Left flap riveting [14.5 hours]

I’ve spent the past few days riveting the left flap together. Turned out to be more work than I expected – glad I’m not building both flaps at the same time. I had my second bucking bar accident for the project. While riveting the very thin (0.016″) top skins to the main spar, just when I was thinking about taking a break, I clumsily allowed the rivet gun to walk off the spar and onto the aft skin, smashing the skin into the edge of the bucking bar. This caused the skin to be stretched and raised where the hit took place, so I had to deal with the problem before closing up the flap.

I used a flat metal surface (the side of a tungsten bucking bar) and a 1/2″ flush die, set up in the DRDT-2 frame, to gently push the stretched area of skin back into place. This turned an outward stretch into a slight inward bulge, which is what I wanted (so it can be filled before painting). Although it would probably be OK as is, I decided to de-stress the area I had worked so I drilled a #40 hole right through the middle of it, and dimpled the hole. I fitted a flush rivet and after doing so the skin was almost dead straight again – just a slight inward bulge which will come up fine with a tiny bit of filler. I hate making mistakes like this, once it is filled and painted no-one will know it is there, but I will…

I bought a cheap USB camera for $5 on EBay, and found it useful while riveting on the bottom skin with the special RV-10 longĀ empennage bucking bar. You get this thing lined up by sighting a line drawn on the centre of the bar through the rivet hole, before placing the rivet in and hitting it with the gun, all while not moving the bucking bar. The camera was great for inspecting the rivets, and any that are under-driven and need a few more whacks, the camera made it easy to line the bar up where it needed to be. On the empennage control surfaces, I had to do all this by feel, the $5 camera made life a lot easier. A few sample views are included in the slides.

I have a few pulled rivets around the flap hinges that I can’t do yet, I either need to buy a long #33 drill or a tiny drill chuck for the angle drill. I also need to grind the top off a rivet puller to get close enough to set them.

For the trailing edge, I’m going to use the same method (double sided tape) that I successfully used for the rudder and elevators. I scuffed the primer up on the wedge, and inside the skins, cleaned all the surfaces with Acetone, and applied the 3M F9460PC VHB double sided tape to each side of the wedge. The most important part is to let this set up for 15 minutes, so that the paper can be easily removed. I slid the wedges in place, and with a helper pulled the remaining paper from both the top and bottom side of the wedge, while quickly getting the wedge in place and cleco’ing it down to the straight edge that I had previously match drilled to the trailing edge. I left it to bond overnight, so apart from the few pulled rivets I need some tooling for, the flap is complete except for riveting the trailing edge.

  • w47a
    Riveting flap ribs to spar
  • w47b
    Flap skeleton riveted
  • w47c
    Flap skeleton riveted, ready for nose skins
  • w47d
    Left flap nose skins, top skin cleco'd in place
  • w47e
    Left flap nose skins, top skin cleco'd in place
  • w47f
    Top skins to main spar riveting, with bucking accident evident
  • w47g
    Bucking bar accident on top skin ... oops
  • w47h
    After flattening out stretched skin, stress relieving with a #40 hole, and dimpling for a rivet
  • w47i
    Left flap - riveting bottom skins to main spar
  • w47j
    Empennage bucking bar used for riveting bottom skins to main spar
  • w47k
    Riveting bottom skin to main ribs, using MS319-BS pulled rivets
  • w47l
    $5 USB camera shot to check riveting of skins to lower spar using empennage bucking bar
  • w47m
    Picture from $5 USB camera to check setting of awkward corner rivet, bottom skins to rear spar and aft rib flange
  • w47n
    Left flap trailing edge wedges after scuffing and cleaning with acetone
  • w47o
    Trailing edge wedges with 3M F9460PC VHB tape applied
  • w47p
    Trailing edge wedge in place, ready to pull paper from tape and cleco to straight edge
  • w47q
    Trailing edge, cleco'd to straight edge while wedge bonds to skins
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