DHeal
Well Known Member
FYI: New SB 18-07-05 on RV-12 Sensenich Props
http://www.vansaircraft.com/pdf/service_bulletins/sb18-07-05.pdf
http://www.vansaircraft.com/pdf/service_bulletins/sb18-07-05.pdf
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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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.
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..
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.
And I'm thinking that installing the new design hub is most important preventative measure...
What is the proper torque for the bolts holding to front spinner attach plate? Are the washers reusable? Thanks!
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.
Is there a PN for the new style hub? I am guessing it requires the blades sent off to be repinned?
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.
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?
I wonder if front spinner plate can be modified with a little "crescent window" to allow visual inspection without removal?
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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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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.
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.
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…