Pop rivets holding 1.5 mm plywood on 15x10mm spruce longerons . Good idea ?

Discussion in 'Wood Construction' started by Speedboat100, Oct 4, 2019.

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  1. Oct 4, 2019 #1

    Speedboat100

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    Just testing.
     

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  2. Oct 4, 2019 #2

    Dan Thomas

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    No. Not one bit OK. All this stuff was learned the hard way, by other people, a long time ago. It's why we have standard aircraft practices now. There were a lot of people killed during the learning process.
     
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  3. Oct 4, 2019 #3

    Angusnofangus

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    Maybe for a mock-up, but nothing else.
     
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  4. Oct 4, 2019 #4

    Speedboat100

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    Added with lots of glue of course.

    Why not ?
     
  5. Oct 4, 2019 #5

    galapoola

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    While we are on the subject of non-standard construction, I have one I've never seen. Has anyone ever metalized a wood wing? Could never find any information on if it was tried. I'm guessing it may have been and it failed? The expanding and contracting differences of wood and aluminum comes to mind. If a wing is sitting in the sun, would their dissimilar properties warp things?
     
  6. Oct 4, 2019 #6

    mm4440

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    Al sheet covering the leading edges on wood wings is common.
     
  7. Oct 4, 2019 #7

    Aerowerx

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    I certainly hope that's a mockup in the pictures!

    To my semi-trained eye, that wood is a long way from aircraft quality. Looks like cheap SPF from the big box store. Maybe good for a window screen frame, but not much else. And in one picture I see a nasty crack emanating from one of the rivets.
     
  8. Oct 4, 2019 #8

    FritzW

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    Good or bad, kudos for thinking outside the box.

    Unless there was a really good reason to do it, it doesn't make a lot of sense to me. Is it just to clamp things together while the glue dries or is that all you plan to use? Was the structure you drilled into designed to work with a bunch of holes drilled in it? ...etc.

    Saying "absolutely no" is just a knee jerk reaction. we'd need a whole lot more information to give you an intelligent answer. It would depend on a lot of different things: the style and size of the rivet (there a hundreds of different kinds of rivets), the size of the hole, how is the joint going to be loaded, etc. Your test obviously was a bad combination (lots of split wood in picture #3). Assuming your gluing the joint, the rivet would be redundant when the glue dried and probably cause more problems than it may have solved.

    I went through the whole rivet/mini-double cap rivet/jewelry rivet/pcb rivet adventure before I decided that removable clecos were best for what I was doing (the Ranger).


    And yes, we have accepted standards for building airplanes but they change every time someone comes up with a new idea. ...I'm old enough to remember when we thought you could never build airplanes out of fiberglass
     
  9. Oct 4, 2019 #9

    TFF

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    I think the answer is how uniform and consistent it split the wood.
     
  10. Oct 4, 2019 #10

    FritzW

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    Because he drilled the wrong size hole ...on his very first attempt. I wouldn't give up after only one try.
     
  11. Oct 4, 2019 #11

    Dan Thomas

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    Two reasons. The hole drilled for the rivet removes a lot of the width of the wood longeron, which weakens it significantly. I could see a 20% loss there. And when the rivet expands it compresses and crushes more wood, expanding the weakened area.

    Pop rivets are designed to expand on the backside of a surface so as to pull the parts together. Wood is far too soft to resist the pulling of the bulging rivet, and the rivet bulge just moves up into the wood without putting any worthwhile tension between the pieces.

    Standard aircraft practice when gluing is to clamp, or usse brass nails that are left in, or wire staples (skinny stuff) to hold it until the glues sets, and then the staples are removed. Wider staples shear the wood fibers and weaken it.
     
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  12. Oct 4, 2019 #12

    Dan Thomas

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    No, it's not. It's a reaction from the experience of building, restoring, maintaining and flying airplanes since 1973. And from seeing and reading about people killing themselves, or at least trying to.
     
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  13. Oct 4, 2019 #13

    rtfm

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    My take: Why would you want to? If this is a mockup, drilling and riveting is way too much work. Use staples. If this is a real plane, then glass fibre staples and epoxy. What worries me is the obvious effort he has gone to to build the ribs. Looks very production-like to me.
     
  14. Oct 5, 2019 #14

    proppastie

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    not following the Ranger but I assume it is wood.....why not brass nails as is standard?
     
  15. Oct 5, 2019 #15

    FritzW

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    Actually AC nails are just brass plated (the nails are steel).

    It's all jig-less and, theoretically, clamp-less construction. The sticks just needed to get indexed to the ply (sometimes in the middle of the sheet where clamps can't reach). It gets built "off the table" so nailing wouldn't work.

    The clecos did a great of locating/aligning the parts but they didn't have enough clamping pressure (I had to come up with some 3D printed "mid-panel" clamps. ...and yes, the cleco holes were taken into consideration. I didn't use them where I couldn't afford the loss of cross section or didn't want a potential stress risers. ---which is why SB's rivet idea could work if he designs for them.
     
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  16. Oct 5, 2019 #16

    Dan Thomas

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  17. Oct 5, 2019 #17

    pictsidhe

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    I have done many things that 'you shouldn't do.' When I have pop rivetted soft materials that 'aren't suitable' for pop-rivetting, I use a backing washer. that stops the pop rivets pulling through or otherwise destroying the thing that it 'shouldn't' be used on. There are no pictures of the backside, but I suspect frrom yhe big crack, no backing washer. If you keep the stresses and strains at the permissible levels, anything goes! Suck it and see is generally a good first test of an idea, followed by a little math if it that test didn't go all splintery on you. I test ideas on scrap...
     
  18. Oct 5, 2019 #18

    BBerson

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    Put the backup washer on then pull it tight and stop. Don't break the stem off, just nip it off and touch it up with a grinder (flapper disc 120 grit) to finish. The glue and rivet should fill the hole. But as always, you are "designer in chief", and responsible for what ifs. So test to destruction.
     
  19. Oct 5, 2019 #19

    Speedboat100

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    There is a washer on the right ...and it did not crack the wood.

    Thank you for all the answers. Staples work fine too...but these can keep the surface in tact while the glue dries and keep it tight even after the glue may deteriorate after time.

    There is a camber on both sides and 1.5 mm ply won't bent to that easily..that is why I decided to turn into this pop riveting system. I hope I can place the washers via the bigger opening on this 68 cm long structure.

    Yes and there is non aviation grade plywood on one of the foils ( 6 mm thick ).

    Also the hole in 4 mm poprivets in just 4 mm...but the hole in the 4.8 mm rivets is 5 mm...and it did not crack ! 4.8 mm pop rivets seem to have a bigger area on the hat too.

    The wood on the right is Black Arder....doesn't crack even when the swollen end is submerged in it.
     

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    Last edited: Oct 5, 2019
  20. Oct 5, 2019 #20

    Speedboat100

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    I think the Hughes H-1 replica was on a wood structure..aluminium I presume.
     

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