Fuse Side Skins

***GOTCHA ALERT*** - This post contains a few items that confused me and required careful read-ahead in the plans, as well as one particularly nasty "gotcha" that appears to have tripped up more than one builder, including myself. The latter is also mentioned in the last entry on Tim Olson's site under "Fuse Tips" (as well as a few other build blogs) but I never saw them until it was too late.

Continued with the deburring tasks today, this time starting with the four Fwd- and Mid-Fuse R/L skins. It took about 4-5 hours to complete all four pieces, which involved tasks including deburring, edge-finishing, scuffing, and dimpling. Then it was time to see what was left to do. I've divided the finish-work into three categories: (1) loose metal parts, (2) skins, and (3) partially-riveted parts already installed in the fuselage structure. At this point, #2 is done and #1 is almost done except for countersinking and a small number of parts to dimple. Then, the focus will shift back to the fuselage for #3, for parts such as the bulkheads and center section side plate that need to be countersunk. I have to admit, countersinking is one of my less-favorite tasks, especially when there is so much of it do to. I guess I don't really *hate* it, but it does make a giant mess of shavings and doing the same thing eleventy-billion times gets a bit tedious.

For the longerons and fuse channels, I set up the microstop and #40 countersink on the drill press and went to town. I had to clamp a 2x4 to the drill press table for the longerons to glide over so that they could be fed through in the proper orientation:

The longeron countersinking process

Otherwise it actually went pretty well, and after a while I had a neat stack of countersunk metal parts, and a pile of metal shavings reminiscent of the pistachio shell scene in The Naked Gun.

One last thing I did before focusing back on the fuselage structure itself was to attempt to solve two mysteries I had running in the back of my mind (little did I know I was about to uncover a third mystery, too).

The first was what to do with the five 3/32" holes directly above the step in the side skin:

The 5 mystery holes above the step in the F-1070 side skin

The plans make no mention of what these holes are for, and there are no drill/dimple/rivet callouts, and no parts attach here at this stage in the plans. I had to dig pretty deep into the plans to discover that the F-1023B-L/R Baggage Floor Angles will attach here as shown in Section 33-2 Step 8 (and Fig. 4). That step mentions that these pieces need to be dimpled, presumably to match the side skins. One problem, the side skins had never been drilled or dimpled here yet! If I hadn't become curious, these holes would have remained untouched and I would have probably ended up in trouble later on. So, I clecoed these F-1023B angles to the skins, match-drilled, deburred, and dimpled them so that things go well in section 33. If you ask me, the steps between these processes should be presented/ordered a bit differently, and there is no reason I can think of that they shouldn't have you take care of this now. Dodged a bullet here for sure.

The second mystery I wanted to solve was the three nutplate holes along the upper flange of each of the F-1040 fuselage channels. The plans make no mention about installing nutplates here (or at least I couldn't find anything), but all the way in Section 35-7 Figure 2 they reveal what they are used for-- retaining the F-1042G wire cover. Looks like they specify a #8 screw, so I'll have to final-drill the nutplate holes #40 and #19, and countersink the #40 holes flush, and then install K-1000-08 nutplates into place. This is just another example of "missing" detail in the plans that I guess they just expect you to know to do it. This could all be done later, except one #40 hole for the aft-most nutplate is awfully close to a gusset attach point, and I think it would be pretty tricky getting a countersink in there at a later time. Better to do it now, I think. (EDIT: This turned out to be a "known" gotcha originally submitted by Chris Johnston and can be found on Tim Olson's GOTCHA page here... glad we ended up at the same conclusion!)

With all that behind us, we put the fuselage structure back into center stage and began countersinking the center section side plates. Before too long, I discovered another issue, this one being a real doozy. The F-1015A Outboard Seat Rib:

The F-1015A-L Outboard Seat Rib

I just talked with a friend and fellow builder Jon, who's building an RV-10 of his own and is pretty much at the exact same stage as we are, to double-check on something. A subsequent google search revealed that Jon and I appear to be the latest two victims of a nasty oversight in the plans. The #40 holes in the outboard face (or "web") of these ribs need to be dimpled. The plans *do* say to do this for the F-1018 ribs, which are part of the next section to the rear (partially visible at the right edge of the photo above). They make zero mention of doing this to the F-1015A ribs, however.

Additionally, there are some #30 holes that get match-drilled from the side skins into the F-1018 ribs, and the three aft-most of these holes need to be dimpled for a CS4-4 rivet according to Page 29-15 Figure 1. It would probably be best to do that match-drilling now in order to get the dimpling out of the way, because it will be very difficult later on.

In summary, here's what I believe really should happen during Section 26-5, somewhere between steps 1-6:

• For the F-1015A-L/R ribs, dimple all of the #40 holes in the web of the piece, excluding the forward-most row that tucks behind the F-1004D bulkhead. Leave the #30 holes alone (careful, they crisscross!)
• Dimple the flanges of the F-1015B-L/R Intercostals to match the dimples you made in the previous step.
• When completing Step 6 on 26-5, the dimple callouts for the #40 holes in the F-1018-L/R are correct; however you should *also* dimple the three aft-most #30 holes that can be seen on the right side of the photo above. Are those holes not there yet? You'll want to fetch the fuse side skins and cleco this rib into place, and match-drill those #30 holes, then deburr and dimple the rib. Trust me, way easier to do now than when everything's all riveted together. As a final clarification on the #30 holes, none should be dimpled EXCEPT for these three. Refer to callouts on Page 29-15 Figure 1.

(Disclaimer: since these recommendations deviate from the order of events in the plans, please don't hold me responsible if they cause more harm than good... I'm only trying to help!)

In order to dimple these holes now, I took a small piece of steel plate and drilled a 3/16" hole near the corner, to fit a female dimple die. Using my rivet gun and die attachment with male dimple die, I carefully created dimples in each location. The dimples aren't the prettiest, but they should be perfectly adequate for the substructure here and I think we're out of the woods now with this particular gotcha... Whew!

Next on the agenda: Finish countersinking and dimpling the fuselage structure for the side skins, and prime all the loose parts and skins. Oshkosh officially kicks off in one week (although we'll be there even sooner than that)... yay!

Forward Fuse Ribs & Bottom Skin

Back in the shop after almost a week off from building! My parents had been visiting from Buffalo, NY over the Father's Day weekend, and although we did get a chance to do a number of aviation-related activities-- including a fly-in BBQ and an attempt at participating in a YE event (cancelled due to marginal weather)-- we actually didn't spend much time in the factory other than showing off our progress so far. Maybe next time they visit I'll try a bit harder to put them to work... or take them for a ride in it, whichever is possible at the time :-)

Anyway, tonight wasn't a night of crazy progress or ground-breaking discoveries, but early on I did catch a mistake I had made while riveting together the firewall. This leads me to my second "GOTCHA" installment: The mystery of the "empty" lower 16 holes on the firewall!

Rivet Diagram on pg. 27-5, holes in question circled in red

The rivet callout diagram on Page 27-5 is misleading, in my opinion (I even pondered what they were for in my entry from 6/11). It shows AN426AD4-4 rivets should be installed into these 16 holes, and they are not included in the markings that say "do not rivet when creating subassembly..." Furthermore, elsewhere in the plans it calls out to dimple all holes, and install 4-4 flush rivets into any unused holes. My conclusion? These holes won't be used and they should be dimpled and filled with 4-4 rivets.

So what are these holes for? It didn't become clear until page 28-7 step 1, where they have you final-drill #30 the holes between the firewall and the Fwd Fuse Floor Ribs. Hey, guess what? They are referring to those 16 holes for the first time ever in the plans... and they really shouldn't be dimpled at this point, or at the very least they shouldn't have rivets installed into them! Aarrgh. Carefully drilled out 16 perfectly-installed 4-4 flush rivets. Not the greatest "first" task after getting back to the project after a week off from building, but hey what can you do. It actually went pretty easy, no holes damaged and we were back to good in short order.

My suggestion if I were to do this again? (1) Do not drill, deburr, dimple, or rivet these 16 holes while constructing the firewall assembly in section 27, leave them completely alone. (2) Final-drill per instructions on 28-7 step 1. (3) Deburr and dimple these holes in the firewall after everything comes back apart on page 28-10.

Side view of the lower firewall after drilling out the rivets in question and drilling/dimpling the mating flanges on the floor stiffeners.

Anyway, other than this ordeal, all we really got done was some more final-drilling of the bottom skin and installation of the Fwd Cabin Floor Panels, which was kind of cool ("This is where our feet will go!"). Here's a pic of the current state of affairs:

R forward floor panel, looking towards firewall

R forward floor panel, looking towards rear

That's pretty much it for tonight! As soon as these floor panels get final-drilled and a bit more prepwork and deburring, looks like we'll be mating the forward and mid fuselage sections for the first time ever... excited for that to come!

Wings

No proseal today, we'll wait until maybe Wednesday or so I think for the next round. Everything in moderation, right?

Instead, we cleaned up the shop a little bit, and I put together a small utility cart we got from HF yesterday. I think it will be nice to use it to hold parts, tools, etc and help keep clutter off the work tables. We'll see how well it works. Certainly, in true Harbor Freight fashion, this thing was... well... "interesting" to put together. The quality of workmanship for the parts in this utility cart were not exactly at the same level as, say, Van's.

Other than that, the only real work on the plane was starting to match-drill the remaining holes in the bottom wing box stiffeners, and preparing for a massive final-drilling event to get both bottom skins complete. That should happen sometime next week, I believe!


***GOTCHA ALERT***
I'm going to start a new tag on this blog called Gotchas, with this being our first installment. On Page 14-6 for the Wing rib assembly (completed by us several weeks ago), there is ONE of the 24 bolts (per wing) that requires two washers stacked on each other instead of the typical single washer. The plans only call this out with a small "2X" mentioned in the parts listing, but it is neither depicted in the graphic; nor is it highlighted, flagged, or mentioned anywhere else in the plans. In my opinion, this is an extremely easy detail for a builder to miss. They call for two washers here in order to keep the nut from reaching the end of the threaded portion of the AN3-20A bolt to be used. I missed this callout when assembling the wing ribs, and the tolerances here are so close that using just one washer will still barely snug up on the two parts (as the nut reaches the end of the bolt threads) just as you reach 25 in-lbs torque on the bolt.

Step 14-6, with the bolt in question circled

You could probably use a shorter bolt instead (like an AN3-17A) with one washer, but I think the reason Van's did it this way is so that the shank of each bolt protrudes all the way through the spar and rib flange, and the threads for each bolt begin past the rib flange. This probably helps with the shear strength characteristics of the fastener.

I doubt I would have ever caught this mistake, and I'm pretty confident it would have never been caught, had my Pitts builder friends Gary and Justin not stopped over to set a few rivets for their project and talk shop for a little while. We got into a discussion about bolt lengths, and I went over to demonstrate the way the spar and ribs had been assembled on our wings, when Gary just so happened to grab the ONE bolt (remember, out of 24) that was incorrectly done and was able to make it twist with his fingers. You can imagine my horror!

It took all three of us a good 20 minutes staring at this page of the plans, and checking our work to realize the problem. After quickly remedying the issue and dabbing an emotionally comforting extra-thick blob of torque seal on the bolt, I showed the plans to another friend of mine who specializes in engineering/installation drawings and diagrams for retrofitting the big jets (Boeing/Airbus) with electrical upgrades. He was appalled by the lack of a flag or some other highlight to point out the discrepancy for that one bolt versus the others, and recommended I contact Van's to suggest they highlight this step a little more clearly. That made me feel a little bit better, and I might just do that... but for now I wanted to at least document this finding here on the blog.

The good news here, folks (read: mom) is that I don't believe this one bolt being out of tolerance would have caused anywhere near a 'real' safety hazard for the airplane itself. With the skins riveted into place, and 23 other bolts and 81 more rivets holding the ribs to the spar, it's not as though the whole wing structure was compromised by this one bolt not being fully snug against the parts. That being said, it wasn't fastened as well as Van's engineers wanted it to be, and that is indeed not a good thing. Care needs to be taken to ensure you don't miss these kinds of details hidden in the plans, and plain and simple we failed with that here. I'd be willing to bet, though, that there's more than one RV-10 flying around out there with a missing washer in this location.