Riveting errata

Discussion in 'Workshop Tips and Secrets / Tools' started by Rick Galati, Mar 2, 2003.

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  1. Mar 2, 2003 #1

    Rick Galati

    Rick Galati

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    In building my RV-6A, I am always surprised by the number of sheet metal aircraft builders who come by to visit my project and have overlooked the utility of using NAS1097 rivets in a wide range of applications. Sometimes, these fasteners are inadvertently trivialized by being referred to as "oops" rivets. They are much more than that. Most aluminum homebuilt designs make great use of .032 and thinner material. Countersinking such thin material for an NAS426 rivet virtually guarantees generating a knife edge, or worse, a wallowed out hole....not a good thing. The NAS1097 rivet has a much smaller manufactured head, and in many cases, you can generate a sufficient countersink by simply placing a large diameter drill bit onto the surface of the material and rolling it through your fingers until an adequate countersink depth is achieved! NAS1097 rivets are ideal for attaching nutplates, installing doublers and many other applications. Available in almost as many diameters and lengths as NAS427 rivets, I have found the NAS1097-3-3.5 to be the most frequently used. :cool:
     
  2. Mar 3, 2003 #2

    orion

    orion

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    Good point Rick.

    Another thing that is often missed by the designers of sheet metal aircraft is the conveniance and structural benefit of pull rivets (also called blind fasteners or pop rivets).

    Solid rivets have become a standard in the industry due to their high use in the mainstream aerospace sector. As a result, they are also used heavily for light arcraft construction.

    However if we compare properties, substituting a good structural pull rivet has several advantages. (But keep in mind, I am not talking about the general hardware store variety of pop rivets.) If we compare the properties of a Monel or stainles steel rivet versus the properties of a structural aluminum solid rivet, we'll see higher shear and pull-out values in the blind fastener.

    The only drawback of course is the higher cost of the pull rivet so basically we trade off the cost versus the convenience and ease of use.
     
  3. Mar 21, 2004 #3

    Davefl42

    Davefl42

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    I am currently working at a flight school, maintaining twenty year old Cessna's and Piper's. I don't like blind rivits. After a little bit of corrosion sets in the blind rivits start working and pretty soon there is a large hole under the head of the rivit. Get a little of oil in the joint, and the problem gets much worse really fast. I've read that blind rivits don't have the clamping force of solid rivits, and some of the joint strengh comes from the friction caused by clamping force.

    Now I'm just an A&P without any engineering education, and don't know all the info about solid verses blind rivits, but I do know I replace blind rivits on twenty year old aircraft more often and solids.

    Thanks Dave
     
  4. Mar 21, 2004 #4

    orion

    orion

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    You are correct Dave, general use of pull rivets may run into issues that you mention however, most of the items you listed occur usually because the individual has selected the incorrect rivet style or alloy combination that is called for in the situation.
     
  5. Mar 22, 2004 #5

    Metalmaniac

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    I've gotta back up my fellow A&P here. There are very few blind rivets in my RV7A so far, and I keep it that way. I also toss the ones included in my kit and use cherry max instead. They're stouter and look a whole lot better (especially in exterior skins). I use them only in spots that are impossible to get behind for bucking.
    I've been in heavy airframe overhaul for many years, and we replace countless loose blind rivets. Also loose huck-bolts, lock-bolts, jo-bolts and probably some other stuff I can't think of off hand. Once in a blue moon we'll see a loose solid rivet, normally when the manufactured head of a flush one breaks off. MS heads handle more tension than NAS simply because they grip more area. It doesn't do much good to have the correct diameter of rivet if the ends won't stay on under a load.
    I've seen some builders do some really scary stuff just because doing it right is too much hassle and takes longer. I'm no engineer either, but I am a pilot and have been in turbulence and a few really less than great landings and it makes me think about how things are fastened together.
    Still, I've looked at a few Zenairs, and that whole plane is popped together. I just think mine is stronger and certainly looks better.
    I guess there's a lot to this, but I know what I see on the job. With a loose rivet, all we have is a hole in the airplane with some trash rattling around in it, and it always enlarges the hole.
    OK, the soap-box is vacant. Richard - Hanger 7A
     
  6. Jun 23, 2004 #6

    Brwood

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    One factor that has not been mentioned is the solid rivet's ability to swell and fill in an imperfectly drilled hole. I suspect a lot of those loose blind rivets, are loose because of imperfect hole preparation. All blind rivets are very sensitive to hole size--Cherry-Max rivets, for example, have a tolerance of around three-thousandths of an inch. (1/8th" rivet, .129 min to .132 max) That's not much tolerance. Whereas a solid rivet will swell and fill in an awful lot of slop, caused by drilling out bad rivets, misalignment, etc. And the comments on countersinking thin sheets scares me. Thin sheets should be dimpled. Look in any basic A+P text, handbook, AC43-13, etc. You can only countersink if the head portion of the rivet stays entirely within the sheet, and you should use a 100 degree countersink, not a drill bit, which is 118 degrees as bought, different if resharpened.

    See attached gif file. Fig. 1 is preferable, fig. 2 acceptable, fig. 3 is not acceptable.

    If the sheet is allowed to creep due to sloppy rivet holes the load is transferred to the neighboring rivets, which conceivably overload them.

    Brwood
     

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  7. Jun 24, 2004 #7

    Craig

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    Riveting

    Well said, Brwood - when I read the first post, I was asking, "why is this guy countersinking .032 alum.?"
    It is easy enough to make a dimpler that works in a pull-rivet tool. Regular dimplers are easy to find and use also!
    Where is Anapolis? I am more familiar with Parana - and enjoy my visits there.
     
  8. Jun 27, 2004 #8

    Brwood

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    Hi Craig,

    Thanks for the nice words. Anapolis is in the central-west highland plains of Brasil, about 120 km southwest of Brasilia, about 60 km north-east of Goiania, capital of Goias state. I teach aircraft maintenance to prospective missionary pilot/mechanics in a small mission aviaton school here.

    What takes you to Parana? I have a friend whose family farms soy and corn there. Have you been to Foz de Iguaçu or Itaipu? Hard to imagine anyone going to Parana and not going.

    Hugs, or as they say here, Abraços

    Brian
     
  9. Jun 29, 2004 #9

    Craig

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    Parana and flying

    I was visiting my wife's relatives there, and contemplating a retirement home.
    The last time I wa in Curitiba, I visited the local airfield. The south half was Brasilian Air Force, the north all civilian. They had two good flight schools there - nice people.
    I was surprised that the government had bought some 400 Argintine copies of the Citabria, and given them to flying clubs. They are remarkably similar to the Citabria, but have a different tail and are not considered aerobatic. Good primary trainers, tho. I think that they were using a Cherokee and a Piper Arrow for the balance of the training.
    Brazil seems to suffer from adequate flight charts I did get the ONC's, but they are really small scale, and don't depict the countryside too well for pilotage.
    Brazil does welcome amateur-built aircraft - and there are thousands of small airfields scattered about in the south. Radar coverage, except near really large cities, seems to be non-existent. Means a lot of freedom. The clear, and uncluttered skies, also help!
    Yes, I have been to both Foz and to Itaipu. One cousin is the head of security there, so I got some real behind-the-scenes looks into the operation. I also got to spend a lot of time in Paraguay with another cousin who grows thousands of acres of grain crops. It amused me that both Spanish and Portuguese are spoken interchangeably there.
    The farthest north that I have been was Belo Horizonte and Ouro Preto - having friends there to visit was really nice.
    Everyone welcomed me in Brazil, and I will return the favor if you get a chance to visit in south Florida. Hopefully, I can get the Duce off the ground and tested, and can show you the area from the bird's eye view.
     
  10. Mar 12, 2015 #10

    DORIGTT

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    So what you're saying is to forego pull rivets and use solids where possible?

    What's the method of selecting the proper solid rivet then?
     
  11. Mar 12, 2015 #11

    cheapracer

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    This is one of those perfect information threads with indisputable facts supported by sound engineering knowledge.

    It is also nonsense and damaging to the sport by making building time slower, harder and more expensive driving potential builders away. The snobby peer pressure comments such as the Zenith one above have no place in a sport struggling to attract new blood.

    There are 10s of thousands of pop riveted planes flying, empirically proven and beyond any doubt of issues. So what if you have to spend a day to replace a few loose ones every 20 years - for goodness sakes.

    Some people love the build itself and like perfection, and I appreciate that, but the main theme should be how to get people in the air.

    Someone owes me .02 cents.
     
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  12. Mar 12, 2015 #12

    cvairwerks

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    Talk about a zombie thread...12 years and 10 days....got to be some kind of a record....:gig:
     
  13. Mar 12, 2015 #13

    bmcj

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    What this forum needs is a pop-up flag for stale threads warning that the last post was 'X' years old when someone tries to post a reply. Nothing wrong with reviving an old thread if it ties into what you want to say, but many 'forum necromancers' are unknowingly responding to dead topics (i.e. - "Is your Flimduwidget-23 still for sale?" while responding to a 5 year old ad).
     
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  14. Mar 21, 2015 #14
    Well, zombies and necromancers aside, this rivet snobbery will always pop up in any case ;) There are differences. When dimpling for solid rivets, one usually use a #30 drill for 1/8 rivets. This works well because the solid rivets swell and fill the hole. When using pulled rivets, of any type basically, using #30 drill and then dimple will produce holes that are too large. The dimpling process widens the holes. You either have to drill a smaller size hole, then dimple, then drill with #30 - or drill with a #31, ease on the deburring and then dimple. The difference may seem minuscule between a #30 and #31 drill, but it does the trick.
     
  15. Mar 21, 2015 #15

    BoKu

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    In my experience, the vast majority of countersunk rivets are 3/32" diameter MS20426AD3 rivets for which the drill size is #40. This is especially true in the RVs.

    I like MK319 pop rivets. They're about as strong as an AD3 rivet. They're 7/64" diameter (#34 drill), so they fit pretty snugly in a hole drilled and dimpled for an AD3 rivet. They're great for those few spots where shop head access is limited. Rather than fuss with a custom bucking bar or contorted access, I'd rather fire in an MK319 and get on with life.

    Thanks, Bob K.
     
  16. Mar 21, 2015 #16
    I'm building an RV-4 and a Onex. The RVs use 3/32 countersunk because that is large enough for the skin size (and they are also easier to rivet, and look good). When "popping", like on Sonex aircraft and many others, 3/32 rivets are not easy to find. The smallest are 1/8, at least the smallest when you need lots of different lengths at a reasonable cost. Structurally the Onex is a "tank" compared with the RV-4, but it also use 6061 instead of 2024.

    The rivet strength between 1/8 stainless and 1/8 bucket is almost exactly the same, so many places I have used bucked rivets on the Onex (partly because I used #30 drill before finding out about how poor fit #30 drill and dimpled skins made :) and partly because at some places where I can use the squizer, bucket rivets are much faster and)
     
  17. Oct 31, 2019 #17

    proppastie

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    sorry about the Zombie thread, but figured the search was better than a new thread.......OK here it is...Dimple 2 sample sheets of .016 with a SS open end rivet (like a pop but Avdel or Baystate) and I can rotate the sheets. If I use an AD-3 no I can not. Is that the List's experience with these blind rivets? I have not done a pull test and it is rated at a higher shear, so I have to wonder if perhaps I need a better puller, however the stem will break at the same time weather I have a good or better puller...or not.

    I have been looking at the 7/64 dia rivets. as Bob talks about too but I do not have samples....I did also try a 1/8 SS rivet standard head .... and even though it was harder to rotate it also would rotate.

    And yes I know the riveted joint is designed in shear.

    Part numbers in the spread sheet are Baystate.
     

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    Last edited: Oct 31, 2019
  18. Oct 31, 2019 #18

    wktaylor

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    There is a VAST difference between commercial blind rivets/bolts and aerospace-grade blind rivets and bolts.

    When I worked at Aerostar factory in 1979-1981 all thin skinned 'closed assenmblies' [ailerons, flaps, elevators, etc] were 'shot together' using Cherry UNISINK blind rivets [NAS term = FLANGED DOME HEAD]. We also used a wide range of blind rivets/bolts all over the Aerostar.

    When I dove deep into military aircraft… especially fighters... I was confronted with HUGE numbers of Blind fasteners and had to learn to deal with repairs, oversizes, substitutes, etc. Over my 40-years, the 'evolution' of Aerospace blind fasteners is amazing... but like everything, requires awareness of design, limitations, strength, proper installation practices, etc.

    Here are a few websites that might prove interesting/insight filled...

    http://www.cherryaerospace.com/documents/catalogs?Catalog=All Catalogs
    https://trsaero.com/allfastinc/products/
    https://www.arconic.com/global/en/products/browse.asp?bus_id=1
    https://www.arconic.com/global/en/products/browse.asp?bus_id=1&cg_id=88
    https://trsaero.com/monogramaerospace/products/
     
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  19. Oct 31, 2019 #19

    proppastie

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    Design involves many compromises...often because of bad design or ignorance (both as is in this case for me). The original plan was to blind rivet the .016 nose ribs/LE because the spar is designed with no lightning holes....with borrowed dimpling tools working out the dimple depth and sample install I discovered the issue with my blind rivet choice. I have not been able to find an aerospace-grade blind rivet -3, 3/32, counter sink head, suitable for -2 length (.031 minimum grip or less).....

    There are many experimental and a few certified aircraft using commercial grade blind rivets....my question involves with proper installation. are others building with these commercial rivets able to twist 2 sheets with one rivet installed between them.
     
    Last edited: Oct 31, 2019
  20. Oct 31, 2019 #20

    narfi

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    I don't see it mentioned much, but a good adhesive eliminates a lot of the issues inherent with blind rivets. (fill the gaps in a non round hole (no hole can be perfect) and preventing them from fretting)
     

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