---------------------------------------------------------- Allegro-List Digest Archive --- Total Messages Posted Fri 10/30/09: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 03:00 AM - Re: Low frequency vibration noise (theo van duin) ________________________________ Message 1 _____________________________________ Time: 03:00:44 AM PST US Subject: Re: Allegro-List: Low frequency vibration noise From: theo van duin 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 : > > 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 * wrote: > > > From: theo van duin > 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 > >: >> >> 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 >> >* wrote: >> >> >> >> From: theo van duin >> > >> Subject: Allegro-List: Low frequency vibration noise >> 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) >> >> * >> >> rel=nofollow target=_blank>http://www.matronics.com/Navigator?Allegr o-List >> et=_blank>http://forums.matronics.com >> llow target=_blank>http://www.matronics.com/contribution >> * >> >> * >> >> target="_blank" href="http://www.matronics.com/Navigator?Allegro-Lis t">http://www.matronics.com/Navigator?Allegro-List >> target="_blank" href="http://forums.matronics.com/">http://forums.ma tronics.com >> target="_blank" href="http://www.matronics.com/contribution">http:// www.matronics.com/contribution >> * >> >> > * > > 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 > * > > * > =========== =========== =========== =========== > * > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message allegro-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Allegro-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/allegro-list Browse Digests http://www.matronics.com/digest/allegro-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.