gmcjetpilot
Joined: 04 Nov 2006
Posts: 170
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 Posted: Mon Dec 18, 2006 6:19 am Post subject: Wood Prop Loss - Cozy (Catto Prop) |
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Charlie from what I know about wood prop harmonics and
fatigue was not the issue, like it can be a failure mode
for metal props. I do think it was manufactured or installation
error. We are talking a natural material, bonding pieces
together.
Usually wood props are very reliable but are subject
to wear and tear to a greater degree than metal. OF course
all wood prop owners should re-torque their prop several
times a year depending on changes in weather (temp/humidity).
Also the engine may be modified. 180 HP puts out a mean power
pulse. With the bolts loose and fretting problems can occure.
Also he felt the vibs for 4 weeks before! LESSON if you feel
somthing figure it out before flying. I thing the prop just started
to fail. Even with tight bolts props take a beating.
The problem is if you suspect a problem finding the
crack in a fiberglass wrapped wood prop may be hard to do
with out some NDT (non destructive test).
Catto has had other failures
and it was in a racing situation. Not a Catto prop put down but
the one that failed was on a formula racer and the bond failed.
The way the joint was made was less than ideal.
Many times
to make up the wood for the prop blank they glue pieces together.
I am sure with a three bladed one piece wood prop Catto has to
make some interesting joints and bond lines.
>>From: Charlie England <ceengland(at)bellsouth.net>
| Quote: | >Subject: Re: Wood Prop Loss - Cozy
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| Quote: | >Hopperdhh(at)aol.com wrote:
> For those of us who fly behind wood props, this is a good
> read. It may give some indication of the symptoms of a wood prop
> beginning to fail. And then failing... 
>
> Dan Hopper
> RV-7A
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| Quote: | Haven't read the whole thing yet, but there's a glaring error in his
analysis:
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| Quote: | My theory is that there was a crack in a blade which was growing,
bringing the resonant frequency of the prop in and out of the RPM
operating range as it got bigger and the vibration mode frequencies
changed. One blade leaves, then 10 seconds later the hub gives up the
ghost.'
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| Quote: | If he had lost a blade, it wouldn't have been 10 seconds; more like 1
second. And it wouldn't have been just the prop that departed.
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[quote]Less than an ounce off a tip will feel like the airframe is coming
apart. An entire blade will likely cause the engine to leave with the [quote][b]
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