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t.j.vanduin(at)gmail.com
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 Posted: Tue Oct 27, 2009 2:30 am Post subject: Low frequency vibration noise |
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Fellow Allegro listers,
When flying my Allegro I regularly do hear a low frequency vibration noise (about 1 to 2 Hz)
in my headphone, especially during climb. The motor is a Rotax 912 UL. The prop is a
Woodcomp Klassic 160/31R.
It might not be a motor vibration, but coming from somewhere else. I'm very curious to
find out from where. Could it be related to an unbalance of my propeller or an incorrectly
adjusted pitch of the blades?
Thanks for any comment on this,
Theo van Duin, France
Allegro 2000 (71MM)
[quote][b]
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Tue Oct 27, 2009 5:55 am Post subject: Low frequency vibration noise |
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Theo:
When did you first begin to hear this noise? I may be wrong, but at one to two Hz, I don't think it would be related to an out of balance prop because the Woodcomp prop blades were balanced at the factory and matched to the hub by numbers 1 thru 3. Because of their construction, they have little rotational mass relative to the rotating mass of the engine. Therefore they would have little effect unless one has been damaged, or one is severely out of pitch. Have you checked the tracking and pitch of your prop? If those two items are correct I would begin to look elsewhere for the cause, such as an electrical problem, but at such a low frequency it is hard to imagine the problem being electrical. Others on this forum may have some better ideas.
Hugh McKay
Allegro 2000
N661WW
Rotax 912
--- On Tue, 10/27/09, theo van duin <t.j.vanduin(at)gmail.com> wrote:
| Quote: |
From: theo van duin <t.j.vanduin(at)gmail.com>
Subject: Low frequency vibration noise
To: allegro-list(at)matronics.com
Date: Tuesday, October 27, 2009, 6:28 AM
Fellow Allegro listers,
When flying my Allegro I regularly do hear a low frequency vibration noise (about 1 to 2 Hz)
in my headphone, especially during climb. The motor is a Rotax 912 UL. The prop is a
Woodcomp Klassic 160/31R.
It might not be a motor vibration, but coming from somewhere else. I'm very curious to
find out from where. Could it be related to an unbalance of my propeller or an incorrectly
adjusted pitch of the blades?
Thanks for any comment on this,
Theo van Duin, France
Allegro 2000 (71MM)
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[quote][b]
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Threadcharmer(at)cs.com
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| Posted: Tue Oct 27, 2009 6:51 am Post subject: Low frequency vibration noise |
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Theo,
Have a passenger check for vibration in the windshield and/or doors. My Allegro experiences something similar on takeoff and we found it to be vibration in the upper corners of the windshield. I also get a small bit of vibration from the doors. It settles down when we power back. Yes, we hear it even though we have the headsets on...
Hope this helps,
Amy Hackworth
Allegro amphib N306AD
Hobe Sound, FL
[quote][b]
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t.j.vanduin(at)gmail.com
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| Posted: Tue Oct 27, 2009 7:21 am Post subject: Low frequency vibration noise |
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Hugh,
The noise was there from the first time we flew with the plane however
remarkably it did not attrack André's
attention, as he told me. André checked the pitch of the blades and these
were found to be O.K.
However, an experienced pilot/instructor told us once that to his opinion
the pitch of the blades was adjusted too coarse. At full power
the tachometer reaches something like 5200 r.p.m.
I don't think that the tracking was checked and honestly I'm not quite sure
what "tracking" exactly means and
how this checking could be done.
About propeller damage: initialy there was none. At one occasion, the engine
was started over a gravel path
and after that I found damages on two blades: 3 small holes of the size of a
match head.
Maybe you are right about the cause of the vibration noise being something
electric. This brings me to the next problem I'ld like to resolve by putting
it on the Allegro list. My radio.
Thank you Hugh for your comments,
Theo van Duin
(France)
Allegro 2000 (71MM)
2009/10/27, Hugh MCKAY III <hgmckay(at)bellsouth.net>:
[quote]
Theo:
When did you first begin to hear this noise? I may be wrong, but at one to
two Hz, I don't think it would be related to an out of balance prop because
the Woodcomp prop blades were balanced at the factory and matched to the hub
by numbers 1 thru 3. Because of their construction, they have little
rotational mass relative to the rotating mass of the engine. Therefore they
would have little effect unless one has been damaged, or one is severely out
of pitch. Have you checked the tracking and pitch of your prop? If those two
items are correct I would begin to look elsewhere for the cause, such as an
electrical problem, but at such a low frequency it is hard to imagine the
problem being electrical. Others on this forum may have some better ideas
| | - The Matronics Allegro-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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brad(at)vision-technology
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| Posted: Tue Oct 27, 2009 1:34 pm Post subject: Low frequency vibration noise |
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This is a long-shot, but I had some vibration that turned out to be from the plastic plug coming out of the gearbox shaft. It was inside the spinner and apparently that was enough to throw off the balance a bit.
Brad Kramer
N221FA
Bismarck/Mandan ND (Y19)
[quote]--
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Tue Oct 27, 2009 5:53 pm Post subject: Low frequency vibration noise |
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Theo:
Just "Google" the words Propeller Tracking and you will find the first listing to be a video of how to track a wooden propeller. The principal is the same for a three blade prop. It is easy to do. For the 912 UL engine I would suggest you remove one of the plugs from each of the four cylinders to relieve the cylinder compression before you track the prop. You can also check with one of your airplane mechanic friends and he can explain tracking further if you need help.
The full take-off power of your engine (5200 rpm) is somewhat low due to the coarse pitch of the blades, but acceptable. Rotax's maximum engine take-off speed is 5800 rpm for no more than 5 minutes, and the maximum continuous engine rpm is 5500 rpm. The maximum rpm for your Woodcomp 3 blade prop is 2700 rpm. At your maximum engine rpm of 5200 rpm, the prop speed is only 2291 rpm which is well below the maximum allowed by Woodcomp. To increase the maximum take-off speed of your engine you would need to decrease the propeller pitch slightly. Unless you have someone who knows how to do this, and has done it in the past, I would not attempt it yourself.
However, you can check the tracking of the blades, and I would recommend that you do so.
Hugh
--- On Tue, 10/27/09, theo van duin <t.j.vanduin(at)gmail.com> wrote:
| Quote: |
From: theo van duin <t.j.vanduin(at)gmail.com>
Subject: Re: Low frequency vibration noise
To: allegro-list(at)matronics.com
Date: Tuesday, October 27, 2009, 11:21 AM
Hugh,
The noise was there from the first time we flew with the plane however remarkably it did not attrack André's
attention, as he told me. André checked the pitch of the blades and these were found to be O.K.
However, an experienced pilot/instructor told us once that to his opinion the pitch of the blades was adjusted too coarse. At full power the tachometer reaches something like 5200 r.p.m.
I don't think that the tracking was checked and honestly I'm not quite sure what "tracking" exactly means and
how this checking could be done.
About propeller damage: initialy there was none. At one occasion, the engine was started over a gravel path
and after that I found damages on two blades: 3 small holes of the size of a match head.
Maybe you are right about the cause of the vibration noise being something electric. This brings me to the next problem I'ld like to resolve by putting it on the Allegro list. My radio.
Thank you Hugh for your comments,
Theo van Duin (France)
Allegro 2000 (71MM)
2009/10/27, Hugh MCKAY III <hgmckay(at)bellsouth.net>: | Quote: | Theo:
When did you first begin to hear this noise? I may be wrong, but at one to two Hz, I don't think it would be related to an out of balance prop because the Woodcomp prop blades were balanced at the factory and matched to the hub by numbers 1 thru 3. Because of their construction, they have little rotational mass relative to the rotating mass of the engine. Therefore they would have little effect unless one has been damaged, or one is severely out of pitch. Have you checked the tracking and pitch of your prop? If those two items are correct I would begin to look elsewhere for the cause, such as an electrical problem, but at such a low frequency it is hard to imagine the problem being electrical. Others on this forum may have some better ideas.
Hugh McKay
Allegro 2000
N661WW
Rotax 912
--- On Tue, 10/27/09, theo van duin <t.j.vanduin(at)gmail.com> wrote:
| Quote: |
From: theo van duin <t.j.vanduin(at)gmail.com>
Subject: Low frequency vibration noise
To: allegro-list(at)matronics.com
Date: Tuesday, October 27, 2009, 6:28 AM
Fellow Allegro listers,
When flying my Allegro I regularly do hear a low frequency vibration noise (about 1 to 2 Hz)
in my headphone, especially during climb. The motor is a Rotax 912 UL. The prop is a
Woodcomp Klassic 160/31R.
It might not be a motor vibration, but coming from somewhere else. I'm very curious to
find out from where. Could it be related to an unbalance of my propeller or an incorrectly
adjusted pitch of the blades?
Thanks for any comment on this,
Theo van Duin, France
Allegro 2000 (71MM)
|
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et=_blank>http://forums.matronics.com
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[quote][b]
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t.j.vanduin(at)gmail.com
Guest
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| Posted: Fri Oct 30, 2009 2:00 am Post subject: Low frequency vibration noise |
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Hugh, Amy and Brad,
Thanks for your comments. I will check on the items you mentioned. It's obvious that the propeller tracking check is a must and rather
easy to perform.
Theo (in France)
Allegro 2000 (71MM)
2009/10/28, Hugh MCKAY III <hgmckay(at)bellsouth.net (hgmckay(at)bellsouth.net)>: [quote] Theo:
Just "Google" the words Propeller Tracking and you will find the first listing to be a video of how to track a wooden propeller. The principal is the same for a three blade prop. It is easy to do. For the 912 UL engine I would suggest you remove one of the plugs from each of the four cylinders to relieve the cylinder compression before you track the prop. You can also check with one of your airplane mechanic friends and he can explain tracking further if you need help.
The full take-off power of your engine (5200 rpm) is somewhat low due to the coarse pitch of the blades, but acceptable. Rotax's maximum engine take-off speed is 5800 rpm for no more than 5 minutes, and the maximum continuous engine rpm is 5500 rpm. The maximum rpm for your Woodcomp 3 blade prop is 2700 rpm. At your maximum engine rpm of 5200 rpm, the prop speed is only 2291 rpm which is well below the maximum allowed by Woodcomp. To increase the maximum take-off speed of your engine you would need to decrease the propeller pitch slightly. Unless you have someone who knows how to do this, and has done it in the past, I would not attempt it yourself.
However, you can check the tracking of the blades, and I would recommend that you do so.
Hugh
--- On Tue, 10/27/09, theo van duin <t.j.vanduin(at)gmail.com (t.j.vanduin(at)gmail.com)> wrote:
| Quote: |
From: theo van duin <t.j.vanduin(at)gmail.com (t.j.vanduin(at)gmail.com)>
Subject: Re: Low frequency vibration noise
To: allegro-list(at)matronics.com (allegro-list(at)matronics.com)
Date: Tuesday, October 27, 2009, 11:21 AM
Hugh,
The noise was there from the first time we flew with the plane however remarkably it did not attrack André's
attention, as he told me. André checked the pitch of the blades and these were found to be O.K.
However, an experienced pilot/instructor told us once that to his opinion the pitch of the blades was adjusted too coarse. At full power the tachometer reaches something like 5200 r.p.m.
I don't think that the tracking was checked and honestly I'm not quite sure what "tracking" exactly means and
how this checking could be done.
About propeller damage: initialy there was none. At one occasion, the engine was started over a gravel path
and after that I found damages on two blades: 3 small holes of the size of a match head.
Maybe you are right about the cause of the vibration noise being something electric. This brings me to the next problem I'ld like to resolve by putting it on the Allegro list. My radio.
Thank you Hugh for your comments,
Theo van Duin (France)
Allegro 2000 (71MM)
2009/10/27, Hugh MCKAY III <hgmckay(at)bellsouth.net>: | Quote: | Theo:
When did you first begin to hear this noise? I may be wrong, but at one to two Hz, I don't think it would be related to an out of balance prop because the Woodcomp prop blades were balanced at the factory and matched to the hub by numbers 1 thru 3. Because of their construction, they have little rotational mass relative to the rotating mass of the engine. Therefore they would have little effect unless one has been damaged, or one is severely out of pitch. Have you checked the tracking and pitch of your prop? If those two items are correct I would begin to look elsewhere for the cause, such as an electrical problem, but at such a low frequency it is hard to imagine the problem being electrical. Others on this forum may have some better ideas.
Hugh McKay
Allegro 2000
N661WW
Rotax 912
--- On Tue, 10/27/09, theo van duin <t.j.vanduin(at)gmail.com> wrote:
| Quote: |
From: theo van duin <t.j.vanduin(at)gmail.com>
Subject: Low frequency vibration noise
To: allegro-list(at)matronics.com
Date: Tuesday, October 27, 2009, 6:28 AM
Fellow Allegro listers,
When flying my Allegro I regularly do hear a low frequency vibration noise (about 1 to 2 Hz)
in my headphone, especially during climb. The motor is a Rotax 912 UL. The prop is a
Woodcomp Klassic 160/31R.
It might not be a motor vibration, but coming from somewhere else. I'm very curious to
find out from where. Could it be related to an unbalance of my propeller or an incorrectly
adjusted pitch of the blades?
Thanks for any comment on this,
Theo van Duin, France
Allegro 2000 (71MM)
|
rel=nofollow target=_blank>http://www.matronics.com/Navigator?Allegro-List
et=_blank>http://forums.matronics.com
llow target=_blank>http://www.matronics.com/contribution
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