Fuselage

As mentioned last night, today’s weather was gorgeous, so my main objective was to get the parts for the forward floor and cooling ramp primed. But that took hardly any time at all, so I spent most of the day working on the right gear tower. I’m modifying my towers, as many other builders have, by making part of the tower face removable. There’s quite a bit of work that has to be done inside these towers, from riveting stuff together in the near term to routing fuel lines and torquing gear bolts in the long term. Normally, all of that work would have to be done working through the lightening holes – not a fun prospect.

The basic idea for this mod is the cut the tower face into three sections, making the center section into the removable cover. The existing rivet holes are drilled up to #19 for #8 flush screws, and doublers are fabricated to allow for nutplates at the top and bottom of the cover.

Here, I’ve marked the cut lines on the right tower face. My initial plan was to make the cuts using a special thin cutoff wheel in my Dremel, so as to minimize removed material, which would leave a gap between the pieces later on. But that didn’t work out to well; the wheel kept binding in the cut, and about the third time this happened, the flexible shaft I as using snapped. Can’t really make these cuts without that shaft, so this was a problem. But after making a test cut in scrap with the bandsaw and comparing, the amount of kerf was essentially identical between the cutoff wheel and the bandsaw. So I just did the rest of the cutting with the bandsaw.

Cut are now finished. To the left is the top of the gear tower. The center piece will be the removable plate, and the right piece will be concealed behind the inner gear weldment.

All three pieces clecoed to the corner angles so I can fab and fit the doublers.

Doublers fabbed from .040 alclad and marked for initial rivet holes.

Rivet holes done and match-drilled to the tower face sections, time to fit the cover plate.

After clecoing the cover plate on, I clecoed the entire tower structure together and match drilled all of the holes, then drilled the cover plate holes out to #19 for the screws. I meant to take a photo of the assembly, but I forgot until I’d already torn everything apart and started deburring, so all I have is a picture of a pile of parts:

I still need to dimple/countersink a bunch of stuff, in addition to drilling all the nutplates for the cover attachment. And then I have to repeat all of this for the left tower. 

Tonight I just caught the left tower up to where I got the right tower on Sunday; cutting the face into three sections, fitting and drilling the doublers, then finally clecoing everything together and getting everything match drilled.

The whole thing clecoed together:

Detail of the upper doubler (the photo isn’t crooked, there’s a slight angle to the cut here):

With all the match drilling done on the gear towers, next it’s time to do a bunch of countersinking and dimpling. Actually, I get to do a lot more dimpling here than the plans specify thanks to my removable cover mod, since I’m using flush screws there.

Most of the countersinking per the plans is on the right gear tower. All the rivets on the forward side get flush rivets; from what I can tell from the plans, this is because the rear wall of the forward baggage area rests against the gear tower. There are also some nutplates on the forward side, which I imagine are also related to the baggage compartment. Anyhoo, lots of countersinking:

Next I moved on to dimpling the tower cover and the dubbers I fabricated. Here I realized that I’d made a slight error when making those doublers. When I laid out the screw hole locations, I neglected to leave room for mounting the nutplates:

This isn’t really a huge deal though, because there are single-side nutplates available, as seen here:

Problem is, I only have a couple of those on hand. They came with the kit and will presumably be needed dow the road, but I don’t have enough anyway. Which means I get to order more stuff from Spruce. I’m pretty sure I’ll end up paying as much for shipping as for the actual parts, but that’s the way things go, I guess. Kind of makes me wonder: out of all the money poured into an RV build, how much of that was repetitive shipping costs from places like Spruce? Probably more than anyone wants to consider…

Anyway, then I moved on the dimpling the covers themselves. The fun thing about this is that the large screw dimples also warp the material, so after dimpling I get to flatten the material out again. It was mildly annoying on the doublers, but slightly more obnoxious on the covers:

Finally, I dug out my #8 screw countersink bit and countersunk the angles to fit under the dimples on the cover:

The only thing really remaining on these parts is to drill and countersink all the nutplate holes for the covers. Maybe I can get that done tomorrow night.

I’d kind of hoped to get all the nutplate holes drilled tonight on the gear towers, but that didn’t really work out. It was kind of tedious to get stuff lined up on the doublers – just try holding a nutplate that’s attached to nothing while tightening a screw to hold everything in place. There are jigs available to make it easier to do this stuff, but they’re like $50 apiece, and so far I’ve always managed to convince myself that they’re not worth it. Tonight was the first time I really found it tedious to deal with this task.

Anyway, here’s one of the doublers with the nutplates in place:

I spent so much time on the doublers that I only made it through one of the four angles before deciding to call it a night. Fortunately, the angle went a lot faster, and I can probably knock out the rest of these in short order another night:

Not much to report tonight. I finished drilling the nutplate holes in the remaining three angle pieces for the gear towers, then went back and countersunk all the nutplate rivet holes. Absent a bit of final prep work, all the gear tower components are ready to be primed and assembled…and of course the priming will have to wait until the weekend.

I guess for the time being I’ll go ahead and rivet the forward floor and cooling ramp assemblies, then see what I can work on next.

Tonight mostly consisted of getting the parts I have lying around fully prepped and ready for priming this weekend. I double-checked the flush screw countersinks in the gear tower angles and found that they were a little shallow, so I countersunk them all a little more. I’m still being conservative on them though, as countersinking too much will compromise strength, and I definitely don’t want that on an area like this that will be taking a lot of stress.

Next I finished the edges of the lightening holes in the gear tower faces along with the larger holes in the tower sides. (I think those are for fuel lines and engine control cables) I also got in my replacement firewall angle from Van’s today, so I final-drilled that, countersunk the holes as needed, and redrilled the 1/4” hole for the rudder pedal assembly.

And now all the parts for the gear towers and firewall are prepped, marked as needed, and ready for priming. Looks like I’ll be shooting a lot this weekend…

So tonight I switched gears back to the forward flow assembly. First order of business was to rivet some nutplates to the lower flanges of both crossmembers. I believe these nutplates are where the gear leg attachment covers will mount. Anyway, here’s a spot where it would have been nice to read ahead in the instructions a bit, because these nutplates are for flush screws, meaning they need to be countersunk. I would have preferred to have done that before priming. In this case, I just spot primed again after I’d installed the nutplates and countersunk the holes.

Nutplates and unprimed countersinks:

Next up was riveting some nutplates to the floor itself. I believe these are related to the forward baggage compartment. Somehow I missed countersinking the rivet holes for these previously, but countersinking for NAS rivets is pretty easy. I ended up clamping the floor vertically to the side of the workbench to get it in a good position for shooting the rivets:

Finally, I clecoed the crossmembers and ribs to the floor itself, in preparation of riveting:

I decided to start off with the rivets between the ribs and crossmembers. The ones on the forward end (background in the above photo) were easy, since there’s ample access on one side. The rear crossmember, on the other hand (foreground above) was tougher since there are ribs on both sides. I was having a really tough time figuring out how I was going to shoot those things when it occurred to me that I could just remove the skeleton assembly from the floor and then I’d have no access problems at all:

It was getting late by this point, so I clecoed the skeleton back to the floor and left it on the workbench. I should be able to back rivet all the flush rivets through the skin tomorrow night, and get the cooling ramp riveted as well. After that, I guess I’ll have to move on to the next assembly to prep, since I probably won’t be able to prime the gear tower and firewall stuff until Saturday, and since those will be getting epoxy primer, I’ll want to let them cure for a few days before I start riveting stuff.

Pretty much just a token hour in the shop tonight. Since Houston drivers can’t handle wet roads without ramming each other, I stayed at work a little late to let traffic die off. When I got out to the garage I still had some residual frustration from the drive home, and it turned out the riveting tonight was more tedious than I expected. I’d figured on back riveting all the forward floor stuff, but the first couple rivets I tried both clinched over badly and had to be drilled out. This is the first time I’ve tried back riveting -4 rivets; they seem to be a little tougher to get right than the -3s.

So I ended up shooting all the rivets with a flush set, which was a little tough since I had to reach all around the sizable forward floor piece. I got all of them done except the eight rivets through the intercostal ribs, between the crossmembers. I just wasn’t up to figuring out a way to tackle those tonight…

Started out today by finishing up the riveting on the forward floor assembly. There were only eight rivets left, through the two intercostal ribs, but getting to them was an interesting undertaking. Actually, even access wasn’t bad at all, it was trying to figure a way to securely hold the assembly to something so I could have both hands free to rivet. I eventually ended up making sort of hilarious use of the bench vise to hold this rather large piece. Looks ridiculous, but it worked like a charm:

Next I moved on to the cooling ramp. Not a lot to do here; the rear angle piece actually gets riveted to one of the crossmembers on the forward floor assembly, and the stiffener is just back riveted to the ramp itself. Based on what the instructions say, it’ll be some time before the ramp actually gets attached to the forward floor. (the exact words were something like “the ramp will be riveted to this angle much later”)

I’d decided against priming today; the weather was generally nice and sunny, but it was quite windy, to the point that it would have probably caused issues for priming. So instead, I moved on to the next step, preparing the forward baggage area. This area generally consists of a shelf located a little more than halfway up the firewall, with a deeper well on the right side. I started out by clecoing together the whole general assembly:

The firewall will attach to the forward ends of the shelf and the vertical wall of the well (foreground), forming the forward side of the baggage area. The rear wall of the deep well area will be formed by the forward bulkhead of the right gear tower. Directly under the shelf will be the rudder pedals, and behind the upper vertical bulkhead will be the instrument panel.

From here there was just a bunch of match drilling, deburring, edge finishing, fluting, countersinking, dimpling, etc. Here’s a photo of the rear baggage bulkhead assembly with the rear brace clecoed in place for match drilling:

With that, all the pieces of the baggage area are also ready to be cleaned and primed. Tomorrow’s weather is looking slightly better, so I’m going to try and get a bunch of priming done. I actually went ahead and cleaned and etched all the gear tower parts in preparation for priming tomorrow; this way, I know they’ll be good and dry in the morning and I can get right to work:

I also want to try and get the firewall angle/reinforcements primed, but for those I’ll just use Napa self-etch instead of the epoxy primer that the gear towers will get. Since the self-etch doesn’t take a couple days to fully cure, if I can get those angles primed, I can move on to riveting the firewall, and then come back to the gear towers a couple days later. Then maybe next weekend I can prime the baggage compartment parts. Before too much longer, all these parts will be coming together to form something that looks like a real structure!

Finally, a good day’s work, Unfortunately, it wasn’t all fun and games, as we’ll soon get to. I wanted to get started priming as soon as possible, since I know the epoxy primer takes longer to spray than the rattle can stuff. I immediately set about getting set up, giving the tower pieces a final wipedown, hanging them on the priming board, getting the spray gun out, etc. Finally, all that was left was to mix the primer. When I opened the can, I found this:

The stuff is now pretty much the consistency of pudding. A look at the label revealed an important bit of info that I completely missed before, something to the effect of “Store in a cool dark place, not to exceed 100°F.” If there’s one word that does not describe a garage in Houston, it’s “cool.” I don’t know if maybe this stuff can be salvaged if I thin it down again, but I highly doubt it. So there’s $200 worth of primer down the drain, all because I couldn’t read a label.

The best part is that it took a solid month to get this stuff from Spruce in the first place. I have no intention of stopping work for a month to wait for more, so my interior finish plans have changed again. It won’t be bare primer after all; I’ll shoot Napa rattle-can as needed and then figure out what topcoat I want down the road.

The interesting thing was that this made the morning go a lot faster; the Napa stuff dries so fast that if it’s at all warm, the stuff flashes dry almost immediately and you can prime just about as fast as you want. Within about an hour, I had all the gear tower components primed:

Once those were done, I also cleaned and scuffed the firewall angle pieces. I left them out to dry in the sun while I took a short break, then I went back out and got those primed too.

A further side benefit of using the rattle can primer is that I don’t feel compelled to wait a few days for it to cure. In fact, about two hours after shooting the gear towers, I went ahead and started assembling them. This is, at first, a simple affair: rivet the corner angles to the tower sides, then rivet the tower web to the side assemblies. Of course, it took me more time here since I had to deal with my access cover modification. Lots and lots of nutplates to rivet:

But before too much longer, I had the basic gear tower structures together (shown with and without the removable cover:

The next steps involved fitting the steel weldments at the base of each tower. There are two bolt holes in the inboard weldments (foreground above) that need to be drilled in assembly; what makes this fun is that instead of just clecoing the weldment in place, the instructions call for bolting it on, presumably to ensure better alignment. That, in turn, makes it a little more tedious to to this work. But with the inboard weldments done, next the outboard weldments get match drilled for a lot of -4 rivets, then bolted in place. And here I ran into another issue; the rear side of both outboard weldments has some extra material from the welding process, such that it interferes with the fit of the washer/nut for the bolt:

A bit of research showed that this had happened to others, and as I suspected, there was no reason not to just trim the weldment a bit. So I went to work with files and the dremel and eventually had removed enough material for a good fit:

Then I spot primed the areas where I’d removed the powder coat:

And now those guys were good to go. And at this point it was a good time to call it a day and enjoy dinner and a movie. Tomorrow I should be able to finish bolting up the fitting the weldments, at which point it’ll be about time to actually attach the gear towers to the forward floor and start making something looking like a structure. And I guess at some point I need to stop, go back, and rivet the firewall together too…

It’s kind of surprising (and nice) how quickly things seem to go together with the fuselage. The wings were lots of endless prep of a ton of components, followed at long last by some actual assembly. Here, the assemblies are smaller and go together faster. It’s definitely more satisfying, that’s for sure.