SB 18-02-02 Potential cracking in the horizontal stabilator front spar

[rvbuilder2002]

The first discovered instance of cracks was by maintainers of an S-LSA operated by a flight school.

Follow-on investigation found cracks in two of Van's Aircraft's demonstrator RV-12's.

The stabilator must be removed from the airplane and the hinge brackets removed from the stabilator to gain visual access to the area potential to crack (the fwd web of the box spar under the hinge brackets) .

The option was given to delay the installation of the updated parts if no cracks are discovered, to allow owners some flexibility if they can't do the parts installation immediately because of lack of skills (weren't the aircraft's builder), haven't yet obtained the needed parts, etc.
In most cases, it would make sense to just install the new parts while the stabilator is removed for the inspection.

It may be difficult to detect cracks depending on the level of crack development (how big they are) and surface condition (primer or paint coatings, etc.). This is another reason it might make sense to just install the parts regardless of what the inspection results are.

I don't know how the cost of parts is being handled. You will have to ask about that when ordering the kit.

There is a variability in the size of cracks that have been discovered so far.
The red prototype (N412RV) with well north of 2000 flying hrs had very small cracks that were at first difficult to detect. The photos in the S.B. are from that aircraft. Another aircraft with only 1/3rd as many hrs had larger cracks.

It is only speculation, but it is thought that an RV-12 that has sat outside in wind a lot with unrestrained controls (I.E., stabilator banging against the up and down stops because of wind movement) could be more susceptible to cracks.

BTW
An evaluation of the problem after initial report, do an FEA model analysis, design of a modification, production of prototype parts, beta installation of the new parts on two different stabilators and writing of the install instructions and SB document and publishing it, were all done in less than 3 weeks.

[JwWright57]

for once procrastination paid off, I'm at the point in my build where this is not a big deal. Also, the hinge brackets did seem a little light, so i'm glad to see they are being beefed up!

[JwWright57]

Kudos to Vans for getting this out so quick

[Jshepherd]

Parts are on the web store $20 plus shipping

[Phantom30]

I kind of wonder if “over-tighting” of control cables might have something to do with this problem....just my trouble shooting mind @ work!

When adjusting and stretching stab cables; I tighten till cable slap stopped which was not as tight as gauge pressure was suppose to be... My concern being the fiber rollers the cables ran over.

Scott....you can jump in here to slap my hand anytime��

[Phantom30]

Originally Posted by TomVal

Since the stabilizer has to be pulled, if you haven't already done so, might as well complete SB 16-08-01 - Stabilizer Bearing Inspection.

Ditto on that....going to replace bearings and install Stab fix parts all at one time to satisfy annual tail end inspection...

[rvbuilder2002]

Originally Posted by Phantom30

I kind of wonder if ?over-tighting? of control cables might have something to do with this problem....just my trouble shooting mind @ work!

When adjusting and stretching stab cables; I tighten till cable slap stopped which was not as tight as gauge pressure was suppose to be... My concern being the fiber rollers the cables ran over.

Scott....you can jump in here to slap my hand anytime��

Not intended as a hand slap, but I don't think that has anything to do with it.

The load cycle that will cause the most flex in the structure and have an influence on causing the fatigue cracks to occur is the load induced when the stabilator bumps the up or down travel stop.

BTW, the fiber pulleys used are standard aircraft components.... same as used in Cessna, etc.
The cable tensions specified for the RV-12 are very similar to what is used in many other aircraft that use the same pulleys.

[TLKRV12]

Cost of the parts for SB 18-02-02 $20 USD + shipping

[epaslick]

Originally Posted by JwWright57

for once procrastination paid off, I'm at the point in my build where this is not a big deal. Also, the hinge brackets did seem a little light, so i'm glad to see they are being beefed up!

I'm right there with you. My stabilator is build but not installed on the tailcone. Counting my blessings.

[Top Cat]

I’m a bit confused ( fairly common these days).

I ordered the 18-02-03 kit. See the home page on Vans website for SB details plus click on to order kit ($20 plus shipping).

However, reading the SB 18-02-02 at the end it says to order the 18-02-02 kit which i can’t find on the Vans site.
My RV-12 is 2014 SLSA.

What am I missing?