T

tvlawyer

Active Member
I put in a long day working on the left HS today which, is probably whay I made the mistake. I know that the plans are sometimes very vague and I should have studied more carefully. Anyway, I drilled the skins with a #30 rather than a #40. My AD3-3.5's are going to have a lot of wiggle room! Can I use AD4 "oops" rivets to cover my mistake?
 
tvlawyer said:
Anyway, I drilled the skins with a #30 rather than a #40. My AD3-3.5's are going to have a lot of wiggle room! Can I use AD4 "oops" rivets to cover my mistake?
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Standard advice here (which is pretty good usually) is to order new parts and chalk it up to a learning experience. It's not worth having a substandard structure that you will worry about later. Cheaper and easier to fix now.

I don't have the spec in front of me, but IIRC the "oops" rivets aren't quite as strong as the standard AN426 rivets, and their use is limited to a certain proportion of holes (e.g. 1 out of every 3 rivets or 3 out of 20 or something to that effect).

That said, if you don't want to get new parts and haven't dimpled yet, you can dimple for #4 rivets (#30 hole) and just use the bigger rivets. It will look a little funny to other RV builders, but if they're all the same it would be OK, as long as you have good edge distance in all the parts.

HTH

James Freeman
 
It is OK to use a larger rivet as long as you have the edge distance. Obviously, that is not a factor on the skins but it might be on the underlying structure. I am not aware of any restrictions on the use of NAS 1097 AD4-(x) "oops" rivets, and I welcome any references to increase my education. That said, the only reason to use "oops" rivets in this case is to make the finished structure look like it was done with the AD3 size rivets. The real reason to buy a new skin, in my estimation, is that the AD4 rivets are harder than AD3 rivets to set, especially bucking blind inside the stabilizer, and at your level of experience you may be drilling out more than a few rivets with the fun meter going way down to zero. If it was me, I'd verify that the edge distance is adequate and then shoot regular AD4 rivets. If that proves too hard for you at your current level of experience you can always buy new parts. Everyone on this list has done that, some more than once I bet. Your level of experience will greatly benefit from this whole affair. Don't get discouraged...Build On!
 
Order new parts

The replacement parts aren't that expensive, so order new ones. While you are waiting continue on to the VS. It will build your confidence.

If this is the worst (most costly) mistake your make you will be fortunate.

Paul
 
Larry,

The so-called "oops" rivets are NAS1097 rivets, which are designed for purely shear applications. The standard AN426 rivets (nowadays known as MS20426) have some tension capability (although in fact rivets are not the best fastener in a tension application). It just so happens that a 1/8" diameter 1097 will fill the countersink of a 426AD3 nicely, so they work well in situations such as yours. So it's less a question of rivet strength than it is of suitability in a particular bit of structure.
The question is, are the holes you went took to #30 in shear (likely) or tension (unlikely)? That is something only Van's (or someone with access to their analysis) can answer. If it were just a few, absolutely go with "oops" rivets and build on. But since it's a couple dozen or more, it would be a good idea to run it by Van's.
Good luck, and let us know what you find out!
 
It has been my experience that Van's will not bless more than a few oops rivets in a row.

Another option may be to use AD4 rivets.
 
The main reason our planes are covered in 3's instead of 4's is that they require lower setting pressures, and thus usually produce a smoother skin. I say get the new parts and do it over. It'll be ok, and as others have said, this will not be your only goof -- it's all part of the "educational" aspect of this hobby.
 
I would put in the AD4s

I would put in AD4s and if I ended up with something ugly, then I would order the replacement parts. This design is not optimized so tightly that the one size larger rivet is going to cause a problem. I would certainly put in the right size rivets for the holes you drilled, not something between what you have and what you wish you had.

Bob Axsom
 
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It is documented

Stephen Lindberg said:
It is OK to use a larger rivet as long as you have the edge distance. Obviously, that is not a factor on the skins but it might be on the underlying structure. I am not aware of any restrictions on the use of NAS 1097 AD4-(x) "oops" rivets, and I welcome any references to increase my education. That said, the only reason to use "oops" rivets in this case is to make the finished structure look like it was done with the AD3 size rivets. The real reason to buy a new skin, in my estimation, is that the AD4 rivets are harder than AD3 rivets to set, especially bucking blind inside the stabilizer, and at your level of experience you may be drilling out more than a few rivets with the fun meter going way down to zero. If it was me, I'd verify that the edge distance is adequate and then shoot regular AD4 rivets. If that proves too hard for you at your current level of experience you can always buy new parts. Everyone on this list has done that, some more than once I bet. Your level of experience will greatly benefit from this whole affair. Don't get discouraged...Build On!
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Steve... there are restrictions that are well documented....

3.4.3 Repair limitations. The combined oversize rivet hole repairs and oversize countersink repairs shall be limited to a maximum of 20 percent of the rivets, or 10 rivets in a single rivet pattern, whichever is less. Repairs to more than two adjacent oversize rivets, or replacing more than half the rivets with oversize rivets in any 10 inch length of pattern is prohibited.

This is from the Mil-Spec., and actually does not even allow a complete replacement with oversize rivets as a repair method. Same would be true for NAS1097 substitutions...

This is standard practise, unless the "Design Authority" (Vans) states otherwise.

The spec. is here on my web site....

http://home.earthlink.net/~gilalex/rivet_spec/rivet_a.htm

gil in Tucson
 
Absolutely just use the AD4's is my first thought if Van's says OK. As others said, if you mess up while riveting those you're not out anything. Replacing the whole HS is expensive (I know, I replaced about 1/3 of mine) so don't go to that expense unless AD4's would compromise edge distance or something. Since it will be your money, don't let others tell you to buy new parts unless it's Van's who tells you.

Although I've never had quite this many in one place, I always use AD4's rather than the NAS rivets so long as I can redimple the hole up to #30. It's stronger and I doubt very many people would ever see the difference, especially after paint.

Good luck, and don't worry about this mishap. You'll learn from it as we have learned from ours.

P.S.--I just read Gil's post (who posted just before me while I was working on my reply). While I don't doubt Gil's accurate reporting of the mil-spec rules, assuming you have edge distance, how could using the next size rivet up (not an "oops" rivet) be a problem? Can you elaborate Gil? I'm genuinely curious. To my (admittedly uneducated) thinking, you'd be producing a stronger product. Thanks.
 
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Gil: I hadn't noticed that before in the mil-specs, thanks for pointing that out. No specific mention in 43.13 that I could find...I wonder if the FAA recognizes mil-specs for repairs on certified aircraft? Van's of course has the last word on this, although with experimental A/C we are all our own little Ceasars.
 
Just something that came in my mind:

You now have #30 holes, so if you wish to use Oops rivets, I quess you should however dimple with #40 dimple dies which would be hard due the centering pin would wobble in the hole. I'm not familiar with oops rivet -- yet needed any of them luckily.


Also using AD4s might work if Van's 'approves' them but I wouldn't do it because:

- Riveting would be much harder work due larger rivets.

- You haven't drilled right skin yet? So better do you decision now how to proceed. I wouldn't use AD3s on other side and AD4s on another...


Hopefully helped even a bit.
 
Don't know

Stephen Lindberg said:
Gil: I hadn't noticed that before in the mil-specs, thanks for pointing that out. No specific mention in 43.13 that I could find...I wonder if the FAA recognizes mil-specs for repairs on certified aircraft? Van's of course has the last word on this, although with experimental A/C we are all our own little Ceasars.
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Steve L. and Steve M....

Yes.... the FAA does recognize Mil-Specs for design (and repair). They refer in 43.13 to the renamed MIL-HDBK-5 - which gives design criteria for metal aircraft.

There is not a separate FAA design guide for strength of structures AFAIK.... :)

As to the not allowing oversize rivets as a complete replacement... I am quite at a loss to explain. I was actually looking for the NAS 1097 replacement criteria when I read the para. I quoted above.

Again, I don't know why, but it is rather specific... but the "Design Activity" (Vans) can over-ride it...

The design specs. in the HDBK for NAS 1097 rivets only cover machine countersink applications, not dimpled applications.

gil in Tucson
 
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az_gila said:
The design specs. in the HDBK for NAS 1097 rivets only cover machine countersink applications, not dimpled applications.
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Ahh, that explains why they say you can't completely replace the 3's with 4's. It's all about the oversized countersinks. I would think that dimpled joints would be just fine.
 
Rivets and shear loads: NEVER!!!

Red Voodoo said:
The so-called "oops" rivets are NAS1097 rivets, which are designed for purely shear applications. The standard AN426 rivets (nowadays known as MS20426) have some tension capability (although in fact rivets are not the best fastener in a tension application).QUOTE]

Rivets should NEVER be loaded with shear force but ONLY with tension!!! A rivet pulls the parts together and the shear loads are transmitted by the friction between the part.
The same goes for scews, exept for some special application.
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"Rivets should NEVER be loaded with shear force but ONLY with tension!!! A rivet pulls the parts together and the shear loads are transmitted by the friction between the part."

In 25 years of building and repairing everything from KC-10s to Gulfstreams, that's the first time I've ever heard that. It defies every design handbook I've ever read. When I refer to shear, I'm talking about two sheets trying to slide against each other, not pull directly away from each other. Are we talking about the same thing?
 
If you have two sheets trying to slide against each other, they are held in Position by the friction between the sheets, as they are pushed together by the rivets. The rivets itself are just loaded with tension.
 
hmmmmm

Ingo Weise said:
If you have two sheets trying to slide against each other, they are held in Position by the friction between the sheets, as they are pushed together by the rivets. The rivets itself are just loaded with tension.
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this sounds like a machinists talk but i have to disagree :(
 
tvlawyer said:
.........drilled the skins with a #30 rather than a #40..........can I use AD4 "oops" rivets to cover my mistake?
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I would check with Van first but getting a truly informed answer will still largely depend upon the training and technical expertise of the person who happens to repond to your query. In the world of production aircraft assembly, such a problem would likely be likely referred to study and cleared by a stress engineering department for an ultimate disposition and you can bet those guys, while very familiar with MIL-HDBK-5 can and will exercise considerable variance with its dicta if need be in any given situation. Often a decision to proceed with a particular repair may well include economic factors as long as design strength is not compromised.

My personal *guess*....and that is all any of us are doing here.....is using NAS 1097's would be an acceptable course of action in your situation. Our Chapter's Mustang 2 project uses AD4's throughout its airframe. I've always thought it was overkill to do so and it is sometimes a bear to rivet, nevertheless, I don't anticipate its airframe is compromised or structurally prone to failure anytime soon.

If you do contact Van's.....ask them if it would be okay to install 1097's, and then let us know on this thread what they recommended you to do.
 
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shear or tension?

"All rivets are shear fasteners. That is, they sustain the load well if it is in the shear direction (across the fastener) as opposed to bolts, which are loaded along the direction of the part (tensile loaded)."

This is a quote I found on the web and supports what is my understanding of how rivets work. They are not used to pull parts together. The parts should fit together without any force. The rivet simply holds them together and a row of rivets keep shear forces from trying to move the parts in relation to each other. Aircraft designers are more concerned with the shear strength of rivets in a given structure. NAS 1097 AKA "shear rivets" are probably called that because they provide additional shear strength with the same head size as what they are replacing and make dandy "oops rivets".

Alles Klar mein Freund?
 
The official answer from Tom @ Van's

Tom's advice is to use 1/8 rivets. He says my left HS will be even stronger. He also suggested making the same "mistake" on the right side to assure symmetry in the dimpling and total weight of the rivets.

whew... what a relief. time to build on!
 
Everyone makes mistakes like this, some more serious than others. For my .02 cents worth - just bite the bullet and order the new parts, it won't be the last time. You're just starting out on this project and the empennage kit is designed to help you learn to rivet. I don't think you're going to enjoy setting the whole HS with AD4 rivets. The learning process also includes drilling out badly set rivets, which you will have, and if your whole assembly is riveted together with oops rivets, then what?
Also, I question the use of these rivets other than for the occasional mistake. They have a much smaller "shoulder" area holding the skins together. It would almost be better to just go ahead and use a 426AD4 type rivet with a larger dimple if you must go that route. Happy building and don't give up.
 
Nobody mentioned that the head of the OOPS rivets is not flat like the others, but rather has a slight dome in the center. Might look kinda weird.

Also, in spite of what Van's said, an inexperienced riveter trying to get a good looking HS skin with 4 rivets is going to be tough. Try it on the botched side before you go and drill the good side. I think you might find it too difficult to get a good result.
 
Buy new parts

szicree said:
Nobody mentioned that the head of the OOPS rivets is not flat like the others, but rather has a slight dome in the center. Might look kinda weird.

Also, in spite of what Van's said, an inexperienced riveter trying to get a good looking HS skin with 4 rivets is going to be tough. Try it on the botched side before you go and drill the good side. I think you might find it too difficult to get a good result.
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Steve.... the slight dome is a feature... When the rivet is set properly, the dome will be "squished" flat, and the slight extra material helps the rest of the head expand tightly into the countersink... quite clever.... :)

I agree with you on the difficultly of setting -4 rivets in the HS, especially for a new builder. For the price of a skin and a few ribs.... I would also say, just replace them...

gil in Tucson
 
I have seen tail sections riveted this way, using the -4 rivets, and they look just fine.
VAN's approves the use of them, as you have stated, so don't worry about it.
 
A common mistake + a TC question

sf3543 said:
I have seen tail sections riveted this way, using the -4 rivets, and they look just fine.
VAN's approves the use of them, as you have stated, so don't worry about it.
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Steve... are you saying this is a common mistake?

I've never seen a tail portion done entirely in -4 rivets.

Have you other TCs seen any?

gil in Tucson
 
Not common, but I have seen two examples, one recently, where a builder did the VS that way, and they looked fine.
 
tvlawyer said:
Tom's advice is to use 1/8 rivets. He says my left HS will be even stronger. He also suggested making the same "mistake" on the right side to assure symmetry in the dimpling and total weight of the rivets.

whew... what a relief. time to build on!
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Just to clarify... Tom said to use AN426D4's, not the NAS1097AD4.

What is the best method for riveting skin to ribs... bucking or back riveting?
 
tvlawyer said:
What is the best method for riveting skin to ribs... bucking or back riveting?
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Bucking.

It would be next to impossible to get the rivet gun inside the HS, but a little bucking bar fits easily.

Good luck,
Martin
 
If this will be your first go at bucking and/or bucking in tight places (probably both, if you're going in Van's order), a few tips:
-Use as massive a bucking bar as you can easily control in there (especially if bucking -4's). If you have or can borrow a tungsten bar, use it.
-make sure your flush rivet set is square to the work and doesn't "wander". I used a swivel set, which is always square to the work, but didn't have the rubber ring around it. The set would wander a bit, and I didn't realize it til after taking the rest of the vinyl off that once the center of the set isn't directly over the rib you get a dent in the skin.
 
Larry,

Just a thought - depending where you are on the learning curve - I think we all have memories of the 'cliff' nature and 'doh' moments.... (and still continue to have some ;) )

If you have space consider putting the current HS parts to one side for a little while - take a break and go and prep / work on the VS. The sequence of construction here isn't that critical (IMO) and the skills learnt / practiced on the VS will give you a bit more knowledge for a slightly harder HS (AD4s).

The second thing - even if you end up having to, don't rush too quickly to re-order parts - make progress in other areas, batch the orders - it saves on shipping and things like an extra HS skin can easily be included with a wing / fuse kit if needed.

Keep pounding those rivets....

Carl
 
tvlawyer said:
What is the best method for riveting skin to ribs... bucking or back riveting?
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In general, any where you can, it is easier and the appearance will be better if you can back rivet.

As noted above, many of the rivets in the stab can't be reached from the inside with a gun, but you can get a lot of the first side you do with a back riveting technique. In other words, try to fold the skin back enough to back rivet the rivets on the top side (where they will be most visible) and finish up with conventional technique on the bottom half. The ones on the edge, of course, can be squeezed.

It would be hugely helpful to have someone experienced to help you buck the rivets. It is an acquired skill, and a little more difficult with #4 than the standard #3 rivets. Also, make sure you are using enough gun--a 2x is easier to control for the smaller rivets, but more difficult to use on the bigger rivets IMNSHO.

James Freeman
 
I'll help you rivet

Larry,
Sounds like you need a rivet buddy to help you out for a few sessions. Whatever you decide (oops rivets, larger rivets or start over) let me know and I will come over to help out for a few sessions until you get the hang of things. I just finished my wings on the 8A and am starting on the fuse. I live in Stone Mountain and can jump on I-285 for a project visit. Feel free to call me at 404-310-5128. Besides, I am a fellow atty. and can consult with you on future liability issues.
Steve Ashby
 
I'm moderately anal-retentive and mildly OCD. Thus, I'll never sleep at night know that I built my stab with the "wrong" rivets. I decided to reorder the parts and start again. This was an expensive, but valuable, learning experience.

Steve, I'll give you a call this weekend. I'm probably 2 or three weeks off from driving my first rivet. But, I sure would appreciate your tutelage before then.
 
I almost used a 30 drill the other day when a 40 was required. Since these bits get used so much, I think I'm gonna dip all my 30's in red paint (all but the tip). I just thought of this, but it seems like a pretty good tip.
 
Every time I chuck up a bit, I check it in a drill gauge. However, the idea of paint (or colored electrical tape?) sounds like a better solution - Thanks!
 
tvlawyer said:
I'm moderately anal-retentive and mildly OCD. Thus, I'll never sleep at night know that I built my stab with the "wrong" rivets. I decided to reorder the parts and start again. This was an expensive, but valuable, learning experience.

Steve, I'll give you a call this weekend. I'm probably 2 or three weeks off from driving my first rivet. But, I sure would appreciate your tutelage before then.
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You mean, you now have a practice piece to perfect your bucking before doing the real one :) Seriously, I would go ahead and dimple and rivet it together. The more practice the better. My system for drill bits: Each size is in its own parts drawer, only one come out at a time, and is returned when finished.
 
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