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Vans say replace main spar

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Little Wing

Little Wing

Active Member
Finally got the news recommending RV8 main spar replacement due to countersinking main spar flange too deep for skin dimples.
My countersink depth measured with an inserted rivet is .015", diameter is .234" with no hole elongation or knife edge.
I now know the ideal depth is .006" past flush but having a hard time believing .009" over is a deal breaker.
I am assuming a new spar would require new Z brackets, tank baffle, and possibly joint plate to get things in proper alignment.
Any advise on how to proceed maybe have a tech inspector put some eyes on it?


33yq36g.jpg
 
I find Van's to except some pretty big flaws ( as per on this site) , so if they said to replace, that's what I'd be doing. I don't think Van's is looking for sales in this case.
 
Ron B. said:
I find Van's to except some pretty big flaws ( as per on this site) , so if they said to replace, that's what I'd be doing. I don't think Van's is looking for sales in this case.
Click to expand...

Agree. I've seen some pretty egregious errors that Vans said are no big deal. Spar structural loading is not something you want to play around with.
 
I think the OP is asking how to proceed with a spar replacement. That is, what does he need to do in order to implement Van's recommendation?

Dave
 
David Paule said:
I think the OP is asking how to proceed with a spar replacement. That is, what does he need to do in order to implement Van's recommendation?

Dave
Click to expand...

Yeah, I think so too, but I am still shocked that Vans engineers rejected this mistake. It must have been that it was more than one.

The OP might get some satisfaction by discussing the situation with these guys : http://www.phlogistonproducts.com/index.html

They make spars for some RV products and maybe made this one.
 
I'm surprised a switch to 1/8 rivets wouldn't work here but since it's a spar, Vans engineers should have the final say.
 
Original Posts

az_gila said:
I'm surprised a switch to 1/8 rivets wouldn't work here but since it's a spar, Vans engineers should have the final say.
Click to expand...

OK, I have no idea why many of the original posts related to this thread disappeared, but Scott McDaniels made it pretty clear why larger rivets weren't acceptable (skin edge distance). And the issue was apparently discussed amongst Van's staff before making the final recommendation to replace the spar.

Skylor
RV-8, Flying
 
With the top of the rivet being so far below the surface of the spar, I doubt you would be able to fully drive a rivet, there would be no firm contact between rivet head and rivetting tool.
 
I'm with Vans on this one...

Rod,
As much as I know this hurts, my recommendation is to replace the spar per Vans:mad::(. There is no way you will effectively set those rivets with them sitting so far below the surface and going to a larger rivet will not satisfy the edge distance requirements necessary for those components.
Yes, its a very expensive mistake BUT when you are cruising through the sky at 160 knots you can feel confident it won't come apart on you...and that is PRICELESS.
Bite the bullet and purchase a new spar. Check with Vans and see if they want you to ship the bulkhead back to them so they can match drill it to the new spar...that would be my only concern. Because the spars are matched to the lower bulkhead.
Good luck to you...
 
Yen said:
With the top of the rivet being so far below the surface of the spar, I doubt you would be able to fully drive a rivet, there would be no firm contact between rivet head and rivetting tool.
Click to expand...

There is no way you will effectively set those rivets with them sitting so far below the surface and going to a larger rivet will not satisfy the edge distance requirements necessary for those components.
Click to expand...

Isn't there skin that goes on top of this area, and the rivet goes into the dimple on the skin? :)

These holes are countersunk to accept a dimpled skin, not a rivet...right?
 
Replace, pls...

Some day in the future this RV will be sold. If you do a repair counter to Van's advice you might sell it, but for a reduced price far exceeding the cost of a new spar. That is assuming the repair is properly documented. Replace the spar, it's the right thing to do, and you will sleep much better.

BTW, I would not rely on Phlogiston over Van's. Van designed the spar not them.

Be safe,

Jerry
 
countersink is for dimple

Your photo of rivet in the countersink looks terrible, but the countersink accepts the dimple of a skin. I'm with RV7aFlyer that you might want to further clarify and make sure you didn't communicate with Vans. How does a dimple and a rivet fit into this countersink?
 
sglynn said:
Your photo of rivet in the countersink looks terrible, but the countersink accepts the dimple of a skin. I'm with RV7aFlyer that you might want to further clarify and make sure you didn't communicate with Vans. How does a dimple and a rivet fit into this countersink?
Click to expand...

I agree. Dimple a piece of scrap .023 and put it in the countersunk hole and see if it fits. Put a little playdoh to check the clearance between the dimple and the countersink. I wonder if there was something lost in the communication of the problem.

Larry
 
Exactly right

Isn't there skin that goes on top of this area, and the rivet goes into the dimple on the skin?

These holes are countersunk to accept a dimpled skin, not a rivet...right?
Click to expand...

Your countersinks may be spot on.
Hard to tell from the picture though.

Are your countersinks painted, is that why the look so bad in the picture?
 
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There are plenty of instances where folks have had problems, called Van's, and been told "You're building an airplane, not a swiss watch - continue and build on."

This is not one of those times. Do the right thing - replace the spar.
 
lr172 said:
I wonder if there was something lost in the communication of the problem.
Click to expand...

From my understanding the OP is aware (now anyway, possibly not when the countersinking was done) that when countersinking for insertion of a dimple instead of a rivet, that you go approx. .006" - .007 deeper (approx. because it varys slightly depending on the rivet size and the thickness of the skin).

He has stated that with a rivet inserted in the hole (as shown in his attached photo), the measurement to the top of a rivet head, below the surface of the spar web is .015". This means that the countersink is about .009" too deep (2.5 times what it should be).

The wing could be built as is, and would probably not have a catastrophic failure because of it. But what would happen over time (many load cycles) is the rivets that attach the wing skins to the spar would start working/smoking.
This would happen because the skin dimples wouldn't fit tightly within the countersinks. There would be clearance that would allow lateral movement of the dimple within the countersink. Because of this minute movement of the skin on the spar, the holes and the rivets would slowly be effected dimensionally. It may even take quite a few years, but the wing would eventually become un-airworthy.
 
rvbuilder2002 said:
From my understanding the OP is aware (now anyway, possibly not when the countersinking was done) that when countersinking for insertion of a dimple instead of a rivet, that you go approx. .006" - .007 deeper (approx. because it varys slightly depending on the rivet size and the thickness of the skin).

He has stated that with a rivet inserted in the hole (as shown in his attached photo), the measurement to the top of a rivet head, below the surface of the spar web is .015". This means that the countersink is about .009" too deep (2.5 times what it should be).

The wing could be built as is, and would probably not have a catastrophic failure because of it. But what would happen over time (many load cycles) is the rivets that attach the wing skins to the spar would start working/smoking.
This would happen because the skin dimples wouldn't fit tightly within the countersinks. There would be clearance that would allow lateral movement of the dimple within the countersink. Because of this minute movement of the skin on the spar, the holes and the rivets would slowly be effected dimensionally. It may even take quite a few years, but the wing would eventually become un-airworthy.
Click to expand...

Not arguing with the result, just trying understand the "why". So, I assume the thickness of this flange is insufficient to simply step up to the next size rivet due to the knife edge at the bottom of the countersink affecting the structural integrity of this rivet (these rivets) joint? I am also assuming that the nesting nature of the countersink gives this joint its significant shear strength.

Thanks,
 
Thanks for the responses. Yes the dimpled leading and main skins are riveted to the spar flange. The countersinks are primed with a qtip that's why the look so bad but are indeed uniform and smooth. I inserted a rivet to show depth.
Yes I have a dimpled test piece which nests nicely into the countersink with no play.
I am going to call tech support just to confirm the understanding of the issue since communication has been completely via email.
New spar is $1625. Its not the money just can't believe what I did. I have built a lot of things in my life and never destroyed anything in the process.
Like they say if your gonna be dumb you gotta be tough!
 
I'll be honest, I was thinking a new spar would be way more than $1,625. I would have that sucker ordered tomorrow and forget about the whole thing.
 
BillL said:
Not arguing with the result, just trying understand the "why". So, I assume the thickness of this flange is insufficient to simply step up to the next size rivet due to the knife edge at the bottom of the countersink affecting the structural integrity of this rivet (these rivets) joint? I am also assuming that the nesting nature of the countersink gives this joint its significant shear strength.

Thanks,
Click to expand...

The additional shear strength resulting from a dimpled joint is not relied upon for in the engineering (just taken as extra) but if a skin dimple doesn't fit a countersink tightly, it will have a lower strength than if it was a joint with just a plain AN470 rivet.
The next larger rivet would start getting close to knifing the edge, and it would be breaking the minimum edge distance rule on the wing skins by about .015"
 
Why phone Vans again? RVbuilder2002 has told you why you should not consider using the damaged spar. He knows what he talking about.
 
That's why

Yes I have a dimpled test piece which nests nicely into the countersink with no play.
Click to expand...

Maybe all this is based on miscommunications.

I am absolutely not saying that you should not follow Van's advise.
But $1600 is worth double checking previous communications.
 
rvbuilder2002 said:
the skin dimples wouldn't fit tightly within the countersinks. There would be clearance that would allow lateral movement of the dimple within the countersink.
Click to expand...

As I read the above, the area where the problem would occur is hidden from view--------so there would be no visible warning of possible failure.:eek:
 
The lesson to be learned is to set up the microstop in some scrap aluminum before hacking up the expensive parts.
 
I'm not sure I understand, if you fit the skin over the countersink and there is no play, and the rivit fits in the skin (because it was dimpled to fit that rivit) , and rivets expand to fill voids, where is the failure point?
Still $1600.00 in the overall sceme of everything is not to bad.
Mike
 
rvbuilder2002 said:
The additional shear strength resulting from a dimpled joint is not relied upon for in the engineering (just taken as extra) but if a skin dimple doesn't fit a countersink tightly, it will have a lower strength than if it was a joint with just a plain AN470 rivet.
The next larger rivet would start getting close to knifing the edge, and it would be breaking the minimum edge distance rule on the wing skins by about .015"
Click to expand...

Good engineering details here. I still wonder how if the dimpled sheet is a tight fit, how could a smaller countersink be correct? Won't the dimpled sheet ride high? I have been countersinking until the the dimple goes in far enough that the sheet and structure mate flat together.

I would still put some playdoh or clay in the countersink, place the dimpled scrap with a rivet and hit it lightly with the rivet gun or light hammer. You will then know what type of gap you are dealing with.

EDIT: Disregard. I just ran a quick test on how I have been doing it and find that I have tight fitting sheets with .008" head depth. That left me a countersink diameter of .200" I don't think that the OP's fittings can be tight with a hole diameter of .230". That would leave the outer hole diameter around .050" bigger than spec.

Larry
 
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Vbug said:
Thanks for the responses. Yes the dimpled leading and main skins are riveted to the spar flange. The countersinks are primed with a qtip that's why the look so bad but are indeed uniform and smooth. I inserted a rivet to show depth.
Yes I have a dimpled test piece which nests nicely into the countersink with no play.
I am going to call tech support just to confirm the understanding of the issue since communication has been completely via email.
New spar is $1625. Its not the money just can't believe what I did. I have built a lot of things in my life and never destroyed anything in the process.
Like they say if your gonna be dumb you gotta be tough!
Click to expand...

But the real question is, is there no play in the un-primed holes, or is the primer itself masking a sloppy fit of the dimpled test piece?

Skylor
RV-8, Flying
 
skylor said:
But the real question is, is there no play in the un-primed holes, or is the primer itself masking a sloppy fit of the dimpled test piece?

Skylor
RV-8, Flying
Click to expand...

Or is it simply the radius of the back side of the dimple sitting on the sharp edge of the countersink?
 
If the fit is that critical, and you over countersink by .003 inches wouldn't you be able to add a piece of .003 aluminum to the top of the spar. Match hole drill it, dimple it, and it should be a perfect fit. .003 is less then the thickness of a piece of typing paper.
If vans says to replace the spar I would without any doubt replace the spar. It would make me sleep better at night.

Mike
 
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Seriously you guys...

We can argue this till we are all blue in the face. You can't rivet two test pieces together, wiggle them and say it feels tight and call it good while assuming what you just did compares to the stress loads experienced in flight.
ARE WE FORGETTING THAT VANS RECOMMENDED REPLACEMENT??? Don't confuse the builder, the precedent has been set. Replace the d@%m spar and move on.
Its only a couple thousand bucks, it was an expensive mistake that we can all learn from.
 
I think it is useful and educational for us all to understand why this is unacceptable. It is not, in my mind an issue of questioning Van's engineering staff, rather an issue of knowledge to be applied here and elsewhere in the construction process
 
brad walton said:
I think it is useful and educational for us all to understand why this is unacceptable. It is not, in my mind an issue of questioning Van's engineering staff, rather an issue of knowledge to be applied here and elsewhere in the construction process
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Yeah, you're right and I do agree that it is beneficial but if you re-read some of the posts it may cause someone to believe they DON'T have to replace the spar. That maybe there is some wiggle room. While in some areas of the aircraft wiggle room is perfectly acceptable...the spar is not one of those areas.
I know from my own experience that I can take what I read on this forum as solid gold advice (there are certainly people on here that I now know who I would take their advice as solid gold). Other people may just be "thinking out loud." I think we need to carefully clarify that is our intent so builders don't unwittingly take advice from this forum that may do them or someone else harm. The OP clearly states that he is having a hard time believing that .009 over is a deal breaker which tells me his intent is try to garner enough advice on here to give him confidence to move forward with not replacing the spar.
I'm just saying that we need to clarify our position on something this serious. If Vans has recommended replacement that is all the advice any of us need. Beyond that we can "think out loud" but we need to be clear that is what we are doing. The Vans staff are the foremost experts on the aircraft. I certainly don't believe they are recommending replacement to generate the sale of a spar.
 
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I can't believe this thread. How can there be any reasonable discussion about not following the factory's advice? I have yet to see any accredited aerospace structural engineer (and I know there are several here) pop up and tell you to ignore the factory.

I know I've spent more than the $1600 and change over the years on various replacement pieces. I can't imagine that I'd contemplate taking a chance on the WING SPAR (for cripes sake!) just to save a few bucks. If you don't have the dollars to replace the spar, then you need to sell the kit, because believe me, you don't have the money to complete it anyway.

Make the right decision.
 
N427EF said:
Yes I have a dimpled test piece which nests nicely into the countersink with no play.
Click to expand...

Maybe all this is based on miscommunications.
Click to expand...

My question, as well. How many people built their planes by countersinking *exactly this way* instead of using micrometers on every countersink???

The OP also said none of the holes are knife-edged.

Sounds to me like he did it exactly the way thousands of other people have done it, and likely the construction manual says (don't recall, don't have it handy, but I don't remember seeing anything about putting a micrometer on a countersink...but I built a -7 started in 2007, so my plans may say something different).

It's worth communicating again with Van's, though...just to make sure *and* understand why they're advising replacement.
 
The reason a dimpled skin will sit in a slightly too large hole without slop is that every dimple has a slight radius at the bend, because it's a bend. Every countersink has a sharp corner at the top, because it's machined. In order for the skin to truly sit flush against the surrounding metal, the diameter of the countersink at the top of the hole would have to be larger than the diameter of the dimple in the skin... At the outermost point of the radius of that bend.

That means that a skin that sits *completely* flush will have a dimple that does not contact the taper on the countersink. Drive a rivet in there, and it won't do much to spread the dimple out against the taper of the countersink... It'll just hold the assembly together, with a couple of thou clearance around the dimple. That gap, in time, will lead to the smoking Scott refers to.

In contrast, if your dimple perfectly matches your countersink, the skin will sit a few thou high off the mating surface. More if you're not using spring-back dies, less if you are (spring-back dies bend a sharper corner). During riveting everything will snug up that last couple of thou as the riveting action will form a sharper corner in the skin using the countersink as a form (actually, as they're both aluminum, they probably both deform and just create a tighter radius).
 
rvbuilder2002 said:
From my understanding the OP is aware (now anyway, possibly not when the countersinking was done) that when countersinking for insertion of a dimple instead of a rivet, that you go approx. .006" - .007 deeper (approx. because it varys slightly depending on the rivet size and the thickness of the skin).

He has stated that with a rivet inserted in the hole (as shown in his attached photo), the measurement to the top of a rivet head, below the surface of the spar web is .015". This means that the countersink is about .009" too deep (2.5 times what it should be).
Click to expand...

RV7A Flyer said:
My question, as well. How many people built their planes by countersinking *exactly this way* instead of using micrometers on every countersink???

The OP also said none of the holes are knife-edged.

Sounds to me like he did it exactly the way thousands of other people have done it, and likely the construction manual says (don't recall, don't have it handy, but I don't remember seeing anything about putting a micrometer on a countersink...but I built a -7 started in 2007, so my plans may say something different).

It's worth communicating again with Van's, though...just to make sure *and* understand why they're advising replacement.
Click to expand...

Reactionary posts and decisions are best avoided and confronted with facts. NO ONE HAS REFUTED VANS RECOMMENDATIONS. Scott has said why (using the OP's dimensions) the dimensions are important from a structural stand point.

The real question (at least for me) is around the original measurements. I have tried to measure these danged countersinks and wished many times for a proper depth gage - I found one on ebay(with calibration ring). I tried many times to measure countersinks with diametral and protrusion and it resulted in many different dimensions. The best one is a rivet and a very straight edge to see if it is proud or sunken. Flush is easy to quantify, larger/smaller is not.

countersinkgage.JPG


If the OP is 100% satisfied with the measured dimensions, then the case is closed. This is important, as it is a significant undertaking to replace the spar and the opportunity for additional issues is increased.
 
aarvig said:
If Vans has recommended replacement that is all the advice any of us need.
Click to expand...

Well...maybe that is all the advice some of us need, but I wouldn't say that is the case for all of us.

I'm not making a statement on the validity of replacing the spar, just reminding us that there is a very wide range of expertise within our ranks. For the builder who has no prior experience constructing an aircraft, then Vans's recommendation should not be taken lightly.

But we have individuals in our community who have built multiple aircraft, some from kits, and others scratch-built from plans, and maybe even some on the gov't's nickel. These very experienced builders who are accustomed to making not only decisions about whether or not to scrap a part, but also how to fabricate the part, are going to be more open to discussions about why a component should be replaced.

Are those who are so strident about following Vans's guidance doing exactly the same when it comes to avionics and firewall-forward decisions? We need to be consistent, and cognizant of the wide range of expertise and risk management tolerance in our community.

Just thinking out loud.... ;)
 
I didn't like countersinking the spar on my -9. I thought it was a questionable way to assemble the skins to the wing. I would guess there are a lot of RV's flying that have a least some degree of knife-edged holes similar to yours. One thing for sure, I'd make sure that "properly" CS holes are significantly better than your existing ones before I would replace the spar. I hate to see you get a new spar(s) only to find that they turn out the same as the old. Also, I'd get some pics of some other RV's spars (preferably flying versions) and see if others have perfectly airborne spars that looked much like your at that stage.
 
What an absolutely timely post.

As a new builder, this touches on my biggest concern with building my new kit. When is a rivet/countersink/dimple too deep or not deep enough? Easy formulas and ways to measure the width/depth of a shop head but what about the measurement we are talking about here. I can't seem to measure it consistently even with my micrometer. I have started just putting a straight edge on the rivet head after riveting and seeing if its flush. This doesn't tell me if the tolerances on the countersink are accurate, or does it? So far I'm just playing with scrap and sneaking up on what seems flush to me.

I'm not at all interested in debating what Vans has to say. With my obvious lack of experience, I would not question them.

I'm betting I'm not the only one reading this thread that would like to know how some of you real experienced folks approach measuring countersink depths and what exactly you want to see in the finished joint. I certainly haven't found much info on the topic.

Anybody help out with this? Should this be a new thread?

Thanks All!
 
I too am watching this thread closely as I'm approaching this point in my build. I'm vacuuming up any advice given!
 
Go for it

I would not hesitate to drill it apart and replace the web. PM me with your e-mail address and I can talk you through it. I have been doing this kind of work profesionally for over tweenty years, and passing along the tricksfor ten.
 
BillL said:
Reactionary posts and decisions are best avoided and confronted with facts. NO ONE HAS REFUTED VANS RECOMMENDATIONS. Scott has said why (using the OP's dimensions) the dimensions are important from a structural stand point.

The real question (at least for me) is around the original measurements. I have tried to measure these danged countersinks and wished many times for a proper depth gage - I found one on ebay(with calibration ring). I tried many times to measure countersinks with diametral and protrusion and it resulted in many different dimensions. The best one is a rivet and a very straight edge to see if it is proud or sunken. Flush is easy to quantify, larger/smaller is not.

countersinkgage.JPG


If the OP is 100% satisfied with the measured dimensions, then the case is closed. This is important, as it is a significant undertaking to replace the spar and the opportunity for additional issues is increased.
Click to expand...

Bill,
I think you will be happy to have that in your toolbox. I have one (of somewhat different design) that I used on occasion.
 
Vbug said:
The countersinks are primed with a qtip that's why the look so bad but are indeed uniform and smooth!
Click to expand...

I don't have much else to add to this thread other than to tell you - it's obvious you are detail oriented....but...might I humbly suggest you throw away the Q-tip, get an alodine pen and spend your time on something else more productive! :)

Sometimes you need to find some levity in building these things. Meant in fun I promise - but I couldn't resist!

Cheers,
Stein
 
This thread is gonna give me a heart attack.

I'm just about ready to rivet my skins on- but my spar looks VERY similar to the original poster's...

I approached these countersinks with much trepidation- I went REALLY slow to be sure I didn't over-countersink, as I knew the ramifications would lead to a TON of lost time, of which I have very little .

The instructions in the wing section said to make a "test patch" dimple on .032, and adjust the countersink until the dimple fits snug in the hole. This is the method I used, and wound up with .2125 diameter countersunk holes. The test aluminum barely fits in there, and may even ride a little high. Again, I was very concerned with over-drilling here.

My LE went on fine and the skin/spar lays good and flush...

Now looking back at the instructions in the construction manual, it says if there's a dimple, go "a few clicks" deeper and that should be enough. These two methods are contradictory. A few clicks deeper (at least on my microstop) will get you almost nowhere- and certainly lead to the skin riding high on the spar- a few clicks certainly wont compensate for the .032 sitting in the hole. I just don't see how a rivet in a countersink sitting .005 below flush would be able to accept the dimple.

I've looked through 43.13, and a couple books and couldn't find anything on the subject- what would be considered the maximum countersink diameter?

I sure hope that simply following the instructions didn't lead me down an expensive and extremely time consuming path....again (z-brackets)

Here's to hoping to wake up to some good news/encouragement...

DB
 
Just thinking about alternative solutions and throwing this out for consideration. The countersinks are too deep for .032. Are they too deep for .040? Several builders have made one piece upper an lower wing skins of .040 in the past. Could this be an alternative solution? Would it be easier than removing and replacing the spar? Acceptable to Vans?
 
When I was starting my -6A in 1994, I was curious about how countersinking, single and double dimples worked. I did some testing that you might try.

Using narrow strips of some scrap material the same thickness as the spar and skin. Drill and countersink a line of holes making the countersinks of varying depths. Rivet the two together. Try some double dimple skins.

Now section thru the rivets and skins leaving about 2/3 of the rivet intact. I used a Dremel and a cutting wheel, the type that break easily, find the thin diamond ones. Polish the cut edge on some 320 wet/dry and finish with finer paper until you can examine how rivet filled the hole and the dimple shaped itself to the countersink.

I did it with double dimples, oversized holes, badly made dimples and under and over countersunk holes. It is amazing how much the rivets expand in the holes and dimples reshape to the countersink. This was long before all the different types of dimple dies were available.

It was an educational experience that was worth the time.
 
brad walton said:
Just thinking about alternative solutions and throwing this out for consideration. The countersinks are too deep for .032. Are they too deep for .040? Several builders have made one piece upper an lower wing skins of .040 in the past. Could this be an alternative solution? Would it be easier than removing and replacing the spar? Acceptable to Vans?
Click to expand...

Negative.

Each rivet joint is compromised by the incorrect size hole and will not develop the needed shear strength compromising the strength of the wing. I am sure no one wants to pull a few "G's" and have the wing fail where the skin was attached to the spar.
 
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