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RV-12: Sensenich Ground Adjustable Prop; Blade Check

Geico266

Geico266

Well Known Member
Please check the blades on your RV-12 Sensenich ground adjustable prop for play (loose blade in the hub) after the correct torque is applied to the 6 retaining bolts.

With the spinner off, grab the blade tip and gently move it "fore and aft" while at the same time with your index finger and thumb grab where the hub and the blade meet. There should be NO movement between the blade and the hub. The blade should be held securely by the hub with no movement "fore and aft" at all, according to Sensenich.

I have been helping another -12 builder put his plane togeather after painting and the FBO / painter found the prop "barrel" (the part that gets clamped on) to be loose. After talking to Sensenich we took the prop apart, inspected all parts for interference and reassembled. There was no improvement and the blade was still loose. Per Sensenich there should be NO movement at the hub, and the blade barrels should be the same size. Sensenich has been very responsive and helpful.

Please do not confuse "play" with Rotax gear box backlash. I could actually see the blade moving in the hub. :eek:

This situation probably is confined to a small number of propellers, but I thought it prudent to post it. Sensenich wanted the prop back immediately for further investigation and replacement.

The prop on my -12 has no movement.
 
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Loose prop-not an isolated case

Larry, it was a year ago (mid December, 09) when I first attached my props, I had the same problem. Made sure all prop bolts were torqued correctly, checked for movement and one prop was loose. Loosened and retorqued the bolts again and the prop was still loose. Removed both props and switched location on the hub, same prop still loose. Checked diameter of both props and there was a slight difference (unfortunately can not remember how much) so assumed it was a bad prop. Called Sensenich, was advised to return both props and hub halves. On 12-23-09 they returned both orginial props but with (I assume) new hub assembly. They advised the problem was in the hub, not in the props. Was advised that the difference in diameter between the two props was within their tolerances. Didn't make sense to me but whatever they sent back to me corrected the problem.

I was led to believe by both Vans and Sensenich, this was an isolated problem so I never started a thread. Now I wonder?
 
There was another RV-12 Sensenich prop blade found loose by an instructor in a Repairman Certificate class in California. An Oregon RV-12 builder let the instructor use his plane as a class "prop" (pun unintended ;)) and the instructor found his propeller was loose in the hub. I talked to one of the instructors involved to confirm the story. Sensenich replaced the prop under warranty.
 
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Here are the pics of the hub and blade after 50 hours of flying. The dark spots on the hub are where the blades were moving and chafing in flight. The chafing is particularly concerning because the composite blade is taking all of the force in this one area instead of the entire area where the clamping force would disburse the energy.

RV-12_attaching_hub__Medium_.jpg

RV-12_Base_hub__Medium_.jpg

RV-12_blade_hub__Medium_.jpg

In this picture disregard the obvious white line. This is the flash reflection and the where the factory ground the "mold seams" of the composite prop. The area I am concerned about is below the obvious mold "flashing" and oliptical matching the hub wear. Concentrating energy in one area on a composite structure is not a good thing, IMHO.


I can only comment on what my hub looks like, and after 175 hours there are no wear areas as seen in these pictures. Please understand this information is "raw data" and you should take it for what it is worth.

If you are flying an RV-12 with the Sensenich prop please inspect it ASAP. If the prop is tight in the hub then fly the heck out of like I am. If it is loose, call Sensenich FOR A REPLACEMENT hub.
 
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Nice catch Larry. No prop should go fore and aft, nor up and down unless a gear box is involved. In fact, this was a three-dimensional prop! Yikes!
 
When my neighbor finished his -12 about a year ago he had the same problem. Sensenich replaced his hub. Problem solved.
 
John, Alan, looks like Steve joins the "bad hub club". Sensenich let me know there were several bad hubs that made it through their quality control checks and made it into prop kits by mistake. They are sending out a new hub and blades today, paying freight both ways (for the returned prop) and a letter of explanation and apology for the inconvenience. Nice to see an aircraft parts company admit to making a mistake, dealing with it quickly & professionally, and moving on.

We ALL make mistakes. It is all in how you deal with them. ;)
 
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prop hub

Thanks Larry, all your work on the maint. issues sure makes it easier for all the builders working on their kits.
 
Prop hubs

Geico266 said:
John, Alan, looks like Steve joins the "bad hub club". Sensenich let me know there were several bad hubs that made it through their quality control checks and made it into prop kits by mistake. They are sending out a new hub and blades today, paying freight both ways (for the returned prop) and a letter of explanation and apology for the inconvenience. Nice to see an aircraft parts company admit to making a mistake, dealing with it quickly & professionally, and moving on.

We ALL make mistakes. It is all in how you deal with them. ;)
Click to expand...

I assume that the QC program identified the bad hubs by serial number and that Sensenich is able to notify those who have been shipped the bad hubs. Is this a safe assumption?
My blades don't seem to have any back and forth movement, but this may not be a definitive test.
Tony
 
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Tony_T said:
I assume that the QC program identified the bad hubs by serial number and that Sensenich is able to notify those who have been shipped the bad hubs. Is this a safe assumption?
My blades don't seem to have any back and forth movement, but this may not be a definitive test.
Tony
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I doubt that is a safe assumption. Sounds more to me like they wait for a call, then replace the hub. No one called Steve and his wasn't the first. I would call if you are concerned. By the way, thanks to you, Marty and the others, I remodeled my shroud yesterday like yours as I was wrapping up my conditional. I also safety wired my exhaust springs since I had to replace two that had worn through.
 
Prop and exhaust springs

My prop track was off by almost 1/4 inch I called them and they sent a pickup for the prop. New one has not arrived as of today. Now on the exhaust springs, I read here that they wear and need replacing. I have not flown my 12 yet but to stop the wear I safety wired the exhaust springs. I looped a safity wire around the exhaust pipe over the top of the springs about in the center of the springs. this would (might) stop the viabration. What do you think? Opinions needed
 
Bump!

I think we got one too!

I just want to swap the prop hub 180 degree and torq all the way before confirming...

Rudi
 
I'm wondering how explicit Van's build instructions now are on this point? (Larry's original post seems to imply that he was checking something beyond what was in the build instructions). It's a Sensenich QA problem, to be sure...but when a manufacturing problem surfaces and it extends across a significant span of time (and is now being reported by John as well as Rudi), I'm wondering if Van's typically issues a Revision Notice to call attention to such issues that are surfaced by their builders?

Has anyone checked for a Revision Notice for this section on this issue? If one doesn't exist, does Van's invite such input? Or do we all assume they read the forums thoroughly and act as needed?

Jack
 
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Moving over from my thread on this topic to this one that Larry originated some time ago and which contains more info.

I removed my prop and hub today. Took photos of the wear marks on the hubs. You can see them on my blog entry for today. They are remarkably similar to the pictures earlier in this thread.

My hub serial number is: 281748 and was the gold color. Mike from Sensenich told me the new hubs are black in color and have been trouble free.

My suggestion to those with flying RV-12's is to check your pitch settings to see if they have "crept" from your original values, especially if you are feeling any vibrations that you think are attributable to the prop.

Packed the prop up and sent it off for a little Florida vacation. (Sensenich is in Plant City, Florida.) I'll report back on findings after the folks down there get a look.
 
RudiGreyling said:
Bump!

I think we got one too!

I just want to swap the prop hub 180 degree and torq all the way before confirming...

Rudi
Click to expand...

Jip I can now confirm we have 1 loose blade in a gold coloured hub. I sent an email to Vans and Sensenich asking for assistance.

Kind Regards
Rudi
 
It appears Sensenich is sitting on their hands by not issuing an SB like they told me they would.

We now have reports of blades changing pitch after a few hours of flight due to the gold hubs not clamping the blade hub tight enough even though the blade does not wiggle in the hub. Please check the pitch of each blade and record it. If the blade moves at all you need a new hub. The new ones are black anodized.

IMHO you should just send your gold hub in for replacement. It is clear the design tolerances are too sloppy for he application.

Sensenich should have done the right thing here and issued an SB. Shame on them.
 
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I guess it will take 100 or more phone calls to Sensenich Monday morning for RA numbers. A customer initiated Service Bulletin? Now that's an interesting way to run a business...keep your problems a secret and hope. Thanks Larry.

Pete
 
I flew about three or four hours over the weekend with the new black hub. Then checked blade angles. No movement at all.

Vibration is better, but I think I could still benefit from a dynamic balance, which I intend to pursue.

Mike at Sensenich treated me very well, helped to solve the problem, and replaced the hub without making an issue of it. Good customer service, as far as I'm concerned.
 
Sensenich has made their choice. It is apparent that the machined hubs were initially built with an excessive tolerance. The non-machine made blades are of course built to a tolerance as well but not one as controllable as the machine made hub. When the limit of the hub tolerance met the limit of the blade tolerance, clamping no longer was possible. How else could some hubs work while others did not. Sensenich has built a new hub with a lower tolerance to guarantee the blade clamping.

Sensenich has not notified existing owners of the original hubs. To their dubious credit, they have agreed (no questions asked) to replace the hub of anyone who calls in concerned.

Why would they not simply replace them all before some poor slob loses a blade in flight. I guess hubs are more expensive than liability insurance. They are not on my Christmas list this year.
 
SERVICE BULLETIN SB11-04-15

I received the bulletin via mail after a question about my hub serial (my hub needs to be replaced).

 
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Nice to see Sensenich finally took this issue seriously. Having an IN FLIGHT adjustable prop is against E-LSA rules! :eek:

;)
 
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My prop hub was a "B" model and the pitch was changing very very slowly. Shipped it 9 days ago. The replacement is to arrive tomorrow.
 
Marty,

I think the new black hubs are also "Rev B", at least mine was. I don't think they changed the revision level, just the supplier and color.

John
 
John,

Does the service bulletin apply to all "B" hubs? Sure looks like it. Are you going to have to return it for a "C" model?? Have you called Sensenich to ask?

Will let you know what they sent me. Will arrive tomorrow.
 
MartySantic said:
Does the service bulletin apply to all "B" hubs? Sure looks like it. Are you going to have to return it for a "C" model?? Have you called Sensenich to ask?
Click to expand...

All I know is the black one they sent me is also a "B". It appears as if they didn't change the "Rev" number between the gold and the black. Let us know what is stamped on your new hub.
 
In talking with Mike at Sensenich last week, the black hubs are not necessarily new. They are re-machining the returned gold B hubs and taking .008 off the mating faces. Then they send them out for the black anodizing. Apparently not re-stamping them.
 
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