Fuselage

I should just stop thinking that, on any particular day, I’m going to finally nail down this throttle stuff. You’d think I would have learned this lesson way back with the empennage, but apparently not.

With the linkage roughly laid out, I figured tonight I’d mark the throttle arms for the linkage connection holes, mark the linkage for shortening (it was still a little long), and finalize the necessary spacer to locate both throttle quadrants correctly. I started by pulling the linkage and shortening it, removing about 1/4” from each end. Then I drilled a little deeper in each and and re-tapped the holes so I could have proper thread depth for the rod ends.

Next, I pulled the rear throttle apart (for the 900th time or so). Going the rod end route here means that I need some extra clearance on the outboard side of the throttle, so I fabricated a 1/8” thick spacer and added it to the assembly. I also had to add washers to the pivot point, which ended up with me realizing that I’ll need yet more bolts from Spruce. I can get the stop nut started on the pivot point, but it doesn’t have sufficient engagement. It’s enough to hold everything together for now, but not acceptable as a long-term solution:

I also went ahead and drilled the new linkage connection point on the rear throttle before reassembling the entire thing. Here’s the new assembly:

Next, I removed the front throttle, disassembled it, and fabricated spacers of aluminum tube to move it outboard to the appropriate location. I also fabricated another 1/8” thick spacer to give the extra space needed for the rod end on the outboard side. The only thing left to do was to drill the linkage connection hole at the spot I’d marked (using the actual linkage in place). As a sanity check, I compared this mark to the hole in the rear throttle, and…uh-oh. The mark on the front throttle is a good 1/4” higher than the hole on the rear one. That’s not good – I want those to be the same distance from the pivot point so both throttles have identical travel. Having the point higher on the front throttle would mean that the front throttle would have reduced travel as compared to the rear one.

So now, the question is: how do I handle this? I’ve worked out a couple options so far:

The simplest option would be to simply drill the hole in the front throttle as marked. Based on my math, this would result in the front throttle travel being reduced by about 6.5° from the rear (43.44° vs 50°). I’m not sure this would make a huge difference, but the bigger question regards how the throttle rigging itself works. I don’t know if proper throttle rigging depends on the lever having the proper travel, or if this is easily adjustable using a linkage at the engine. I need to do some more research before I know whether or not this is a feasible option.

Another option would be to use the rear throttle arm as a template, drill the front arm to match, and enlarge the bulkhead passthrough holes as needed. By my calculations, I’d need to enlarge the center section bulkhead holes by roughly .2” downward. This would put the lower edge of each slot roughly vertically in line with a rivet hole shared with the bulkhead cap. I think this could be down without causing edge distance issues, but it would be close. This would probably be the most preferable option, assuming it causes no edge distance issues. I’ve only done rough measurements regarding edge distance, so I need to go measure precisely to determine the feasibility of this option.

The third option would be to drill the front arm as marked, and then red rill the rear throttle arm to match. This would allow me to basically leave the passthrough holes in the center section alone. The passthrough in the armrest bulkhead would need to be expanded, but I’m far more comfortable enlarging the hole there instead of the center section. The big downside here is that I’m 99% sure this can’t be done without replacing the throttle arm. I could probably just fabricate a new arm from 1/8” bar stock. The only other consideration would be finding somewhere local to black anodize the arm so it would match the rest of the quadrant.

Off the bat, #3 sounds the best to me. #2 might work, provided edge distance isn’t an issue. #1 seems like a bit of a hack that requires justification. I’ll have to think this over before deciding how to proceed.

In the meantime, here’s a photo of both throttles mounted with the linkage sitting in place:

So after examining my options for dealing with the linkage mount hole location – in particular taking a close look at potential edge distance issues on the center section bulkheads – I decided that I could proceed by simply enlarging the passthrough holes in the bulkheads. I carefully drew lines on each bulkhead so I’d know where my edge distance limits were, then went to work enlarging the holes.

Here’s the enlarged forward hole. The vertical edge distance guide line can be seen, along with a horizontal line showing how far downward I wanted to enlarge the hole:

Meanwhile, I disassembled both throttles (…again…) and used the rear throttle arm to mark the hole location on the forward arm. Blue marker doesn’t show up very well on the black arm, so I added some blue masking tape around the perimeter of the hole location to provide a better visual guide. Then I reassembled both throttles (…again…) and mounted them both in place (…again…).

Getting there:

At this point, the linkage was interfering with the rounded “corners” of passthrough holes, not the absolute bottom, so after removing both throttles (…again…), I filed the holes outward and downward to provide some more clearance. Then I reinstalled both throttles (…again…). Even closer this time (sorry, no photo), but now there’s a new issue. This is the current interference point, preventing the linkage from going lower:

To get more clearance here, I’d have to file the hole basically straight towards the rivet hole, but I’m not comfortable removing any more material in this area. Both passthrough holes have ample clearance on the outboard side of the linkage though, so I think what I’ll do to address this issue is move the forward throttle outboard a bit. That should move any potential clearance issues to the outboard side of the passthrough holes, where I’m much more comfortable removing material.

But that requires removing and disassembling the throttles (…again…), and I’ve had enough for one night.

Really, I should be more upbeat, because I’m finally closing in on the end of this semi-farce. I did a couple more iterations of enlarging the passthrough holes, and finally got to a point where I was comfortable committing to drilling the linkage mount hole in the forward throttle arm. (which required disassembling both throttles…again…) Then I did two test fits of the linkage; the first test fit showed that the holes needed a little more work, so I filed away at them some more. The second test fit is looking pretty good, but still not perfect. The linkage is still making light contact at the bottom of two of the holes:

Just needs a little bit more filing…another day…

Here’s the linkage in place:

And a close-up of the front throttle attach point:

Once I get those holes taken care of, I’ll be pretty much done here. The only other thing to be addressed is the friction lock for the front throttle; since I moved it away from the mounting plate, I’ll probably need to swap out the bolt there to account for the difference. Oh, and I still need to fabricate a new top cover plate for the front throttle.

Well, I think I can finally put this throttle hilarity behind me. Funny how this started out as “let me take care of this one thing before I move on with prep work.” And that was about three weeks ago.

I started out today with a few more iterations of gradually enlarging the passthrough holes. After the second attempt, I was close enough that instead of actually removing the quadrants again, I just moved the linkage out of the way and filed the edge of the hole with the linkage in place. And finally, I got what I wanted: full movement of the throttle with no rubbing of the linkage.

Whew.

OK, so the final piece of the throttle puzzle was fabricating a new cover plate for the forward throttle. As I probably mentioned before, there’s a cover plate included with the kit, but it seems to be pre-cut for a three-lever quadrant. For whatever reason, the cutout in the thing is significantly wider than my quadrant. Making this piece was actually kind of fun, though there was some tedium towards the end.

To start with, I cut a form block out of scrap wood, using the original cover plate as a template to lay out the cut lines. I also used sandpaper to round the corners a bit where I’d be bend material later, to help promote an appropriately gentle bend:

Checking fit of the form block in the throttle quadrant mount:

I used the block itself to make the initial marks on my sheet stock, then marked off ~7/8” for the flanges:

For the corner of the plate what will have flanges, I punched and drilled a #12 hole to ensure there’d be no sharp corner here. This also adds some relief to account for the bend in the mount plate, which is a bit rounded. Then I used the edges of the hole to mark cut lines for the ends of the flanges:

And here’s the piece after making rough cuts, filing down edges, and smoothing everything with the bench grinder. I’ve also drilled two tooling holes, which are used to positively locate this piece on the form block. These two holes are in the area that will be later removed for the quadrant itself:

Here I’ve bent the flanges and made notches to fit over the throttle mount spacers. I’ve also test-fit this piece with the quadrant attached to the mount (sans levers), and drilled the screw holes where it will attach to the mount. And finally, I’ve marked the cutout for the quadrant. The outermost lines are the actual perimeter of the quadrant faceplate; inside that are my expected cut lines, inset 1/8” on the sides and 1/4” on the ends. Inside the cut lines at the corners are center marks for #12 holes that I’ll drill to serve as the corners of the cutout:

This was where things got fun. After drilling the corner holes, I started making cuts with a Dremel cutoff wheel. I made the short cuts at the ends with no problem, but I was just starting one of the long cuts when the cutoff disc jammed up and completely stopped the Dremel. Before I could switch it off, it turned off on its own – and notably, refused to turn on again. Not sure if I blew some internal fuse or what – after a quick Google session, I checked the motor brushes and they seemed OK, but I never could get the thing to turn back on.

So I just proceeded with my rough cuts, using snips instead. I used a unibit to open the tooling holes up to the largest possible size so I could get the snips in to work with. This worked decently, but I wasn’t able to cut as close to my cut lines as I could have with the Dremel, so when it came time to file the cut lines out to their final locations – well, let’s just say there was l-o-t-s of filing to be done. That was the tedious part I mentioned earlier. It doesn’t help that it’s hard to figure out how to clamp this piece for filing some of the locations.

But al that filing paid off, as the end result fits quite nicely:

The only thing left to do was to reassemble the throttle and try fitting everything in place. But first I had a modification to the throttle. Since I’d moved it outboard a bit to accommodate the linkage, the pivot bolt was now too short to fit the friction lock lever. The bolt is retained by a little clip riveted to the inboard quadrant plate, so I had to drill out those two rivets. I had just the right length AN bolt lying around, but I noted that the original bolt had a much longer threaded shank than the AN bolt. So after riveting the new bolt in place, I got out the tap & die set and added another inch or so of threads to the new bolt. And finally, the whole thing went together. (…again…)

Test-fitting everything in place revealed that I needed relief notches in the outboard corners of the cover plate, to accommodate the flanges of the center section bulkhead and the gear tower. Pretty simple modification really…and then finally, I had everything in place!

The only thing left to do on that cover plate is drill the screw holes on the outboard edge. There’s a piece of angle mounted to the forward side skin that the cover plate will attach to – the fun part will be figuring out how to mark and drill those holes. Next time, I suppose I’ll cleco the forward side skin in place again, both to try and get those screw holes drilled, and to perform a final check of the linkage with the additional bracing of the skin.

But finally, the end is near!

So all I had left to do before I could put this throttle stuff to bed permanently was to figure out how to drill the cover plate for the outboard angle screw holes. I wasn’t quite sure how to do this, but it couldn’t be that bad after everything else, right? Oh, how I make myself laugh sometimes…

The perceived difficulty here was due to the need to cleco the angle in place on the forward side skin, and then figure out some way (in tight quarters) to clamp the cover plate to the angle and drill the holes from below. This promised to be an unpleasant experience, but then I had a sudden bright idea. What if, with the mid side skin still off, I clecoed the original cover plate in place, clecoed the angle to the plate, and then figured a way to clamp the angle in place using the center section bulkhead and gear tower? Then I could simply swap cover plates and drill my holes with ease. What a bright idea, I thought!

So I swapped out the cover plates. Uh-oh, this does not bode well:

I can’t believe how far above the quadrant this plate sits. It doesn’t even make any sense to me – the quadrant mount holes were predrilled, so there’d be no way to mount this quadrant any higher so it would sit flush against the plate. But the bigger issue was that this implied that when clecoed in place on the side skin, the angle would be too high for my custom cover plate. Guess I’d better cleco the side skin on and verify the bad news.

Yep. Hard to tell from this blurry photo, but the angle sits something like 1/8’1/4” above the top of the quadrant. ARGH

OK, so now what? I could make a new replacement angle, but with the rivet holes prepunched in the side skin, it might be impossible to move the angle far enough down. To test this idea, I cut up a piece of scrap hardware store angle I had lying around. I used a couple more pieces of scrap angle to create a jig to hold the test angle level with the top of the quadrant for test fitting:

Next, I went to the outside of the skin and marked the rivet hole locations with a sharpie. After drilling a #40 hole in one of these locations, I was pleased to see that while the hole was close to the vertex of the angle, it seemed like there was enough room to set a rivet head in there. The only possible downside – if I was to make this piece out of actual angle – is that the good angle has a larger radius inside the vertex, which diminishes the available room for a shop head. Worse yet, when I clecoed the angle back in place using my test hole, I found that I’d drilled it a bit too low. Between needing to move the angle down a bit, and the larger radius of the angle stock, I don’t think that’s a viable option for this piece.

So tomorrow I guess I’ll see about forming my own angle piece out of sheet stock. I don’t think this piece needs to be particularly strong, so I may be able to mitigate the issues by using fairly light sheet stock, but I’ll just have to see how that goes. I’ll also throw this tale of woe up on VAF and see if I get any interesting ideas from other builders. Another possible solution – which I haven’t really thought through at all – could be to fabricate an angle piece that rivets directly to the center section bulkhead and gear tower flanges, instead of the side skin itself. Then I could just fill the side skin holes with rivets that attached to nothing – though I wonder if there’d be any concern of the skin flexing and rubbing against the angle mount.

I dunno. I’ll figure something out, as usual…

For real this time, it’s done.

To start off with tonight, I decided to try making a new support angle out of sheet stock, hoping that with a tighter corner bend, I could get away with locating it a bit lower. But after doing a test fit, during which I marked the rivet hole locations, it was pretty clear that those holes would be really difficult to dimple. So instead, I decided to investigate the possibility of simply adding a bend to my cover plate. I was able to conclusively measure the required offset, which turned out to be only a hair over 1/8”.

Based on the space I had outboard of the quadrant cutout, I figured I could make my bend without moving the outboard edge inboard too far. So I clecoed the cover plate in place, then clecoed the angle to the side skin, and traced the edge of the angle on the cover plate. This would be my outboard bend line. Then I drew a straight line aligned with the outboard edge of the quadrant cutout line; this would be the inboard bend line.

Making the first bend was pretty easy I just clamped two pieces of scrap wood at the line and pressed against the workbench to get the slight bend I was looking for. Making the second bend was less fun, as there was only about 1/2” between the two. I ended up clamping the whole assembly in the vice and carefully tapping the bend line with a piece of wood and a hammer until everything looked good. This didn’t get me the same crisp bend as the first one, but oh well. Some fine-tuning with the hand seamers, and it was time for a test fit. And it worked great!

That still left the issue of drilling the three screw holes to attach to the mount angle. I prefer to drill stuff like this in assembly, but it simply wasn’t possible here. Instead, with the angle clecoed to the side skin, I measured the distance from the side skin to each hole center, then marked the centerline of each hole on the skin. Once I had the cover plate in place, I transferred the lines from the side skin to the plate, then measured out from the skin to mark the center lines. I was a little worried about things not lining up, but it ended up fitting nicely. (well, after a few more rounds of tweaking the plate to get a nice snug fit to the quadrant itself)

Close-up look at the bend:

Boy, am I glad to be done with this. Now to resume tearing everything apart and getting some prep work done. I haven’t even looked at the instructions in weeks!

Not a lot of time tonight, but I ‘m finally back to semi-actual work; that is, doing stuff from the instructions instead of dealing with throttle stuff. Tonight I just removed the forward and mid left side skins, followed by basically everything that wasn’t permanently attached: gear tower plates, center section plates, auxiliary longerons, lower longerons. Then I did a little bit of cleaning up.

Now I think I can finally get to some deburring and countersinking and other fun stuff…

Well, not exactly a hugely productive day, but at least I did something…which is more than I can say for, oh, the past month. Funny how these little breaks happen…you decide to skip a day, then a couple more, and then you put some stuff in the garage temporarily and now you can’t work cause it’s in the way, so now you’re trying to make time to tidy up the garage before making time to work on the airplane…and so on.

Anyway, I finally got the garage tidied up, mostly. Today I finished up the cleanup and did some deburring on the forward longerons and some other small parts. There’s some countersinking to be done next, but I didn’t do that today. Next time…

Man, there’s a whole lot of prep work to be done. The first half-page or so of the instructions here specify a bunch of places that need to be countersunk to accept dimpled skin parts. When I looked at this over the weekend, I started marking the first item on the list, the lower longerons, with the intent of doing the actual countersinking in my next work session. Thing is, since I’m a little OCD (and cautious) about countersink depth, every time I use he cage, I feel compelled to readjust it. So every work day that includes countersinking has some built-in setup time. With that in mind, I decided to do all this countersinking in two passes; first, I’d set aside all the parts that needed to be countersunk, marking the locations as I went, and then I could go back and do all the actual countersinking in one batch instead of a bunch of little work sessions.

So tonight was just getting through that first step; finding the parts, deburring them as needed, then marking. Among other things, I marked the lower and auxiliary longerons, the gear tower and center section reinforcement plates, and the seat back support plates and spacers. That’s actually not all the things that need to be countersunk, but the other items are all large and unwieldy – the 16’ long upper longerons and the not-quite-as-long-but-still-cumbersome mid and lower aft longerons. Those, I think, merit their own work session. Plus the lower/mid aft longerons are still attached to the aft side skins, which are in turn sort of serving as a table for other parts.

In other news, I keep thinking about rearranging the garage, but I’m just not sure how to go about doing it. Space was pretty tight when I had the fuselage temporarily assembled, and once I get things back together and somewhat structurally sound, I’m going to want to put the fuselage in a rotisserie setup to make it easier to work on. That’ll mean even more length to the fuselage assembly, and thus an even tighter garage. Problem is, I’m just not sure how to go about making this extra room. If I could get the wings out of the garage, that would help, but I don’t have anywhere else to put them.

So I dunno. I’ll have to solve this problem at some point, I’m just not sure how yet. One solution might be to rent a self-storage unit for the wings, but that’s money out the door that’s not going to actual building – plus moving the wings to/from storage would be obnoxious since I don’t have a pickup truck or trailer. Maybe I can figure out a better use of space in the garage…

UPDATE: So I went back out in the garage and did some thinking and a lot of measuring, and I think I have a workable solution for rearranging the garage. If the weather holds out, I think Saturday or Sunday might be a garage cleanup/reorg day.