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Prop blade failure! RV-12

yankee-flyer

Well Known Member
Had my excitement for the week. Shot a couple of touch & goes at Greene County (I19) and was heading over to Richmond. About 3 west of I19 started a VERY severe vibtatiion-- only slightly less at lower power settings. First thought I'd lost part of a prop blade and then that I'd had a motor mount fail. Scared me! Nursed her back for a straight-in to 07 and when I got to the hangar I found a big bulge-- 6" long and max 3/16 to 1/2 inch deep-- on both side of one blade just inboard of the tip stripes. New blade, less than 40 hours time.

Will post photos later

Wayne 120241/143WM
 
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Do you know when the prop was purchased??

Somewhere back in the dusty corners of my brain seems to be remembrances of this happening before.........not sure if it was on the 12 or not.
 
If the prop is that new, I would expect it to be under some kind of warranty.

Time for a phone call or two.
 
After Seeing Photos

Sensenich says this is what they thing happened. There's a "plug" at the hub end of our hollow blades. They think it came loose and was thrown outboard inside the hollow blade causing it to "bulge". So one blade was not only about a half-inch thicker just inboard of the tip, but it was also statically and dynamically unbalanced. They are sending new blades! I'll pull the cowl and check engine mounts, etc, VERY carefully.





 
If the engine vibration was severe enough to make you want to check the engine mounts, do you also need to inspect the crankshaft and gearbox?
 
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I am anxious to see a response from Sensenich. Will this turn into a recall?. How do you inspect for a loose internal plug ?.
 
Acording to Sensenich

They've seen this once before in 500,000 props. I did request, and am supposed to be getting, two new blades since both were from the same batch and I have zero confidence in the second one.

Wayne
 
They've seen this once before in 500,000 props. Wayne

There is no way that there are 500,000 Sensenich props out there manufactured like the RV-12 prop. Are there even that many prop aircraft in the world?

Even if they were talking 500,000 blades that would be 250,000 aircraft assuming 2 bladed props and none of those on air boats.

I am sorry that you are in this position but glad you made it home safely. Like Katie said, I would check more than engine mounts. You should talk to Sensenich about having your engine/aircraft inspected by someone and them covering the cost. You won't know unless you ask.
 
There is no way that there are 500,000 Sensenich props out there manufactured like the RV-12 prop. Are there even that many prop aircraft in the world?

There's an article about Sensenich on AVWeb today. They state they manufacture 3000 - 4500 props a year. At 4500/year that's 111 years to build 1/2 a million props.
 
I would expect that they include airboats in that number. Those props are much the same as the prop that failed. Can't speak at all to the total number, though.
 
Since I have one of those, I was thinking . . . .
Couldn't one say drill a hole thru the hub at that plug, and maybe drive a roll pin thru to keep it from ever slinging out to the end of the blade?
 
I am guessing drilling the hole for the roll pin would compromise the hub structure. I hope Sensenich responds as I am flying behind one of these.
 
Mine has like a bulge on the hub end, mostly something to keep it from slipping out in case the clamp got loose enough to do that I would suspect. I would guess there is no structural strength to that bulge, it is just something to put the plug into I think. We will just have to wait and see if Sensenish comes out with a fix for it.
 
Mine has like a bulge on the hub end, mostly something to keep it from slipping out in case the clamp got loose enough to do that I would suspect. I would guess there is no structural strength to that bulge, it is just something to put the plug into I think. We will just have to wait and see if Sensenish comes out with a fix for it.

There is a huge structural strength reason for that bulge.

The centrifugal loads on a prop blade spinning at full RPM are very high.
The hub halves alone, clamping around the shank end of the blades would probably not have enough clamping pressure to stop the blades from moving outward.

These high loads are a big reason that messing with modifying the shank of the blade would not be a very good idea.
 
Number of props built per year

There's an article about Sensenich on AVWeb today. They state they manufacture 3000 - 4500 props a year. At 4500/year that's 111 years to build 1/2 a million props.

I believe the article was referring only to the number of wooden props built exclusively in their Florida shop.
 
I'm guessing that 500,000

was just a number pulled out of the air-- like "one in a million". Not a big deal; Sensenich guy was trying to make the point that it was a very rare ocurrence and I didn't need two new prop blades. I was making the point that once was enough and I didn't trust the other blade. Pointed out that we'd just had our spring thaw and that was the first good day after a week of rain (it's Ohio!) and that if it had waited another two or three minutes to come apart there was an excellent chance the airplane would be on its back upside down in a muddy field instead of my hangar. I really wouldn't be comfortable flying with another prop from the same day/batch!

Not fun, no damage (I think) except losing several days of the best flying weather we've had this year. Hope Sensenich comes up with a better idea when they get this one back.

Wayne 120241/143WM
 
When you had the prop strike with old prop, did you have the hub checked to make sure it still meets mfg specs??

Grinding off a bit of the tip puts a pretty small load on the end of a long arm----I think folks would be surprised at the total force applied at the hub.

and there was about 1/16 inch ground off one prop tip and just slightly more off the other. There were no prop marks on the runway at I19 bet there were at I73.
 
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There's an article about Sensenich on AVWeb today. They state they manufacture 3000 - 4500 props a year. At 4500/year that's 111 years to build 1/2 a million props.

That's about right, Sensenich started their business in 1903 selling their first two propellers to two guys from Dayton Ohio I have heard.:D
 
But not in 1903! The Wrights designed and built their own props (at least initially), and they were quite efficient. Some say that the prop design was a tougher aerodynamic challenge than the wing design.

And I've seen the spokeshaves they used to carve those first props! Definitely homebuilding at its best.
 
Their realization that an airplane prop should be

a rotating wing, twisted appropriately to provide an even disk loading instead of a ship's screw or flat windmill blade was probably at least as great a contribution as the three-axis control. Ask Langley's pilot just how well the Professor's flat surface blades worked.

Wayne N143wm waiting on prop blades
 
New Prop blades installed

Checked engine mount and hardware thoroughly-- no visible cracks in powder coating or welds. Attach bolts OK. no firewall deformation. Engine attach bolts torque mark unbroken. Lifted nose off ground by prop, no visible movement. No visible damage to hub or attach bolts. Fitted new blades, prop tracks perfectly. Ground tested, no vibration or unusual signs. Will flight test as soon as weather permits. Strange-- it took six weeks to get the previous set of blades from Sensenich-- they put these in the mail the next day after the call.

Wayne 120241
 
Hello Wayne;
What was the response from Sensenich regarding the defect with your prop ?. I have the same prop and am wondering.

Thx
Tom O.
 
Maybe not 100% related to this issue but I think is important to share.
After 10 hours TT in my RV-12 I made de prop dynamic balance. The result was 1.3 IPS ( inches per second),that according with the prop shop is the lower limit of a destructive vibration.
I went to the Sensenich factory and they said that the blades had 2.2 grams unbalance on the tip.
Sensenich also makes mistakes
Jose del Peso (120633)
 
Props are not things to be trifled with - I have seen airplanes that had their engines ripped out in flight by the imbalance caused by losing the outboard 2" of prop blade.

The previous damage makes one suspicious. I too am an aero engineer, but since I have not worked for years in prop design and mfg, and forensic investigation of prop failures, my engineering background only gives me a very general overview - a knowledge of what I don't know if you see what I mean.

Is Sensenich aware that there was a previous incident on this hub?
 
Not a problem with the hub

The problem was the plug at the inboard end of the blade apparently wasn't correctly glue in place and that plug wound up 10" from the outboard end of the blade.
 
prop damage

nxrfcm.jpg


I just discovered this. It is on a stock E-LSA RV-12. It looks like an outer gelcoat has delaminated over top of the carbon fiber. I don't think I want to fly as is, so I imagine it will be going back to Sensenich for evaluation and or repair.
Anyone out there seen anything like this ?.
These props are nice, light, adjustable, efficient, but it only has 155hrs on it, I am a little disappointed. There is no indication on the leading that I picked up a rock or any FOD. Never saw anything like this on an aluminum propeller.
 
Harvey, your prop is definitely not airworthy. Looks like a manufacturing defect to me. I'm sure that Sensenich will be quick to determine the cause, and to get you back in the air. This also gives crudence to our preflight actions. Please post the results of you experience with Sensenich.....Tom
 
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