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FYI: New SB 18-07-05 on RV-12 Sensenich Props

How nice of them to release that the day after we pulled the spinner off to start our condition inspection.
 
This SB is a visual inspection of the front prop hub. Unfortunately, on the RV-12 there is a Front Spinner Plate blocking the view necessary to inspect the front prop hub. To remove the Front Spinner Plate all six bolts that hold the front prop hub must be removed. Blade pitch angle will need to be re-established when front prop hub is reassembled and re-torqued. This is a lot of work for a repetitive inspection every 50 hours of flight. I fly ~ 150 hours/year so I will have to do this inspection three times annually.

At some point Sensenisch redesigned the front hub to eliminate the pitch cylinder. Perhaps the large hole in the aluminum hub reduced strength and now cracks are developing along the thinnest edge at 90? to the axis? Maybe this becomes a problem because of the way the Rotax 912 stops so suddenly when you shut it down.

The new design front prop hub eliminates the large hole and instead has three smaller holes along the central axis of the hub. See drawing below. Special pins are inserted in the two outer holes to rough in the blade pitch angle. Once set, the pins are removed. No more large pitch cylinder and corresponding large hole in front prop hub.

So I?m wondering if Sensenich will offer the new front prop hub as a one-time fix for this service bulletin. Perhaps discount price, or free replacement, like they did for SB11-04-15 where 2A0R5 revision B Hubs were replaced free because a small percentage of hubs were prone to prop blade pitch loss.

It will be real nice if I don?t have to disassemble my prop three times/year?


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HUB FAILURE

Reference this SB and Sensenich Service Bulletin. I was the single failure on a Rotax 912ULS in a 2013 RV12 SLSA. Happened on 6/19/1018 while returning to Prescott, AZ. Was flying at 11,500 at 5300 RPM when a sudden significant harmonic vibration occurred. Not sure what it was but suspected the Prop. Safely returned to Prescott. Upon examination, a crack was observed in the front hub. The crack started at the first pitch setting mark and propagated around the hub. After removing the six bolts, the hub fell off in TWO pieces.

I strongly recommend that anyone who has a Sensenich Prop with the nylon plug for setting pitch, closely follow Sensenich?s SB and inspect their prop ASAP. Had I shed a blade, probably would not be writing this.

Hopefully these links to the photos will work. If not, PM me and I'll sent the pictures of the broken hub.

https://www.dropbox.com/s/r9y0zdwzl...opbox.com/s/6mi823v5g8gsoc8/IMG_0148.jpg?dl=0
 
Holy S..t!!! n233va - I'm going to insert your picture in this post. That be the case, this should be listed as a Safety Alert by Vans just like the SA for Incomplete Welds on Flaperon Torque Arms and not a Service Bulletin. Holy S..t!!!

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Holy S..t!!! n233va - I'm going to insert your picture in this post. That be the case, this should be listed as a Safety Alert by Vans just like the SA for Incomplete Welds on Flaperon Torque Arms and not a Service Bulletin. Holy S..t!!!

am5u2s.png

Jim,
Are there different prop options for an RV12? I don?t know what they would be. Maybe Cato?

Doug
 
There's nothing wrong with the Sensenich 2-Blade Ground Adjustable Prop.

I just need assurance that hub isn't going to break.

And what I mean by assurance is not having to look every 50 hours to see if hub is broken...
 
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How many hours were on the failed hub? Was there any evidence of a manufacturing flaw? I have a Rev C prop so I am very interested in this.
 
Hi Bob
Just wondering if you performed a dynamic prop
balance
Mine was 2 grams out of balance in the tip
and had to be repaired
Jose del Peso 120633
 
Here is the complete narrative of the circumstances of the hub failure on N233VA. The narrative was provided to Van's.

PROP HUB FAILURE IN FLIGHT

Vans Aircraft SLSA RV12 N233VA Serial # S12007 882 hrs TTSN Hobbs .

On, 6/19/2018, while flying from Big Bear California to Prescott, AZ, at 11500 ft. I experienced a harmonic vibration that was different than anything I have experienced in an RV12. Although running with some harmonic vibration, I was able to safely return to Prescott, AZ.

After returning, I removed the top cowl and the spinner. I suspected the prop but also checked the prop blade pitch. The blades had not moved. Checked the slipper clutch and it was at 456 Inch lbs. Checked the torque on the prop bolts and they were all at 240 inch lbs. While checking the torque on the prop bolts a crack was observed on the front hub. After further examination it was determined that there was a crack on both sides of the hub. Once the prop hub bolts were removed, the front hub fell off in two pieces.

The aircraft is equipped with a Sensenich Ground Adjustable Prop 2A0R5R70EN-V. Hub Serial Number 21193C , Blade Serial Numbers 34421/R70E and 34218 /R70E.

I contacted Sensenich and spoke with Don Rowell. He stated that there was a service bulletin for cracks in the hub of earlier model hubs, such as the one on my RV12. I told him the details of my experience and he asked me to send Sensenich the hub and blades. He advised that Sensenich would replace the Hub with a newer version and also replace the pins in the prop blades to fit the new version. Prop was a ?C? hub.

The Prop Blades and Hub were shipped to Sensenich for examination. Van's Aircraft was also notified of this incident.

I checked Vans Support site for bulletins/notifications and could not find any reference to Sensenich prop hubs on Rotax engines. I also checked Sensenich. and found one service bulletin (SB2016-06), "Inspection of adjustible pitch Jabiru hubs for cracks". It also references, "2 blade aircraft hubs with pitch cylinder for Jabiru or other direct drive engines". It does not mention Rotax Engines, which are a geared engine. However, this bulletin does show exactly the crack location and propagation of the cracks that occurred in this aircraft.

Feel free to contact me at 928-899-0277 or by email should you have further questions.

Photos Available.

Robert J. Liddell
3110 Adobe Springs Drive
Prescott, AZ 86301
928-899-0277
[email protected] or [email protected]
 
I didn?t sleep well last night after seeing the picture of the broken prop hub and thinking about what could have happened if one blade separated from the hub. The remaining blade would cause horrific imbalance and most likely shake the engine loose from its mount thus causing an uncontrollable CG shift.

So today I have decided that I will not fly my plane again until the prop hub is replaced with the improved design. It is unconscionable that I should have to examine the prop hub every 50 hours to look for an eminent failure mode that is documented and known to the manufacturer.
 
I didn?t sleep well last night after seeing the picture of the broken prop hub and thinking about what could have happened if one blade separated from the hub. The remaining blade would cause horrific imbalance and most likely shake the engine loose from its mount thus causing an uncontrollable CG shift.

So today I have decided that I will not fly my plane again until the prop hub is replaced with the improved design. It is unconscionable that I should have to examine the prop hub every 50 hours to look for an eminent failure mode that is documented and known to the manufacturer.

Everyone is of course entitled to deal with things like this in their own personal way but I suggest people consider the following......

Things designed and manufactured by humans fail.
Failures can be caused by many different things.
As far as I am aware, this mentioned case is the only failure like this with the Sensenich prop installed on a Rotax 912.
It is entirely possible that this one cracked because of a manufacturing defect.
Because the cause is not immediately known, it is entirely appropriate for Sensenich to issue the S.B., but just because they have, doesn't mean that failure is imminent on every Sensenich prop with this style hub.
 
I inspected my front hub cover i/a/w the SB and found what appeared to be two cracks in the areas indicated in the SB -- the cracks are very difficult to see. I shipped the hub to Sensenich for their evaluation. My 4.5-year-old RV-12 has 650 hours, the prop was dynamically balanced, and the prop has not been used for pushing/pulling the aircraft on the ground. It will now be interesting to see how Sensenich responds to this issue and how long impacted aircraft will be grounded.
 
Just adding to what Scott said...

... it seems to me that if Sensenich finds that this incident was an anomaly due to manufacturing defect or other cause, the SB for 50 hour inspections might be recinded, or at least eased. I hope the community is kept informed as the analysis by Sensenich proceeds.

Addition: I was still typing when Dave posted just above. Maybe not an isolated incident then. I hope Sensenich is able to react quickly to this situation.
 
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Everyone is of course entitled to deal with things like this in their own personal way but I suggest people consider the following......

Things designed and manufactured by humans fail.
Failures can be caused by many different things.
As far as I am aware, this mentioned case is the only failure like this with the Sensenich prop installed on a Rotax 912.
It is entirely possible that this one cracked because of a manufacturing defect.
Because the cause is not immediately known, it is entirely appropriate for Sensenich to issue the S.B., but just because they have, doesn't mean that failure is imminent on every Sensenich prop with this style hub.

The possibility of a blade departing, when even a single hub has failed, is too risky for me. Could be manufacturing defect. Could be improper installation. Bottom line is hub design needs to be robust. Sensenich redesigned the hub and eliminated the large hole - we don't know the reason, but suffice to say, the original design is no longer available.
 
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I inspected my front hub cover i/a/w the SB and found what appeared to be two cracks in the areas indicated in the SB -- the cracks are very difficult to see. I shipped the hub to Sensenich for their evaluation. My 4.5-year-old RV-12 has 650 hours, the prop was dynamically balanced, and the prop has not been used for pushing/pulling the aircraft on the ground. It will now be interesting to see how Sensenich responds to this issue and how long impacted aircraft will be grounded.

People keep talking about dynamically balancing prop. Yes, this is good practice but not required by the manufacturer. Prop hub is (should be) designed to withstand significant weight difference in a pair of blades. Manufacturer would do over-stress testing for a critical safety-of-flight product.
 
With this type of failure is it feasible that the blade(s) would depart as long as the bolts continue to clamp the ends of the shanks?

I?m not suggesting the problem is not severe or something not to be taken seriously. I am just asking the question.
 
With this type of failure is it feasible that the blade(s) would depart as long as the bolts continue to clamp the ends of the shanks?

I?m not suggesting the problem is not severe or something not to be taken seriously. I am just asking the question.

My take they are fixed by thru bolts so immediate BLEW blades less likely...

On the same note....I'll bet cracks will be a challenge to discern....maybe need 10x magnification and or penetrant...All just guessing..
 
My take they are fixed by thru bolts so immediate BLEW blades less likely...

On the same note....I'll bet cracks will be a challenge to discern....maybe need 10x magnification and or penetrant...All just guessing..

Whoa Nelly... front hub cracked in half and blades retained by shear (not tensile) strength of two remaining bolts per blade compounded by increased vibration.

Not a good warm feeling here...
 
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Wow Nelly... front hub cracked in half and blades retained by shear (not tensile) strength of two remaining bolts per blade compounded by increased vibration.

Not a good warm feeling here...

Thinking, an even tightening/torqueing technique is most important preventative measure.
 
What is the proper torque for the bolts holding to front spinner attach plate? Are the washers reusable? Thanks!
 
What is the proper torque for the bolts holding to front spinner attach plate? Are the washers reusable? Thanks!

It's in the KAI and the maintenance manual - I always look it up and never rely on memory. The bolts use Nord-Lok washers, reusable if you have to remove them.
 
Sensenich prop torque values and maintenance requirements are also listed in the applicable Sensenich Installation Instructions document at:

http://www.sensenich.com/documents/

Also, be sure that you install the Nord-Lock lock washers with the proper orientation -- see Sensenich Installation Manual - Figure 4.
 
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Newer style Hub PN

Is there a PN for the new style hub? I am guessing it requires the blades sent off to be repinned?

Could not find a PN or price on Sensenich website for the hub only.

Have not looked in the KAI yet, anyone know off hand what size the Nord-Locks are? 9/16" or 1/2" is a guess.
 
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I inspected my front hub cover i/a/w the SB and found what appeared to be two cracks in the areas indicated in the SB -- the cracks are very difficult to see. I shipped the hub to Sensenich for their evaluation. My 4.5-year-old RV-12 has 650 hours, the prop was dynamically balanced, and the prop has not been used for pushing/pulling the aircraft on the ground. It will now be interesting to see how Sensenich responds to this issue and how long impacted aircraft will be grounded.

DHeal -

Were you able to inspect the front hub per the SB with the front spinner plate remaining in place or did you have to remove six thru bolts, spacers, and then the front spinner plate?
 
Is there a PN for the new style hub? I am guessing it requires the blades sent off to be repinned?

I have set blade pitch on one of the new hubs and it isn't necessary at all to use the rough-in pins for setting initial pitch - just position blades by hand. So my guess is if one were able to get a new design hub with the three smaller holes the existing prop blades can be used as-is.
 
It's in the KAI and the maintenance manual - I always look it up and never rely on memory. The bolts use Nord-Lok washers, reusable if you have to remove them.

During my first annual last year I of course removed the prop for inspection and noticed the Nord-Lock washers no longer had sharp edges to the tooth pattern ... they had become rounded so I did not feel comfortable using them again.

I attributed this to the need to tighten and loosen the bolts during the pitching process (which I needed to do twice prior to first flight). So I think one may get by reusing the Nord-Lock washers once, but I would suggest if the washers show the slight amount of rounding of the tooth pattern that they should be replaced.

The washers are quite inexpensive from Senenich so I ordered a handful and plan on replacing them every inspection. As a side note, I attempted to procure Nord-Lock washers locally and discovered the outer diameter of the Nord-Lock washers Sensenich uses is much larger than the standard AN5 Nord-Lock washer size typically stocked in nut & bolt supply houses here locally.
 
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DHeal -

Were you able to inspect the front hub per the SB with the front spinner plate remaining in place or did you have to remove six thru bolts, spacers, and then the front spinner plate?

After I removed the spinner I looked at the small bit of hub cover that was visible behind the still-installed front spinner plate -- I saw what appeared to be a very small crack located near one of the pitch degree indicator marks. That was enough for me to be concerned and I proceeded to remove the six bolts, front spinner plate and hub cover. Further close inspection of the now-removed hub cover revealed the cracks. I strongly encourage all to remove the hub cover for the inspection per the SB.

ps -- Today I assisted a fellow RV-12 builder/pilot in complying with the SB on his aircraft. His is an older RV-12 (circa 2009? with 800+ hours) with a gold-anodized prop hub that did not appear to be on the compliance list. His hub cover looked fine -- no evidence of cracks. He is going to ask Sensenich if his prop hub's serial number (we could find no "model number" on the hub) is outside of the compliance list.
 
I wrote an email to Sensenich on Weds, July 11 asking them if they are going to offer a replacement hub if affected by the SB. Late last night I received a reply as follows:

We're working hard on an FAQ to address all the questions swirling about the recent Service Bulletin revision.
Bear with us while this is finished up over the next several days.

Feel free to call me with any questions.


Steve Boser
Sensenich Propeller
2008 Wood Court
Plant City, FL 33563
813.752.3711 x1133 office
813.752.2818 fax
 
As others have pointed out already, there just isn't enough room to adaquately inspect the hub without removing the spinner plate. Fortunately, mine looked good after 450h but its tedious to re-pitch each blade to the exact same angle as before.

After putting her back together, I flew down to Maryland and had Dave Farmer balance the prop (had been meaning to do this for a while). With a couple of small weights the IPS reading was 0.04 which apparently is good. Started out at 0.19. Definitely flys smoother.

I'm comfortable flying her to OSH, but I would hope Sensenich would set up some sort of credit or trade in program to replace these hub setups with something deemed more reliable. These inspections are not something I want to add to my list of chores every 50h. (I'm also going to need a larger RV-12 SB binder after this year...)

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I wonder if front spinner plate can be modified with a little "crescent window" to allow visual inspection without removal?
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2uy3brt.png
 
I wonder if front spinner plate can be modified with a little "crescent window" to allow visual inspection without removal?
-
2uy3brt.png

Jim,

Is the newer hub displayed in the diagram above also subject to those inspections?

I just ordered this prop from Sensenich on Monday followed by the SB being issued just a few days later. Gads...the paper weight of all SB's issued on the -12 these past two years exceeds the weight of the airplane!
 
Tom -

You should be fine. My guess is you will receive an rev. "E" Hub which is what is being shipped now. Yes, it is the one pictured with the three small holes aligned with the prop axis. For you... no worries.
 
I did my inspection today at 761 HRs. No cracks, but I see what people mean when they say it is difficult to inspect with the forward bulkhead installed. With a really bright flashlight I was able to do an inspection. There are tool marks from the milling cutters that took some time to determine they weren?t cracks. I?ll probably go to the new hub at next annual unless Sensenich determines the failures have no generic implications.
 
I complied with Sensenich SB2016-06A today and was able to make a good inspection with front spinner plate in-place. 10X magnification and a bright LED flashlight did the trick. As mentioned above, the milling cutter marks add a little challenge.

My original “B” hub was sent back to Sensenich on 9-16-16 with 168TT for SB11-04-15 (loss of pitch) and replaced with an exchanged “B” hub. This replacement hub is anodized a shiny yellow/gold color which I think would show crack propagation easily. TT on this hub is 198 hours. I also don't know if this hub was new or someone else's hub that was reworked.

Its hard to say how many prop hubs with large pitch cylinder are flying on RV-12’s. Say 1000 RV-12’s flying and maybe half with the old style hub. One catastrophic failure and one hub found with cracks per the SB does not make a good warm feeling. A critical part that is safety-of-flight would need a failure rate something near six sigma (3 per million).

I will wait for Sensenich follow-up on this SB. Hopefully a replacement hub is in the offing...
 
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I preface the following by saying that I have not yet heard back from Sensenich as to their lab verification of the two "cracks" I believe I found in my black-anodized #2AOR5 hub cover. That being said, one of the two "cracks" I discovered was only visible to me after I removed the hub cover and looked inside. Just saying ....... YMMV.
 
I completed the inspection today, likewise with a bright light and magnifier. I was able to visualize all affected areas and kept a photo record. Now, where does the entry go? Prop log seems the correct logbook, but want to confirm.
 
Dave,

Please post the results from Sensenich on the questionable crack indications. I would be very interested to know if they turn out to be tooling marks.

Thanks,

Rich
 
I completed the inspection today, likewise with a bright light and magnifier. I was able to visualize all affected areas and kept a photo record. Now, where does the entry go? Prop log seems the correct logbook, but want to confirm.

I made entry in my Prop Log Book that Sensenich SB2016-06A was complied with and also noted TT when next 50 hour inspection was due...
 
Reference this SB and Sensenich Service Bulletin. I was the single failure on a Rotax 912ULS in a 2013 RV12 SLSA. Happened on 6/19/1018 while returning to Prescott, AZ. Was flying at 11,500 at 5300 RPM when a sudden significant harmonic vibration occurred. Not sure what it was but suspected the Prop. Safely returned to Prescott. Upon examination, a crack was observed in the front hub. The crack started at the first pitch setting mark and propagated around the hub. After removing the six bolts, the hub fell off in TWO pieces.

I strongly recommend that anyone who has a Sensenich Prop with the nylon plug for setting pitch, closely follow Sensenich?s SB and inspect their prop ASAP. Had I shed a blade, probably would not be writing this.

Looking at this photo, I?m struck by three things. 1- The surface finish of the entire part (ignoring the paint) is riddled with irregulaities- not done to the standard I?d expect on a modern critical part. 2- It appears that one of the deep hatch marks may have served as a stress riser from which the crack initially propagated. 3- The irregularity and extreme granularity of the face of the actual failure zone makes me wonder about the consistency of the alloy.

You are fortunate that the secondary failure was symettrical to the first, such that each blade was retained by three bolts, as I doubt that two bolts could have retained a blade for very long.

If my math is correct, 50 hours at 2500 RPMs equates to 45 million power strokes(actually, multiply that by the gearbox reduction ratio). After seeing this photo, I?d want to inspect this part far more frequently than that. I?ll bet there is a lot of scrambling behind the doors at Sensenich right now- it will be interesting to see what they come up with as a final fix here.- Otis
 
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I?ve been thinking more about add?l prop hub stresses imposed by the Rotax 912.

Older engines (incl mine) don?t have soft-start ignition feature. Maybe more important is the sudden stop when the engine is shut off. The 912 is a high-compression engine with 2.4:1 gear reduction. The lightweight hallow carbon fiber blades don?t have very much inertia to back drive the engine when it shuts off unlike a low-compression Continental or Lycoming.

Just thinking ? that?s what I do?
 
The throttle

I have also been thinking about this for the last few days and It has me puzzled
Not knowing if the crack started at the base or the hole in the front .

If the crack started at the hole it would lead me to think that the problem may be related to cutting power to quickly causing a high stress at the front of the hub from the air pushing on the prop trying to turn the engine thru the gear box.

I think closing the throttle very slow until the problem is fully understood may be a good idea.

Joe Dallas



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I’ve been thinking more about add’l prop hub stresses imposed by the Rotax 912.

Older engines (incl mine) don’t have soft-start ignition feature. Maybe more important is the sudden stop when the engine is shut off. The 912 is a high-compression engine with 2.4:1 gear reduction. The lightweight hallow carbon fiber blades don’t have very much inertia to back drive the engine when it shuts off unlike a low-compression Continental or Lycoming.

Just thinking – that’s what I do…
 
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