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Pop rivet -4

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titanhank

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I did a prebuy inspection on a -4 today that was built entirely with pop rivets. I could not believe my eyes. At least they look cherry rivets, I think. Shortest prebuy in history. The airplane is in corpus christie tx and has 750 hr tt according to the log books. I am pretty sure this airframe needs to go the crusher.

I am always amazed at some of the things people think are airworthy.


016-C6-D88-2-FB0-4-A55-B4-B6-850423-EF5902.jpg

DEFDCC7-B-69-F9-4361-A039-1-D391984-BBC8.jpg
 
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I did a prebuy inspection on a -4 today that was built entirely with pop rivets. I could not believe my eyes. At least they look cherry rivets, I think. Shortest prebuy in history. The airplane is in corpus christie tx and has 750 hr tt according to the log books. I am pretty sure this airframe needs to go the crusher.
I am always amazed at some of the things people think are airworthy.

If I remember correctly, back in the RV-3/4 early days, Van stated that pullled rivets could be used almost exclusively with the exception of certain structural points.

Those rivets appear to be "Avex". If so, they are good quality. All Zenith aircraft are built with Avex.
 
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I would love to see documentation on the pulled rivets use. This airframe is going to get a sawsall pretty soon.
 
What is the workmanship like, otherwise?

Would be curious to know what is holding together the main wing spar and whether AN470AD6-x rivets were used.
 
Well, those rivets are no Cherrymax for sure.
On the other hand there are quite a few aircraft types flying safely around held together by pop rivets... mostly non-aerobatic.
 
I sent the pics to vans support for their opinion. I did not inspect it close enough to determine if it is sound or not. I stopped the prebuy when the rivets were discovered. I am ok with the “experimental” in experimental aircraft, but i am not sure this one should bear a vans make and serial number.
 
I hope you'll post what Vans has to say when you hear back from them.

Me too. I am of the opinion that a blind rivet ( if you want to call them “pop rivets”) installed properly, is a lot better than a poorly installed solid rivet.
 
No crusher!!

Id love to have it to play with..I have yet to see any RV just "fall apart" no mater how constructed. What does the spar and fuselage carry through look like? May even be a Phlogiston built one. How are the empennage connections? Anyone who has built a -3,-4 or -6 knows the challenges of laying out every fastener much different that the pre-drilled most have had. If those rivets aren't "working" they are doing their job. I have seen several with all the lower skin rivets "pulled" as that is what comes in the kit, and was the norm for some. No RV should ever get a crusher!!
 
I will post vans response for everyone to see. I bought 3 aircraft from this estate sale. I will decide on what to do with it only after hearing from them.
 
Somebody please post some specs on pulled rivets in shear and in tension. .last I recall, pulled aircraft rivets were stronger than vans solid AD rivets in both shear and tension, I just don't recall which brand or style of pulled rivet that I saw this data on. .
 
Here is mitch lock’s response to the support inquiry. I am not surprised at all from a liability standpoint. The airframe has 750tt and shows no real signs of distress which is a shame.

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thanks for the Vans FB titanhank, interesting indeed.

As for a pulled rivets construction (or assembly...), to the best of my knowledge, the -12 of whatever version there is, is assembled by the "same" rivet type... and still being called a Vans by Vans.

Sure have no clue about the rest of that very -4, but my guess would be ok to fly but for any aerobatics, i.e. normal category limits only.

As to the given name :eek:

PS
Vic, same situation and no loose jamnuts, what would you do?
 
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Be aware that when citing other aircraft that are extensively assembled with pulled rivets (RV-12, Zenith, etc) that they are designed that way.

The key question of riveted assemblies is whether the rivet spacing is adequate for the shear flow in the joint.

There are many factors that determine the shear strength of a pulled rivet, such as material for the pulling nail, features to assure that the nail stays in place, sufficient reach to produce the proper flare on the backside, alloy used for the rivet body, etc. So it is impossible to make a blanket statement about this.

The structure would have to be re-analyzed with the known properties of the rivets used.
 
I believe this to be the reference published by vans in the rv aviator on page 8 that mel asbury was talking about in the above comment. Vans was stocking the rivets and stated they were acceptable, but expensive and the final finish as not as nice. I bet it was expensive, but not unsafe. I emailed vans again citing the reference. I do not expect them to respond due to liability, i get it. I am having a hard time destroying an airframe that has 750tt, aerobatics and absolutely no signs of fretting or destress. I know the resale value will not be as high as a “properly” built rv4, but has got to be worth more than scrap aluminum price.

I am going to bring it home, finish a detailed inspection and fly it. I can then make an informed decision on how to proceed.
 

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How will flying it, assuming it hangs together though that experience, demonstrate anything about it?

Unless you test it to a known g level above limit load, you haven't proved anything.

Seems to me that you can sell it as-is, destroy it, or perform the full set of strength tests to the loads that Van's supplies - if they will do that. But flying it won't do much except tell you that yeah, if flown within its unknown limitations, it'll hang together.

Dave
 
I did a prebuy inspection on a -4 today that was built entirely with pop rivets. I could not believe my eyes. At least they look cherry rivets,

016-C6-D88-2-FB0-4-A55-B4-B6-850423-EF5902.jpg

Do you have any pictures to post of what the outside looks like?
Any builder documents on what type of pulled rivets they are?
 
I understand why Van's would deny parentage. However, a serious educational question...isn't this really a matter of (a) spacing, and (b) fastener properties?

Put another way, if the fasteners are in the standard locations, and the rivets can be identified as equal to the standard driven rivet, is there some other structural consideration?
 
From my circa 1991 RV6 builders manual:

"Blind rivets, often referred to a Pop Rivets, are used only in area where access is not available to buck heads on standard AN rivets and where loads are light enough to be carried by them. Low strength blind rivets are used to attach the fiberglass wing and tail tips, attach baggage and seat floor skins, and to close most of the control surface skins."

Would be interesting to find an earlier builders manual for the RV3 and RV4 to verify what Mel says in Post #3.
 
pulled rivets for wing skin

The RV-6A manual specifies that the bottom wing skins may be installed using CS4-4 or MK-319-BS POP blind rivets. It is mentioned that these rivets do not leave as smooth a finish as AN426 rivets, hence the suggestion to use POP rivets on the bottom skin and AN 426 rivets on the top skin.
 
The RV-6A manual specifies that the bottom wing skins may be installed using CS4-4 or MK-319-BS POP blind rivets. It is mentioned that these rivets do not leave as smooth a finish as AN426 rivets, hence the suggestion to use POP rivets on the bottom skin and AN 426 rivets on the top skin.
That's exactly what I did on the bottom skins of my -9's QB wings with several hundred MK-319-BS rivets. IT was a lot more expensive than solid rivets, but from what I could find, structurally identical and much better than drilling out any mis-set rivets I'd incur by building solo.
 
Do you have any references for the comparable strengths of the two rivets?
Yep.

MK-319-BS (Source)
Tensile Strength: 292Lbs
Shear Strength: 258Lbs


AN426AD3-3.5 (Source)
Tensile Strength:38,000PSI / 244Lbs
Shear Strength: 26,000PSI / 167Lbs

3/32 * 24.5 = 2.29mm diameter then / 2
= 1.15mm radius then 1.15*1.15*3.1415 =
= 4.14mm2 cross-sectional area

645mm2 per square inch
38,000 / 645
= 58.91 lbs per mm2 * 4.14
= 243.9Lbs for Tension

645mm2 per square inch
26,000 / 645
= 40.31 lbs per mm2 * 4.14
= 166.8Lbs for Shear
 
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Yep.

MK-319-BS (Source)
Tensile Strength: 292Lbs
Shear Strength: 258Lbs


AN426AD3-3.5 (Source)
Tensile Strength:38,000PSI / 244Lbs
Shear Strength: 26,000PSI / 167Lbs

3/32 * 24.5 = 2.29mm diameter then / 2
= 1.15mm radius then 1.15*1.15*3.1415 =
= 4.14mm2 cross-sectional area

645mm2 per square inch
38,000 / 645
= 58.91 lbs per mm2 * 4.14
= 243.9Lbs for Tension

645mm2 per square inch
26,000 / 645
= 40.31 lbs per mm2 * 4.14
= 166.8Lbs for Shear


Thank you. You may have just saved the airframe. I will get the logbooks next week when i go to pick it up. Hopefully it will have a reference to the rivets, but i doubt it. I have had an airline sheet metal mechanic look at the pics. He swears they are the mk319 rivets.
 
Thank you. You may have just saved the airframe.
So it's your shout then? :p :D

IF they are the -319-BS and they're used anywhere an AN426AD3-3 or 3.5 (maybe even -4 depending on grip length) is called out, you could be reasonably comfortable with it. IT might not be as pretty as a solid rivet, but it should certainly be as strong as a solid rivet everything else being equal.
 
Thanks to KRaviator for his informative post, but I was really hoping to see someone specifically address Dan Horton's question:

"Put another way, if the fasteners are in the standard locations, and the rivets can be identified as equal to the standard driven rivet, is there some other structural consideration?"

I remember using a few Cherry Max rivets in difficult locations during my build. At the time, my research convinced me that these pull rivets were superior to the solid rivets they replaced in everyway but price. Given that they had the same diameter but supported greater shear and tension. Is this wrong?
 
So it's your shout then? :p :D

IF they are the -319-BS and they're used anywhere an AN426AD3-3 or 3.5 (maybe even -4 depending on grip length) is called out, you could be reasonably comfortable with it. IT might not be as pretty as a solid rivet, but it should certainly be as strong as a solid rivet everything else being equal.

One thing to watch out for here in making that assertion that you could be comfortable with it is whether the grip length of the MK319 rivet was approriate to form a proper flare on the end. The photo of the tails of the pulled rivets on the longerons look to me a little marginal in terms of pull length/flare.

The fact that there is no evidence of working/smoking of the rivets along the joints after 750 hrs bodes well.

I might consider a program of progressively replacing the rivets over time. Just on the longerons and spar shear flanges, maybe do every other one with a AN426AD3 during each condition inspection for a few years.

I would consider the pulled rivets on the bulkheads, ribs, and skin laps just fine as they are.
 
Thanks to KRaviator for his informative post, but I was really hoping to see someone specifically address Dan Horton's question:

"Put another way, if the fasteners are in the standard locations, and the rivets can be identified as equal to the standard driven rivet, is there some other structural consideration?"

I remember using a few Cherry Max rivets in difficult locations during my build. At the time, my research convinced me that these pull rivets were superior to the solid rivets they replaced in everyway but price. Given that they had the same diameter but supported greater shear and tension. Is this wrong?

The key question to answer DanH's question with a question is whether the grip-length of the pulled rivets was proper for the location. In particular, on the longerons, the photo seems to suggest a rather marginal flare on the tail of the pulled rivets.
 
New static display at OSH.

Titanhank,

How about donating it to EAA, to put on static display at OSH. Maybe as an example as to what not to do. Remove the data plate and registration, so it is not airworthy.

If they don’t want it, maybe some local airport will take it for a display.

You might also get a tax write off if you can.

Good luck.

Brian
 
The key question to answer DanH's question with a question is whether the grip-length of the pulled rivets was proper for the location. In particular, on the longerons, the photo seems to suggest a rather marginal flare on the tail of the pulled rivets.

The grip range is specified as "Maximum Grip, 0.000 - 0.090 Inch"


They could also be MK321BS rivets with a Maximum grip of 0.109 Inch, which would be the longerons with 2 layers of skin.
 
I agree with Dan. If the rivets are in the right place and have equal strength as installed to the rivets called for in the plans (a big if) then the structure has equal strength. Let’s be realistic about the strength of ad426 rivets. They are solid soft aluminum. You hold the plane together by using 1000s of them.

Having said that, if the builder did something that outlandish, what other bizarre things did he do? And would I buy it? No.
 
Having said that, if the builder did something that outlandish, what other bizarre things did he do? And would I buy it? No.
Outlandish? Given the data posted above, the builder made a *stronger* airplane by using pulled rivets. Unless you meant "what else did he do to improve it structurally?" in which case I agree, that would be neat to find out.
 
AN426AD3-3.5
Tensile Strength:38,000PSI / 244Lbs
Shear Strength: 26,000PSI / 167Lbs

Unfortunately, tension strengths of driven rivets are usually less and occasionally more than the basic stress x area equation would suggest. This is due to the sheet thickness and head type having a major effect. The only tension data strength that I've seen was in the old Martin Marietta Stress Analysis Handbook and did not list data for either -3 rivets or flush-head rivets.

Although no reason was given for some numbers in the table showing greater strengths than ultimate material strength would suggest, I suspect it was due to the higher strength of the cold-worked rivet, which is an unquantifiable number, determined by testing.

The authoritative reference for single shear strengths is MIL-HDBK-5 or the later MMPDS. (worth noting - these references do not list rivet tension strengths) For -3 AD rivets, that number is 217 pounds. But in a joint, there are a number of factors similar to those for the tension, plus whether the sheets are dimples or countersunk, which affect the joint strength. The basic rivet strength is only one of the major factors.

To answer Dan's question, the only other consideration is another unquantifiable number, the amount of preload force the rivet generated when set. I'd call it the "clinch" force. It's a number which can only reliably be determined by test, and which would vary with head type, sheet thicknesses, etc., plus the amount the rivet is driven. More clinch would give you a stronger joint, one less likely to work over time.

I have no data comparing clinch for different rivet types or sizes.

Dave
 
426 rivets start soft but harden substantially when driven, let’s not forget the aircraft is not airworthy no matter how many experimental mechanics tell us so. It does not meet design spec period. There is no way around that. There is also the fact that if it has N numbers, the FAA has failed. This is one of my big issues with the FAA giving repair cents to builders after a build, yes they know how to pound rivits and that deserves great respect but almost none knows the hows or whys something is built the way it is or how to diagnose, troubleshoot, or properly repair their aircraft or even has a basic understanding of the systems involved. The same hold true for all the DER’s and DAR,s I’ve dealt with in the last 30 something years, great respect for their function, but none I’ve met could carry out the repairs or modifications they designed.

Off my soap box now...
 
Where is the requirement that any experimental aircraft meet a "design spec" in order to be considered airworthy?

Also, making a thing stronger is not always better...
 
The guy's other airplane was a Harmon Rocket. How do you figure he flew if for more than 700 hours? No matter what the FAA says we kinda know it is airworthty.
 
Where is the requirement that any experimental aircraft meet a "design spec" in order to be considered airworthy?

Also, making a thing stronger is not always better...

Design spec is the set of prints it’s built to. It is granted special airworthiness based on being built to those, nothing more, nothing less. The inspector is responsible for seeing that it meets the prints as designed unless one comes up with his own new design then it’s a whole other ball game.

Never said anything about being stronger is better, many times it’s worse.
 
The guy's other airplane was a Harmon Rocket. How do you figure he flew if for more than 700 hours? No matter what the FAA says we kinda know it is airworthty.

And this is why I stated the above, Vans, the designer, has told us it’s not airworthy and a retired, certified professional in the field told us so, but you still claim it’s good because it held together so far. There is a lot of info your missing here...
 
And this is why I stated the above, Vans, the designer, has told us it’s not airworthy and a retired, certified professional in the field told us so, but you still claim it’s good because it held together so far. There is a lot of info your missing here...

Vans said it doesn't conform to his design. You figure anything the Wright Brothers built could be considered airworthy? I figure this pop rivet RV-4 is probably safer than the Harmon Rocket in the long run.
 
Interesting discussion...not for or against pulled rivets, some very successful designs with either. As others have said, properly designed for.
A little perspective....
In Canada, no amateur-built aircraft is "Airworthy".
Comparing any amateur-built design to a Type Certified aircraft is apples to oranges, but that's a whole other topic in itself.
Airworthy means conformity to a Type Design and fit and safe for flight.
Since no amateur-built has an approved Type Design they can only be fit and safe.
The fit and safe is demonstrated by the "25 trouble free hours" fly off after the final inspection and subsequent maintenance iaw applicable standards after that. Our US friends have Phase 1/2 etc.
FYI, US homebuilts can only be imported into Canada if they have a minimum of 100 hrs flight time.

There are standards for amateur-builts with regards to wing loading, minimum useful load and equipment etc.
There are no "design" standards for structure...that's why the 25 hours, passenger warning placards and such.

1) So say I took a Stits Playboy and built a set of cantilever wings for it ?
Would Mr. Stits "approve" it ?
Would the data plate still say Stits Playboy...probably, if I was building it from scratch maybe I could call it a XV-1 ?

2)What about taking an RV-4, clipping the wings and installing a 6 cylinder Lycoming ? Would it still be an RV-4 ?

3)What if I built an RV-3 and it was 950 lbs empty ? I'm flying the airplane a full 200 lbs over the original design's gross weight.
Should it still be called an RV-3 ?

Take care,
Mike
 
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Design spec is the set of prints it’s built to. It is granted special airworthiness based on being built to those, nothing more, nothing less.

Jeff, there isn't any such criteria for EAB aircraft.

The inspector is responsible for seeing that it meets the prints as designed unless one comes up with his own new design then it’s a whole other ball game.

Many DARs make a sincere effort to inspect and advise regarding best practice. However, they have no "print conformance" responsibility.
 
Jeff, there isn't any such criteria for EAB aircraft.



Many DARs make a sincere effort to inspect and advise regarding best practice. However, they have no "print conformance" responsibility.

AC20-27G is a great starting point as well as order 8130.2H... This is a kit with plans, acceptable to FAA classifications and listed on the FAA List of Amateur-Built Aircraft Kits. as such, we are to follow those plans exclusively or seek professional assistance if we deviate and notify the FAA of those deviations during the certification process . Simply stating “ it’s flown 700 hours so far” as a basis for airworthiness or safety ( you choose what word you like here) is foolish.
 
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