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Check those tails

vic syracuse

Well Known Member
Advertiser
Mentor
I have been doing lots of prebuy inspections over the course of the last year, and one issue keeps coming up a whole lot more than I care to see. In about 30% of the RV's I inspect the tail is improperly mounted, some to such a degree that they are unsafe. The tail is the area of the airplane where most everyone learns the skills they will need throughout the rest of the build. It is also the area where I see the most problems.
Since these issues continue to manifest themself on so many RV's,(and I know I am not seeing all of them), I figured it was time to bring it to everyone's attention, and especially to those of you who did not build your airplane.
Take the time to pull the tail fairing off and carefully inspect for proper mounting of the horizontal stabilizer to the fuselage longerons. Inspect it for proper bolts, proper edge distance, and for proper riveting.
In the 2 pictures below you will see that the bolts that hold the stabilizer to the longerons do not have proper edge distance. In fact, they may have compromised the structure itself. There are even multiple holes in the attachment, and you can even see where the pilot hole is located and that's where it should have been drilled. This is on an RV-6. I have seen 7's, 8's, and 10's just as bad. The bottom line is that the tail is not properly attached to the fuselage.

The pictures are taken from inside the fuselage looking UP at the attach points. You will need a mirror and flashlight, or an IPhone camera to see it clearly.

If you happen to see something like this on your particular airplane, send a picture to Van's. I have seen them recommend engineered solutions for these problems. In the meantime, be careful. :)






Vic
 
A few more pics on this topic...

While searching for my RV, I too was mentored (Thanks Walt!) to look closely at the tail.

Here are a few examples of bad builds I came across in the tail feathers:

https://photos.google.com/share/AF1...?key=QzUzcmJzZlc0Qk1TQWJ1MXNlMTJNSEQ0YU14ZjFn

And:

https://photos.google.com/share/AF1...?key=QzUzcmJzZlc0Qk1TQWJ1MXNlMTJNSEQ0YU14ZjFn


In fact, it got to the point where I wouldn't make the investment in cross-country travel before asking if the seller would pull the fairings and send me some pics of this area. If they refused, I moved on to the next target.

Now, in finding the one I eventually bought...even it had some problems back there-but they were less severe than some of the ones I had seen, looked like there might be workable fix available and the rest of the build was outstanding. I gained a real appreciation for just how difficult it can be to hang the tail on these aircraft...

So here was mine before:

AF1QipN-6Y8QOTpzcV6FbHtYTyAbg3L9TWu5bgnbYkviNYBPlLp3tx6KwioxuMWlSBly5A


And here it was after a call to the Mothership for an approved fix to the bad edge distance issue on those two outboard bolts:

https://photos.google.com/share/AF1...?key=QzUzcmJzZlc0Qk1TQWJ1MXNlMTJNSEQ0YU14ZjFn
 
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I'm working on this problem on my RV6 right now. Robb, does the triangle shaped shim go through to the back side of the horizontal spar with another bolt back there? What is done on the under side of the deck? Thanks for posting your fix.
 
I'm working on this problem on my RV6 right now. Robb, does the triangle shaped shim go through to the back side of the horizontal spar with another bolt back there? What is done on the under side of the deck? Thanks for posting your fix.

Steve,

No, IIRC it doesn't take up any more real estate back there than the original shim did.

Mine was a pretty simple fix, all in all and the problems weren't as gross as some of the pics I posted.

All that was done was the addition of two more bolts inboard of the original inboard ones, the new (larger) shim, and rivets were drilled out that were under the top of the triangles and bolts put in there to hold that section firmly in place.

Nothing was done on the lower deck under that flange or behind the spar, and as I recall, the new shim didn't extend aft behind it.

I'm out of town now, but can pull the fairing and post up some pics over the weekend if needed.

The guys at Van's suggested this fix after we sent them some pictures to examine-If I were you, I'd document the problems you're facing and get their thoughts on a proper fix for YOU vs what they came up with in my case (My fix may turn out to be not be the proper course of action for your particular situation...)

Good luck with it,

Rob
 
The triangular fix plate looks good but do check your bolt length, three threads maximum extending from the nut. Hard to imagine that one would take the time to apply "witness" seal and not notice the bolts were too long?
 
The pictures that Rob posted show a very common fix. It works and is approved by Van's. But don't hesitate to check with them for your particular situation.

Vic
 
The triangular fix plate looks good but do check your bolt length, three threads maximum extending from the nut. Hard to imagine that one would take the time to apply "witness" seal and not notice the bolts were too long?

Tom, do you have a reference for that spec? The only application I can think of when that may apply is with some close tolerance short thread fasteners.
 
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Tom, do you have a reference for that spec? The only application I can think of when that would apply is with some close tolerance short thread fasteners.

It's a rule of thumb, not a spec as far as I know, and even then is specious since different hardware will have different implications (MS21042 vs AN364 vs AN365 etc). But on those AN365 nuts, I would wonder if they bottomed on on the shaft given the length of thread protruding from the top of the bolt. Maybe the photo makes it look worse than it really is.
 
Hey Vic,
My -6 was supposedly the fifth plane built by the builder. Do you think he had the tail mastered by then? (Inside joke)
 
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I contacted Van's when I mounted by HS to the fuse because it was obvious I wasn't going to have proper edge distance on the longeron as you noted.

The response, which surprised me, was basically "yeah, there often isn't." And they suggested it wasn't a deal breaker, which, again, surprised me.

WHY isn't there often proper edge distance with these holes? That's the question I never got an answer to.
 
Thread length protruding from the nut is a rule of thumb " no less the one thread, no more then three threads". I thought this was common knowledge!
As mentioned by Walt, there are slight differences between bolts but if there are more then three threads showing there is a chance that the nut tightened on the shoulder of the bolt shank and not on the parts themselves.
In the case of the picture posted it appears to be more then that. Shorter bolts should be used with the appropriate thickness of washers to make the " rule of thumb" work.
The other rules are
No more then three washers on a bolt

And where possible bolts, the threaded portion, should be pointed down, pointed towards the fuselage centre and pointed aft

Why these directions? If a nut were to fall off there is a good chance that the bolt will at least stay in place.

While these may just be rules of thumb they are indeed something that my inspectors always check.
 
Great thread

I wish we had a section in this forum that addressed these types of build errors and areas to be especially vigilant . I can see how someone could make these mistakes or maybe modify to repair a slight mistake only causing the structure to be truly dangerous. And some of these mistakes can be hidden for years until a keen eyed inspector finds them before the NTSB does. Thanks Vic, you may have saved somebody's life here.
 
"WHY isn't there often proper edge distance with these holes? That's the question I never got an answer to."

Bob,

It is because the HS-614 is made too short. It is supposed to be 11" long which would not fit between the horizontal skins and rib flanges. There is a Note on my RV6 drawing 3PP, Section A-A, that says to notch the skin and rib flange 1/8" and trim the HS-614 to fit with clearance. Mine was made like the photos above in which none of them show the ribs and skins notched. I don't know if the RV7 drawings call for the same notching requirement. The old RV6 drawings are deceiving because they are not really drawn accurately.
 
I contacted Van's when I mounted by HS to the fuse because it was obvious I wasn't going to have proper edge distance on the longeron as you noted.

The response, which surprised me, was basically "yeah, there often isn't." And they suggested it wasn't a deal breaker, which, again, surprised me.

WHY isn't there often proper edge distance with these holes? That's the question I never got an answer to.
Edge distance is important when the load is pulling the fastener toward the edge. In this case, the load is axial along the bolt, so edge distance really doesn't really come in to play. Even the 'really bad' picture Vic sent (with blue paint), the major problem is uneven loading of the bolt head, not the edge distance (from a structural standpoint). The normal edge distance (2D of the fastener) is mostly important for sheet metal - to prevent 'zippering' of the joint. On thicker material, like the angles in this case, a different edge distance would apply for a load perpendicular to the fastener.
(I did aerospace structural design a few jobs ago)
 
Thread length protruding from the nut is a rule of thumb " no less the one thread, no more then three threads". I thought this was common knowledge!

Just for curiosity sake to test the "rule of thumb" I ran an AN365 nut onto a AN3 bolt and counted 5 threads showing when it bottoms.

It's generally pretty obvious if the bolt fails to clamp the pieces up after tightening (still spins freely in the hole) indicating you need another washer. Personally I'd rather have more treads showing than the minimum otherwise the grip shank of the bolt will not be fully engaged in the hole. I don't like threaded surfaces in holes.

But to each their own... :cool:
 
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Yes I totally agree that the preference would be to have the shank of the bolt fully engaged in the hole. This is what a combination of thick and thin washers will usually allow to happen. There will of course be circumstances when the rule of thumb does not work, but what it does allow you to do, is just by looking at the number of threads extending, know that you are not finishing that tighten job half on the shank of the bolt and half on the work that is supposed to be done.
Not all AN3 bolts are exactly the same, mic a few for diameter and you will find a few thou difference in bolts. Thread numbers could vary between batches or manufacturers. The rule of thumb is meant to err on the safe side.
This rule does not work with thin nuts or metal locking nuts.
But at the very least it does make you wonder about the bolts in that picture, in that critical location.
 
As I was asking in another thread

We don't always see the edge distance we want, even when everything is exactly per plans. Here's a critical flight control surface with room inside the clevis fork for a wider part with more edge distance, yet the part as supplied offers less than 1.0 clevis pin diameter edge dx, loaded in shear -a thin sheet metal horn.

No one seems to think this could be an issue (and I sure as heck hope it isn't!)


Sometimes I'm not sure I understand all that I know about this :eek:
 
On the other hand you also know that if you have just one washer and one tread showing you will have threads in the part and not the bolt shank as it should be. Sound judgement overrides general rules of thumb.
 
Edge distance is important when the load is pulling the fastener toward the edge. In this case, the load is axial along the bolt, so edge distance really doesn't really come in to play.

The two photos Vic posted (post #1) illustrate a different problem; the bolt notched the inboard edge of the longeron. You can't see the notch in the photos, but it's there, ....outboard AN3, under the white angle. The view in Vic's is from the underside, which is why he talked about using a mirror or camera. Thanks Vic...that's firm addition to the inspection list.

The other photos (post #2) are all from the top, looking down, thus we can't see the longeron at all. However, judging from the rivet locations, the outboard bolts appears to be properly centered in the unseen longeron flange. If confirmed (the mirror or camera inspection Vic discussed), that just leaves the edge distance issue where the hole goes through the end of the angle on the stabilizer spar. The bright blue example is awful. The dark gray example with the green trim cable is iffy because of the extra bolts in odd places, but the outboard bolt edge distance is fine. I don't think I'd condemn Rob's (see the last two photos), but hey, the fix is so easy.
 
"WHY isn't there often proper edge distance with these holes? That's the question I never got an answer to."

Bob,

It is because the HS-614 is made too short. It is supposed to be 11" long which would not fit between the horizontal skins and rib flanges. There is a Note on my RV6 drawing 3PP, Section A-A, that says to notch the skin and rib flange 1/8" and trim the HS-614 to fit with clearance. Mine was made like the photos above in which none of them show the ribs and skins notched. I don't know if the RV7 drawings call for the same notching requirement. The old RV6 drawings are deceiving because they are not really drawn accurately.

For the -6 models -

The drawing was revised to 3a in 1992. and a Detail A showed the notch in the lower horizontal spar angle.

I don't think the original pre-1992 drawings showed that and many tail sections were built before that time period. These would have been the not pre-punched versions. The 3PP drawing is dated 1996.
 
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Walt, you got my curiosity going and so I too went to the shop. There is quite a variance in bolt length within a certain dash number. The shanks are almost exactly the same length but the threaded portion can change by up to one thread. I measured 25 bolts and there was one thread difference in length between the shortest and longest bolt. These are new bolts, same stamp, from Van's
The other interesting thing was the difference between different bolt sizes

2zyyaog.jpg


All fasteners tightened to just snug on the shank

Note the top two AN3-3a bolts. There is one thread difference in the bolts, one with five visible one with 3.5 showing.


The flat screw headed bolt, unusual yes, has just over three threads showing when snug.

Of interest is the AN4 bolt that has 3.5 threads showing. The AN4 bolts were more consistent in their length and thread size.


This has been a good discussion and whether you use a rule of thumb, and or, just sound judgement, the ultimate goal is to have as much of the shank in the hole as possible, with no possibility of the nut engaging the shank of the bolt before the fastener is properly torqued.

I would still like to know if the bolts in the "fix" picture are too long.
 
Tail

I haven't seen any mention of some really ugly riveting. Rivets that were obviously too short and over driven to compensate. Rivets that were under driven. The rivets bother me more than the misplaced bolt holes. One has to wonder if all the rivets in the airplane are that bad.
The end of the angle that was notched could have been handled much better by cutting a large radius on the corner of the angle with no loss of strength.
The rule of thumb for exposed threads is just that, a very approximate rule of thumb. Threads vary from 32 per inch to perhaps 20 on some very large diameter bolts..
 
I am Sooo glad you are all noticing ALL of the problems. Yes the riveting in some cases was horrible, as are the notches, and the bolt locations. The same issues are very common across many of the RV's I inspect.

My primary purpose was not so much a "lookie what I found" and crucify the current example, but an attempt to raise awareness that I think a large number of tails out there should be looked at. That should include a bright light and mirror/camera. Hopefully, that will happen. :)

Vic
 
Walt, you got my curiosity going and so I too went to the shop. There is quite a variance in bolt length within a certain dash number. The shanks are almost exactly the same length but the threaded portion can change by up to one thread. I measured 25 bolts and there was one thread difference in length between the shortest and longest bolt. These are new bolts, same stamp, from Van's
The other interesting thing was the difference between different bolt sizes

<snip>

All fasteners tightened to just snug on the shank

Note the top two AN3-3a bolts. There is one thread difference in the bolts, one with five visible one with 3.5 showing.


The flat screw headed bolt, unusual yes, has just over three threads showing when snug.

Of interest is the AN4 bolt that has 3.5 threads showing. The AN4 bolts were more consistent in their length and thread size.


This has been a good discussion and whether you use a rule of thumb, and or, just sound judgement, the ultimate goal is to have as much of the shank in the hole as possible, with no possibility of the nut engaging the shank of the bolt before the fastener is properly torqued.

I would still like to know if the bolts in the "fix" picture are too long.

Not to surprising. If you look at the specification for AN3 bolts the "grip length" has a tolerance of +/- 1/64 and the total length has a tolerance of + 1/32 and - 1/64.

If the tolerances all stack up the threaded length can vary by 3/64 on an inch, or 1.5 screw thread turns.

Add the variation in nut thickness for a AN365 nut... Nut Height 0.208 inches minimum and 0.281 inches maximum and your pictures don't show the extreme, but possible cases... :)


ADDED

The numbers can be expanded... :)

For a nominal dimensioned bolt there are 12 threads available, and a nominal dimensioned nut has 8 threads.

Gives 5 threads to spare... :)

But bolt tolerances can lose an extra 0.5 of a thread in the bevel at the end of the bolt, lose another 1 thread in the grip+length tolerances, and the nut can grow by 1 thread.

So the 5 extra threads can drop to 2.5 threads.

BUT, the nut has a slight countersink at the start of the threads, so if this is about 0.5 threads it will make the 3 threads visible a very safe "rule of thumb".

It also says that 5 to 5.5 threads visible might be a typical value if checked for no bottoming using nominal dimensioned hardware.
 
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"The drawing was revised to 3a in 1992. and a Detail A showed the notch in the lower horizontal spar angle."

Gil,

It isn't the stress relief notch in the horizontal spar angle that I was referring to.

My drawing has a revision R5 dated 1/01 that refers to the note I previously posted about. In that detail it shows how the HS404 Rib and skin are supposed to be trimmed to allow the spar angle to be made long enough (11") to allow the mounting bolt to be installed in the correct location, through the fuselage longerons and the bolt wouldn't be as close to the end of the angle brace.

Trying to make this clear for those building or fixing the problem.
 
"The drawing was revised to 3a in 1992. and a Detail A showed the notch in the lower horizontal spar angle."

Gil,

It isn't the stress relief notch in the horizontal spar angle that I was referring to.

My drawing has a revision R5 dated 1/01 that refers to the note I previously posted about. In that detail it shows how the HS404 Rib and skin are supposed to be trimmed to allow the spar angle to be made long enough (11") to allow the mounting bolt to be installed in the correct location, through the fuselage longerons and the bolt wouldn't be as close to the end of the angle brace.

Trying to make this clear for those building or fixing the problem.

That notch and the Detail a is in the 92 version of the none pre-punched plans.

The note on trimming the inboard rib to clear a straight cut flange is also there.

I still don't think it was on the original version of drawing 3 as opposed to the 3a version.
 
The f&$?ing Bolts

I did the repair on the much debated stab! It was discovered during a prebuy.
The plane being sold was a friend, and the buyer (Robb) would be having Walt do condition inspections from here on out.
I can assure all who read this that the next size shorter bolt was fitted and had only ONE thread showing! I knew that there may be a question from many eagle eyed builders if that picture ever made it onto VAF that I would be chastised!
The next size bolt was fitted and we made assurance that the nut did NOT bottom on the shank! I have never heard of the "not more than 3 threads" showing. If I had, I probably would have just given up and went drinking!

The bolts were even properly torqued to 50 foot lbs!

I hope this clears everything up!😜😜😜😜😜
 
I did the repair on the much debated stab! It was discovered during a prebuy.
The plane being sold was a friend, and the buyer (Robb) would be having Walt do condition inspections from here on out.
I can assure all who read this that the next size shorter bolt was fitted and had only ONE thread showing! I knew that there may be a question from many eagle eyed builders if that picture ever made it onto VAF that I would be chastised!
The next size bolt was fitted and we made assurance that the nut did NOT bottom on the shank! I have never heard of the "not more than 3 threads" showing. If I had, I probably would have just given up and went drinking!

The bolts were even properly torqued to 50 foot lbs!

I hope this clears everything up!&#55357;&#56860;&#55357;&#56860;&#55357;&#56860;&#55357;&#56860;&#55357;&#56860;

Thanks for the update. If the builder was paying attention, then more threads are not necessarily a bad thing, as you have nicely pointed out. Visuals can be deceiving, but can certainly invite further investigation.
 
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When I went to attach my tail to the fuselage I realized that there was no way I was going to get proper edge distance. I called Vans and they gave me a fix:

Yikes, not going to work
FP04032012A0004Q.jpg


They didn't have me add any bolts, just said to "pick up a few rivets at the longeron".
FP04032012A0004S.jpg

FP04032012A0004V.jpg
 
The next size bolt was fitted and we made assurance that the nut did NOT bottom on the shank! I have never heard of the "not more than 3 threads" showing. If I had, I probably would have just given up and went drinking!
Or you could add one washer and bring it into the "3 threads showing" range. 40 years in aviation and i'm still learning all of the rules-of-thumb that are there for good reason. I've learned a few along the way that aren't there for any good reason either, but that's another story...

The bolts were even properly torqued to 50 foot lbs!
Ah, so they were *stretch* bolts. :)
 
When I went to attach my tail to the fuselage I realized that there was no way I was going to get proper edge distance. I called Vans and they gave me a fix:

Yikes, not going to work

They didn't have me add any bolts, just said to "pick up a few rivets at the longeron".
FP04032012A0004V.jpg

That fix seems so clean and easy it should simply be incorporated into the plans..:)

It completely gets rid of the required 2D (3/8") dimension accuracy of getting the outer two AN3 bolts into the 5/8 flange of the longerons which are tapering together towards the tail.
 
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bolts

I like how the flat bars hold the rear spar on why not a pair on the front also for more dynamic rigidity.
Bob
 
When I went to attach my tail to the fuselage I realized that there was no way I was going to get proper edge distance. I called Vans and they gave me a fix:

FP04032012A0004V.jpg

Interesting...the spar is no longer bolted directly to the longeron. It would clamp the longeron quite nicely (in concert with the angle under the deck), if the shim (seen here unpainted under the spar) was extended out to the stabilizer rib.

Colin, what was the material callout for those triangular gussets, notably thickness, and are you sure it is supposed to have both shims and gussets? Seems like having both would raise the leading edge of the stabilizer just a tad.
 
Holy Cr*p!!!

So...I was in the middle of an overseas airline trip back when I piggy-backed onto Vic's original (very informative) post to folks about things he was discovering while doing pre-buys, and I was trying to "help" illustrate the problems he described by sharing a few photos of some of the things I came across in my >1 year search for my RV...as well as what I considered an awesome fix for a similar (minor) problem on the aircraft I finally settled on....

An oceanic crossing followed by a quiet evening at home with the Missus (with no time spent in front of the square-headed girlfriend (computer)) and I log in today and find this thread has blown up into 5 pages! Yikes!

And some of it is due to some of the stuff I posted!!! :eek:

Vic, I'm sorry if what I posted caused your thread to drift so far off course! :eek:

First off, to Walt and Jon, many, many thanks for your mentoring and mechanical expertise in keeping this "the EA-B world is all new to me" newbie safe, and for walking with me while I was on my journey to find "My" safe and carefully-built RV!

You folks were awesome and very patient while working with me, and I cannot say enough how much I appreciated your opinion and skills! I hold each of you in very high regard!!

Thanks as well to Tom Martin for his observation and question that got the entire discussion regarding "thread count" going-I learned a LOT from the ensuing conversation, and I appreciate so much how this site brings many folks together from so many parts of the globe to assist, encourage, mentor, support...and critique each other! Good stuff!!

I guess the main point I was trying to make on my follow-up to Vic was...for you folks that are out there searching for YOUR RV...there is a world of knowledgeable and/or skilled help on VAF! I was a beneficiary of the generosity of this community and wanted to "pay it forward" by contributing the experiences of my own pre-buy journey for those who are walking this path as I did!

To a rookie (like me) the EA-B world can be a bit of an intimidating and scary place...but because of folks like Vic, Walt, Jon, Dan and the many others here that freely share their wisdom, talent and experience that help to bring the comfort level UP and the worry factor DOWN. Thanks to all!

Now, with a rainy weekend ahead of me in Texas and nothing on my schedule other than futzing with 75WV, it looks like I'll get some quality time in pulling some fairings and taking a few photos for documenting things now to compare to how they'll look at the next condition inspection. In other words...other than getting to fly her...a perfect weekend! :D

My very best regards to all,

Rob
 
Rob, you didn't cause it to drift at all. It's exactly the discussion I was hopeing to initiate. And since I have been receiving emails from some of you who have gone and looked at your airplanes and found problems, I thought I would share some other ones. BTW, my hat is off to those of you who have gone and checked. :)

The first one shows an RV-10 vertical fin attached with 3 bolts! The plans have it as one center bolt with a castellated nut, as there is movement here!


This next one is the attachment of the horizontal stabilizer on the RV-10 depicting some poorly driven rivets:


This one was amazing to me in that the bolt in the crossmember had a piece of aluminum underneath the head of the bolt. When I removed the bolt there was a "binocular-shaped" hole. Hiding the problem won't make it go away. :)


This one is the vertical fin on an RV-7. Lost of bad examples here----wrong length bolts, wrong nut, and not drilled and bolted in the proper locations.
 
1,800 miles from home looking out to a beautiful caribe sea, sit down on the deck with a cuppa for some Sunday morning reading, now all I can think about is going home to look my plane over. I have a disease.
 
Some of these pix are simply amazing and baffling. Why anyone would do such a thing, specially the very last pix with the wrong side bolt/nut or the covered up hole.
 
So, as I understand it, the bulk of these have been found during pre-buy inspections or by current owners going out and looking.

I hate to ask, but wouldn't one expect flaws like this to be caught during the initial airworthiness inspection?
 
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