Picking up where I left off yesterday, today I got to work finishing up those side rails. I clecoed the rails back on the fuselage so I could mark the trim at the aft end, then removed them again to get the trimming done. Nothing special here, I just roughed the cut on the bandsaw and then went to work with a file to finalize things. Making the relief cut for the aft screw heads was a bit more fun. At first I tried just filing the relief cuts, but quickly decided that would take about half of my remaining lifetime. Instead I did the rough cutting with the Dremel and a rotary file, then just used the hand files to finish up the shape of the cutouts.

Here, you can see the relief cuts, as well as the slight taper from the trimming:

Then it was just a matter of getting the rails screwed in place on the fuselage. Next up was the anchor block back behind the rear seat; this was the only remaining component that wasn’t attached to the airplane yet. The anchor block just attaches with two screws through the back seat bulkhead. The location of the two holes is specified relative to the anchor block itself, but they actually get drilled through the bulkhead first, so a little math and thinking is required to get the layout right.

Next, the block needs some more work: on the forward side it needs to be countersunk to accommodate the dimples in the bulkhead, and on the aft side it needs to be counterbored for the attach nuts. Since the receptacle area is pretty right, the nuts get pressed into the counterbored holes and become captive nuts. The counterboring part was a bit interesting; I’d seen another builder mention that the specified 1/4” depth wasn’t enough, and I saw the same thing. Going 1/4” deep doesn’t even allow the screws to engage the nuts when inserted into the block, much less with the additional thickness of the bulkhead in play. So I went up to 1/2” instead.

The fun here is that the nuts need to be pressed beyond flush. Getting them started was pretty easy using my vice, and to press them further in I picked a small socket from my wrench set that fit nicely inside the hole. This worked great for one nut, but the other one turned sideways somehow, and I had to drive it out with a punch and start over again. On the retry, I pulled the nut into place using a longer #6 screw instead of using the vice; this ensured that it went in straight.

So here’s the back end of the finished anchor block, turned upside down mainly so it looks more like a funny face:

That just left dialing the bulkhead, which was definitely easier said than done. None of the squeezer yokes I had would work in the tight space, and I was kind of at a loss as to how to proceed. At one point I was really considering putting the dimple dies in place and trying to squeeze them between the jaws of a big pair of pliers, but fortunately I didn’t go through with that…I think I might well have damaged stuff that way.

Finally I came up with an idea. The problem here is mostly with figuring out how to handle the female dimple die inside the receptacle…but really I just needed something in there with the right shape. For example…the anchor block itself. With the countersinks made for the flush screws, I thought it might just do the job of the female die. So I dropped it back in place, closed the canopy frame to lock it in place, and installed one of the screws for good measure. Then I stuck the mail dimple die in the arbor of my C-frame, lined it up on the hole, and gave it a good couple whacks. The resulting dimple wasn’t perfect, but no worse than what I usually get out of pop rivet dimple dies (which would have been the other option here, and I would have had to buy a #6 set). A little work with the #6 countersink made everything all right, and then I repeated the job with the other hole, then finally installed both screws.

With that, I now have a fully functioning sliding canopy frame, with the exception of the latch, which will come later. And I now really have nothing else to do but to start working with the actual canopy bubble. To prepare for that fitting, I got out the forward upper skin and clecoed it in place again. I’ll likely have to remove some of these clecos to accommodate the actual bubble, but that I’ll just figure out on the fly.

In the meantime, I have an even more airplane-looking device sitting out in the hangar:

So the goal for today was to get to the point of finalizing the placement of the side rails. Getting this done required doing some work with the frame itself to get the fit correct. The main goal was to get the sides of the frame to line up properly with the fuselage sides; this will ensure that the canopy skirt pieces fit nicely down the road when that time comes. The fit here is checked by cutting some thin strips of scrap aluminum, curling them a bit to match the curvature of the frame, and clamping them in place so their fit against the fuselage can be evaluated. With this done, we get a setup like this:

The previous photo was actually taken after frame tweaking, which is why the strips are fitting nicely against the fuselage. At first, though, the frame was a bit too wide, and the strips didn’t quite make contact with the fuselage, which meant I needed to squeeze things together a bit. The force for this was provided by a ratchet strap across the hoop at the front of the frame, but the other thing I needed was some way to reliably visualize how much I was bending the frame. This has more to do with the bending operation than the final dimensions of the frame, which can just be checked by re-checking the fit of the strips.

But for the bending portion, what I wanted to be able to do was to pull the frame to a certain point, relax and check the fit, and then pull it just a bit further on the next iteration. So I needed a good indicator for this purpose, and I went with a yardstick positioned across the top of the frame a little ways back, and clamped on only one side. To ensure precision, I put strips of masking tape on each frame and drew reference marks. The resulting setup:

After several iterations, I had the fit I wanted, with the strips just barely making light contact with the fuselage sides. At this point, I started making preparations for drilling the mount holes in the canopy rails. There are two prepunched holes towards the aft end of the rails, which get drilled from below, but the other four holes get laid out on the rail itself and drilled from above.

This was a spot where my level of trust in the plans was a bit on the low side. Not that I thought they were wrong, but more that it wasn’t quite clear where the reference point for measuring was, and it seemed a good idea to really understand where the rail mount holes would end up on the fuselage. The longitudinal measurements are made from the front of the rail – but my question was, did this refer to the very front of the rail, or the relief cutout I made to fit around the roll bar base?

The first hole was to be set 2 1/16” back; measuring from the back of the roll bar base put this hole just behind the joint between the aft spar carry through bulkhead and the canopy rail mount on the fuselage, which seemed like the right idea. But continuing to measure backwards, the third and fourth holes clearly needed to be positioned around the seat back support bracket – and starting with the roll bar base put the third hole obviously in conflict with that bracket, while the fourth one had lots of extra room.

This indicated to me that I should be measuring from the front of the rail instead; doing this moved all the holes forward by about 3/8”. Measuring this way, the third and fourth holes ended up nicely positioned around the seat back bracket, but now the first hole seemed to interfere with the carry through bulkhead joint. This seems wrong and baffled me for a good amount of time, but after evaluating the layout a bit more, I realized that the lateral position of the hole put it almost exactly between two of the attach rivets – which are spaced kinda far apart. OK, this was starting to seem a bit more reasonable.

Still, I was unsure, so before committing to anything, I went in and did some research – which yielded absolutely nothing. That is, no one saying “oh yeah this is how it works” but also not “oh no no no don’t do that.” That was enough for me to decide that the intent of the drawing was for this screw hole to go through the bulkhead flange.

So I drew the hole layouts on the bottom of the rails, intending to drill those pilot holes on the bench and then use them as a template later on. But before that, I laid each rail in place to recheck that the hole positions appeared rational. The only tweak I made from this fit-up was to adjust that first hole forward a bit, in order to have it land directly in line with the rivets in the bulkhead. To do this, I just laid a ruler along the rivet centerlines and under the rail, and drew a new mark to adjust my hole layout (the mark hasn’t yet been drawn here):

And so I finally got my mount pilot holes drilled in the rails…but then while reviewing he construction manual, I realized I wasn’t done tweaking the frame itself. The one adjustment left to be made was to get the proper vertical distance between the aft tip of the frame and the center slide rail. I figured this was unlikely to tweak the width of the forward end of the frame, but better safe than sorry.

The called-for spacing here is 5/8-3/4”, and I was well in excess of that. With a piece of 3/4” MDF on the rail, there’s still a good inch and a half of extra space:

To do the actual bending, I screwed a piece of scrap lumber into the tabletop, using a couple of 3/4” spacers to create a nice gap in the middle, with the entire apparatus spaced a few inches shorter than the length of the back end of the frame. This allowed me to tuck the aft end under the lumber and simply push down on the forward end of the frame to get my bending done. I would have preferred something more controlled, like I did with spreading the forward end, but I couldn’t figure a way to really do this with controlled force. Instead I just sort of estimated where the frame was sitting relative to my body while bending.

Here’s a look at the bending “jig:”

Also, rather than doing a lot of installing/removing the canopy to check the fit, I instead did measuring off the table for the rough bending. I already knew how much I needed the aft end to come down, so I set the frame on the table, measured the vertical distance from the table, and figured the new height I was going for. After a couple bending iterations, I was getting close and so I verified the fit on the fuselage before doing the final tweaking. It all ended up working quite well and now I’ve got a much nicer gap from the center rail:

After a final double-check of the fit – as I’d figured, the front of the frame still fir just fine – it was finally time to clamp the rails in place and do some drilling. This is kind of fun because it’s a little hard to work out a clamping strategy. Notably, the manual says you can also tape the rails in place, but that just seems nowhere near accurate enough. I ended up with a C-clamp at the back of each rail, and another about 6” back from the front end.

To position the rails for clamping, I started with the frame nearly full-open – just far enough forward that I could still get the clamps installed (once in, m the clamps would block movement of the frame). I got the rails set an equal distance in from each side of the fuselage, and with the rollers roughly centered, and clamped the back ends. Then the frame went forward and I repeated this exercise up there.

As a final sanity check, I measured the distance across the rails at a couple different spots. This showed that the front ends were about 1/8” further apart than the backs, so I did a little more adjustment of the spacing. I really would have preferred to be able to run the canopy through the full range of motion with everything clamped in place, but that simply wasn’t possible. In the end I just had to measure multiple times and then just kind of go for it.

Drilling started by taking the existing #40 holes (the four I drilled in each rail, plus the two prepunched holes in the fuselage) and using them to drill into the mating piece. The holes laid out in each rail were easy; the other prepunched ones were a little more fun. Those required laying inside the fuselage in various uncomfortable positions while wielding an angle drill (for the forward pair) and a cordless with a 12” bit (for the rear pair, which sit really close to the bulkhead behind the rear seat).

It was only after drilling all these initial holes, adding clecos as I went, that I finally got to test the full motion of the frame. Whew…no binding. That was a bit nerve-wracking.

Next, I needed to create access holes for the rearmost hole in each rail. All the other screws sit outboard on the flange of the rail, and are easily accessible from above, but the rearmost is inside the rail, so a larger hole has to be drilled in the top of the rail so a screwdriver can pass through for installation. This hole also had the benefit of allowing me to do all the rest of the drilling from above.

With the access hole done, the rails got clecoed back in place and I enlarged each hole first to #30, then to the final size of #21. Then I got to pull it all apart and deburr the holes I’d just made. Remember those forward most holes whose placement I worried about so much? While they didn’t quite land exactly between the two rivets, they’re pretty close, and are nicely in line with the row itself:

This was about the point where I was ready to call it a night. One thing I’d noticed earlier was that all the fitting had scraped up the powder coat on the roll bar base, so I wanted to touch those areas up before installing the side rails for good. So I hit those with the touch-up paint, and then as a last act took a look at those aft most screw holes in the rails. As mentioned before, the screw placement here is further inboard, inside the channel itself. A consequence of this is that the screw head actually interferes with a raised part of the channel, and I’ll have to relieve that a bit so the screw can actually sit flush.

The interference, along with my marks for making the relief, can be seen here:

So that’ll be a good spot to pick up tomorrow (which I happen to have off). I’ll actually need to do one more trial fit, because I forgot one thing: the outboard part of the aft end of the rail actually sticks out past the fuselage sides, and will need to be trimmed. I should have marked that before removing the rails tonight, but I forgot. That’s OK, there were much worse mistakes I could have made.

Once the rails go on for good, there won’t be much left but to start messing with the actual canopy bubble…

This past weekend I found a nice goody in the mailbox – a package from Van’t containing my replacement slide blocks. Yes, that’s “blocks” plural, because I ordered two of them, just in case I messed up a second time. Things have been busy since then but I got some time tonight to give this a second try.

Looking at the first block, I laid the holes out in what was a pretty good spot, but the actual holes ended up a bit lower. So for this attempt, I mostly focused in being more precise with the drilling, but also shifted the hole location up just a hair. As before, I used the center punch to spot the hole locations, but this time, instead of going straight to the drill press, I started the holes with a #40 drill bit I spun with my fingers. This way I could ensure things were starting off lined up. I also put together a spacer of scrap wood to put between the “ears” of the block to prevent the plastic from flexing while I was drilling; this was probably a big part of why the last block got mis-drilled.

From there, I opened the holes up gradually on the drill press; first a #40 bit using the holes I’d already started, then up to #30, and finally #12. That yielded a very snug fit with the pin, so I finished things off by running a #10 bit through both holes just using a hand drill; this gave be a better slip fit for the pin and also ensured both holes were collinear.

The first test fit on the canopy worked great; the anchor pin now sits just a bit above the center rail, and when the frame is slid all the way forward, the pin engages in the anchor block with the slide block fitting nicely between the frame and slide rail. With all that validated, there were some finishing touches to put on the block (or, as I thought about it, a few remaining opportunities to ruin the part).

First, one side of the block needs to be counterbore a bit to allow the clevis pin to sit flush. According to the plans this is required for the assembly to fit in the socket on the fuselage, though from my previous test-fit it worked just fine. But I’m not one to ignore instructions, so I used a 5/16” bit to make a nice little recess, so now the pin sits nice and flush.

The second thing that’s needed is a smaller hole from front to back on the block; this allows a cotter pin to be inserted through the end of the clevis pin and hold it in place. I was a little nervous about this since it required both precisely measuring the distance rom the block edge to the hole in the clevis pin, and also ensuring the hole was vertically aligned with the clevis pin hole. As before, I marked the spot and then started the hole by hand, before drilling all the way through with a #40 bit.

I think this is all that’s needed; there’s no real guidance given here other than “make a hole for the cotter pin.” I think the only thing that bothers me a bit is that the provided cotter pin doesn’t go all the way through the block, so it’s not really secured to my way of thinking. I’m somewhat inclined to look for some longer pins to use here, so they go all the way through the block and the ends can be bent out. Something else to think about…

For now, though, it’s done. Here’s a look at the clevis pin sitting flush, also showing the cotter pin head on the other side. I inserted the pin this way because with the canopy closed, gravity will be helping hold it in, for whatever that’s worth:

Here’s a better view of the cotter pin from the other side. Initially I’d thought of making the hole large enough for the head of the pin – or at least counterboring it like the clevis pin hole – but on second thought that’d make the pin really, really difficult to remove. Keeping the head exposed seems like a better choice to me:

Finally, we can see everything mating together nicely with the frame all the way forward:

Between the slide rail and the anchor block, the rear of the frame is rock solid in this position, though it can still move side to side since the rail isn’t yet secured. But having this done means I’m finally feeling confident about centering up the slide rail and getting it drilled and screwed into the fuselage – and once that’s done, the two forward rails can follow, and then I should be ready to move on to the canopy bubble itself.

So, the saga of the canopy fit continues. Yesterday I got in the special drill bits I’d ordered to open up the anchor block hole a bit. Good thing I ordered a couple sizes, because the amount the hole needed to be opened was more than I anticipated. But after a couple runs, the pin now fits in snugly, so all’s well with the anchor block.

Next up was continuing to consider the fitment interaction between the frame, anchor block, rail, and slide block. Taking care of the anchor block removed one variable from this scenario, but that still leaves two: the position of the hole in the slide block, and the position of the slide rail itself. Initially I was focusing on the rail itself. This piece basically has two “points” of contact with the fuselage, which in turn control its location. The first “point” is where the straight portion of the rail rests on top of the turtledeck. The second is where the bevel at the forward end contacts down inside the recess where the canopy drops in.

The goal I was going for here was to get the right gap between the canopy frame bracket and the slide rail – after all, in practice the slide block is what connects these two piece together, and it has to fit in that gap. To start with the gap definitely seemed too small, and the most obvious way to tweak this is to remove more material from the beveled area of the slide rail; doing this allows the rail to move further aft and increase the gap. So I filed some more material off the rail and fit it again, but couldn’t tell very well just how much the gap had changed. The reality is that it’s pretty hard to find an effective way to measure the gap in here.

So I decided instead to try something practical – I put the slide block on the rail, and figured I’d see if I could slide it in place between the rail and the frame. And while the gap looked on the small side, the block actually slid in place OK, though the fit was pretty snug. At this point, I decided to continue with this practical idea – if I could go ahead and drill the slide block, I’d remove another variable and be able to work just with the slide rail, and maybe even get everything finalized.

What I decided to do was to lay out the hold in the block such that the canopy frame sat as low as possible, so I measured the clearance between the pin hole in the frame and the edge of the bracket, and used that to work out the vertical positioning of the hole. For the horizontal positioning, I just put it on the centerline front-to-back. Then I went to the drill press and made the holes, before heading over to the fuselage to try a fit.

Unfortunately, I couldn’t get the pin to go through – the resulting hole in the block was a bit too low. There were a couple factors here – first, I probably should have given myself a little more margin for error when laying out the holes. But more importantly, when drilling the block, I should have put a wood block in the open center to help support things. With no support, the slide block wanted to deform a bit when I drilled, and I think that contributed to the holes wandering a bit too.

I didn’t quit at this point, though…I decided to see if I could work out a way to make this thing fit. It was probably already junked anyway, so I didn’t have a lot to lose. First idea was to open the hole in the block up slightly to #10 instead of #12…maybe that would give me just enough extra wiggle room to get the pin through. I reasoned that some slop here wasn’t a problem since this interface only locates the canopy frame when it’s open. Lo and behold, the slightly larger hole allowed me to get the pin through…but it took a good bit of encouragement. It was just occurring to me that this was still way too snug to work in the real world when I spotted another problem – with the hole in the block so low, the tip of the anchor pin was dragging on the slide rail. That took care of any brief thought I might have had to open the hole up even more – I’m not going to want that pin marking up the slide rail for the plane’s entire life. 

So it’s time for another parts order from Van’s, I suppose. As per usual, the part itself is pretty cheap, it’s just the shipping cost and the waiting that’s mildly annoying. Then again, I’ve got other stuff to work on around the house this weekend so maybe it’s not that much of a loss.