Fuselage

OK, we left off last time when I’d clecoed the seat back support into place. The support attaches to the side mount plates with AN4 bolts, and to the cockpit rails with a combination of -4 rivets and flush screws. The prepunch situation here is kind of odd; the cockpit rail holes that will hold rivets are prepunched in the rails and the spacer between the rails and the support. These holes are simply match-drilled through the support. But the holes that will hold screws are prepunched in the support, but not the rails or spacer, so they have to be match-drilled from below. (aka inside the cockpit)

The instructions say to drill the screw holes from below first, then the rest of the holes from above. But an issue here is that the 3/8” clecos I used to initially hold the support in place weren’t strong enough to pull the support fully into position. This is easily fixed with some clamps, but it makes drilling from below even more difficult. So I decided to drill the holes from above first, with the support clamped firmly in place. Then, with clecos in all those holes, the clamps could be removed and the support would stay in place.

That part was pretty easy, but next came drilling the support from below. I experimented a bit with trying to do this while leaning over from outside the cockpit, but I wasn’t at all confident in my ability to drill square to the surface, so I resigned myself to working inside. I prepared for this by tossing some scrap 2×6 pieces in the cabin. These are thick enough to at least make the rear seat crotch strap mount not jab into me while I work:

And of course, once I climbed in there and laid down, I immediately realized I needed something else. Fortunately, I was able to get Josie’s attention so I didn’t have to climb back out. And of course, she couldn’t resist getting some photos of me being uncomfortable:

With that annoying task taken care of, I finished the support by drilling the screw holes out to #19, then match-drilling all the remaining holes. Next the center section bulkhead caps are match-drilled, then removed. I’m not sure why they were called out to be removed at this time, but I guess I’ll find out later…

Next up were the rudder stops. When I was cutting the piece of stock containing these pieces before, the blade on my bandsaw snapped and put a nice nick in one of these. At that time, I just decided on a whim to skip these external rudder stops in favor of an aftermarket solution that went inside the vertical stab spar. However, I did some more research on this topic today and it seems that there’s significant debate about those internal rudder stops. While there don’t seem to be any cases of damage or accidents resulting from the internal stops, a fair number of people (including one of the Van’s engineers) have expressed concerns with the internal stop causing increased stress on the vertical stab spar and the rudder hinge points.

After thinking it over, I’ve decided to use the factory external rudder stops instead of the internal ones. It turns out that the nick the saw blade put in the stop isn’t a problem anyway, as that part of the stop will be trimmed off later on. So I went ahead and clecoed and match-drilled the rudder stops in place:

Next up is fitting the tail spring mount. Previously I drilled the mount hoes in the aft most bulkhead, and now with the tailcone together, it’s time to fit the mount and drill the holes in the next most forward bulkhead. The first thing that has to happen is the removal of the aft bottom skin. Well, that’s kind of a problem, since that’s exactly what’s resting on the sawhorse holding the tail up! Hmm, what to do…I considered modifying the saw horse so I could support the tail under the longerons, but that would have left the saw horse in my way while I worked on the tail spring mount. Finally, I realized that the two interior garage door track mounts in the ceiling were almost directly overhead the fuselage, just aft of the cabin. I tried running a ratchet strap between those two mounts, slung under the fuselage, and found that it was in a good location – about 6” aft of the aft cockpit bulkhead, and under the area reinforced by the baggage ribs. I lifted the fuse gently at first, confirming there wasn’t any distortion or buckling happening underneath, and it worked out great. (except I forgot to take a photo and now I’m too lazy to go back out and take one, so you’ll have to use your imagination)

Next I marked the forward bulkhead with a reference line, which I’ll want to align the top of the forward end of the mount:

With the mount in place, there’s a bit of a gap between the forward end and the bulkhead. This is somewhat expected, as the instructions call for making shims as necessary to fill any gap:

Here I departed slightly; the instructions specify 3/4” square shims, one for each of the two bolt holes. I elected to make a single shim that stretched all the way across the top of the mount; for one thing, it seems this will prevent the annoyance of individual shims spinning in place, plus there’s a little more contact surface between the mount and the bulkhead. That may well not make any difference, but I like it anyway.

Now the forward portion of the mount gets moved carefully into position and clamped in place. In addition to using the reference line drawn previously, the instructions say to use the tooling hole in the forward bulkhead as a reference also, by sighting down the mount tube and centering it like so:

Finally, there’s nothing to do but check everything one last time and drill the holes. Here’ the mount in its final position, held in place only by clecos:

Now the aft bottom skin has to be trimmed to account for that mount passing through it. There’s a nice full-size template in the plans for this, which I traced onto a sheet of paper:

Then taped in place on the skin:

And then a cut line is traced onto the skin:

I’m not really 100% satisfied with how that traced cut line ended up though; it looks asymmetrical to me. I know it’ll end up being tweaked to fit the mount, but I want it to start off being straight. In any case, it was getting late by this time and I didn’t want to get into making the cut anyway, so I quit for the night. I’ll do some more research and see if I can get good ideas on marking and cutting here from other builders.

So yeah, tonight I worked on trimming this skin for the tailwheel mount. First I came up with a slightly better way to draw out the initial cut line: I measured and made a few guide marks on each side, then used those to position a template and draw each side of the cut line individually. This ended up with a much more symmetrical pattern than I had last time:

I made the initial rough cuts using the bandsaw, then went to work with a Dremel and cutting bit to get everything looking good:

This is where the real fun began; at this point, it became a highly obnoxious trial-and-error procedure. I’d go sit on the floor under the tail, try to fit the skin in place, mark where it was interfering with the mount, go back to the bench and remove some more material with the Dremel, go sit on the floor again, so forth and so on. All the care I took to make a nice symmetrical pattern for the initial cut was pointless, because the symmetry goes away once the fitting and trimming show starts. That nice smooth sweeping curve from the plans is pretty much impossible, because the weld joint at the aft end of the mount interferes with the skin. I was trying to maintain a somewhat smooth curve as I removed material, but by the time I got the skin to a point where I could cleco it in place, there was a pretty big gap everywhere *but* where the weld was.

Here’s the skin clecoed in place:

Clearance between the skin and mount is still pretty uneven; there’s plenty of clearance on the aft end, but further forward I can’t even slip a little piece of aluminum in the gap. So I need to trim this some more, but I’d had enough of dealing with this for one night. I think I’ll do better tomorrow, when I’ve made peace with the fact that this cut isn’t going to be beautiful, just adequate. You’d need a mirror to even see this with the plane on the ground anyway.

So I didn’t get a whole lot done today in terms of shop time, but I’m well on the way to getting started on the monumental task of preparing all these parts. First off, though, I took a second look at the aft bottom skin. I made a few guide marks, removed the skin again, and took the Dremel to it. This time, it fit in place with good clearance from the mount all around. Here’s the final state, from below:

And with the tail spring in place for a sort-of big-picture view:

Here’s another view of the mount and the cutout, taken later in the afternoon after I’d removed the aft bottom skin and the bulkheads as a unit. The edges of the cut are still pretty rough; once I finish pulling this apart, I’ll file them smooth and deburr and so forth:

There’s a lot more clearance around the mount than I would have preferred here. The weld on the aft portion of the mount, where it attached to the bulkhead, was the big clearance issue, and rather than shape the opening to fit around those, I was trying to maintain the smooth curve of the cutout. So by the time I had clearance around the welds, there was a ton of clearance everywhere else. But again, no one is ever going to see this, and it doesn’t really look that bad, just not-as-good-as-it-could-have. Not bad enough to need a new part, that’s for sure.

Trimming that skin was the last task prior to beginning disassembly, but first I went back through the instructions to review and ensure I didn’t miss any match-drilling. I was particularly concerned with the turtleneck skin (top portion of the tail); this was never match-drilled to the bulkhead tops. I was pretty sure it wasn’t called for but I wanted to be really sure – and it wasn’t. It’s probably not too surprising, since that piece won’t go back on again until much later. So, assured that I was done with it, I removed the turtledeck:

The tail cone contained an absolutely ridiculous amount of aluminum chips from all the longeron drilling:

The real fun here was getting the forward aft bottom skin (the big obnoxious one) off. Try as I might, I could not get that thing to slide out from where it was sandwiched at the forward end. I actually ended up removing the aft side skins first and setting them aside; this gave me better access to really yank on the bottom skin, and finally I got the thing loose. For the moment, it’s sitting on top of the newly truncated fuselage assembly:

Next up, the mid side skins will come off, and then the mid fuselage/seat rib assembly will be detached from the forward fuse. Then comes lots and lots of prep work. Unfortunately, I’ve got a lot going on tomorrow and I don’t think I’ll have a chance to get out in the garage, so further work will have to wait until next week.

Yup, I finally did some work again. Motivation has been waning a bit lately, maybe because of the perceived negativity of taking everything apart again…not quite sure really. Anyway, I continued disassembly of the fuselage, first removing the mid side skins, then separating the seat rib/mid floor assembly from the forward fuse. I got Josie to help me move the forward fuse assembly back onto the workbench, with the center section hanging off. This was so I could go ahead and countersink the forward floor where it will eventually rivet to the center section flanges, mid floor, and I think maybe one other skin.

It’s hard not to look at this photo and think that this is exactly where I was three months ago: (even though I know better)

Next I removed the forward side skins. This was sort of a moment of truth regarding the auxiliary longerons; I was sort of drilling them blindly earlier. I’d drawn guide lines that were slightly visible through the side skin rivet holes, but despite all my care, there was that slight fear that I’d pull the skins off, find edge distance issues, and have to possibly replace parts. Fortunately, that wasn’t the case; the longerons look great!

Next up is preparing the mount for the fuel selector, which sits to the left of the front seat, between the auxiliary longeron and mid-cabin brace. This is a spot where I get to do custom work; instead of the Van’s-provided selector, I went with the much-nicer unit from Andair:

The downside is that the Andair selector is larger than the Van’s one, and so the provided selector bracket is no good. The common mounting solution I’ve seen is to basically just install two short angle pieces between the longeron and brace, with a piece of sheet between them for the selector to mount to. So that’s what I did.

Here’s the mount location mocked up with cardboard:

Unfortunately I got stupid here; when I drilled the outboard hole for the aft angle, I didn’t think through the hole location, and the drill bit wandered to boot. The result was a #30 pilot hole that’s way too close to the end of the angle:

Considering that that hole needs to be enlarged to #19 for a flush screw, this is definitely not going to work. Fortunately, there’s room to move the aft angle back about an inch without interfering with anything, so I cut a new piece of angle and redrilled it, being much more careful this time. That auxiliary longeron will just have an extra hole in it…

Here are both angle pieces clecoed in place, along with the piece of sheet that the selector will actually mount to:

This bracket will actually be hidden when the interior is together; there’s a large plate that covers the entire area between the longeron, brace, gear tower, and center section. Tomorrow I should be able to finish up this mount, at which point there will be a bit more disassembly, followed by probably lots and lots of deburring, countersinking, and so forth…

OK, started out tonight by continuing with the fuel selector mount. I positioned the face plate on the selector mount where I wanted it, mark the screw hole locations, and drilled them, then cut the large center hole where the valve body itself projects through. Here’s the valve and face plate clecoed in place on the mount:

The angle pieces needed to be relieved slightly to allow for the mounting “ears” on the valve:

And finally, here’s the whole assembly clecoed in place on the left side of the cabin. I haven’t drilled the inboard holes out to #19 yet, since the instructions say to wait on those until the side skin is riveted, in case the longeron shifts a bit:

Next, I had to do some backtracking. I was reading ahead in the instructions and ran across a line about countersinking the #19 screw holes in the gear box plates. I remembered drilling two #19 holes per side, but not in the plates. Upon reviewing the plans, I realized that there were a lot more than two #19 holes in each side. In fact, there are a total of 17 on each side. Here’s where I marked the skins tonight for all the holes:

So I had to cleco both forward side skins back in place and get all those holes drilled. I actually kept the left skin in place even after the drilling, as I’m going to go ahead and address positioning the throttle quadrants and doing the necessary modifications for the linkage to the rear throttle. That’ll be my next task when I get back to work again.

Again, not a lot done tonight. I wanted to at least get moving in the direction of hashing out the linkage between the front and rear throttles, but I ended up with more questions than answers when it was all said and done. It started off easily enough, with me bolting the front quad to its mounting bracket and then clecoing said bracket in place. Kind of cool to see:

But this is where it got interesting. The linkage to the rear throttle must pass through both center section bulkheads, but with the throttle mounted as seen here, it appears the linkage would end up interfering with the rivets along the edge of the bulkheads where the bulkhead caps attach. I think part of the problem is this two-lever quadrant. Obviously a three-lever quad would be wider, and the top quadrant cover (not pictured above) seems to be cut with that in mind. The takeaway is that with a three-lever quad, the throttle would be located probably 1/2-3/4” further outboard, and the issue with the linkage interfering with the rivet line wouldn’t be such an issue.

I’ll need to do some research before committing, but my current tentative plan is to add spacers to the inboard side of the throttle, to locate it in the “normal” position further outboard. I’ll definitely be needing to fabricate my own top cover for things to look nice here, but that was always going to be needed with this narrow quadrant anyway.

The other contributing issue is that I want to see about mounting the rear throttle, but I’m either missing a part, or that part isn’t in the fuselage kit, which I’d find bizarre. Basically, it’s a cover plate that mounts below the rear armrest, and the rear throttle bolts to it just like the front one bolts to the front mount. There’s clearly supposed to be a plate there, as the surrounding bulkheads have prepunch holes for nutplates, and I’ve seen plenty of photos of finished aircraft with this plate in place. But I don’t see it depicted anywhere on the plans, so I don’t know what the part number is, and nowhere in my parts stash do I see anything that looks like this piece.

So basically, I’m pretty confused right now. I guess I’ll ask around at VAF about the part number, and try to figure out from there if it’s missing or what.

UPDATE: I was just looking through the electronic copy of the all the plans I had and found a drawing for doing the rear throttle, which includes the part number. I gather you only get this piece if you order the rear throttle kit from Van’s. Guess it’s time for another order…

So before going to bed Thursday night, I worked up and put in an order with Aircraft Spruce for all the raw materials I was going to need for the throttle quadrant stuff. I was a little bummed that I figured out so late that I needed to order stuff, as I’d hoped to spend this weekend hashing out the linkage between the throttles. Well, I shouldn’t have been worried, as I spent the entirety of today just getting the rear throttle quadrant mounted.

Instead of ordering the throttle mount plate from Van’s – which, based on photos I found, I’d have to modify anyway – I decided to just make my own from scrap I had lying around. Really, it’s fairly simple for this piece – I figured out how tall it needed to be and cut the sheet with that dimension, then clamped the whole thing in place and marked the forward and aft edges to match the angle of the two bulkheads. The real fun is taking the resulting nice trapezoidal piece of sheet and match-drilling all the mount holes with the armrest and bulkheads, and then figuring out how to mock the throttle up in position to drill those four bolt holes. Once I got that done and I was sure of where everything would mount, I bent the excess material at the bottom of the plate inward to provide some rigidity to the lower edge of the plate.

Here it is clecoed in position on the still-unmodified armrest:

Here’s the flange I bent on the bottom edge:

Next came the real fun: very carefully laying out the cut on the armrest. The throttle quadrant’s face plate sits beneath the armrest, so the desired end result is for the armrest to overlap the faceplate on all four edges (as opposed to leaving visible gaps), while of course leaving room for the lever to move. I also wanted to have the nice-looking markings on the faceplate visible. Needless to say, I took quite a bit of care in laying out these lines. I drilled holes at the corners to make a nice radius, then made the straight cuts with a cutoff wheel in the Dremel. That, in turn, was followed by a whole lot of filing to clean up the cut edges and move them out to the desired cut lines.

I was pretty nervous about messing the armrest up, but it ended up looking pretty nice:

Here’s a wide view with the quadrant clecoed in place. I also clecoed the seat back support mounting plate to get an idea of how much clearance there’d be above the lever. The answer is “not a lot:”

I still wasn’t done, though. I discovered my first issue when I tried taking the throttle out. The armrest will be riveted in place, so removal of the quadrant will be accomplished by removing the throttle grip, then the screws holding the mount plate in place. At this point, the idea is for the quadrant and the mount plate to come out as a unit. Problem is, those upper two bolts go through the flange of the armrest. I’d cut slots there so the bolts would be able to slide out, but with the bolts tightened, they were still clamping the armrest flange. Well, that’s an issue.

What made it more fun was that I was using some washer stacks on the bolts to move the throttle outboard. The main reason for this was to account for the radius of the armrest where the flange is bent. If I had cut slots large enough to accommodate the washers, they’d be visible above the mount plate. Not a huge issue, but I didn’t like it. So I decided to replace the washer stacks with spacers made from some leftover aluminum tubing; these would be smaller in diameter than the washers and also be less annoying to deal with. But here I kind of fouled up. I had two short pieces of tubing left, one of which was barely long enough to make one spacer. I used that piece for the first spacer, then went to grab the second piece for spacer #2. This piece of tubing took a lot longer to cut, which I found bizarre. Then, when I compared it to the first spacer, ti was wider. Wait, did I have two different sized of tubing? Then I figured it out. I had’t cut my second piece of tubing, I’d cut one of the aluminum spacers that came with the throttle quadrant itself. Well, that was pretty stupid. I have some more tubing coming in my Spruce order, so I guess I’ll be cutting replacement spacers for the bottom of the quadrant as well.

In the meantime, I cut spacer #2 (using the correct piece of tubing this time), and marked and cut the enlarged slots in the armrest:

Initially, I’d decided not to bother cutting lightening holes in the mount plate. But then I realized that installing or removing the quadrant would require working behind the plate to connect or disconnect the linkage to the forward throttle. With that in mind, I decided that lightening holes would be a good idea after all, since they could also serve as access holes. So off came the plate again, and I laid out and cut two lightening holes:

At this point, I finally considered the rear mount to be complete. So I moved on to worrying about the holes I’ll need to make in the bulkheads for the linkage. With the rear throttle quadrant faceplate bolted in place, it was easy to use the slot for the handle to draw an extended centerline forward on the armrest, then transfer it to the bulkhead and extend it downward. So now I have a reference line for the lateral position of the throttle lever. The more challenging part is creating reference lines for the vertical location of the hole. For one thing, I don’t know for sure where the hole in the throttle lever will be. There’s a predrilled hole, but it’s at the same level as the predrilled hole in the forward throttle, and that hole will be used for attaching the actual throttle cable. So I know I’ll be drilling a second, lower hole in both levers, but I’m not 100% sure where yet. Another consideration is that there will be vertical movement of the linkage; it’ll be lowest with the throttle at idle or full, and highest with the throttle at the halfway point.

For now, I went ahead and drew two reference lines on the inside of the mount plate, using the existing hole location. Once I decide how far down to drill the second hole, I can simply shift these lines down by that amount, then transfer the to the bulkhead and work out the location of the pilot hole. I’m still not sure how I’m going to work out where to drill the holes in the center section bulkheads though…anyway, here are those two reference lines, showing how much vertical movement is expected from the linkage:

I also realized that I should have ordered some bolts from Spruce while I was at it. I’m relatively certain that I’ll end up shifting the forward throttle outboard by 1/4” or so by adding spacers. That means I’ll need longer bolts for the quadrant – which I knew, but I figured I’d have some longer bolts on hand I could use at least for temporary assembly. Wrong – the next longer bolts I have are a *lot* longer, to the point that I don’t think they’ll fit between the forward mount and the side skin. I don’t really want to go placing yet another order with Spruce and paying shipping on a stupid small order like this. Actually, it occurs to me as I write this that I could just get some hardware store bolts for temporary assembly, and put the proper AN3 bolts on my shopping list for later. I’m trying to get in the habit of maintaining shopping lists for Spruce and Van’s, so that I can delay non-critical items until I run into something that I need soon, at which point I can combine it all into one order and save shipping.

Anyway, that’s enough blathering for today. Hopefully tomorrow I can settle on the new pivot point for the linkage and at least drill my first pilot hole in the bulkhead, then try and work out the rest of the layout from there.

Ugh, slow going. The good news is that I got in my order from Aircraft Spruce, so I could at least start to move on. First I used the aluminum tubing I ordered to make new spacers for the rear throttle. I already had to replace the one I mistakenly cut, so I just went ahead and made two spacers. At least this way, I’m not using stacks of washers to space the thing out properly:

So I clecoed the rear throttle back in place (for what seems like the 500th time or so) and resumed staring fixedly at the whole setup, trying to figure out how to hash out the drill locations in the bulkheads. The problem I always had was trying to work out a way to mock up a straight line parallel to the rear throttle and extending forward to the front throttle area. I wasn’t convinced that I could rely on the skin being parallel all the way up. Tonight, though, I hit upon a ridiculously simple way to handle this. The rear throttle is parallel to the edge of the armrest, which in turn is located at each end by the bulkhead. All I had to do was find a piece of angle and cleco it to the two armrest bulkheads, and I’d have a reference all the way forward!

I didn’t have any actual angle of an appropriate length, but this untrimmed stiffener stock worked just fine:

Now I could simply measure the distance from the angle piece to the rear throttle arm, and then roughly lay out the horizontal position of the matching potential hole location in the center section bulkheads:

Well, that’s a problem. I’m quite sure there’s not enough room right between those two rivet holes to cut the hole for the linkage and still maintain acceptable edge distance. And I’m certainly not going to flirt with edge distance issues here.

I think what I’m going to have to do here is use rod end bearings at the ends of the linkage, instead of the clevises I ordered from Spruce. That would allow me to offset the linkage outboard by probably half an inch or so. Of course, if I do this, I’ll have to order stuff from Spruce…again. More money tossed in the wind for shipping costs.

Anyway, that’s pretty much where I quit for the night. I feel like I’m closing in on a solution, but at an almost maddeningly slow pace. After how quickly and easily the rest of the fuselage went together before, this is a rather frustrating change of pace.

Overall, a much more productive session tonight. I think I’m finally over the hump of all the throttle head-scratching now (famous last words…). I put in another Spruce order today for a pair of rod ends and some other associated hardware, for v2.0 of the throttle linkage.

One thing I did last night that I didn’t mention was a test run at tapping the ends of my linkage. The linkage is 1/4” steel tube, which will be cut to length, and then the ends will be drilled to size and tapped for 10-32 threads. Originally I was going to put threaded rod into each end for the (female) clevises to attach to, but with the new setup, the rod ends will thread directly into the linkage. Anyway, last night I cut off a short section of the tube, with the intent of seeing how the tapping worked out. Based on some quick Googling, it seemed that the proper drill size was #21, so I drilled the tubing using that, then went to town with the tap.

It went pretty horribly. It was almost impossible to turn the tap, to the extent that I was worried I was going to break the thing a couple times. I ended up with a mangled piece of tubing and something of a foul mood. Some further research turned up a more detailed chart, which called out different drill sizes for, say, aluminum vs. steel. Specifically, it called for a larger pilot hole for steel, perhaps to account for the harder material. According to this chart, #18 was the proper drill size.

So I started out tonight with some tapping experimentation. I had an extra little piece of 1/4” aluminum bar lying around, and I decided to drill three different hole sizes and try tapping them. For the first hole, I used the same #21 as before. I didn’t have a #18 drill bit on hand, so in its place I used a 11/64 bit, which is .024” larger. I did have a #17 reamer, so I used that for my third hole. (#17 is another .011” larger than 11/64) As expected, tapping the larger holes took much less effort than the #21, though none were especially difficult thanks to the soft aluminum.

Next, I wanted to get a ballpark idea of the relative strength of the threads. Presumably the downside of a larger hole would be reduced thread depth, and thus reduced strength. To test this, I decided to thread a bolt into each hole, snug it down, and then proceed to tighten it with the torque wrench until the threads failed. To be clear, this is in no way intended to be scientific or representative of real-world strength; I was just looking to compare the three holes relative to each other.

The results were quite interesting. The #17 hole gave up the ghost at only 30 in-lbs, while the 11/64 hole made it to 60 in-lbs and the #21 to 70 in-lbs. It would seem that that extra .011” from 11/64 to #17 makes a substantial difference. Based on these results – and keeping in mind that the steel rod should be significantly stronger, along with this being a fairly low-stress application – I believe that 11/64 is a perfectly acceptable pilot hole size here.

Here’s that aluminum test piece after I finished ruining the holes:

Next, I moved on to my favorite topic, trying to locate the bulkhead holes for the linkage. I decided to go ahead and lay out the holes; since I know the dimensions of the rod ends I ordered, I can determine where the linkage’s centerline will sit relative to the throttle arm (and by extension the side skin and other stuff) in the horizontal plane. I decided to use the rivet holes in the center section bulkhead to locate the linkage vertically; maintaining edge distance to those holes is the most important consideration. Since I’ll be drilling new holes in the throttle arms for the linkage anyway, I’m free to locate it vertically where it best suits me, and then drill the throttle arms to match later on.

So with all that in mind, and once again using my trick of clecoing some angle in place as a guide, I got my hole center locations laid out:

The second photo is of the center section bulkhead. Here I’ve clecoed the bulkhead cap in place to help evaluate the placement; I’ll definitely be needing to remove some material from the cap here for clearance. But even if I made a 1/2” hole on this center point (which would be a very generous size), I’d still have 5/8” edge distance to the rivet holes. I’ll need to be very careful here to make the passthrough hole only as large as necessary; I’d prefer a good margin over minimum edge distance in this location.

I briefly considered going ahead and drilling pilot holes in these locations, but I’m going to wait until I get the hardware from Spruce (hopefully on Saturday) just so I can double-check the dimensions of the rod ends. Considering how much time I’ve put into puzzling over this setup, it would be pretty dumb to get head of myself now and bugger up the whole works.

For a final task, I went ahead and fabricated a second mount plate for the rear throttle. Ever since I made the first one, the more I played with this setup, the more clear it became that my two large lightening holes weren’t going to be much help in proving access to the lever for rigging the linkage. Even with the lever full forward or back, it was mostly blocked by the web between the holes. So I decided to make a new plate with three lightening holes, where the central one would provide good access to the lever.

Fabrication went pretty quickly (I think it took about an hour) since I was able to use the first plate as a template. About the only unexpected development was that the first lightening hole I cut was larger than I wanted it to be by about 1/4” –  I guess there’s a little slop in my circle cutter. Fortunately, I cut the center hole first, so when I readjusted the cutter to make the other two holes smaller, the whole thing ended up looking nice and symmetrical. And now I really do have good access to the throttle lever:

From here, I figure that once I get the hardware from Spruce and confirm the rod end dimensions, I’ll drill the pilot holes for the passthrough, mock up the linkage location, and use that to figure out how far inboard I need to move the forward throttle. Once the positioning of the forward throttle is nailed down, I can fabricate the top cover plate there and finally put this task to bed.

So I didn’t get a whole lot done today. We spent most of the day doing a bit of kayaking around Lake Houston. I still coaxed myself into doing some work in the garage afterwards, mainly because my stuff from Spruce came in and I was kind of excited to move forward with the throttle stuff.

After inspecting all the stuff and verifying that the rod ends were the same width that I used for laying out the holes for the linkage, I decided that I was happy with the layout. So it was time to take the big step and start making holes. I started out with #20 pilot holes, then broke out the Unibit and enlarged each hole to 5/16”, which I figured would be a good baseline size for the 1/4” tube. Next, I clecoed the forward quadrant back in place so I could verify that the positioning looked good. Whoops, turns out there was one thing I didn’t think about: the forward quadrant mount.

That blue at the end of the far hole is the quadrant mount:

Even better, the positioning is such that the hole lies right on a bend on that quadrant mount:

The good thing is that the mount is quite beefy and there are no potential edge distance issues, so I didn’t have to be extremely precise when making this hole. I decided to start by making a 9/16” hole, drilling square to the angled portion of the mount (that is, the part that doesn’t lie against the center section bulkhead). I figured this would give me a hole that was roughly oval in profile when viewed from directly behind – and it did.

After thinking over a few ways to enlarge and finish the passthrough holes in the bulkheads, I decided to just lay out the required vertical size of the holes and go ahead and enlarge them with a Dremel cutting bit. Originally I’d had thoughts of carefully enlarging the holes so they were just large enough, but that would require a ton of trial and error. Furthermore, I could enlarge to the expected vertical size without getting anywhere near edge distance issues, so I figured there was no need for the tedious trial-and-error.

Here’s a (horribly blurry) photo of the enlarged holes in the center section bulkhead:

I’d previously removed the forward and mid side skins so I’d have access to make the center section holes; at this point, I left the forward side skin off but reattached the mid side skin to the center section bulkhead. With the forward throttle quadrant in place, there’s sufficient rigidity to work on the linkage, and this way I have much better access to the inside of the forward quadrant:

I finished the night by laying the linkage tubing out, cutting it to length (being conservative, since as always, removing material is much easier than adding it back), and drilling and tapping the ends for the rod end bearings. Tomorrow I should be able to work out final positioning of the forward quadrant, and drill the new linkage holes in both levers. Once positioning is finalized, I can fabricate the new top cover plate for the forward throttle. That should be fun, as it’s a bit more complex of a piece than the rear throttle mount plate that I spent so much time on the first time around…