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Incidence of bearing bracket brace cracks?

I just checked mine at 133 hrs TTAF, no cracks present.
I'm happy, I don't know how you would get in there to replace it.
 
I have over 700 hours flying off grass strip on the farm . No cracks.




Brad Stiefvater
Salem SD
124BJ first customer built Rv 12 to fly on Sept.19th 2009
 
Thanks guys!
I have an SLSA which I, of course, didn't build so the fix would be a major problem..... more than for a builder it seems.
EBB
 
The SB from Vans says 3 hours to repair. If you took it to an A&P, I don't think they would do it for 3 hrs labor = $240.
after looking closely at the structure, I don't see what great loads are acting on the brace to cause it to crack ?.
 
I thought that lowering the flaps below 82 knots would put a load on the bracket and maybe cause it to crack....so I chicken out and lower them at or below about 75 knots.
EBB
 
N712BK Cracks found at 229 hrs

Inspected mine after the SB was posted. Had a crack so installed new bearing bracket and bearing bracket angles in Feb 2015. I believe that there was a thread on the subject that was started in Dec 2014.

Bob Kibby RV-12 N712BK 291 hrs
 
I replaced my bracket at 200hrs prophylactically . No cracks but wanted to take care of it while I had the tank out and it wasn't too bad, especially since I had the help of an experienced builder!
 
Bruce,

True confession time! I have not always got the flaps up before 82 KTS -- like maybe once had them at one notch at 105 KTS. Fortunately no cracks at 438 hours. I always use one notch of flaps. My reasoning, right or wrong is that if the limit is based on full flaps I have at least some margin for error at half flaps. Like I said "right or wrong". All I know for sure is there are no cracks.

Rich
 
If the cracks are the result of stress on the flapperons, I wonder if the systematic use of full flaps and steep approach angles (like for short field landing) might be an aggravating factor more than having by mistake 1 notch of flaps at 100 kts. I have to confess I forgot a couple of time to retract the flaps after takeoff and finding out by just sensing that the plane was not feeling right, by which time I was at around 100 kts. Like for every stupid mistakes I have made in my last 200 hours of flight, I suspect I'm not the only one (which makes me feel better!)... My last inspection did not show any sign of cracks on the bracket brace (which made me feel even better!).
 
I also have pretty much figured out that I don't usually need flap for take off....with only me aboard the airplane leaps into the air about 50 knots and climbs like the "homesick angel" we all know about at 60 knots VX and 75 knots Vy just fine.

Gotta fess up the ONCE I did use flaps with a passenger aboard and he started asking questions and then I FORGOT to raise the flaps until about 100 Kts. Bummer.

EBB
 
If the cracks are the result of stress on the flapperons,

There not. (at least not because of deploying them as flaps)

The loads might be a bit higher with flaps deployed but the cycle loads are there from movement of the flapperons (in aileron mode) regardless of whether the flaps are deployed.

A crack such as this that occurs after many hours is a result of fatigue failure due to repetitive load cycles.
The same as if you bend a piece of aluminum back and forth in your hands over and over. If the piece is stiff enough, you wont be able to impart enough pressure with your hands to cause any flex so the load cycle has little effect on its fatigue longevity. If hand pressure allows it to flex a lot, after repeated cycles it will crack and then eventually break.

The modification to the bracket makes the area that was flexing much stiffer so that it is not flexing during normal load cycles which will in turn prevent the fatigue failure.
 
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There not. (at least not because of deploying them as flaps)

The loads might be a bit higher with flaps deployed but the cycle loads are there from movement of the flapperons (in aileron mode) regardless of whether the flaps are deployed.

A crack such as this that occurs after many hours is a result of fatigue failure due to repetitive load cycles.
The same as if you bend a piece of aluminum back and forth in your hands over and over. If the piece is stiff enough, you wont be able to impart enough pressure with your hands to cause any flex so the load cycle has little effect on its fatigue longevity. If hand pressure allows it to flex a lot, after repeated cycles it will crack and then eventually break.

The modification to the bracket makes the area that was flexing much stiffer so that it is not flexing during normal load cycles which will in turn prevent the fatigue failure.


Interesting. May we anticipate then that the extensive use of the Autopilot could be an aggravating factor? Indeed, the fast reaction of the A/P to any low wing induced turbulence is likely to increase the cycles by an order of magnitude compared to a human reaction. Has any correlation been made between the use of autopilot and these cracks?
 
On new construction

It was easy to complete this project when building the fuselage assy. and the cost was minimal. Do it then so you won't have to do it later
 
It was easy to complete this project when building the fuselage assy. and the cost was minimal. Do it then so you won't have to do it later

For those who have a flying airplane an interesting question is: do it now or wait until a crack appears? The recommendation in the SB to inspect the bracket periodically implies that you can wait.
On the other hand if you wait, the cracks have already weakened the bracket. On the other-other hand drilling holes in an intact bracket may also weaken it... And I am afraid than any further advice on this forum will make things even more complicated! :eek:
 
Scott,

Remember the fatigue usage factor is based not only on cycles, but the stress associated with the cycle. I dread that cycle at 105 KTS because I know it had a higher usage factor than one at Less than 82 KTS. I'm not talking about an over stress crack, but rather a reduced number of design cycles to cracking as a result of some over design stress cycles.

In the end all that really counts is no cracks yet!😀

Rich
 
Scott,

Remember the fatigue usage factor is based not only on cycles, but the stress associated with the cycle. I dread that cycle at 105 KTS because I know it had a higher usage factor than one at Less than 82 KTS. I'm not talking about an over stress crack, but rather a reduced number of design cycles to cracking as a result of some over design stress cycles.

In the end all that really counts is no cracks yet!😀

Rich

Sure, but I was speaking in simple terms.

I big misconception seems to be that there is zero load on this bracket when the flapperons are in trail. This is not correct. The flapperons are part of the airfoil so when they are in neutral trail there is a lifting load on each. When you move the stick to bank left or right, there is a load reversal on one and an increase of the lifting load in other. This constant loading/unloading regardless is what caused the problem based on the stiffness of the material the bracket was made out of.
 
This is an interesting discussion because of the introduction into the comments about AP use. My bracket was cracked in two places at 230 hours, and I did wonder why at such a low time. But in thinking back on it, a lot of the hours were in cross country flights with autopilot engaged. Hmmmmm.
 
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I was helping a friend with his conditional inspection yesterday and we found a crack! He bought an EAB and has 300hrs on it, most of it by the builder.
 
FWIW, I had 438 hrs at my last annual with no crack, and I would guess 3/4 of that time was on the autopilot. Out here in the Phoenix thermals the AP gets a work out.

Interesting response, Scott. I didn't think about the constant load issue. Any chance there is some manufacturing issue that causes some to crack while others soldier on?
 
FWIW, I had 438 hrs at my last annual with no crack, and I would guess 3/4 of that time was on the autopilot. Out here in the Phoenix thermals the AP gets a work out.

Interesting response, Scott. I didn't think about the constant load issue. Any chance there is some manufacturing issue that causes some to crack while others soldier on?

There are many possible factors.
A number of different ones have been mentioned in previous threads.

The most basic one is how well the part was deburred or whether it even was at all.
 
Well, I am a fanatical deburrer, and my part failed after only a couple hundred hours. I worked on another 12 yesterday that has over 400 hours on it, and the part was fine. As analytical as we builder types are, some things just dont have an answer that we can put in a neat little box. Best just to fix it, and move on!
 
Well, I am a fanatical deburrer, and my part failed after only a couple hundred hours. I worked on another 12 yesterday that has over 400 hours on it, and the part was fine. As analytical as we builder types are, some things just dont have an answer that we can put in a neat little box. Best just to fix it, and move on!

Thanks for re-enforcing my statement that there are many different factors involved.....
 
Jane's Turn - Found cracks

Jane is the name I gave my RV-12. Since she reminds me of the George Jetsons flying machine. Well Jane got the case of the cracks.
The first photo is what got our attention. It looked like a very fine hair line on the surface.
Went back in and pushed a bit on the surface and sure enough it was a crack.
The second photo is of the bracket after removing.
The cracks were opened up when I pulled up on the bracket to get to the 4 forward rivets.

N470MB has been flying for 3 years 2 months 474.4 hobbs

SUYAbWjX


The cracks were opened up when I pulled up on the bracket to get to the 4 forward rivets.
bCthcLsm
 
Well, I am a fanatical deburrer, and my part failed after only a couple hundred hours. I worked on another 12 yesterday that has over 400 hours on it, and the part was fine. As analytical as we builder types are, some things just dont have an answer that we can put in a neat little box. Best just to fix it, and move on!

Same for mine. A little over 200 hrs.There was just one small crack from the rivit to the edge.
 
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