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And this is why you do condition inspections...

Didnt the Rv12 thing turn out to be ramp damage?
Cm
No one will ever know, I suspect. Sensenich isn't saying, and the OP is no longer with us.

I do a pretty thorough pre-flight inspection of the prop on our RV-12, and usually a pretty thorough post-flight as well. I like to think I've always examined it closely enough to catch a crack like that, but you can bet your propeller my level of pre-flight scrutiny will be raised a notch now.
 
Just spoke with Don Rowell at Sensenich. He is going to send me the findings from his engineers, but net-net, they couldn't find a specific reason for the crack. It was indeed cracked through the laminate. According to Don, due to the construction of the prop and the metal spar inside, there was no danger of a catastrophic failure, but they have not been able to determine the cause.

I should have two new blades in hand by the end of next week. Needless to say, my preflight routine will involve a flashlight and a tactile and visual examination of the prop, as well as wipedown after flights.

I'll post the info from his engineers (with his permission) when I get it.
 
NTSB Report yet to be published

No one will ever know, I suspect. Sensenich isn't saying, and the OP is no longer with us...

The NTSB Final Report has not been published yet. I wouldn't expect Sensenich to say anything about that propeller while the NTSB is investigating. The accident happened in January of last year, so it may still be several months before they publish the Final, and of course, the propeller may or may not be a topic of interest in their investigation. If the NTSB does not report anything of interest regarding the propeller, then I agree with you..."no one will ever know..."

That report will probably be read by many people, for varying reasons.
 
The NTSB Final Report has not been published yet. I wouldn't expect Sensenich to say anything about that propeller while the NTSB is investigating. The accident happened in January of last year, so it may still be several months before they publish the Final, and of course, the propeller may or may not be a topic of interest in their investigation. If the NTSB does not report anything of interest regarding the propeller, then I agree with you..."no one will ever know..."

That report will probably be read by many people, for varying reasons.

The prop split happened long before the accident, he was flying with two nearly new blades when he crashed.
 
Correction

The prop split happened long before the accident, he was flying with two nearly new blades when he crashed.

OK...I wasn't aware of that as I didn't keep up with all the details of his RV experience. Thanks for correcting me.

So, your statement that "no one will ever know" is probably right.
 
Closing this out, here's the statement from the engineers at Sensenich published with Don Rowell's perimission:

"The crack occurred at the 30% ply drop. While the crack did not and likely would not have propagated into the spar, it did go through all layers of the skin laminate. We cut into the laminate at the crack location, but we were unable to find any abnormal type of discontinuity. This is the first like this we have observed on a production propeller blade.

It is our recommendation that we replace both blades free of charge. At this point, we believe this to be a discrete failure due to an irregularity that industry standard quality control practices were unable to diagnose.

We have sectioned the blade, and will certainly continue to diagnose and if needed correct the issue that caused the failure. We do feel strongly that the alternate load paths found in the blades would have prevented this failure from becoming catastrophic."

As I said above, I will monitor the new blades carefully. As someone else said, there's no such thing as a company that hasn't supplied defective product. I expect to have a good experience with the new blades and think that Don and his staff have done all that can be expected.
 
Thanks for posting that. I'm glad it had a good outcome for you, both financially (blades replaced) and otherwise. I also found the engineer's statement at least somewhat reassuring.
 
Thanks for the update. Glad they are owning the responsibility and giving you a new prop and even happier that it all ended up well.
 
One last post to REALLY close this out. My new prop arrived this afternoon:

newprop.jpg


This is what the 3D carbon fiber looks like...AWESOME!

Now I'll have to really baby this baby!
 
Metal spar!

Mark, you said something that raised a flag for me. Metal spar, carbon skin.

Have you exposed it to unusually high temperatures?
There is a big mismatch in thermal expansion coefficient between metals and carbon fiber. Good design can mitigate this some. Its usually fine. Sometimes it isn't. Presumably Sensenich has done thorough testing of this.
Totally speculative on my part, but.......
 
99% of its life was sitting in my hangar. It hasn't sat outside much at all so i don't think heat was an issue
 
Prop construction

I recently had an excellent tour of the composite blade buildup area at the Plant City Sensenich facility.
I certainly don?t recall seeing any metal used as a ?spar? in the blades. The only metal in the assembly is the leading edges, and the hub assembly.
Dale
 
Something I learned recently from a neighbor that did some high-speed video when testing a Honda reduction drive. A propeller can shake like a noodle along its longitudinal axis at certain RPM's where a resonance occurs. I suspect that's what's happened here.
 
Mark, you said something that raised a flag for me. Metal spar, carbon skin.

Have you exposed it to unusually high temperatures?
There is a big mismatch in thermal expansion coefficient between metals and carbon fiber. Good design can mitigate this some. Its usually fine. Sometimes it isn't. Presumably Sensenich has done thorough testing of this.
Totally speculative on my part, but.......

And for less informed (me), what is thermal expansion for a matrix of carbon fiber? I looked up and found it was near zero or negative, or it shrinks with higher temps. Is that correct?

BTW, V-belts shrink with temp to aid in slippage.
 
Mark, you said something that raised a flag for me. Metal spar, carbon skin.

Have you exposed it to unusually high temperatures?
There is a big mismatch in thermal expansion coefficient between metals and carbon fiber. Good design can mitigate this some. Its usually fine. Sometimes it isn't. Presumably Sensenich has done thorough testing of this.
Totally speculative on my part, but.......

What's a high temp? My uninsulated, not climate controlled metal hangar gets pretty darn hot on a sunny summer day here in Indy ... I've not measured, but I bet 120F+ isn't unrealistic on a sunny day in the high 90's
 
Something I learned recently from a neighbor that did some high-speed video when testing a Honda reduction drive. A propeller can shake like a noodle along its longitudinal axis at certain RPM's where a resonance occurs. I suspect that's what's happened here.

It's why the standard for prop certification is a set of strain gauges on the test prop, and a series of inflight loads.

An accurate rate-adjustable strobe will show things about propellers and airframe parts which will make you question your desire to fly.
 
And for less informed (me), what is thermal expansion for a matrix of carbon fiber? I looked up and found it was near zero or negative, or it shrinks with higher temps. Is that correct?....

Yes it is, but the actual value depends on a number of things, including the particular materials used and their orientation.

Dave
 
Please

One last post to REALLY close this out. My new prop arrived this afternoon:

newprop.jpg


This is what the 3D carbon fiber looks like...AWESOME!

Now I'll have to really baby this baby!

Hopefully not the last post, really would like to hear if you like how the new prop performs.Thanks
 
Cool

Is that how all the Sensenich GA props are going to look (the 3D carbon fiber look)? Or was that a special request option?
 
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