SB 00036 (cracked horiz stab spar) Installation Notes

[Sam Buchanan]

Originally Posted by Taltruda

Are you guys doing the repair on the plane? Or is everyone pulling the HS to work on the bench?

Did mine on the plane with the tail propped up, think it is easier than wrestling with a stab sliding around on a bench not to mention the additional time required. The kit installation really isn't a job to dread, just be methodical.

[wawrzynskivp]

https://www.google.com/search?q=vans...id:lb9miRllZDo

[srbooher]

Originally Posted by srbooher

After borescoping my horiz spar bracket repair I found that half of my Cherry Rivets had the mandrel recessed into the rivet head, and sticking out of the spread rivet (see attached photo). The Vans engineers say this is unacceptable because if the mandrel should vibrate out there is little strength to the rivet. This problem apparently exists with the RV-12 Cherry Max rivets as well. There is a Vans YouTube video on dealing with the problem, and the engineers recommend heating the rivet while soaking in lubricant to “prep” it for installation. This means I need to remove the elevators again, drill out the bad rivets, and reinstall.

After drilling out Cherry rivets and lubricating new ones as indicated in Vans YouTube video reinstall went smoothly. Since old mandrels were recessed in head it was easy to drill out head and then punch mandrel out.

[Sam Buchanan]

Anyone who uses the Cherry Max rivets to install the kit would be well served by borescoping the rivets after installation. It can be difficult to judge the quality of the installation otherwise especially for those of us who don't have prior experience with them.

[Traash]

I too was bit by the poorly documented fact that two different sized Cherry Max rivets are in the repair kit. The ONLY place it's called out is in a note on figure 5 which starts out "If there are no cracks". I have cracks so crossed out the note, hence, didn't see that there are two sizes. Plus the kit didn't come with a contents list.

Enough whining.

So, on inspection I have determined that the depth of the grip falls between 3 & 4. The -3 rivets pulled up to a "minimum" depth and the -4 rivets showed as the "maximum". Cherry's come in 1/16" increments so it's possible to see no stem or 1/16" stem protruding from the set end. This is explained in the Cherry Max literature. I decided to leave well enough alone in order to not do any damage trying to drill out the difficult to drill Cherry rivets.

Note: the q-tip was something I stuck in the hole to identify bottom vs top in the boroscope picture. It can be confusing.

[agent4573]

This is only based on personal experience, but likely half the cherry max rivets I've set by hand in the past have broken early. Using the pneumatic puller, I think I've had 1 set incorrectly. You should definitely boroscope after install, but also consider the tool to decrease side loading and bending on the stem while setting the rivets.

[Tony Kirk]

I don't intend to get in an argument with anyone here and I appreciate the sharing of knowledge and experience by everyone.

But, I need to point out the proper selection method for CherryMax rivets and my recommendation for adherence to the instructions in the Service Bulletins.

According to the CherryMax Process Manual CA-1015, page 11, when using the CherryMax 269C3 Grip Gage, Step 4 says "Select the fastener with a grip equal to the next higher number. If the number reading is directly on a line you may use either that grip or the next higher one." It does not call for the use of a shorter rivet when in-between marks on the gage. See their example #1.

Also, take note, when the Service Bulletin calls for a specific fastener (or an alternate), the use of those specific fasteners are the only approved method of compliance.

So in this case, when the Repair Doubler is used the only approved fasteners are AN470AD4-6 or the CherryMax CR3213-4-4.

My personal preference is, if I have the bottom skin opened up to install the Repair Doubler, I would choose solid rivets over the CherryMax rivets every time. I'm sure not everyone feels the same way.

The biggest mistake I see is not keeping the rivet puller totally perpendicular to the surface being riveted, this will almost always cause premature breakage of the stem, resulting in an improperly set rivet. CherryMax rivets do not tolerate any misalignment when setting the rivet. Be very aware of this if your rivet puller has interference with the part being riveted.

The CherryMax Process Manual has great information on the installation and removal of CherryMax rivets, so it should be required reading for everyone using them. KAI Section 5 also has extensive information on using CherryMax rivets.

Have a great weekend!
.

[tracy]

Anyone know how many rivets needed to be removed on the 8 in order to get a bucking bar on front side of spar. After reading posts, I don’t want to try the cherrymax.

[Sam Buchanan]

Originally Posted by tracy

Anyone know how many rivets needed to be removed on the 8 in order to get a bucking bar on front side of spar. After reading posts, I don’t want to try the cherrymax.

The -8 has the same stab as my -6. I drilled out the bottom skin trailing edge rivets from the outside corner to the first interior rib. The tip rivets were drilled out from the trailing edge corner to the trailing edge of the fiberglass cap. In other words the rivets that can be easily installed with a squeezer. This allows the skin to be pulled down enough to squeeze your hand and a bucking bar into the stab so the hinge bracket rivets can be driven. It only took a few minutes to drill out the rivets, well worth it to be able to use solid rivets in my opinion.

[Webb]

Parts arrived in mail today. I’ve already primed and will let the primer cure for a few days unless I put the parts on top of the heater and bake them.

The black coating on the non-powder coated brackets comes off easily with a solvent like naphtha.

I’m going to follow Sam’s lead and lift up skin to put in solid rivets.