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First screw up - lots of oversize holes

DaX

DaX

Well Known Member
It was bound to happen - I'm only surprised that it didn't happen sooner. Just broke 100 hours and have been working on the rudder. I match drilled and deburred (what I thought was lightly) the stiffeners to the skin with a #40 bit. I did not knife edge any of the holes. After dimpling with the C-frame (no DRDT-2 here) I found that every one of my holes was oversized. 3/32" rivet diameter is 0.094" - all my holes fell between 0.110" - 0.115" after dimpling.

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I decided to run to Spruce (only a 10 minute drive - lucky me, I know) and pick up some oversize rivets - same mfg head as a AD3, but shank diameter of an AD4. I re-clecoed everything and match drilled to #30.

My question is that is it OK for me to use the oversize (oops?) rivets for all the holes for rudder skins to stiffeners? Kind of too late to ask this question, as I've already drilled everything. I guess if it's not OK, I could re-dimple everything and use regular AD4 rivets.

The bad day didn't end there - I got my first "figure-8", dinged my first skin with the C-frame, and got a ticket on the way home.

n12804481_32535608_1005.jpg


n12804481_32535609_1415.jpg
 
Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.
 
DaX said:
It was bound to happen - I'm only surprised that it didn't happen sooner. Just broke 100 hours and have been working on the rudder. I match drilled and deburred (what I thought was lightly) the stiffeners to the skin with a #40 bit. I did not knife edge any of the holes. After dimpling with the C-frame (no DRDT-2 here) I found that every one of my holes was oversized. 3/32" rivet diameter is 0.094" - all my holes fell between 0.110" - 0.115" after dimpling.
Click to expand...

It is normal for the dimpled hole to have some clearance over the 3/32 rivet. Some people use #41 drill bits to minimize this effect.
 
Matt.
Dont worry about the sligtly oversize rivet holes. Deburr before dimpling and go easy, the skins are very thin. Dimpling streches the hole to a larger diameter. Ideally rivets neet to fit into a slightly loose hole, a rivet reaches its full shear strength after it is shot , (cold working), thus it needs a loose fit to swell. Sometimes I use a half grip length longer rivet than the callout to fill a slightly larger hole. The ding in the skin can be filled in before painting, and the figure 8 stiffener hole, I would remake the stiffener.
 
Brantel said:
It is normal for the dimpled hole to have some clearance over the 3/32 rivet. Some people use #41 drill bits to minimize this effect.
Click to expand...
Don't use an undersize drill bit. There are TOLERANCES associated with every tool -- including dimple dies. If you get a batch of dimple dies that are on the PLUS side of the tolerance range, and you get a batch of drill bits that are on the MINUS side of the tolerance range, what do you get?

The tolerances are intended to work with each other, and if you go undersizing one of the tools but not the other...have fun!! :rolleyes:
 
Mel said:
Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.
Click to expand...

I have already drilled to 1/8". I guess I'll try dimpling one of them to a standard AD4 rivet and see how it turns out. I don't want to dimple again and it be enlarged again. Oh well, if it's really screwed up, I guess new skins and stiffeners will be my first re-order!

I'm used to the rivets being a little loose, but these are 0.094" going into 0.115" holes - 0.020" larger - I didn't feel comfortable doing it.

Any others think it's a bad idea to use all "oops" rivets? I guess I could call Van's about this...

I was intending to build on with the figure-8 - does anyone concur with me on that thought?
 
Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.
 
hmmmm

if you drilled to 40 then dimpled to the 3/32 dimple put rivets in it and shoot. the hole enlarges with dimpling. thats the way it is.
 
cytoxin said:
if you drilled to 40 then dimpled to the 3/32 dimple put rivets in it and shoot. the hole enlarges with dimpling. thats the way it is.
Click to expand...

I've already enlarged to #30.

I have emailed Van's about it, but will probably move forward with NAS1097 rivets unless they scream NO! to me.
 
Tolerances...

dan said:
Don't use an undersize drill bit. There are TOLERANCES associated with every tool -- including dimple dies. If you get a batch of dimple dies that are on the PLUS side of the tolerance range, and you get a batch of drill bits that are on the MINUS side of the tolerance range, what do you get?

The tolerances are intended to work with each other, and if you go undersizing one of the tools but not the other...have fun!! :rolleyes:
Click to expand...
Dan is correct on tolerancing....

However, drill bits are remarkably close, so I would believe that most of the tolerance is in the "pin" portion of your dimple die, since these tend to be hand made (or at least low volume) items from multiple vendors.

Try the #41 drill in a test piece, and if your dimple dies work, then use the #41 drill.... :)

The other tolerance issue you might run into is the "pin" on your clecoes... make sure you can cleco the #41 holes with your clecoes...

I've used #41 drill bits almost exclusively in dimple holes, and I get a bit less slop... :cool:

Try your tools and equipment on test samples and use what works for you.... :)
 
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rivetshaver said:
Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.
Click to expand...
But, the MD88 was designed to be riveted with NAS 1097 rivets, so the designers made sure those rivets would be acceptable. How many 0.020" thick skins does the MD88 have?

Van designed the RVs assuming that the builder would use AN426 and AN470 rivets. While it is acceptable to substitute the occasional NAS 1097 rivet, as other have noted we shouldn't do several in a row unless the consequences of that rivet line failing were benign. If the rudder stiffener rivets failed, that would significantly reduce the stiffness of the rudder, which could reduce the speed at which flutter would occur. This could lead to a fatal accident. Don't cut corners anywhere that could affect structural integrity.

Either redimple for 1/8" rivets, or order new parts. Pick your poison.
 
Thanks for all the input guys. I have had no issues with oversize holes until I started working with the very thin rudder skins. I am going to proceed more cautiously with the elevators.

Tomorrow I am getting together with a fellow RVer and we're going to work it out. Thanks again for all the input. I'm also waiting to hear back from Van's about the matter. I'll post their response when I get it.
 
Regarding the figure 8's: How does this happen?

I don't know how this happens unless you have the male die on top and the female on the bottom, line it up & then hit it with the hammer, letting it slip out of position in between steps.

Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?
 
No spring

RScott said:
Regarding the figure 8's: How does this happen?

I don't know how this happens unless you have the male die on top and the female on the bottom, line it up & then hit it with the hammer, letting it slip out of position in between steps.

Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?
Click to expand...
Another option is to not use the return spring if the male die is in the upper position.
Lift the rod, and let gravity hold the die in position inside the hole, and then hit it.
It's a little more work this way, but practically guarantees no "figure 8's"

gil A
 
RScott said:
Seems to me to be safer to put the male die on the bottom, then when you put the hole over it, the die will hold it in position. Using the male die on the bottom, I haven't had any figure 8's. Maybe I'm just lucky? Am I missing something?
Click to expand...


Nah, you're not missing anything...your method sounds foolproof! Of course, you know what they say....make something foolproof, and someone will invent a better fool..... :rolleyes:

I found that even with the male die in the bottom, you get into a rythm...pound, move, pound, move...and then you get to an awkward spot, you have to bend the skin back or something, and...WHAM! something slips....

Maybe my next airplane won't have any extra dimples or holes...but I bet you can't find the ones on the current plane either! (Bondo covers all sins!)

Paul
 
rivetshaver said:
Matt.
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic. A MD 88 is riveted together with NAS 1097 rivets and is pleanty strong.
Click to expand...

This is apparently very true, as I've read much on the subject. There was even a quote on an RV forum from years ago, stating that what some are calling "mistake" rivets, were the norm for some commercial airliner construction.

An interesting subject anyway......... :D

BTW, someone told me that the rivet heads on an F1 were smaller than the normal AN3 rivet we use. Is this true?

L.Adamson RV6A
 
what is going to make you sleep at night.....

DaX,

Here is my guideline on something like this, regardless of the part in question. If you have to ask the question about something "being ok", it is probably best to choose a solution that is known to be ok. Now, I know we have several aeronautical engineers on the forum and their advice may be sound -- however, you can't deny the fact that they didn't design the RV. I know if I was in your situation, every time I flew the plane in a little rough air or a super stiff cross wind, my thoughts would immediately jump to that rudder. Are those "oops" rivets going to hold enough pressure when it really matters? Who knows....

If this were my rudder, I would put in the -4's or replace the skins and stiffeners.
 
DaX said:
.......... I'm also waiting to hear back from Van's about the matter. I'll post their response when I get it.
Click to expand...
rivetshaver said:
I would continue with the NAS 1097 head rivets, I base my decision on 20 years experience as a sheet metal aircraft mechanic.....
Click to expand...
I think the oft repeated and common notion that too many 1097's in a row as an inherently bad thing is painting with too broad a brush. It all depends on the load path and other anticipated and locally specific demands placed upon a given fastener or series of fasteners. What may be an acceptable fix in one area may be unaccceptable one fuselage station over. This is why the big manufacturers employ stress engineers who's function is to calculate an appropriate fix for any given situation.

In this case, all you want to do is replace AN427AD3 with 1097AD4 rivets in a rudder assembly. Sounds perfectly reasonable to me because the 1097AD4 has a slightly larger manufactured head than the AN427AD3 so it would seem obvious that its manufactured head will be a bit more robust in tension. It gets better because in shear, it is even stronger than the AD3 because it is a 1/8" rivet as opposed to the blueprint 3/32" rivet normally installed in this location. What you are really doing is "bulking up" that general location, making it stronger. That may or may not be a good thing, but I suspect it is. Then to, I have to wonder about the questionable virtue of redimpling that thin rudder skin to accept a larger rivet head when a rivet already exists to fill the countersink just as it is.

I'm not saying this logic will hold up under all circumstances but in this specific case I would have to be convinced otherwise....all the better by a qualified engineer schooled in such matters. I am not (nor should you) be easily swayed by boilerplate bromides dispensed on this and other forums and to be fair....that includes my opinion. Count me among those who advocate the obviously simpler approach of using a series of 1097's to address this particuliar problem.

Let us know what Van's recommendation is.
 
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Logic error?

Rick6a said:
......In this case, all you want to do is replace AN427AD3 with 1097AD4 rivets in a rudder assembly. Sounds perfectly reasonable to me because the 1097AD4 has a slightly larger manufactured head than the AN427AD3 so it would seem obvious that its manufactured head will be a bit more robust in tension. It gets better because in shear, it is even stronger than the AD3 because it is a 1/8" rivet as opposed to the blueprint 3/32" rivet normally installed in this location.
......
Let us know what Van's recommendation is.
Click to expand...

Typo above... I believe your AN427AD3 should have been AN426AD3

Rick... I think your comment on the rivet strength in tension may be incorrect...

Yes the 1097-4 rivet head is slightly larger than a 426-3 rivet head - by about 0.012 - but the amount of the rivet head that is resisting a tensile pull is way less for the 1097 than the 426, since we are dealing with the amount of material left in the head after the much larger body of a 1/8 1097 rivet vs. a 3/32 426 rivet.

Do we know if the failure mode in tension is in the body of the rivet, or in the head pulling through the material? - since you use head diameter in your comment, I assume you think it is in the head pulling trough failure mode...

The 1/8 rivet will have a much larger shop head, but when you pull the joint in tension, it seems reasonable to me that it will be the much smaller amount of material at the manufactured head side that will fail.

The joint should be in shear, but all of the practical testing done on RVs (4000+) hasn't measured the difference between shear and tensile loads..... :)

Interestingly enough, the MIL-HDBK-5 (now MMPDS-01) only gives design strengths for the NAS1097E type rivets in machine countersunk applications.

gil A
 
OK, I heard back from Van's, here's the conversation:

Matt,

It sounds like you have over deburred the holes initially, then drilling out to
#30 finished it off. What I would suggest is to start over with new rudder
skins and stiffeners. That way you can be ensured that your plane is built to
spec. The skins are .020" rather than .016". We have no technical data on
what issues you would run into if you used all NAS1097 rivets on your
rudder. Let me know if you need additional assistance.
Thanks

Joe
Vans Aircraft

**********

I then replied asking what he thought about re-dimpling for AD4 rivets, and this is his reply:

Matt,

I would think that the AD4 rivets would work fine. They are just a little harder
to rivet due to their size. Good luck!
Thanks

Joe
Vans Aircraft

**********

I have decided to re-dimple for AD4 rivets and use all AD4 rivets to hold the stiffeners to the skins. I'll just be more careful when working the other holes in the thin skins.

Also - I have decided to build-on with the figure-8 - I'm just going to use a doubler plate over where the figure-8 is.

Thanks all for the input!
 
AD4 Rivets

Be careful. AD4's are much tougher to set than the 3's. It will be a challenge to get them set without damaging the .020 skins. You will be backriveting these, so get a helper to hold you skins tight down to a very solid backing plate and make sure you get the back rivet set flush to the stiffner and skin and the skin is flat against the backing plate. This will be tough to do on the trailing edge rivets but probably doable. It is worth a try, and if it does not work, you are back into new parts anyway, so why not.
Good luck and let us know how it turns out.
 
JonJay said:
Be careful. AD4's are much tougher to set than the 3's. It will be a challenge to get them set without damaging the .020 skins. You will be backriveting these, so get a helper to hold you skins tight down to a very solid backing plate and make sure you get the back rivet set flush to the stiffner and skin and the skin is flat against the backing plate. This will be tough to do on the trailing edge rivets but probably doable. It is worth a try, and if it does not work, you are back into new parts anyway, so why not.
Good luck and let us know how it turns out.
Click to expand...

Thanks and I will let you know how it turns out. Just to clarify though, I did not screw up ALL the holes in the rudder, just the stiffener-to-skin holes - the trailing edge and the rest of the rudder will still be AD3's (I hope).
 
Rick... I think your comment on the rivet strength in tension may be incorrect...

Yes the 1097-4 rivet head is slightly larger than a 426-3 rivet head - by about 0.012 - but the amount of the rivet head that is resisting a tensile pull is way less for the 1097 than the 426, since we are dealing with the amount of material left in the head after the much larger body of a 1/8 1097 rivet vs. a 3/32 426 rivet.

Do we know if the failure mode in tension is in the body of the rivet, or in the head pulling through the material? - since you use head diameter in your comment, I assume you think it is in the head pulling trough failure mode...

The 1/8 rivet will have a much larger shop head, but when you pull the joint in tension, it seems reasonable to me that it will be the much smaller amount of material at the manufactured head side that will fail.
Click to expand...

Actually, the head area minus the shank of a 1097 versus the same on a 426-3 is very little difference.

.0140 sq. inches for the 1097 against .0144 for the 426-3. The 1097 also has a dome head for additional material. I also gave the 426-3 a slight edge in my random sampling.

1097's averaged a head diameter of .183 to .185

426-3's averaged .163 to .167 which is a difference of .018 to .020 in head diameter for the larger 1097 rivets.

A few were a bit larger or smaller, but same with the 1097's.

Using the smaller .183 and a middle ground of .165 for the 426-3's, I came up with the above figures.

L.Adamson

PS-- the F1 aircraft rivet heads didn't look any smaller than the 426-3's as I checked one today.
 
We know that the joint is strong enough if AN426 rivets are used. If NAS 1097 rivets are used we don't know. We can guess, we can surmise, we can whistle in the wind. But we don't know. I'll take the known strong enough joint over the unknown one any day.

It would be interesting to conduct some pull tests to compare AN426 riveted joints against joints with NAS 1097. Drill, deburr and dimple 0.020" 2024-T3 for 3/32. Rivet half the specimens with 3/32 AN426 rivets. Drill the other half out to #30, and rivet with NAS 1097 rivets. Compare shear and tension strength of the two joints.

Once someone does the above test on a statistically significant number of samples we will know which joint is stronger. Until then we are just guessing.
 
Kevin Horton said:
It would be interesting to conduct some pull tests to compare AN426 riveted joints against joints with NAS 1097. Drill, deburr and dimple 0.020" 2024-T3 for 3/32. Rivet half the specimens with 3/32 AN426 rivets. Drill the other half out to #30, and rivet with NAS 1097 rivets. Compare shear and tension strength of the two joints.

Once someone does the above test on a statistically significant number of samples we will know which joint is stronger. Until then we are just guessing.
Click to expand...

I thought about riviting two sheets an inch wide by approx twelve inches, with one rivet each, and then bending sheet (strap) into a loop. Secure the bottom loops to the floor, and then use a cable attached to the 426-3 & 1097 loops over a pully.

Each rivet test would look like a figure "8" with a rivet attaching the two circles. Slowly lift the cable with an engine hoist, and see which gives first.

Using the pully, the tension would be equal. And of course, this would test the rivet heads in tension; as I'm sure that the 1097 does better in shear.

Do the test several times, including additional rivets. Then pull the attached strips straight for shear.

I've also heard that the 1097 does better with dimpled joints, than machined..........but can't be sure on that.

L.Adamson
 
DaX said:
I've already enlarged to #30.

I have emailed Van's about it, but will probably move forward with NAS1097 rivets unless they scream NO! to me.
Click to expand...

Setting those rivets takes significantly more pressure and will probably result in some pretty lumpy skins. I'd just bite the bullet and get a new skin. Trust me, this won't be the last thing you have to make twice ;)
 
L.Adamson said:
Actually, the head area minus the shank of a 1097 versus the same on a 426-3 is very little difference.

.0140 sq. inches for the 1097 against .0144 for the 426-3. The 1097 also has a dome head for additional material. I also gave the 426-3 a slight edge in my random sampling.

1097's averaged a head diameter of .183 to .185

426-3's averaged .163 to .167 which is a difference of .018 to .020 in head diameter for the larger 1097 rivets.

A few were a bit larger or smaller, but same with the 1097's.

Using the smaller .183 and a middle ground of .165 for the 426-3's, I came up with the above figures.
Click to expand...

Actually, I'm not sure the above calcs tell the whole story. The area of contact between rivet head and dimple is not annular, but rather a frustum of a cone. The surface areas of these, using the same numbers as above comes out to .019170 sq. inches vs .20585 sq. inches, a difference of over 7.4%. If we use the worst case numbers given above we get a 9.7% difference. I sure don't know if this is significant or not, but it is what it is.
 
szicree said:
Actually, I'm not sure the above calcs tell the whole story. The area of contact between rivet head and dimple is not annular, but rather a frustum of a cone. The surface areas of these, using the same numbers as above comes out to .019170 sq. inches vs .20585 sq. inches, a difference of over 7.4%. If we use the worst case numbers given above we get a 9.7% difference. I sure don't know if this is significant or not, but it is what it is.
Click to expand...

Yes, I remember looking at the cone surface area under a magnifying glass, and wondering the difference; because the 1097 has that extra "dome" of material on top to smash down, to farther confuse the matter. Does that add back that 7-9% or not....? :D

L.Adamson
 
Numbers....

L.Adamson said:
Yes, I remember looking at the cone surface area under a magnifying glass, and wondering the difference; because the 1097 has that extra "dome" of material on top to smash down, to farther confuse the matter. Does that add back that 7-9% or not....? :D

L.Adamson
Click to expand...
Actually, it's a real interesting problem in tolerances... taking the spec. numbers and doing a worse case analysis, it can be +20% or -40% for the NAS1097 head area.

If you assume that the 1097 rivet head squishes out to the entire diameter of the dimple, it becomes +34% and -24% for the NAS1097 head area.

There are quite a few tolerances in place, and all of the numbers came from the MIL Specs here...

http://www.av8design.com/Hardware/MS20426.pdf
http://www.av8design.com/Hardware/NAS1097.pdf

It's not as obvious as I thought, and a nice exercise in tolerancing... :D

According to the drawings, your 0.163 head AN426 rivets are at the absolute minimum dimension....

thanks for putting my assumption on areas into actual numbers, and for detailing the head sizes.. they sort of look identical to the naked eye, but the NAS 1097 heads are larger than the heads of the next size down AN426 rivets...

gil in Tucson ... enough mathematics for to-nite... :)
 
az_gila. said:
Yes the 1097-4 rivet head is slightly larger than a 426-3 rivet head - by about 0.012 - but the amount of the rivet head that is resisting a tensile pull is way less for the 1097 than the 426, since we are dealing with the amount of material left in the head after the much larger body of a 1/8 1097 rivet vs. a 3/32 426 rivet.......
Click to expand...
Gil,

I totally agree with your statement...........if we were comparing apples to apples. In this situation, we are in a sense comparing apples to oranges.... AD3's to AD4's. To wit: The structure is designed to normally accept 426AD3 rivets. By replacing those fasteners with 1097AD4 rivets, we are exchanging a smaller diameter rivet for a larger diameter rivet yet the manufactured head diameter remains the same (though in reality the 1097 is slightly larger). The calculated design forces anticipated on the (rudder) structure remain unchanged either way. All we are really asking those rivets to do is keep a stiffener firmly attached to the skin. Therefore, I expect that in this application, an 1097AD4 rivet is stronger than a 426AD3 rivet....an apples to oranges comparison.
 
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szicree said:
Setting those rivets takes significantly more pressure and will probably result in some pretty lumpy skins. I'd just bite the bullet and get a new skin. Trust me, this won't be the last thing you have to make twice ;)
Click to expand...

The way I see it, I'll try the AD4's, and if I screw the skin up, I'll re-purchase. What do I have to lose? :D
 
DaX said:
The way I see it, I'll try the AD4's, and if I screw the skin up, I'll re-purchase. What do I have to lose? :D
Click to expand...

only a little time.

i don't think you'll have much trouble -- after all, you're back-riveting, aren't you? seems to me back-riveting is the easiest kind to do well. (just don't rivet past the end of the back plate.) ;)
 
Well, I finally had a chance to work again last night - I fired up the compressor, set everything up, and actually sunk two rivets before I stopped. I noticed that there were radial cracks in almost every hole on the stiffeners. I assume this is from drilling dimpling drilling dimpling.

I bit the bullet and ordered new skins and stiffeners. I now have a large quantity of scrap 0.020". I guess I'll just drink a beer to the first of many (but hopefully not too many) re-orders!
 
Opps rivets...

Mel said:
Matt,
"oops" rivets are not intended to be used in a continuous row. They are only for one here and one there. If you have drilled to 1/8", then you should use AD4 rivets.
Click to expand...
In a highly stressed location, I'd agree. But for rudder stiffeners, using 'oops' rivets in this situation will not cause a problem (I'm an AE who did structural design for McDonnell Douglas - now Boeing).
 
DGlaeser said:
In a highly stressed location, I'd agree. But for rudder stiffeners, using 'oops' rivets in this situation will not cause a problem (I'm an AE who did structural design for McDonnell Douglas - now Boeing).
Click to expand...
Dennis,

I talked with an IA & DER who before retirement was chief flight test engineer at McDonnell-Douglas in St. Louis about this very issue. In short, he knows his stuff. Confirming my suspicions, according to him, ANYPLACE on the RV airframe where it is called out to use MS426AD3 rivets, it would be perfectly acceptable to substitute NAS1097AD4's with absolutely no loss in strength. In fact, sheer strength would increase dramatically and according to him, tension concerns are a non issue. Why? I touched upon it in a previous post....the head diameter is virtually the same. Interestingly, the tension policy established at McDonnell was arbitrary because failure of a solid rivet in tension is highly unpredictable. In reality, failure in tension is largely influenced by the quality of the SHOP head. He mentioned that tension failure calculations for solid rivets were actually different between the F-4 program and the F-15 program and both were established as business decisions more than anything else.

He suspects that Van's curious policy of discouraging the use of too many 1097s in a row is for one reason or another merely a business decision and is not supported by engineering facts. He said anyone who seriously doubts should refer to MIL-HDBK-5 which in the aerospace industry is considered the "bible."

Similarily, I also talked with a long time Van's employee about why Van's does not actively encourage the use of 1097s when installing nutplates....even though their own shop uses them in the application! He too was at a loss to explain the policy, begging he was to far down the food chain to know for sure. He guessed that if given the choice, some foolhardy builder out there might attempt to use 1097AD3's in place of 426AD3 rivets and that would be a bad thing. He further guessed that rather than risk that happening, Van's made a business decision.
 
I looked it up...

Rick6a said:
.....
He said anyone who seriously doubts should refer to MIL-HDBK-5 which in the aerospace industry is considered the "bible."
......
Click to expand...
Rick, I did this, and the MIL-HDBK-5 only give numbers for NAS1097 rivets when used in fairly thick skins in a countersunk hole... unlike the 426AD rivets, which are listed with shear and tension numbers for both double dimpled and countersunk applications...

gil A
 
Ah, you've reached a critical point in the build process, and I don't mean a particular screw-up on a particular part. You've reached the point where you get to set your standards. Whose advice are you going to take? What is your level of comfort with conflicting advice? What will be the ultimate arbiter, the experience of some people who say one thing, even if it disagrees with standards and the advice of other people with experience? What the situations at which you'll compromise your standards.

I don't mean to be flip at all, but I can overstate how important these questions are and the standards you establish here will be the standards to which your plane is built, of course.

To me, this is the hardest part of homebuilding -- deciding when good enough is good enough based on whatever evidence you gather.

Good luck.
 
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