RivetBangers.com

All,

There are now two new service bulletins on the Van's Aircraft website...

Several of you have probably seen the first one about cracking near the bend in horizontal stabilizer front spars on the RV-6/6A,7/7A and 8/8A.

The second just came out last night, it covers cracking in elevator spar webs near elevator attach points on the RV-3, 4, 6/6A, 7/7A, and 8/8A.

Just making sure you non-VAF-surfers see this stuff - although the second one just came out last night and I only caught it on Mike Bullock's Facebook page. There seem to have been several instances of both in flying RVs. Get out your screwdrivers and inspection mirrors/lights...

Dave

RV-9A builder here breathing a sigh of relief that I'm not affected. I will definitely be keeping an eye out on these areas in the future.

I'm glad to have Van's acknowledge that there have been some issues with the strength of the tail after more than a couple of big accidents and others finding cracks during inspections. It will be interesting to see how many are affected by the SB in the future. Is it a design weakness, or a sensitive area to quality of construction, (or both)?

I've always wondered about the 6/7/8 HS front spar area that's affected by the SB...putting a bend in the web right next to the web/flange angle seems to me to make that area more prone to cracking if good construction practices aren't followed.

That said, there have been some builders reporting no cracks on airplanes that have been flown pretty aggressively - regular aerobatics, lots of load cycles. Perhaps that means construction quality makes a difference?

Scott McDaniels from Vans posts pretty regularly on VAF (rvbuilder2002, if you want to do a search) and he was emphatic that the HS spar SB had nothing to do with any recent accident. The problem was uncovered during an inspection of one of the factory demonstrators.

(update - there's now a letter on the Vans Aircraft front page that references a statement from the NTSB that neither of the two SB conditions was found on Tony Kelly's RV-7)

Dave

Just checked my 6A today. No cracks. Will be adding this inspection to my annual conditional inspection list.

Sure do feel sorry for those that need to do the modification. I don't care how "easy" some are saying this repair is. It would be a real pain to remove all the required rivets.

I'm wondering...I haven't installed my horizontal stab yet. Would it be worth doing the mod now to eliminate the repetitive inspections?

On the other hand, this same HS design has been around for years with no failures so I may be overthinking the risk.

Dave

Dave:

The inspection itself is no big deal. Removing the empenage fairing is pretty quick and easy to have a look.

As to fixing it now, Man, that's a tough call. I wish they could make some sort of association as to the cause of these cracks. Is it high horsepower? Metal props? Acro? Riveting with your eyes closed? What??!

I honestly don't know at this point what I would do if I were you. Maybe you should hold tight for a bit to see how all this shakes out. Perhaps more info will be forthcoming.

I am going to do the inspections and leave it alone.

When I install my elevators, I am going to put washers under the jam nuts for the heim joints.

My two...

CJ

Dave

Who - Wrote earlier

RV-9A builder here breathing a sigh of relief that I'm not affected. I will definitely be keeping an eye out on these areas in the future.

- - - - -

But no more than any other area of the -9 as this problem doesn't effect us

.....

John

painless wrote:I honestly don't know at this point what I would do if I were you. Maybe you should hold tight for a bit to see how all this shakes out. Perhaps more info will be forthcoming.

Thanks Jeff, I think that's exactly the right thing to do. My HS plans called for making the larger relief notch - which I did - and I deburred and smoothed the living merde out of them because I was concerned about just this problem. So...I'm reasonably confident that I won't have any cracks in the long term.

But I haven't match-drilled the HS to the fuse yet, so the option to build another HS if I really think it's necessary - but I doubt it.

Dave

Oh my word!

Now they have superseded the one from the 5th to one now from the 13th!

Does the tail wag the dog or what!?!

Hang onto your hat with this one guys!

This is going to get ridiculous!

I think I am going to make my own emp! hahaha

Maybe I should steal Vlad's -9 tailfeathers?

Think he would notice them missing?

CJ

Again, I'd just like to know what the *causes* of these cracks are.

I somehow am comforted that I chose an engine/prop combo that would reduce vibration trying to shake the airframe apart. This was "back in the day" when we used .016 skins for tail feather control surfaces. Back when men were men!

Anyway, the buzz at that time was cracks associated with rivets holding stiffeners for the rudder. Since then, Vans has gone to .20 skins in this area. The previous size skin was obviously too thin to take some of the vibration associated with larger engines. Case closed.

But these SB's really haven't been explained, except to release the "fix of the day".

I admire Vans for addressing the issues, but show me the reason please. Would make it clearer for guys like Dave who are mid build or those that want to act on a preventative basis.

painless wrote:Again, I'd just like to know what the *causes* of these cracks are

Jeff,

Scott McDaniels made a pretty revealing statement that might help answer your question. Other than the RV-8 wing spar analysis that Vans did several years ago, it's the most information I've ever seen from them on structural analysis and design margins of a particular part.

Ideally, the HS front spar should be a continuous c-channel across its span but that wasn't practical from a manufacturing or building standpoint. So, there's a gap in the "ideal" spar flanges where they transition from the HS spar channel to the center carrythrough angles, and that gap forms an area of increased stress in the structure. If you imagine bending the HS at its root you can easily visualize how the spar web in the affected area might be in strain (strain = stretching or bending due to stress) because there's no flange there to react the tension and compression of bending loads.

Vans went back and did some additional finite-element analysis and found out that the design margin in that area wasn't as much as they had thought, which explains why that location is prone to cracking - especially if there's no relief cutout (there was in my plans) or if the builder didn't do a good job of deburring and edge finishing, or if the airplane has seen a lot of use.

As a DER I've managed issues like this in the past and I'm very comfortable that Vans has a good handle on the cause and corrective action. I'm still left with the question of whether to install the HS with a known design weakness, but I'm going to let it slide for a few months - I have a lot of other things to do on the airplane.

Dave

After spending an hour on another forum reading about this I think I am going to sit back for a while and see what comes from the repairs done by others or more info from Vans. I have plenty of time to decide being how I am a year or more from having to mount it on the fuselage. Right now my gut tells me to do it while it’s still hanging in the garage and part of me says it will be worse by removing all of the rivets and redoing them. It’s much more fun when I can just live in LALA land

Well, I for one have decided to go ahead and install the SB now. My HS is still sitting in the cradle, waiting for final assembly in the not-too-distant future. I've had it mounted on the plane and it's drilled, ready to install. But just sitting here. I thought, it's easier now than having to pull it all off the plane later on. It's easier now than after the plane is painted and I'd have to be so much more careful. If there's any question of any potential weakness here, I want the peace of mind and I just want to get it done.

So I went down and got the kit from Vans. It's only $15 and it's well documented with rivets, nutplates, everything you need. I started on it Saturday afternoon, wondering how long it will take me. There are lots of rivets to drill out. I won't kid anyone. It's time-consuming and tedious work, and I really took my time because I don't want to mess anything up. The worst of them are on the "fingers" that extend inside on the spar. You can only reach them with a right-angle drill, and only after you have the ribs removed from the HS so you can reach in there. I wore a pair of magnifying glasses and took my time. I actually spent all my available shop hours this past weekend just drilling out rivets, probably about 7 or 8 hours all told, but I got them all out. I believe the worst of it is behind me.

I'm taking pictures, and as soon as I can get them uploaded I'll document my work and post it here for anyone interested in seeing how I did it. I'm glad I made this decision, but I can't blame anyone who decides to wait either.

Very cool, Bruce, I'm looking forward to seeing your pictures. They may help me make the decision about what to do with my HS.

Drilling out rivets with a right-angle drill gives me the creeps...

Dave

Dave, drilling out those rivets turned out to be much less of a nightmare than I had thought it might be. One of my most-used pieces of equipment in my shop is a pair of headset magnifiers. I bought it at Harbor Freight for cheap! And I use it all the time for all kinds of close-up detail work, wiring, soldering, anything and everything. Seriously, every builder should have a pair of these!



They came in handy here with my right-angle drill and a short bit to drill out those rivets without much trouble. I could see close-up and move the bit as I was drilling, to keep it centered on the rivet. Go slow and this will work fine. (picture below)

The worst thing in my case, was that back when I was a newbie builder I failed to put the manufactured rivet head on the thinner material side. That meant when it came time to drill these out, I was drilling on the bucked tail side of a lot of the rivets. It would have been much easier to drill through a rivet head and snap it off, then remove the angle stiffeners and take the rest of the rivet shanks out of the angle pieces on the bench. Nevertheless, I still got it all done. It just took me more time and more care.

I'm finished now, and as I promised, I'll post some pictures and comments in order to (hopefully) help someone else out.

Here's the start of the project... there are lots of rivets to drill out. Here are all 4 ribs after successfully removing them. (I know... I have mis-matched primer. New builder at the time ) I drilled out about 15 extra rivets out along the aft edge of the rear spar on the top side, in order to enable me to lift that skin up and reach in. This helped out when it was time to rivet it together again.



With the ribs out of the way, you can reach in and drill out the rivets in the angle stiffeners and remove them, too. Here's what I was talking about above. It would have been easier to have the mfr. heads on this side. Now's my chance to fix that! You don't see it in this picture because I was holding the camera with one hand to take this pic, but when I was actually doing the drilling, I had one hand in there on the end of the drill to help carefully guide it, center it, and apply some pressure to drill the rivet. I used a slow speed and took my time.



Once the ribs and stiffeners are out of the way, you trim off the corners of the spar flanges as shown here. Top and bottom, both sides, there are 4 of these to do. When flipping the HS over, cleco the stiffeners back on. Without them, there's nothing holding the spar together in the center. The structure pulls apart and could twist on you! Be careful.



Vans put together a terrific kit for this SB. It only costs $15, by the way. I can't imagine they're making a nickel on it. It even includes a piece of stainless steel sheet just for this purpose. You slip it in under the spar flange, so when you cut off the corner, you don't damage the skin underneath your cutting disk. I used my dremel tool for this. Easy job.



There will be 4 of these "orphaned" holes in the skins that you fill with a short rivet, just to fill the hole.



This is actually one of the hardest tasks in the whole project... deburring and smoothing the cut-off corner of the spar flanges. You're supposed to radius them and smooth them nicely. I tried lots of methods, and finally settled on this small jewelers file and a piece of emery cloth (actually a piece of an old belt sander belt), folded to slip under the flange and work it to smooth the cut. I was glad when I got this done.



Clamping the new stiffeners in place, carefully positioning them before drilling. I took my time here, considering edge-distance issues, to make sure I would have good edge distance on the "fingers" before drilling. Especially on the top side... the holes are pretty close to the top. You may choose to poke a sharpie through some of the holes and mark the piece, then take it out and check it to make sure your holes will be good BEFORE you drill them. I had lines drawn on mine, but they didn't exactly line up with the holes as good as I would have liked.



ALSO, you want to double-check the distance between the inboard ends of these stiffeners, to make sure you have room for the VS mounting plate, where it bolts to the HS spar. I had plenty of room, but I've read that especially on RV-8's it might be an issue. It's far easier to check now than to have to try and trim some off after they're riveted in place.

Once you're sure you have it clamped in the right position, you can start drilling and clecoing. You drill through both sides to get all the holes drilled.



Then after the usual deburring, cleaning and priming, the riveting begins. Here's where drilling out those extra rivets on the back side of the top skin allowed me to lift the skin a bit and give me some additional room in there. I was able to use my straight rivet set on all the interior rivets (I don't like the offset rivet set very much, and I avoid it if at all possible). I messed up a couple of rivets before I got the hang of it, and had to drill them out and do them over. This greatly adds to the time this whole project will take you. But I got it done okay.



(continued...)

Okay... continued...

Due to the thickness of the new added stiffeners, the ribs you drilled out won't fit back in place as they were. So you have to cut off the flanges on the ends, and new angle pieces are made and riveted to the ribs to make new flanges. So I proceeded to mark the flanges and cut them off per the directions. Like a big dummy, I cut off the wrong flange on one end of one of the ribs. (This is easy to do, they look so similar. Pay attention and be careful!) Rather than cut off the correct end and have to rivet a new flange on both ends, I opted to just buy a new rib from Vans. I didn't know they had changed the old HS-405 to the new HS-00005 until I went back to work and noticed the differences.

The older style HS-405 didn't have the relief notches that the new one has. It required more work to bend the flanges to 90° and flute them to straighten out the rib so it isn't warped or twisted. The new style is very nice in this regard. The flanges are perfectly bent at 90°, no fluting is required.

These parts are among the few in the kit that aren't pre-punched, if you recall... so there is potential difficulty in positioning and drilling them to skins that are already dimpled. If you've ever noticed, dimpled holes become slightly larger than the drilled #40 hole, so careful drilling techniques are necessary to make sure the new holes you drill are centered under the dimpled holes in the skin.

I learned one more thing about these new ribs... after the fact. I wish I had known that these new ribs are slightly shorter to account for the thickness of the doubler. Guess what I did? The first thing I did when I got back in the shop was to cut off the forward flange and proceed with the directions. I could have saved myself all that trouble... they're already made to fit! Doh!! Anyway, it's done and here are some pictures:

Here's the new rib, being carefully drilled into place. It was nice not to have to do any fluting or bending of the flanges. Note that the doubler is already positioned and clamped in place as well. I drilled the rib before I riveted the stiffener in place.



Later on, the rib is now deburred, dimpled, and primed as normal. The doubler has been riveted in place. Now comes the clamping and drilling of the new angle piece to make a new flange. As I said above, I wish I had known that I could have avoided this. On the new rib anyway!



When I got all that work finished and the new flanges finished, primed and riveted to the ribs, here they are before final installation back in the HS. Interesting side-by-side comparison of the new rib with the old.



Here's the back sides:



And finally, here's the new rib, riveted in place:



Just for comparison, here's the old one back in place as well, on the right side.



Here's the aft side of the spar, all riveted back together with the new stiffeners in place. The only place I had to use an offset rivet set was when riveting the nose rib and the other rib to the spar. I was careful and it went well, although there was one rivet I had to drill out and replace.



And here's the forward side:



Funny how an airplane that isn't finished and has never flown can look so beat up! The primer paint, that is. I'll shoot some touch-up primer on those spots before final mounting this on the fuselage. I wanted you to see how it came out, as is.

I won't kid anybody, this is a fairly big job. But if you've come this far building an RV, you have all the skills to accomplish it. It just takes time and care. There are lots of details that I haven't mentioned or taken pictures of. Follow the directions very carefully and you'll avoid "big dummy" mistakes like I made. My hat's off to Vans for putting together a plan and a really good kit for this SB. The estimate of about 20 hours' work is probably pretty accurate if you don't mess anything up. If you're more like me and you have to drill out some rivets again, or you mess something up like I did, it can easily add significantly to the number of hours you'll spend on this job.

To sum up, I'm very happy to have this finished. In my case, it was a good decision to do it now before my plane is finished. Easier now at home in my shop than to have to dismantle a finished, painted plane later on. There's peace of mind, having this done. That was the main reason, personally, for me. Possibly higher resale value, although I don't plan to ever sell my airplane.

Cheers!

Bruce,

AWESOME write up! I plan to do the mod proactively over a rainy weekend this summer.

I am going to be in Portland for about 8 hours on April 7th....Got time for a late lunch and some beers?

bullojm1 wrote:Bruce,

AWESOME write up! I plan to do the mod proactively over a rainy weekend this summer.

I am going to be in Portland for about 8 hours on April 7th....Got time for a late lunch and some beers?

Thanks, Mike,

Heck yeah! Let's get together when you're here!

It's funny, I was just wondering when you might be out this way again. Terrific!

bullojm1 wrote:


I am going to be in Portland for about 8 hours on April 7th....Got time for a late lunch and some beers?

Are you flying your RV all the way Mike?