Elevator rigging refinement

Not a ton to report tonight, and no photos. My intent was to just have a short work session, mainly focused on getting all the rod ends installed correctly with spacing washers, and their bolts torqued down, to take the slop out of the system and get me setup for the upcoming work. Unfortunately this turned out to be easier said than done. The aft end at the elevator horns wasn’t too bad, despite access being a little hairy. The bell crank was actually fine as-is, and the connection for the aft pushrod there actually requires no washers.

The other end of the bellcrank, though, is where things got fun. This spot calls for a couple of thin washers to space out the rod end. Presumably this is to account for lateral movement – since that rod is connected to the control column, it’ll move side-to-side a bit with roll inputs. The problem is, this is the bottom of the bellcrank, it’s in a confined space between the two baggage ribs, and it was hard enough just to get the bolt threaded in there, never mind trying to do the frustrating-in-the-best-of-circumstances work of squeezing washers in. I gave it several tries, and even went so far as to lay down boards in the fuselage, climb in, and try working on my knees – all to no avail.

So I ducked inside for a quick VAF search. And there was a brief moment when I thought I’d found the solution. Someone recommended removing the rod end from the pushrod, installing it on the bellcrank out of the plane, then putting then bellcrank in place and finally threading the rod into it. Seemed like a genius plan, except…the bellcrank can’t be installed with that rod end in place. The extra width means it can’t be loaded in from above, and it’s not physically possible to weasel it in from below.

I came pretty close to admitting defeat at that point, but then decided to take a totally different tact – just gluing the two spacer washers inside the bellcrank. The only concern then would be that sliding the rod end in might knock them loose, so to help with that I bent the two bellcrank ears out just a hair – they’ll be pulled tight again when the pivot bolt is torqued.

So that’s sitting on the workbench letting the superglue cure (yes, I used superglue…), and we’ll see if tomorrow I can go back to making useful progress on this thing. Tonight wasn’t a lot of fun, but it was still educational. Also, I can’t begin to think of how obnoxious it’d be to install these pieces with the aft top skin on. Rather than leaning over the side, I’d have to be lying in the cabin with my head stuck into the tail…that’ll be fun one day…

Posted in Empennage, Fuselage | Hours Logged: 1

Elevator rigging – first pass

So…not a ton of detail to provide tonight, despite this being a solid two-hour work session. Basically, what I did was install the control column + sticks into the fuselage, and then rig up the pushrods all the way back to the elevators. Seems straightforward, but there was definitely some tedium to be found here. In general, it was annoying working leaning over the side of the fuselage (really makes me miss being able to roll the fuselage with the rotisserie), and in addition to that, there are some interesting limited access spots, oh, and it’s just dealing with things designed to move around.

In the end, while I got everything hooked up, there’s a lot of slop in the system, because I didn’t go to the trouble of installing all the proper spacer washers on rod ends, or of torquing down any of those connecting bolts – I just threaded them through and put a nut on to keep anything from falling out. Since the point of all this rigging is to get the pushrods adjusted properly, and to set up the elevator up/down stops, I think I need to do all this the right way…even though it’s going to be highly annoying.

I did reward myself after all this was done bye installing the forward seat floor and front seat, then throwing in a lawn chair cushion so I could climb in and make airplane noises:

And I figured a short video of the sticks moving the elevators was worth capturing:

Posted in Empennage, Fuselage | Hours Logged: 2

Control column/stick fitting

As alluded to yesterday, today was all about doing the fitting work for the control stick pivot bushings. The nature of these joints is that the bronze bushing, when its pivot bolt is torqued, will be held in place between the “ears” of the control column. The control stick, in turn, will rotate around the bushing. With this in mind, it’s necessary to work down the ends of the bushings, getting them to the proper length to be trapped between the ears, as well as adding a slight angle to match the slight taper of the column ears.

I approached this task essentially in two phases. The bushings were a good 1/8” or so too long, so I started by removing material from the ends to shorten them to roughly the correct length, prior to working on the angle. To do this, I used my calipers to get a rough idea of the width between the ears at the widest point of contact, then used that to mark the bushing. Then I simply chucked the bushing into my drill, and clamped the drill into the vise to make a poor man’s lathe. I just used a vixen file against the spinning bushing to gradually remove material while retaining the square end profile:

Once the overall bushing length was about right – which is to say, I could slip it between the ears about 1/8” short of the pivot hole – I got to work on adding the angle. To do this, I put sharpie marks on one side of the bushing, at each end – these were to mark what would become the “high” point of the angle, that is, the widest point. Then I simply used a plain file to very gradually work an angle to each end of the bushing. This was just a trial-and-error process – tweak the angles a bit, do a test-fit, tweak them a bit more, over and over again.

Pretty soon – on a geological time scale, at least – I had a nice snug fit at both ends:

But this is only half the work for this particular pivot point. The next bit that needs attention is the sleeve on the control stick itself, in which the bushing rotates. This sleeve also needs to have material gradually removed, so that it’s slightly shorter than the shortest length dimension of the bushing. Since the stick rotates around the bushing, these ends need a hair of clearance to the column ears – but not too much, in which case the stick will be able to slide back and forth on the bushing.

This actually took more time than the bushing itself, partially because unlike the soft bronze of the bushing, the stick is steel. Additionally, each time I removed a bit of material, it raised a slight burr inside the sleeve, along with depositing removed material inside the sleeve. Both of these wanted to make the bushings bind, so each instance of removing material meant deburring the end of the sleeve and cleaning out the sleeve with a rolled-up paper towel. Oh, and the only way to really test the fit was to insert the bushing, orient it correctly in the column, insert the pivot bolt, torque it down, and see if the stick moved freely.

And then I repeated all of these steps again for the front stick.

Next up was drilling the hole that will allow for the rear stick to be removed. Nothing too crazy here, just laying out the hole points on opposite sides of the stick base, and drilling #12 on the drill press in assembly with the stick itself:

And then comes the real fun! Both sticks get bolted in place on the column, and the interconnect pushrod is threaded through the column and attached to both sticks. The length of this rod was previously set based on the plans callout, but now that can be fine-tuned; the goal is to get both sticks parallel. I started to try to figure out a way to use a tape measure to do this, before realizing this was a perfect job for the digital level – just move the forward stick to the limits of its travel, get its angle from level, then compare that to the angle of the rear. They were pretty close – only off by half a degree, So of course, I adjusted the rod ends to make that better, because filing those bushings really put me in a mood for precision. So now I have the sticks within a tenth of a degree of parallel.

And of course I had to take a photo of the assembly:

So that was a good solid work day. Looks like the next task will be hanging this assembly in the fuselage, and then presumably connecting it to the elevators themselves. Which probably means that I’ll have no choice to sit in the fuselage and make airplane noises…

Posted in Fuselage | Hours Logged: 4

Control column stuff

Well, today was mostly a lazy goof-off day, so not a ton of progress. I got the final pushrod done – just had to prime the inside of the thing, get the rod ends inserted and riveted, and that was that. That let me move on to the next big thing – the control column.

The basic deal with the control setup is this: we start with the control column, a large tubular thing that hangs from two rod-end bearings, fore and aft. Roll inputs will cause this entire assembly to swing left/right, sort of like a pendulum, from those bearings, and attach brackets at the bottom of the column will move the aileron pushrods. Meanwhile, the control sticks mount on pivot points at the forward and aft end of the column, which allow for pitch input. These inputs move the three longitudinal pushrods I just got done prepping.

The first operation here is to work on those pivot points between the column and the sticks. The sticks pivot on bronze bushings, which will be trapped between the column parts when torqued down. Since there’s some variance in the control column weldment, these bushings first need to be worked to establish a nice snug fit in the column. This is made especially fun because the two “ears” on the column, between which the bushing sits, are not parallel, which means I’ll have to not only trim them to length, but also put a matching angle on each end of the bushing. If I just made the ends square, then torquing the pivot bolt would tend to bend the bushing a bit, thus binding the controls.

So anyway, I didn’t do any of that today. I did get the various pivot holes final-drilled on the column, and then did some finish work on the bushings and their matching channels in the sticks to get a nice smooth fit. Out of the box, both bushings fit pretty tight and didn’t easily move. A little bit of work with some emery cloth on the channels, plus a little polish on the bushings, took care of that.

It’ll be another day that I get going on the ends of these bushings. Maybe tomorrow.

Oh, and no photos, today, oh well.

Posted in Fuselage | Hours Logged: 1.5

Pushrods. That’s all, just pushrods

No, really, that’s all I did today, just work on pushrods.

First up was the large pushrod that will go from the bell crank back to the elevator horns. This one is made from large-diameter, thin-wall tubing. Just trim it to length, clean up the cut area, fit the rod end inserts, then mark and drill the holes. Marking the holes is kinda fun, you just stretch a strip of paper around the tube, fold it three times to make eight sections, then wrap it around the tube again and mark where each crease is – and now you’ve got eight evenly-spaced holes!

See, look, paper:

I recruited Josie’s help to get those holes drilled – trying to support the entire rod (which is a good 5’ long) while positioning it precisely at the drill press isn’t really a one-person job. Then there was a lot of priming, followed by some riveting, and this thing is done:

Next up, basically the same process is repeated for the smaller of the two pushrods; this one will connect the bellcrank to the rear stick. This one is smaller-diameter tubing, but with a thicker wall, and the rod end inserts here are male instead of female. Additionally, the inserts here are plated, unlike the previous ones, so they don’t need priming. I got as far as drilling the small one, cleaning it up, and priming the outside tonight. I figure I’ll let that dry overnight and tomorrow I can deal with priming the inside and getting those inserts in place.

In between priming the second pushrod (ie while letting the coat on one end dry so I could then hold that end while priming the other one), I grabbed the third pushrod of the night, which will connect the front and rear control sticks. This one, at least, is prefabricated, with the inserts already in place and the whole thing powdercoated. All I had to do was thread in the proper rod ends. Well, actually first I had to clean the thing, because mud daubers had built nests in both ends of the thing. I ended up having to run a tap through the inserts to get all the crud out.

But hey, now this one is done too:

And that’s it for tonight. Maybe tomorrow I can get that second pushrod done, and then move on to prepping the actual control column, which I believe is the next thing on the list. Which will put me a little bit closer to actually rigging the controls and making control surfaces move…

Posted in Empennage, Fuselage | Hours Logged: 3

V-stab mounted, elevator horns drilled

So in between smoking a turkey, eating said turkey, taking the obligatory post-turkey nap, and giving the parents a call, I did find some time to get out and work on the plane.

First up was picking up where I left off on the vertical stab. I laid out the four extra rivet holes, as directed by Van’s to account for the edge distance issues, drilled them in the splice plate, and then used those as a guide to drill through the spacer and spar. Then I deburred the new holes before riveting everything together:

Then it was back over the fuselage, where I bolted the stab in place, semi-permanently this time:

Next up was drilling the elevator control horns for the pushrod attach point. These holes aren’t pre-drilled, as the horn parts frequently have some variance in them; it’s for the same reason that the pivot holes in the horns are drilled in assembly as well (waaaay back in the empennage build phase).

To start with, both elevators are clamped into a neutral position, in line with the stab. The position of the horns is examined, and the one that’s furthest back is chosen as the on to drill the first hole in. The reason for this is that the hole is laid out relative to the forward and bottom edges of the horn, to ensure proper edge distance. Since the second horn will be located further forward, we can be sure that the edge distance there will be OK as well; if we did it the other way, we’d potentially have an edge distance violation on the second horn.

Anyway, in my case the right horn was further back, so I laid out and then drilled the bolt hole there (note that here I’ve moved the left elevator to get its horn out of the way for the photo):

The next challenge is to drill a hole in the other horn in the matching location. The problem here is that there are a couple inches between the two horns, so we need to make sure that we drill straight across. To do this, a drill guide block is made from hardwood. In my case, I reused the piece of poplar that I’d previously used as a drill block for the horizontal stab. I had to trim it a bit to get it the proper width for a snug fit between the horns, and then I drilled a new 3/16” hole using the drill press to make sure it was properly square. Then the block gets clamped between the horns, in alignment with the first hole:

And then the hole gets drilled:

And that’s it – a quick pass with the deburring tool to clean up the holes, and these guys are now ready to accept the pushrod, which I’ll be fabricating next.

Posted in Empennage, Fuselage | Hours Logged: 1.5

More elevator work

Not a lot of time in the shop tonight, but I did get the elevators fixed up where they move freely. After some more experimentation, I determined that the right elevator was OK, and it was only the left one that was binding up. I arrived at this conclusion by torquing down all the hinge points, then loosening the center bearing bolt. When that’s tight, it pretty effectively ties the elevators together, so it’s hard to tell if only one side is binding. With it loosened a bit, the right elevator moved freely, but the left one still wanted to stick a bit.

I ended up pulling the left one off and bringing each rod end in half a turn. After that, getting the center bearing bolt through was a lot easier, verifying my suspicion that that was the source of the binding. And once I torqued everything down, both elevators move nice and free now.

And yes, it really took an hour to do this. Installing and removing every single one of these bolts is tedious, especially the center one.

Next up: finishing and installing the vertical stab, then some control system work.

Posted in Empennage | Hours Logged: 1

Elevator spacer stuff

So I did hear back from Sterling at Van’s today – as expected, there’s a simple fix for my edge distance issues, and it’s just adding another row of rivets. But for tonight, I decided to go back to working on the elevator spacers. My reasoning here is that once I get the vertical stab squared away, I’ll want to bolt it back onto the fuselage, but having it there will make access for the spacer stuff annoying.

So on to that topic – here’s a look at the center bearing area, with just the left elevator in place:

Of interest here is the gap between the bearing itself and the elevator horn to the left. This is the gap that needs to be filled with a spacer. A missing or badly-sized spacer would mean that, when the bolt through the center bearing is torqued down, a side load is placed on the other elevator hinge bearings. The plans call for stacking washers here, but the preferred method for getting really nice elevator movement is to fab up spacers to really get the thickness precise.

So I went to town on my little aluminum pieces from Ace, worked them down to size, and then installed the bolt through the center bearing. Wheee:

However, things aren’t quite right here. With everything torqued down, the elevators move without noticeable effort, but stop immediately when I let go. I’d prefer to have them move a bit more freely. I don’t think this is an issue with the spacers, though, especially because when I placed the center bearing bolt, I had to work it a bit to go through the horns and the bearing. Not a lot, but I suspect even that bit of force is enough to bind things up just a hair.

To verify this, I decided to remove the bolts through the middle hinge point on each elevator. This was to test the idea that one or more of the elevator rod ends (which serves as the hinge on the elevator) maybe needed adjustment in or out – that is, all three holes weren’t in the same axis. And I found that with those two bolts removed, the elevators moved quite freely.

I think I may just need to go out half a turn on both inboard rod ends…but doing that means removing some annoying bolts (especially the center bearing one), so I called it a night rather than go further down that rabbit hole. Unfortunately, getting this right is just going to require some tedious trial and error.

Posted in Empennage | Hours Logged: 2

V-stab fitting: pt 2

After attending the usual Sunday morning coffee club meeting here at Sport Flyers, and then enjoying some lunch, I got right back to work on getting the stab fitted. When we left off yesterday, I’d done the initial setup of the strings I’d use to properly position the stab. However, after thinking about the setup overnight, I decided to do some fine-tuning.

First, for the string going through the rudder hinge brackets, instead of having it hang on a plumb bob, I instead pulled the slack out and just let it be stretched between the top and bottom brackets. Using the plumb bob is good for checking true vertical, but I don’t need that – I just need to be sure the brackets are in a straight line. So stretching the string is actually better for that.

Second, for the longitudinal strings, last night I’d tried just tying the ends of the string to checks in the forward upper brace. The thing there is that the string isn’t necessarily perfectly positioned on the rivet holes, since it could come off the cleco on either side. Also, it was difficult to pull the string taut and get it clecoed, and I wanted some good tension on the strings. So I tied up two short loops of string, each one attached to a split ring, and hung one on each cleco. Then I tied my actual one string to one split ring, and tied a trucker hitch on the other one, which let me get some good, solid tension on the whole setup.

That meant it was time to start doing the actual alignment. The basic idea here is that the forward spar is clamped to the joint plate to the h-stab, and that interface can be moved laterally to fix the longitudinal alignment, and vertically to get the hinge brackets in alignment. But there’s a problem here – in addition to the joint plate (which is clecoed to the h-stab) and the rudder spar, there’s also a spacer between the two. And that spacer needs to be carefully aligned with the joint place. Well, this gets fun, because as you move the rudder spar around to get alignment going, the spacer moves around. And then when you try and move the spacer, the stab wants to move around. This pretty quickly seemed like an exercise in frustration.

So I came up with an alternative method. I placed scrap lumber across the top of the h-stab, under the bottom of the vertical, and used that to support the weight of the front of the stab. Since the bottom of the stab skin slopes downward, moving this lumber setup forward or backward moves the nose up or down, allowing the hinge alignment to be worked out. And the stab can just be moved laterally to get it properly on centerline. Small clamped hold the lumber in place on the h-stab, and two quick-grips on either side of the vertical prevent it from moving laterally when I don’t want it to. And the real payoff is that the spar doesn’t need to be clamped to the joint plate, so the spacer can be easily and carefully positioned without disturbing the position of the vertical stab.

A look at this setup:

And a look at the forward spar, with the spacer lined up properly and clamped in place:

Then it’s time to double- and triple-check the alignment before drilling. The string through the rudder hinges is bang-on:

Back up front at the joint plate, we’re just using the prepunched holes in the joint plate as a drill pattern. The bottom row is easily access with a long drill bit. The middle row requires the use of an angle drill. The top row seemed impossible to access with the stab on the plane, so I decided to stop drilling here, remove the stab from the plane, and drill the last four on the bench. Even then, I had to switch to a super-short #30 bit in the angle drill to get in here. The basic issue is that the forward spar and the root nose rib form an acute angle, making things tight.

Here’s the whole setup prior to me pulling it off to finish the drilling:

At this point, I was ready to just pull everything out, deburr the holes, rivet that joint plate and spacer on, and bolt the stab back on, this time semi-permanently (ie long enough to get some control systems put together). Unfortunately, when I removed the joint plate and spacer, I found a major problem. The bottom row of rivet holes is far, far too close to the end of the spar:

Minimum edge distance between a rivet and the edge of the material it’s in is 2x the rivet diameter from the hole center (or, by extension, 1.5x from the hole edge). For these 1/8” rivets, that makes the minimum edge distance from the hole edge 0.188”. The actual distance here varies from 0.129” all the way down to 0.103”. This isn’t just a case where things are a hair too close, this is a significant discrepancy – almost half of the margin gone in the worst spot. Moreover, these are the rivets that will hold the vertical stab onto the airplane, which is to say that they are in a structurally critical area. This is not a place where I am remotely OK with reduced margins.

Some searching on VAF reveals that this isn’t an uncommon problem (not surprising since you just blindly chop off some of the spar before fitting anything), and it sounds like the Van’s-recommended fix is just adding another row of rivets. There have been times when I’ve had a goof and reading secondhand Van’s engineering recommendations has been good enough for me, but on this case, I’m definitely going to email Van’s support and get a real, solid professional opinion.

Anyway, the end result of this is that that was the end of work for the day (I had other stuff to do around the house anyway). I’ll pick back up on the stab once I get a remedy from the mothership, and in the meantime I can probably go back to re-fabbing the center bearing spacers for the elevators. I’ll want to do that with the vertical stab off anyway, since its spar makes access to that area more difficult, and I need to work this out before I move on to rigging up the elevator control system.

Hopefully the Van’s office isn’t closed all week or anything like that…

Posted in Empennage, Fuselage | Hours Logged: 2

V-stab fitting: pt 1

I managed to get in a solid afternoon of work today, after meeting my brother and his wife for lunch as they were passing through town. As fun as it was to clamp the v-stab in place yesterday, the first order of business today was to take it right back off and move to the workbench, where I set about trimming the forward spar. It seems slightly odd to me that I have to do this – it’s not trimming to fit anything, it’s just a blanker “remove this much” directive. I guess maybe this part is shared with another model, and in that case the full length is needed? That’s all I can think of…

Anyway, with the spar trimmed, the stab got clamped in place yet again, this time in a more semi-permanent manner. The first major operation is to lay out and drill the bolt holes that attach the rear spar to the aft bulkhead. Initially, the rear spar is held on by a single cleco, on which it can pivot. This mean that before the bolt holes can be drilled, the stab has to be carefully positioned so it’s perfectly vertical. The method for checking this is pretty easy – just measure from the tip of the vertical to each tip of the horizontal, and tweak the positioning until the measurements are equal. And really, there’s not a lot of tweaking to be done – the lower portion of the rear spar just barely fits between the aft side skins, so there’s barely any room for movement. Once the positioning is set, then the rear spar is clamped tightly against the bulkhead to hold it in position. I, of course, rechecked the positioning after clamping, because I kind of expect everything to move when I’m not looking.

Now comes the really fun part – laying out the three lower bolt holes. I found the plans to be difficult to follow here, and even figuring out the easy part – the lower/center bolt hole – took some looking. Finally, I figured out that its vertical position was established by using a line drawn between two flush rivets on the bulkhead. The horizontal position was easy, it just went on centerline.

The top two were quite a bit more fun. In a similar situation to the h-stab, there are two critical pieces here that the bolts will go through. On the aft side, on the stab spar, there’s one half of a hinge bracket, whose edge faces downward. On the forward side, there’s the tailspring weldment, whose edge faces up. The bolts must pass through both pieces and maintain sufficient edge distance.

The plans give some measurements with which to lay these holes out, but they made no sense. In fact, they made little enough sense that I went inside to look at my electronic plans, suspecting that there might have been a revision – and I was right. The new planes were much clearer, though the overall guidance was “make sure to maintain edge distance on the bracket and weldment.” So I decided to dispense with the plans measuring meshing – which uses the low/center bolt hole as a reference, and gives a vertical offset – and instead plotted out the position of the tailspring weldment, drew it on the hinge bracket, and located the bolt holes midway between the two lines.

I did this by using a piece of aluminum angle, just long enough to sit on top of the auxiliary longerons in the tail, and I kept trimming a bit off one side of the angle until that side was flush with the top of the weldment. Then I was able to take that same piece, hold it against the hinge bracket, use the longerons as a visual reference, and draw a line. The rest was cake, just getting the midpoint lines and then a vertical line with the proper offset from center.

The resulting layout, center punched and ready for drilling:

These holes will be for AN4 bolts, so the holes eventually get to be 1/4”. I started with #30 pilot holes, again using my hardwood drill block to ensure square holes, then opened them successively to #12 and 1/4”. At that point, the stab came off again so I could deburr the holes and ensure nothing was getting trapped between the spar and the bulkhead, then it went back on and bolts went into the three new holes.

Next up was using the angle piece on top of the aft deck as a pattern and drilling two more bolt holes through the stab spar, this time for AN3 bolts. The bolts went into those as well.

Close up of the three lower bolts:

Longer shot showing all five of the bolts I made holes for:

That settled all the attach work for the rear spar, the next part is the real fun. The forward attach point must be carefully positioned, to achieve two goals: 1) centering the stab on the fuselage centerline and 2) keeping the rear spar straight – the hinge points need to be in line for the rudder to move freely. Working out all this positioning requires some setup work.

First off, as a reference for centering the stab, a string system is set up along the longitudinal axis of the plane. The manual calls for using a piece of wood or striaightedge across the rear of the spar, and running strings from either end to a centerline reference towards the front of the plane. I chose to use an 18” piece of aluminum tubing instead of wood; instead of having to tie two pieces of string, and ensure they were both perfectly position, I just ran the string through the tube and, from each end, to the front of the plane. By ensuring the tubing was properly centered on the stab, the strings would in turn be positioned correctly and incapable of moving. Centering the stab then becomes a matter of measuring from each string to the side of the stab, and moving the forward end until the measurements match.

Getting the rear spar straight is simpler; the manual calls for using a straightedge, but this seemed like a perfect opportunity to use a plumb bob and string as well. Just run the string through the hinge bracket holes, secure it at the top, and then keeping the spar straight just means ensuring the string stays in the center of the holes.

A couple pictures of the resulting setup:

I didn’t actually do any positioning work yet. I think i want to refine the longitudinal strings a bit (mostly getting them nice and taut) before I go measuring, and by this time it was about time to call it a night. So I’ll maybe pick up tomorrow with the positioning, and see how that goes.

This thing is looking more airplane-y by the day…

Posted in Empennage, Fuselage | Hours Logged: 4.5