Got rolling on riveting the right flap tonight. I’d hoped to get further, but Josie had to work late and couldn’t help me out, and some of this riveting is definitely better done with two people on the job. I’d intended to kind of document my riveting procedure in detail, since the instructions are rather sparse here, but of course that kind of fell by the wayside once I got going. It’s a wonder I even get any photos half the time…

Anyway, I started by riveting the interior ribs and the inboard rib to the bottom skin. I’m skipping the outboard rib for now; since its flanges face the outside of the flap, those rivets can be easily squeezed any time. First I squeezed the -4 rivets between the trailing end of the interior ribs and the pseudo-spar (Side note: I wonder if there’s a technical term for that that I should be using. My aero engineer coworker who reads this blog hasn’t made fun of me for calling it a pseudo-spar yet, so maybe I’m not too far off base.) Next I shot all the skin-run rivets. These were pretty straightforward and easy to do with the mini tungsten bucking bar:

The only issue I had with a rivet was this one on the inboard rib:

Note how the rivet sits right below the protruding part of the nutplate. I briefly tried shooting that rivet, using my narrow footed bucking bar, but it turned ugly pretty quickly. So I just drilled out the nutplate rivets, shot the offending rivet, and then reriveted the nutplate in place. That rivet on the left end of the nutplate clinched over a bit – it was tough to get the squeezer in there with the skin in the way – but since this is a nutplate, I’m not especially concerned with the rivet.

Next, I set the top skin on my work surface, slipped the bottom skin-rib assembly in place, and clecoed the line of holes that join the two skins. This is the riveting job that I figure should be done by two people. It’s pretty tight quarters back there where I’ll have to buck these rivets, and trying to shoot and buck is probably a recipe for disaster.

As for bucking those rivets, I’ve seen where guys used their back rivet plates to buck the rivets, but I don’t think it’s necessary. My mini tungsten bar is small enough to get on the rivet head, though it’ll be challenging to hold it straight. My plan for the moment is to hold the skin open with some wood blocks to improve my working room, sort of like this:

In that photo, you can see the little J-bend in the bottom skin, the pseudo spar I keep talking about. The row of rivets I have to shoot is just ahead of that. Once we’ve shot all those rivets, I’ll flip the assembly over, clamp it down tight to the work surface, and we can shoot the rest of the skin-rib rivets. After that, the rest should be a cakewalk; all the remaining rivets are either blind or accessible with a squeezer. Though it occurs to me as I write this that the downward-curving portion of the top skin may make doing the blind rivets between the spar and the ribs difficult. Oh well, we shall see.

Whee, time to break out the C-frame! Well, actually, first I got out the edge rolling tool and put a little roll in the edge of the top skins that will overlap the bottom skins. Then, since I already had the squeezer out with the dimple dies in it, I dimpled the spots that weren’t good for the C-frame. Then I went back and C-framed the majority of the rivet holes.

Dimpled skins:

I didn’t really intend to start doing any riveting tonight, but I figured I’d at least read over the instructions and get an idea of the procedure. I’ve seen where other builders weren’t happy with how the instructions are here, and at first glance, I agree. The instructions basically just say to cleco everything together minus the spar, then start riveting the skins to the ribs. But doing it that way would remove access to rivet the internal ribs to the pseudo spar on the bottom skin.

So far, I think my general plan will be to first rivet the internal ribs to the bottom skin with the top skin not in place. This will allow good access to shoot the skin rivets and squeeze the spar rivets. Next I can cleco the top skin in place and shoot those skin-rib rivets. The rivets joining the top and bottom skins should be lots of fun, there’s not much space to get in there and buck. I’ve seen others use a back rivet plate as a bucking bar back there; I guess that’s probably what I’ll try to do.

I clecoed the internal ribs to the bottom skin while thinking this through. Oh look, here’s a picture:

At this point, I decided to instead go ahead and rivet the reinforcement plates to the spars and inboard end ribs. Fairly straightforward stuff here, though I came frighteningly close to riveting the spar reinforcement to the wrong side of the spar when I did the first one…

Inboard spar ends with reinforcement angles:

Inboard ribs with reinforcement plates, also showing the nutplate inside the rib where the actuator will attach:

And now I’m going to do some research to get a better handle on how to approach riveting. Hopefully I can get started on that tomorrow night…

Short night tonight. I got out the die grinder and went to work on the edges of the flap skins. Turned out to be a kind of tedious job what with all the odd bends and such, but not too horrible. I decided not to go ahead and dimple the skins; for one thing, it was about 11 by this time, and for another, I think I want to roll the edge where the top skin overlaps the bottom. I’ll do a bit of research before I decide to do that though.

I wasn’t quite ready to quit, so I decided to test-fit the two piano hinge halves for the flaps and figure out where to cut each half…in half. The instructions give two options for dealing with the hinge pin here; the first is to leave each hinge half in one piece, use a single pin for the entire flap, and drill a hole in the aileron bracket to allow for removing the pin for maintenance and such. The second option is to use two shorter pins, with a gap in the middle of the flap; in this case, the pins are removed from that center gap. I’m going to do the latter option, since it means not having to disconnect the aileron every time I need to remove the flap. That explanation probably doesn’t clarify much, but it should make more sense once I have some assembly photos later on.

Once again, no photos tonight.

Whew…now that was a good day’s work. Since the weather was nice, my primary goal was to finish prepping the flap components so I could shoot primer. First order of business was to countersink the bottom spar flange where it mated with the hinge half. But first I wanted to figure out the final length of the hinge half (I knew it wasn’t the full length of the spar), which in turn meant doing a rough fit-up on the wing. The flap is positioned 1/4” from the aileron…so now I needed to be sure the aileron was located correctly before doing anything else. I’d followed the plans for the washer stickups at the hinges, but an examination of the wingtip showed that the outboard edge of the aileron wasn’t aligned with the outboard edge of the top skin. Was that intentional or not? A look at the plans seemed to show this misalignment, and to make double sure, I pulled down a wingtip and held it in place to get a look at how everything lined up.

So finally, I was convinced that it was OK to position the flap off the aileron. I made a 1/4” spacer out of two paint stirrers glued together, lined the flap spar and aileron up, and marked three hinge tooth segments to remove from the inboard end. The other flap spar came out the same way (as it should have), and finally I was able to proceed with the countersinking. Then I dimpled all the other spar flange holes along with the ribs. 

I was taking a final look at the inboard reinforcement pieces when I noticed a small imperfection right beside one of the rivet holes. At first I tried buffing it out with the scotchbrite wheel, but it seemed to be surprisingly deep. Eventually I realized what it was – a center punch mark. Apparently when I drilled this hole, the drill bit wandered far enough that the original punch mark was still there:

Probing it with a punch, I verified it was quite deep. In any other area, I’d remove some material until the mark was gone, but here, that would mean impinging on the rivet hole, which I wasn’t comfortable doing. And I didn’t want to just leave the mark either. Fortunately, there was enough of the original angle material left to just make a replacement, so that was what I did. All in all, it was pretty straightforward, only cost me about half an hour or so.

Finally, I was able to go clean all my parts. In addition to the flap parts, I cleaned the aileron pushrods, which also needed a coat of primer. I worked up a fun bit of redneck engineering to hold the pushrods for priming. Basically I just stuck a 3/16” dowel in each end, then stuck the dowels through holes in the saw horses. This gave me access to shot the whole pushrod without it resting on anything:

After a whole lot of time in the driveway, I had a nice bunch of primed ribs:

Next I figured I’d start deburring the flap skins, so I started pulling off the blue plastic. I’d read before that it was necessary to be careful while doing this, lest you accidentally bend your piece. Well, I think I was probably daydreaming about how careful I needed to be when I did this:

Urgh. That’s the little bend at the very leading edge of the top skin, resulting in a slight bow to the curved portion which fits under the trailing edge of the top main wing skin. Thankfully, fixing it wasn’t that difficult. I clecoed the spar in place to apply some straightening force to the skin, then went to work on the creased area with a hammer and wood block, along with some hand seamers to apply some targeted force. The end result looks practically good as new:

Finally, I went to work deburring the rivet holes in the skins. That seemed like a good stopping point for a good day’s work, so I quit. That just leaves deburring the edges of the flap skins and dimpling them, and then it’ll be time to do some riveting. And then I’ll be closer to getting rolling on the fuselage!