Hi Ken and Graham,
Thank you for the informative replies.
Ken, I can confirm everything inside the hub is secure and a good fit. There is
very little play in the system now. I learnt a lot last year when I stripped
the propeller down with Pete Jeffers; and put into action some of his excellent
advice. What I am referring to, with the tick sound of something loose, is when
one of the blades is removed from the assembly and you rotate it around, such
the tip faces upwards then rotate 180 downwards you can hear a tick sound
---From the (I think) lead weights inside the blade In other words the static
balance
mass seems to have come loose. It only got noticed because the airfield was
so quiet on Saturday. Its also consistent with Grahams 300mm comment. The sound
ticks towards the tip when held downwards, and mid-blade when held tip-upwards.
Therefore, with the information provided by both of you, my current hypothesis,
which fits the evidence, is that the weight has loosened itself from
the epoxy resin on the side towards the tip but the resin has remained fixed in
place.
I was concerned that I do not have enough skills to address the issue, but from
what Graham has written I might.
Graham, can I explore this a bit more with you? I understand in principle all
that
you are saying, and you wrote, regarding the blade-moment jig, a similar thing
to me about a year ago. I have constructed a jig, which has a pivot point
in-line with the centre of rotation and a balance support which can be placed
along the blade to measure the moment.
>From the polar plot of my vibration analysis, I can see that at cruise RPM the
imbalance is aligned perfectly with the blade with the loose weight. This would
be consistent with a mass that moves outwards in the rotation radius and pulls
more.
What is not clear to me, using your method are the following: -
1) In my single blade, where as I mentioned above, the epoxy seems to still
be in place, how could I remove this without damaging the blade, in order to
remove
the weight and reset it?
2) What is the best method to install the weight once its out? I guess its
along
the lines of bathe the lead weight in epoxy and slide it along until the
desired blade-moment is achieved and then wait for the epoxy to set.
Then I have one last question: -
3) If I cant remove the lead weight from inside the blade, I am thinking
about
removing one of the washers currently installed on the dynamic balance arm
to see if this moves the dynamic balance towards the polar centre? Is this a
reasonable
approach?
I am going to revisit the blade-moment measurements. When I tried a year ago,
everything
was OK. But, the method I used was to lower the tip on to the mass scale;
which would, of course (if the assumptions above are correct) reset the
lead weight to the correct position for the measurement. I will ensure that the
weight is towards the tip, on the suspect blade and then re-measure.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=466109#466109
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