade is not
present. Maybe if you could terminate the exhaust further away from the
prop arc.
Just a thought.
Boyd Young
mkiii
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Boyd/Gang:
I don't know if it is caused by exhaust and prop or not.
If Cowan is running a 912UL with a three blade WD prop and Titan Exhaust,
why aren't all combos like this, with many of them operational in the field,
having the same problem?
Some time ago I related the problem Ronnie Collins had with his Sling Shot
powered by a 582 turning a 3 blade Warp Drive. The harmonic racket on
Ronnie's Sling Shot is exactly the same as the harmonic racket produced by
Cowan's Sling Shot. I have listened to both of these aircraft fly. The
harmonic in both aircraft is loud and very much the same. May be a little
difference because of different gear box ratios, but hard to tell the
difference.
Ronnie's harmonic was caused by disturbed air produced by loose fabric which
billowed up on the inboard aft corner of the right wing. If this is what is
causing Cowan's Sling Shot harmonic, then the left inboard aft corner of the
wing would be suspect because the 912 turns opposite the 582.
After securing the loose rib stitching in Ronnie's wing, the harmonic
mysteriously disappeared. To me, this proves if part of the wing surface,
or other part of the aircraft, produces disturbed air, it can also produce
harmonic noise.
I flew Ronnie's Sling Shot before the fabric was reattached and before we
discovered that this was the problem. Not only was the harmonic loud in the
cockpit, it also created a vibration that could be felt in the airframe. It
was bad enough I would not fly the airplane unless the problem was fixed for
fear of damaging the aircraft.
I believe I shared with the List what I would do if it was my airplane.
1 - Pull the gear box and insure it is shimmed correctly and snugly as
possible. Shimming controls how the dogs perform to overcome torsional
vibration. Could loose shimming cause the blades to constantly change phase
enough to produce the harmonics that are so loud and so obvious?
2 - Some part of the aircraft is producing disturbed air, which, in turn, is
producing the harmonic as the prop blades drive through it.
This is an isolated problem with Cowan's engine, prop, exhaust system
combination. There are many, many more like combos flying with no
harmonics.
Many years ago when I was flying with my 912UL 80 hp, I picked up a harmonic
in the airframe at cruise flight, 5000 rpm. Immediately I suspected the
prop, so I insured all blades were flying with the same pitch. Did not
help. Warp Drive props normally do not have a balance problem. My harmonic
did not feel like an imbalanced prop. Flew down to Ronnie Smith's, pulled
the gear box, to find washers and shims had worn over the hours. Reshimmed
as snugly as possible and the harmonic also disappeared.
Hope Cowan can get his problem corrected. A problem like that would turn me
off to the flying that airplane. I got turned off to my airplane when the
exhaust system I was using caused different engine performance on different
days. Take off and climb 5400 normally. Next morning take off and it would
only pull 5200. Drove me nuts until I replaced the Rick Thomasson STE
Exhaust with a new Titan Exhaust. First take off with the Titan Exhaust and
I had a new engine. Now, every time I fly the 912ULS performs exactly the
same, 5400 climb. Again, I look forward to flying my airplane.
john hauck
mkIII
titus, alabama
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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by0ung(at)brigham.net
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| Posted: Wed Feb 03, 2010 2:53 pm Post subject: rum rum |
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Boyd/Gang:
I don't know if it is caused by exhaust and prop or not.
If Cowan is running a 912UL with a three blade WD prop and Titan Exhaust,
why aren't all combos like this, with many of them operational in the field,
having the same problem?
john hauck
mkIII
titus, alabama
>>>>>>>>>>>>>>>>.
john / gang
when the air is still and smooth and when you feel like you are in a suspended state, totally relaxed with just one finger on the control stick, (you know my kind of flying), you hear every little noise and feel every vibration. I have heard the rum rum a tiny bit at certain rpm. I have never felt anything, if I take my headset off the rum rum is overcome by the other noise. I am trying to paint a picture in your mind here,,,,, if you have to think about anything, an extra movement in your arm to right the plane from a thermal that rolls the plane 5 deg. just the noise of the gears turning in my head, any and all of these distractions will cause me to loose track of the rum rum that I hear
now if the rum rum is large or loud enough that you cant get away from it,,,,, that is another story.
I don't know if you could plot the rotation of the prop as a sign wave maybe with a different line for each prop. then post a vertical line through the sign waves for every pulse of the exhaust, then see what the timing would be at the given 2.27 to 1 timing of the gear box. then add to the mix the position of the blades as they pass through disturbed air caused by the airframe etc.
just hit delete, this is kind of out on a limb.
Boyd young
mkIII Utah
do not archive
[quote][b]
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zeprep251(at)aol.com
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| Posted: Wed Feb 03, 2010 4:56 pm Post subject: rum rum |
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Boyd,
Tried that too.I think it helped some.Can maybe see the exhaust in this photo.
G.Aman
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Wed Feb 03, 2010 5:22 pm Post subject: rum rum |
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Gary/Gang:
Got a bigger photo?
Thanks,
john hauck
mkIII
titus, alabama
| Quote: |
[img]cid:90387D0752D146CD8ED24392E1448E69(at)hauck[/img]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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Richard Pike
Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee
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| Posted: Wed Feb 03, 2010 7:09 pm Post subject: Re: rum rum |
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| John Hauck wrote: |
<snip>
Ronnie's harmonic was caused by disturbed air produced by loose fabric which
billowed up on the inboard aft corner of the right wing. If this is what is
causing Cowan's Sling Shot harmonic, then the left inboard aft corner of the
wing would be suspect because the 912 turns opposite the 582.
After securing the loose rib stitching in Ronnie's wing, the harmonic
mysteriously disappeared. To me, this proves if part of the wing surface,
or other part of the aircraft, produces disturbed air, it can also produce
harmonic noise.
I flew Ronnie's Sling Shot before the fabric was reattached and before we
discovered that this was the problem. Not only was the harmonic loud in the
cockpit, it also created a vibration that could be felt in the airframe. It
was bad enough I would not fly the airplane unless the problem was fixed for
fear of damaging the aircraft.
<snip>
john hauck
mkIII
titus, alabama |
John, you have jump started my brain to add another "what if" to the mix:
Using a 582 and B box, my MKIII developed damaged fabric along the right side of the fuselage below the right wing. The Stits paint cracked along the outside over the diagonal steel tube, and I ended up laying extra fabric tape along both the inside and outside fabric along the diagonal tube on that side to spread out the pulses off the prop and keep the fabric and paint from deteriorating any further.
Point is, there is a pulse produced by the prop that interacts with the airframe, and depending on the weight and tautness of the fabric, may be a factor.
Perhaps duct tape something to the inside of the left fuselage fabric wall to dampen things down and go for a test flight? Be like feeding crackers to a dead man - couldn't hurt anything.
Richard Pike
MKIII N420P (420ldPoops)
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Wed Feb 03, 2010 8:03 pm Post subject: rum rum |
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> Perhaps duct tape something to the inside of the left fuselage fabric
wall to dampen things down and go for a test flight? Be like feeding
crackers to a dead man - couldn't hurt anything.
That's right, Richard/Gang:
A lot going on back there with the prop on our pusher Kolbs.
And...everything in front of the prop affects its performance, good and bad.
My mkIII had a fabric tail cone initailly, like the original Firestar,
lasted about 100 hours before the 582 with 3 blade GSC wooden prop beat it
to death. That is why I replaced it with sheet metal and haven't had a
problem since, nearly 2,900 hours ago.
This is just the hunch of an old guy that has been around Kolbs a long time.
It is pretty obvious the noise/harmonics is being produced by the prop
because of some other problem with fabric tautness on wing, fuselage,
radically disturbed air flow created mechanically in front of the prop
somewhere on the engine or fuselage, like open rear quarter windows,
parachute canisters mounted in front of the engine on top of the center
section, faulty shimming of gear box torsional vibration dampening system,
and about anything else one could think of.
I can see disturbed air fed into the 3 blade prop causing those blades to
really move back and forth in the dogs and ramps of the gear box. Seems it
would be easy enough to get the right frequency to cause the very
undersirable, noisy harmonics that Cowan's SS experiences. If he ever
discovers the problem, I have a feeling it will be something simple that he
looks at everytime he looks at that airplane, but hasn't identified yet. I
hope he does.
john hauck
mkIII
titus, alabama - Gantt IAP, 60 sm west of Circle C, Ted Cowan's beautiful
airstrip and homestead.
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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