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1. 05:55 AM - Re: Prop Failure (Vaughn Brock Capt ESC/AWXO)
2. 05:59 AM - Re: Prop Failure (Vaughn Brock Capt ESC/AWXO)
Message 1
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| Subject: | Re: Prop Failure |
--> RV3-List message posted by: Vaughn Brock Capt ESC/AWXO <Brock.Vaughn@hanscom.af.mil>
I spoke to Mike DeMuth yesterday for over an hour. I seems I was incorrect
about the manor in which things happened. After a response from a helpful
person replying to my message I realized my first message was not objective.
Mike DeMuth was a fountain of knowledge and I am grateful he imparted some
of his 30+ years of prop experience to me. After speaking with him I could
not help but agree that the spinner came off first and the prop failure
resulted in the spinner hitting the weakest part of the prop (trailing edge)
resulting in its failure. The TE and spinner were not recovered and there
is little evidence of exactly what happened. Regardless, the chain of
events makes sense and is good enough in my book.
The summary of this issue is to ensure your spinner has at least 3/8 to 1/2
" of clearance around the prop (mine had ") and to ensure the screws
holding the spinner are properly torqued. If the screws are ever over
torqued and you have a wood prop, it would be in your best interest to
replace the spinner immediately or not fly with the spinner. Repairing a
$100 item that if it fails can kill you is not worth the effort or repair
and replacement is more sound in my mind. The proper torque is probably
around 10-15 inch pounds, roughly setting 1 or 2 on a Makita drill. When
the fiberglass is over torqued it fractures. The fractured hole may fail
and then another because the load is increased on the surrounding hole
because of the previously failed hole. The extra load fails the next hole,
etc... Since wood props require re-torquing every 25 hours or at major temp
changes (seasonal changes), it is likely that you will eventually run the
risk of over torquing a screw. Given my spinner was 10 years old and the
plane always had a wood prop, the spinner more likely came off 25-50 times.
Likely chance of getting over tightened.
I learned that the trailing edge can easily be damaged by simple ground
handling. Given the fact that many planes are in shared hangers and moved
w/o your knowledge, I would highly recommend you consider posting a sign on
you prop clearly stating something to the effect of "WOOD PROP DO NOT
PUSH/PULL". It is possible to move an airplane and put too much force on
the trailing edge and fracture it. Add sloping ramps, snow, grass fields
and unfamiliar people (students pilots) having poor ground handling skills,
and you can see the probability of inadvertently damaging the TE w/o
realizing it.
BROCK VAUGHN
781 354-6656
Message 2
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| Subject: | Re: Prop Failure |
--> RV3-List message posted by: Vaughn Brock Capt ESC/AWXO <Brock.Vaughn@hanscom.af.mil>
I spoke to Mike DeMuth yesterday for over an hour. I seems I was incorrect
about the manor in which things happened. After a response from a helpful
person replying to my message I realized my first message was not objective.
Mike DeMuth was a fountain of knowledge and I am grateful he imparted some
of his 30+ years of prop experience to me. After speaking with him I could
not help but agree that the spinner came off first and the prop failure
resulted in the spinner hitting the weakest part of the prop (trailing edge)
resulting in its failure. The TE and spinner were not recovered and there
is little evidence of exactly what happened. Regardless, the chain of
events makes sense and is good enough in my book.
The summary of this issue is to ensure your spinner has at least 3/8 to 1/2
" of clearance around the prop (mine had ") and to ensure the screws
holding the spinner are properly torqued. If the screws are ever over
torqued and you have a wood prop, it would be in your best interest to
replace the spinner immediately or not fly with the spinner. Repairing a
$100 item that if it fails can kill you is not worth the effort or repair
and replacement is more sound in my mind. The proper torque is probably
around 10-15 inch pounds, roughly setting 1 or 2 on a Makita drill. When
the fiberglass is over torqued it fractures. The fractured hole may fail
and then another because the load is increased on the surrounding hole
because of the previously failed hole. The extra load fails the next hole,
etc... Since wood props require re-torquing every 25 hours or at major temp
changes (seasonal changes), it is likely that you will eventually run the
risk of over torquing a screw. Given my spinner was 10 years old and the
plane always had a wood prop, the spinner more likely came off 25-50 times.
Likely chance of getting over tightened.
I learned that the trailing edge can easily be damaged by simple ground
handling. Given the fact that many planes are in shared hangers and moved
w/o your knowledge, I would highly recommend you consider posting a sign on
you prop clearly stating something to the effect of "WOOD PROP DO NOT
PUSH/PULL". It is possible to move an airplane and put too much force on
the trailing edge and fracture it. Add sloping ramps, snow, grass fields
and unfamiliar people (students pilots) having poor ground handling skills,
and you can see the probability of inadvertently damaging the TE w/o
realizing it.
BROCK VAUGHN
781 354-6656
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