Fuselage

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…

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…

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.

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…

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:

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…

No build activity yesterday, thank to some other stuff going on, but today I got a few hours. My idea of gluing the spacer washers inside the elevator bell crank worked out nicely, and I started off today by reinstalling the bellcrank and pushrods. With everything aft of the control column torqued down, the play in the system was all but gone, so the first step was to clamp the elevators in-trail and then adjust the large aft pushrod until the control sticks were vertical. I measured this by just sticking the magnetic smart level to the stick. It only took a couple turns of the forward rod end to get things nailed down.

That meant it was time to move on to the elevator stops. These are two pieces of aluminum at the tail, positioned so that the elevator control horns contact them at the extreme ends of their travel. Elevator travel is set up by trimming these pieces until both horns contact them at the desired limits.

The rear stop is pretty easy to get to – it’s a piece of angle that also bolts to the vertical stab. The forward one is a different matter – it’s a piece of flat stock that sits between the aft deck and a piece of angle on top of one of the bulkheads. Also there’s hardly any clearance in front of the horns to get to it. Basically, tweaking this piece was going to involve removing it, removing material, then reinstalling it…over and over and over. But I couldn’t even get a straight look at the thing with the vertical stab in place – so I ended up deciding to remove it. It’s beyond me why they have you install the vertical stab prior to trimming these things, there’s absolutely no need for it to be in place at this point.

Anyway, the elevator down travel (controlled by the forward stop) was already sitting within the allowable range (20-25°), so I figured I could probably get away with just removing the material necessary to get both horns to come into contact at the same time – remember that they’re not perfectly in line, the right on sits slightly aft of the left. I used drill bits as discount feeler gauges to figure about how much material needed to be removing, then got the stop out and went to work. It only needed about 1/16” off the one side to even things out:

And I only ended up needing to remove/reinstall it a couple times before everything contacted at once. Here’s a poor attempt to show this piece place. The horns  and center bearing are visible in the foreground, and to the left the stop piece can be seen peeking out from under the aft deck:

The rear stop was much more straightforward. As before, I figured out the rough amount of material to remove to account for misalignment of the horns, and did that work off the airplane with a cutting bit in the Dremel. The rest of the tweaking I did with the stop in place, filing away at each half of the stop. At first I made no effort to make things smooth, I just wanted to be removing material where the horns made contact:

Once the travel was correct and the horns were both making contact at the same time, it was time to remove the stop, make the transition between halves nice and smooth, and clean up all the rough edges:

And then it was time to final check the travel one more time. Acceptable ranges for up and down travel, respectively, are 20-25• and 25-20°. I ended up with just under 25 down and 26 up:

Then I reattached the vertical stab, mainly because it’s about the easiest way to have it stored in a safe place. Next step by the book is to do the rudder control stops, but I think I’m going to diverge from the plans here. The factory rudder stops are small angle pieces mounted outside the tail, which contact the rudder horn at the extremes of its travel. But there’s an aftermarket solution as well – a piece of delrin that attaches to a rudder hinge bracket, and limits the travel by contacting the spar. This will make the tail a little bit cleaner, and should also be less trouble to adjust. Problem is, I don’t have that part on hand yet, so I suppose I’ll order that tomorrow. In the meantime, I can move on to installing the flap motor.