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SB 00036 (cracked horiz stab spar) Installation Notes

My first attempt at this didn't go well. 5 out of the 8 cherrymax rivets came out bad. Luckily the stems weren't retained and they were easily knocked out so I could drill out the cherrymax and try again. Both my hand puller and the pneumatic puller had too wide of a tip and were side loading the rivets. I bought an extended nose hand puller, modified it to fit without hitting the brackets or skin, and with lubed up rivets was able to successfully pull the 5 bad ones that were on the right side, and all 8 on the left side without issue.

I ended up with a single oops rivet on the right lower skin due to a mis-squeeze. Now I just have to do some touch up paint work.
 

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The issue is that the elevator hinge creates a point vertical load and its associated fore/aft moment needs to get reacted into the skin with a fore/aft couple into the skin. The spar web has flanges that attach to the skin and transfer the load into the skin forming a closed cell torque box. (With bigger loads this would be helped out by a rib backing up the fitting and spar web with multiple fasteners to get that couple into the skin.) It is not a “bending” load as you describe. It is a vertical load and moment couple between upper and lower fasteners that attach the fitting. “Thicker spar web” may help with the load at the rivets attaching the fitting but then that load is transferred in the spar web through the rivets and goes around the 90 deg bend in the spar web to get to the skin attach fasteners. Going around that bend is the material thickness of the spar web and therefore a prime location for crack. A doubler may solve the current crack location in the vertical web of spar but will probably cause new cracks at edge of the doubler in the corner of the 90 deg flange that attaches the skin. If you think this through it is pretty intuitive. In my opinion that corner is the fatigue detail that Vans second iteration in the repair SB solved by having the new doubler nest and pick up skin fasteners.

Putting a large steel plate on the spar web may have another negative consequence related to horizontal tail bending. Bending due to lift on the tail is a reacted into the skin in a inbd/outbd couple (not fore/aft couple like i explain above for the point hinge fitting load) The spar is aluminum of a particular web thickness and a particular stiffness. All of a sudden the bending inbd/outbd in the spar web hit a very very high increase in stiffness of a steal doubler. Rapid increases in stiffness is prim location for cracking. This is why spar always taper in thickness changes. Think of tree branches always break at intersection to thicker branches.

No good engineering is ever presented without its caveats.
-A freebody diagram would be helpful for both of these I explain above but I am on vacation with only an iPhone to write this response.
-I am a structural design engineer so some strength engineer my give a better explanation, since they always want to prove us designers wrong.

Hi Philip,

Thanks for the suggestion of a FBD. Since the pivot cannot transmit a a moment, the applied elevator load is limited to the reaction force applied thru the bolt. Of course the magnitude and direction will vary depending upon elevator deflection/loading. This force can put both a shear and tensile load on the rivets holding the hinge to the spar. In addition, when the force is anything but horizonal, a couple is introduced into the spar.

The issue of the abrupt change is spar stiffness is a good point and not one I have not fully considered. I assume Van's uses the "fish mouth" design of the aft doubler to minimize this. I carried the same idea to the one-piece bracket I am considering, but may need to do more given the higher modulus of the 4130. I'm looking at tapering the thickness of doubler portion. I'll compare the relative stiffness of various section (locations) of the spar (E x I) and compare them to Van's new design.

Thanks for the help,

Dean
 
Let's stay on the rails.....

Putting a mod hat on for a moment....

This thread was started for the purpose of sharing notes about installing the SB kit provided by Vans. Engineering discussions that don't apply to the Vans kit need to be in a different thread so helpful hints about the Vans installation don't get lost in the clutter.

Thank you.
 
Putting a mod hat on for a moment....

This thread was started for the purpose of sharing notes about installing the SB kit provided by Vans. Engineering discussions that don't apply to the Vans kit need to be in a different thread so helpful hints about the Vans installation don't get lost in the clutter.

Thank you.

Understood! Thanks to all for the input.
 
Are there any alternative access points for borescope inspection for those with glassed in end ribs? What about small access hole on bottom skin?
 
Are there any alternative access points for borescope inspection for those with glassed in end ribs? What about small access hole on bottom skin?

On our RV-3, we don’t have balance weights, so with glassed-on tips, there is no way to go in from the tip end…so we took off the empennage fairing and went in from the root end. Worked great - however, there are no intermediate ribs on the RV-3 (just root and tip) and the distance is only about two feet to the outer hinge…. But it might get you thinking!
 
Are there any alternative access points for borescope inspection for those with glassed in end ribs? What about small access hole on bottom skin?

On our RV-3, we don’t have balance weights, so with glassed-on tips, there is no way to go in from the tip end…so we took off the empennage fairing and went in from the root end. Worked great - however, there are no intermediate ribs on the RV-3 (just root and tip) and the distance is only about two feet to the outer hinge…. But it might get you thinking!

See this post:

 
RV8 1485hrs right stab spar cracks. Spar replacement

Sigh. I found a couple cracks on the right stab aft spar. I was hoping to just deal with the repair compliance but the cracks are a bit too close to the bend radius of the spar so the factory advises on spar replacement, which is what I had assessed as well. It looks like I'll have to remove the stabilizer to do the spar replacement on the bench. I'm good with all of that. I will do the beefing up with the compliance kit as well. What leaves me in the corner sitting and whimpering is that the back order is now end of May. I hate being grounded because of back orders. Sigh.
 
Anyone think about installing inspection plates in lower skin so this can be inspected/ repeated at a later date? My build isn’t painted yet but my HS tips are filled and that is a pain to do again! I think I’d rather cut 2 new holes and install a doubler and cover plate.
 
That looks familiar.......

I decided to forget the Cherry Max rivets and drilled out the rivets on the bottom skin so I could access the front of the spar. It only took a few minutes, wish I had done that first instead of messing with the Cherry's. Driving the hinge rivets went well and now I know the hinges are secure.

My A&P friend told me the Cherry's can't be drilled out but I was able to use a #40 drill to remove enough of the mandrel so the heads could be popped off with a flat drift and hammer without damaging the hinges.
The collar needs to be drilled or ground to get Cherry's out. I have a tiny ball rotary file for just that purpose.
 
Cherry rivets have a shelf life and are supposed to stay in their unopened bag until needed, it contains lubrication. If Vans is sending lose Cherry rivets I suspect they have dried out.
When I was at Eclipse (contractor) the FAA found Cherry rivets soaking in lubricant and they went insane. That place was straight up scary.
 
Has anyone else noticed that the new hinge brackets don't quite fit into the web of the nested spar doublers? They ride up on the flange radius slightly, the outboard ones more so as the size of the spar and nested doubler decreases.

It isn't terribly obvious unless you look along the spar web from the end after clecoing them on, and it isn't beyond the bounds of possibility that some may have riveted them on without noticing it and thus have a gap between the hinge bracket and the spar assembly.

The solution evidently is to radius off the lower corners of the hinge brackets, but that is somewhat surprising with a powder coated steel part which I would normally take to be 'finished', at least in terms of external dimensions.
 
Has anyone else noticed that the new hinge brackets don't quite fit into the web of the nested spar doublers? They ride up on the flange radius slightly, the outboard ones more so as the size of the spar and nested doubler decreases.

It isn't terribly obvious unless you look along the spar web from the end after clecoing them on, and it isn't beyond the bounds of possibility that some may have riveted them on without noticing it and thus have a gap between the hinge bracket and the spar assembly.

The solution evidently is to radius off the lower corners of the hinge brackets, but that is somewhat surprising with a powder coated steel part which I would normally take to be 'finished', at least in terms of external dimensions.

Which kit are you referring to as there are differences depending on model?
 
Has anyone else noticed that the new hinge brackets don't quite fit into the web of the nested spar doublers? They ride up on the flange radius slightly, the outboard ones more so as the size of the spar and nested doubler decreases.

It isn't terribly obvious unless you look along the spar web from the end after clecoing them on, and it isn't beyond the bounds of possibility that some may have riveted them on without noticing it and thus have a gap between the hinge bracket and the spar assembly.

The solution evidently is to radius off the lower corners of the hinge brackets, but that is somewhat surprising with a powder coated steel part which I would normally take to be 'finished', at least in terms of external dimensions.

Yes, I noticed the same issue. Just on the outboard brackets. I put a radius on them before installing. (RV8) No cracks S/B installed.
 
RV4 Cracks

It's going to be a long summer... One is too close to the bend for comfort. #$%&!!!
 

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Non-PP installation on -6A

There are no cracks on my -6A HS because it is not yet flying, however I'm taking the opportunity to do the SB during construction before it's painted.

The kit is not pre-punched and one of the tasks is to match drill the hinge bracket mounting holes and the revised position (+.040) for the pivot bolt. Pics attached of the process that used match drilling and transfer templates.
 

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Nested doublers

The next task is to fit the nested doublers. They need to be back drilled to match the existing holes in the spar and will be installed with solid rivets rather than with the Cherry Max rivets that came in the SB kit. For adequate access, I removed the end rib and 15 rivets on the trailing edge top and 10 from below.

The match drilling is in 2 steps, first a pilot hole drilled from the inside and then upsized to #30 from the outside. I used a drill guide to center the pilot hole. The guide is a 1/8 pulled rivet with the mandrel removed and the compressible surgical tube on the 2mm drill bit is to hold it in position. The band aid is for the hole in my finger from drilling out a rivet.
 

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Re-assembly

I primed the nested doublers and the hinge brackets and installed using solid rivets. It was possible to get a bucking bar inside the HS, though it is a bit tight.

In total this SB took me 2 days effort and involved removing and replacing 45 skin rivets per side.

The most time consuming aspect was match drilling the blank hinge brackets and the nested doublers to fit the existing holes.

Note the HS skins were originally machine countersunk and the lack of dimples probably made it a bit easier to fit the doubler.
 

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HS-00716A

I'm installing this Service Bulletin.
Did anyone else have an issue with HS-00716A Nested Spar Doubler?
It doesn't fit in the spar very well. I countersinked the holes for the skin dimples. New part ordered. I will dimple the next one. That still doesn't explain why it fits so tight it spreads the flanges of the spar apart. I can see the buldge.
 
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HS-00718A

Did anyone install the HS-00718A Repair Doubler on the forward side of the spar even though there were no cracks found?
 
Yup. I had one crack on the right HS so I did both sides including the doubler. I wasn't worried about the unpainted rivets on the bottom so I "unzipped" the lower skins and went at it.
 
Did anyone install the HS-00718A Repair Doubler on the forward side of the spar even though there were no cracks found?

I considered it but figured that the Van's engineers had determined that it was not needed and it would just mean extra weight that serves no purpose, so I did not install the internal doublers. I am trying really hard to build my plane as light as possible. I had both upper and lower skins unzipped already for solid rivets, so there wasn't an issue for access.
 
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HS-00718A Repair Doubler

Yup. I had one crack on the right HS so I did both sides including the doubler. I wasn't worried about the unpainted rivets on the bottom so I "unzipped" the lower skins and went at it.

There's no question about installing the SB-0036 kit. There's no question about installing the HS-00716A Nested Spar Doubler. FYI, that's the part on the aft (outside) of the spar.

The question is about the doubler that goes on the forward (inside) web of the spar. There are no cracks. It's never flown.

Did anyone install the HS-00718A Repair Doubler on the forward side of the spar even though there were no cracks found?
 
There's no question about installing the SB-0036 kit. There's no question about installing the HS-00716A Nested Spar Doubler. FYI, that's the part on the aft (outside) of the spar.

The question is about the doubler that goes on the forward (inside) web of the spar. There are no cracks. It's never flown.

Did anyone install the HS-00718A Repair Doubler on the forward side of the spar even though there were no cracks found?

Yes!

Mike said he did, on one side that had no cracks.

I also know of another builder that did.

If you want to install it, go for it, it will be stronger, the only downside is weight and getting access.
 
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HS

Yes!

Mike said he did, on one side that had no cracks.

I also know of another builder that did.

If you want to install it, go for it, it will be stronger, the only downside is weight and getting access.

Thank you.
 
Shipping cost

Need SB-0036 kits for an RV-3B and an RV-4.

Anybody recently ordered either of those to be shipped near Florida?
What was your shipping cost?

Finn
 
I found a crack on one side and read over the bulletin a couple times. I am unclear on Step 53. Can anyone expand on this?


Step 53: Match drill the .189 hole in the hinge brackets to .191.
 
I found a crack on one side and read over the bulletin a couple times. I am unclear on Step 53. Can anyone expand on this?


Step 53: Match drill the .189 hole in the hinge brackets to .191.

I didn't understand why either. It's an AN3 bolt. I ran a #12 reamer through the pair each side. .189".
 
Did anyone install the HS-00718A Repair Doubler on the forward side of the spar even though there were no cracks found?

I just did this repair on my 7 about 3 weeks ago while I was waiting on firewall sealant. I did indeed install the doubler on the forward side. Wasn’t much of an issue to drill out the skin rivets to the center rib. I was able to get my squeezer in there to squeeze all of the rivets. It was a pretty easy peezy process. I figured why not use it and make it even stronger. No cracks, haven’t flown yet.
 
Guys I have to do the SB on a RV-6 Non Pre-punched. During the boroscope inspection we have observed a few small cracks.

I have done of reading here in order to prepare myself. I cannot see when to match drill the 8 hinge bracket holes into the HS-00716B Nested Spar Doubler?

I do think it should be in Step 32 where it states that you should match drill the holes common to the skin and rear spar into the nested spar doubler? It does not specifically mention the eight hinge brackets holes through the Nested Spar Doubler. I can see that it should be done in this step? Also it should be drilled from the FWD side through the existing holes in the spar.

Thanking you in advance.
 
Guys I have to do the SB on a RV-6 Non Pre-punched. During the boroscope inspection we have observed a few small cracks.

I have done of reading here in order to prepare myself. I cannot see when to match drill the 8 hinge bracket holes into the HS-00716B Nested Spar Doubler?

I do think it should be in Step 32 where it states that you should match drill the holes common to the skin and rear spar into the nested spar doubler? It does not specifically mention the eight hinge brackets holes through the Nested Spar Doubler. I can see that it should be done in this step? Also it should be drilled from the FWD side through the existing holes in the spar.

Thanking you in advance.
The instructions for the non-PP are not very complete! I drilled the 8 holes for the hinges in the nested doubler just before drilling the flange skin holes. The rationale for drilling in this order is so that the doubler can be secured with clecos to pull it tight up to the rear spar before drilling the skin holes.

There are pics and description of how I did this in post #68 above. Post #67 was how I duplicated the holes from the old hinge brackets to the new ones. The other way of trying to do this would be to back drill the hinge brackets through the spar but it would be very difficult to hold everything in alignment I think.
 
Thank you very much Paul. I went through your posts again. Do you think it can be done without removing the end rib?
 
Thank you very much Paul. I went through your posts again. Do you think it can be done without removing the end rib?
Hi Jan, I think it would be difficult to get enough access without removing the end rib because the skin can flex up only a limited amount due to the rivets in the centre spar that are holding down the skin. When the tip rib is off it gives good (relatively) access to be able to see the work area and to get in with the angle drill and bucking bar.
 
Ok It is a few weeks later but here I am. Doing the SB went quite well on the RV6. We lifted the tail high enough to do all the drilling out of the HS skin rivets from the bottom. With my angle drill and a second person peeping in there and holding back the skin, it was quite easy to carefully drill a few holes from the inside through the spar doubler supplied in the kit. The rest was done outside after clecoeing everything together. We have also used the repair doubler that comes with the kit on the inside. We finished in one day. Gald it is done now.
 
This is a great reference post started by Sam.
For those contemplating the SB, be aware that initial, then annual, inspections are in compliance providing no cracks are found.
There is no way I would do the SB modifications on a flying aircraft unless there where, was, a crack. Some aircraft have thousands of hours with no cracks.

All that said, these types of posts are excellent reference for anyone needing, or wanting to do the mods.
 
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