Today's Message Index:
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1. 11:37 AM - AW: Re: 912 with low RPM--- new vibration problem (Thom Riddle)
2. 09:55 PM - Vibration due prop irregular blades (Fergus Kyle)
Message 1
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| Subject: | Re: AW: Re: 912 with low RPM--- new vibration problem |
Gtblu,
In answer to your question about vibration smoothing out at 5400 rpm, yes, it is
possible. As the centrifugal forces increase with increasing rpm, the apparent
out-of-trackness at places other than the tip could disappear. Do you know
which blade is running out of track? You might consider removing the blades and
comparing them to each other on a true flat surface in several directions. If
one of them is measurably out of synch with the others that could be your problem
and a blade replacement might resolve the issue.
--------
Thom Riddle
N221FA Allegro 2000 912UL
N197BG FS1/447
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Believe nothing, no matter where you read it or who has said it, not even if I
have said it, unless it agrees with your own reason and your own common sense.
- Buddha
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=170197#170197
Message 2
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| Subject: | Vibration due prop irregular blades |
I have read the considerable discussion regarding 912 and vibration,
and the possibility of improper prop blade angles of pitch.
I have a 914 with a Woodcomp CS prop which I put together after
shipping. At one stage, the maker suggested I check the accurate duplication
of pitch angle of each blade against a made-up stand and a common angle
standard. I couldn't afford to make this, nor to transport it to someone who
had the jig.
I did have a number of paper clamps which slide onto small groups of
printed 8.5x11inch sheets - and make them into a temporary booklet. You may
have seen these OR have a source of small ID straws or alu tubing.
I used these by marking a fixed distance inboard of the prop tips on
all three blades, then covered one with release plastic film and made an
composite mask around the blade. When it hardened, I checked to see that it
sat in exactly the analogous site on each of the 3 blades. I then glued one
of the above-described sighting tubes such that when viewed from one end,
the straw sighted to exactly the same spot on the preceding blade trailing
edge. If it does so, the prop blades must have the same pitch angle,
whatever that may be.
Thus, if you change the common pitch angle, you would have to repeat
the fabrication of a new sighting tube to gauge its new commonality.
Maybe that's not too clear. If someone wants, I'll post a photo or
two, or a sketch.
Ferg
Europa 914 mono classic CS prop
90% done, 50% to go
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