Flaps

So my first order of business for the day was to run to the nearest Napa and buy up their entire stock of 7220 self-etch primer. I should be set on that stuff for a while now, I think. Back at home, it was fairly rainy today, so I ended up priming just inside the garage door again. First up, I shot 7220 primer on the aileron spars. Next, I mixed up a small batch of EkoPoxy for the counterweights. Since I knew that I’d have a ton of extra epoxy primer mixed up, I decided to use the surplus to prime the insides of the counterweights as well as both pairs of aileron pushrod. The instructions recommend pouring the primer into the pushrods to do this; I decided to just spray it into one end with the spray gun until it ran out the other. It worked, but there’s a whole lot of waste in this technique:

The bigger issue was that instead of using the surplus primer for this, I used all of the batch just on coating the insides. And I hadn’t sprayed the outside of the counterweight; that was going to be my last step. Fortunately, it’s acceptable to apply this primer with a brush, so my ghetto solution was to dip a paintbrush in all that extra primer that had run out of the tubes, and then I brushed that onto the counterweight tubes. The finish will look cruddy, but that’s OK, it won’t be on display.

Next, I went to work riveting the aileron skeletons, though I didn’t get very far. Step 1 was to rivet the hinge reinforcement plates onto the spar. Most of the rivet holes remain unfilled, since they rivet in assembly with the ribs:

The next step in the instructions is to rivet the counterweights to the nose ribs. The counterweights that still had wet primer on/in them. So that was the end of aileron work for today. Time to move on to the flaps. First step was to match drill the ribs to the spars, then the bottom skin gets clecoed on, the holes in the reap spar are drilled to the internal ribs, and finally the bottom skin is match drilled.

Next up is drilling the piano hinge half that the flap will rotate on. The provided hinge pieces are much longer than needed; the plans say the hinges should be 56”, but the spars are a little longer, so I cut the hinges to be the same length as the spar. I realized about halfway through the drilling, when checking the plans, that the hinge doesn’t actually go the full length of the spar, hence why it should be a little shorter. I just went ahead and drilled the entire length of the hinge; I’ll trim it to the proper length when the time comes.

Anyway, drilling the hinges was fairly repetitive: After clamping the hinge in place, I just went down the spar, drilling, reclamping, and clecing as I went:

All done!

Finally, I clamped the top skin into place on the right flap:

The next step is to match drill this skin, but I stopped short of doing that. We’re going out to catch a movie, so I needed to get showered and ready to go. I guess I’ll keep going on the flaps for the time being, since my workbench is now covered with all the stuff I’ve been using for the flaps.

In other news, I called Van’s last week to check on the status of my fuselage kit. The only big piece I’m waiting on is the roll bar, which is off getting powder coated now. Sounds like the kit will be crated and shipped this coming week!

Started out tonight by match drilling the left flap skin, which I’d clecoed in place before knocking off last night. To be really careful about avoiding putting a twist into the structure, I put 2×4 blocks under the flap so it was resting on those instead of the clecos while I match drilled. Per the instructions, I match-drilled the top holes before flipping the flap over and doing the joint between the top and bottom skins.

The next order of business was to take care of the reinforcements in the inboard end; these provide the mount point for the flap actuator. There are two parts; the first is a flat plate that rivets to the end rib, and the second is fabricated from aluminum angle. Here’s the flat plate clecoed in place and drilled to the end rib:

But there’s more fun to be had here. The inboard rib isn’t perpendicular to the spar, so that reinforcement has to be bent so the portion forward of the spar mates correctly with the angle bracket. And that plate is pretty beefy, so it takes a good bit of force. At first I just tried clamping the plate in the vise between two pieces of scrap poplar, but it was hard to get everything aligned properly. So I ended up using the bracket as a guide to drill holes in the poplar blocks, then I ground the heads off two rivets and used them as pins to hold the entire assembly together:

After committing repeated acts of violence on that plate, the bend was finally correct and I was able to cleco it back in place, clamp the rough-cut angle bracket on, and drill the rest of the rivet holes. Here’s the final reinforcement assembly in place:

Now I just get to repeat all this with the right flap tomorrow…but it should go a lot faster since I figured out a lot of stuff tonight.

Not a lot to report tonight. Mostly it was a replay of last night – match drilling the right flap top skin, then fitting and drilling the reinforcements for the inboard end. As I expected, it went quite a bit faster the second time around. Once I’d finished getting the right flap to the same point as the left, I needed to prep each inboard flap end for the pushrod attach point. This just involves drilling a previous hole out to 1/4” and then drilling for a nutplate that will mount inside the inboard rib.

With that done, I tore both flaps back down to bare parts, peeled off all the blue vinyl, marked each part, and now everything is ready for a good long deburring session:

Now to decide whether to keep trucking on the flaps, or go back and start riveting the ailerons together. I’m leaning towards the latter right now, but we’ll see how I feel tomorrow, I suppose…

After giving myself a day to think about it, I decided to go ahead with the idea of filling the remaining rod ends with epoxy. The main thing that had kept me from doing this last night was worrying about the rivet holes. I didn’t want to totally fill the rod ends and then have to drill those holes again; to me, that was just asking for a misdrill and who knows what kind of ugliness.

So the plan I came up with was to basically cast the rivet holes in place, as it were. First, I set aside six of the AD4-12 rivets. These are the rivets called out for the pushrod ends, but they’re too long and so I’m not going to use them anyway. I coated each rivet with a thin layer of car wax to act as a release agent. After all, I don’t want to permanently install the rivets at this stage! Next, I mixed up a batch of epoxy, stuffed each rod end with epoxy, and then inserted the waxed rivets into each hole. Finally, I cleaned up the squeezed-out epoxy as best I could.

The end result:

Once that epoxy hardens, it should provide some extra support for the rivet shaft and hopefully prevent the shaft from buckling during riveting and contributing to the clinching problems I had.

With those sitting aside to cure, I got out the flap components and went to work preparing them. I knocked down the edges of the inboard reinforcements with a vixen file, then finished polishing the edges on the bench grinder. Then I sat down with the ribs and spars and took care of deburring all the holes.

I suppose I should shoot an email or phone call to Van’s to see if my fuse kit shipped yet, and if they can get me the tracking info. I’m kind of surprised that they don’t notify you of the shipment without being asked; I figure most people probably prefer to have more than a couple days advance notice of the delivery date so they can arrange to be home, or on my case, to go pick up the kit.

I also gave Grove a call last Friday and it sounds like my gear legs should ship out in the next couple of weeks. I’m about to be up to my ears in airplane parts…

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!

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.

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…

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.

Whew, finally back to work. First order of business tonight was to start riveting the joint between the top and bottom skin. I’d been intending to have Josie come out and help with this, but she was working late again, so I examined the situation again and decided that I could shoot these rivets solo. And in fact it turned out to be really straightforward; I had no problems at all. The only tough spots where where the two skins are also riveted in assembly with the ribs.

Here, access was tight enough that even the tungsten bucking bar was to big. I had a different bucking bar that would fit, but holding it in the tight space was going to require both hands. So I got Josie to pause work long enough to come out for about five minutes and help me shoot those. Overall, they weren’t bad at all.

The joint turned out really nice. I was a little concern I overdid it rolling the top skin edge, but the lap joint is really tight, with no gap visible at all:

Next I flipped the flap over and clecoed the top skin to the top of the ribs. This is where things are going to get fun for sure. Doing the bottom rivets, I could pull the top half of the skin out of the way for better access, but that’s no longer possible with everything clecoed together. And to make matters worse, the downward cube of the leading edge of the top skin really limits access inside the flap. There’s no question this is going to be a two-person job:

Since there was nothing else I could do with the right flap, I moved on to working on the aileron bellcranks. I’d temporarily assembled the left one once just to watch the aileron move; now it was time to do it for real. First I used a green scotchbrite pad wrapped around a drill bit to clean up the inside of the bellcrank pivot point, then I chucked each bushing into the drill and gave it a once-over with the green pad. That made the bushings nice and shiny:

Then I clamped the bell cranks in the vice, covered each bushing with a coating of grease, and installed both bushings:

Finally, I bolted each bellcrank in turn into a pair of brackets so I could bench-test them and ensure that they moved freely even when torqued down. Better to do this on the bench than in the wing!

And that’s it for tonight. If I can’t get Josie to help me tomorrow night, I’ll probably just move on to doing the solo riveting on the left flap. I also need to fabricate some spacers for the bellcranks and aileron hinge brackets before things can go together properly.