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1. 03:00 AM - Re: Low frequency vibration noise (theo van duin)
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Subject: | Re: Low frequency vibration noise |
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@bellsouth.net>:
>
> 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 i
s
> 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 track
ing
> 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 bl
ade
> 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@gmail.com>* wrote:
>
>
> From: theo van duin <t.j.vanduin@gmail.com>
> Subject: Re: Allegro-List: Low frequency vibration noise
> To: allegro-list@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 Andr=E9's
> attention, as he told me. Andr=E9 checked the pitch of the blades and the
se
> 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 su
re
> 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 o
f
> a match head.
>
> Maybe you are right about the cause of the vibration noise being somethin
g
> electric. This brings me to the next problem I'ld like to resolve by putt
ing
> 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@bellsouth.net<http://us.mc838.mail.ya
hoo.com/mc/compose?to=hgmckay@bellsouth.net>
> >:
>>
>> 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 beca
use
>> 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 t
hey
>> 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 th
e
>> problem being electrical. Others on this forum may have some better idea
s.
>>
>> Hugh McKay
>> Allegro 2000
>> N661WW
>> Rotax 912
>>
>> --- On *Tue, 10/27/09, theo van duin <t.j.vanduin@gmail.com<http://us.mc
838.mail.yahoo.com/mc/compose?to=t.j.vanduin@gmail.com>
>> >* wrote:
>>
>>
>>
>> From: theo van duin <t.j.vanduin@gmail.com<http://us.mc838.mail.yahoo.co
m/mc/compose?to=t.j.vanduin@gmail.com>
>> >
>> Subject: Allegro-List: Low frequency vibration noise
>> To: allegro-list@matronics.com<http://us.mc838.mail.yahoo.com/mc/compose
?to=allegro-list@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 noi
se
>> (about 1 to 2 Hz)
>> in my headphone, especially during climb. The motor is a Rotax 912 UL. T
he
>> 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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