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  #1  
Old 07-10-2018, 06:42 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 721
Default FYI: New SB 18-07-05 on RV-12 Sensenich Props

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

http://www.vansaircraft.com/pdf/serv...sb18-07-05.pdf
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  #2  
Old 07-10-2018, 09:02 PM
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DaleB DaleB is offline
 
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Default

How nice of them to release that the day after we pulled the spinner off to start our condition inspection.
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  #3  
Old 07-11-2018, 07:18 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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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 90į 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 Iím 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 donít have to disassemble my prop three times/yearÖ


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Jim Stricker
Hinckley, Ohio
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PPL/ASEL 1970 - Sport Pilot since 2004
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC Jul 2012 - Bought Flying Oct 2015 with 48TT - Hobbs now 402

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  #4  
Old 07-11-2018, 07:25 PM
n233va n233va is online now
 
Join Date: Jul 2014
Location: Prescott, AZ
Posts: 31
Default 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 Sensenichís 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/r9y0zdwzlo..._0148.jpg?dl=0
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  #5  
Old 07-11-2018, 07:30 PM
n233va n233va is online now
 
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Location: Prescott, AZ
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Default Correction

Date of occurrence was 6/19/2018.
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  #6  
Old 07-11-2018, 08:04 PM
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Piper J3 Piper J3 is offline
 
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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!!!

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Jim Stricker
Hinckley, Ohio
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2004
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC Jul 2012 - Bought Flying Oct 2015 with 48TT - Hobbs now 402

LSRM-A Certificate 2016
Special Thanks to EJ Trucks
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  #7  
Old 07-11-2018, 09:17 PM
AirHound AirHound is offline
 
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Location: OFallon IL now, everywhere before
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Quote:
Originally Posted by Piper J3 View Post
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!!!

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

Doug
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  #8  
Old 07-15-2018, 08:51 AM
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Hartstoc Hartstoc is offline
 
Join Date: Aug 2017
Location: Sebastopol,CA
Posts: 132
Default

Quote:
Originally Posted by n233va View Post
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 Sensenichís SB and inspect their prop ASAP. Had I shed a blade, probably would not be writing this.
Looking at this photo, Iím struck by three things. 1- The surface finish of the entire part (ignoring the paint) is riddled with irregulaities- not done to the standard Iíd 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, Iíd want to inspect this part far more frequently than that. Iíll 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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Last edited by Hartstoc : 07-15-2018 at 08:58 AM.
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  #9  
Old 07-15-2018, 10:17 AM
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Piper J3 Piper J3 is offline
 
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Iíve been thinking more about addíl prop hub stresses imposed by the Rotax 912.

Older engines (incl mine) donít 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 donít have very much inertia to back drive the engine when it shuts off unlike a low-compression Continental or Lycoming.

Just thinking Ė thatís what I doÖ
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Jim Stricker
Hinckley, Ohio
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2004
80 hrs Flying Aeronca Chief 11AC
1130 hrs Flying 46 Piper J-3 Cub
RV-12 E-LSA #120058 AWC Jul 2012 - Bought Flying Oct 2015 with 48TT - Hobbs now 402

LSRM-A Certificate 2016
Special Thanks to EJ Trucks
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  #10  
Old 07-15-2018, 10:52 AM
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joedallas joedallas is offline
 
Join Date: May 2010
Location: Spring Hill Fl
Posts: 710
Default 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







Quote:
Originally Posted by Piper J3 View Post
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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