Finishing up canopy frame stuff

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:

Posted in Canopy | Hours Logged: 3.5

Fitting the side rails and tweaking the canopy frame

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…

Posted in Canopy | Hours Logged: 5

Attaching the center slide rail

OK, it’s time to get back to airplane working again, after a week or so of Other Stuff® going on. Today I decided it was time to grit my teeth, make some holes, and get this center slide rail installed.

Doing this meant first removing the canopy frame and the rail so I could mark a centerline on the turtledeck, which I did by stretching a piece of string between the forward- and aftmost bulkheads. With a few Sharpie marks made, the canopy rail went back in place, as did the frame. The latter was to ensure that I kept the spacing I wanted up in the receptacle area, with the slide block, anchor block, and so forth.

I already had the pilot holes in the rail from before, so I used those to initially drill #30 through the skin, which was easy except for the hole in the forward end of the rail. This sits down inside the receptacle area, and there’s absolutely no space to get a drill in there. That’s probably why the instructions said to drill this hole from the inside, but I couldn’t figure how I’d position it accurately doing that, which is why I drilled the pilot hole.

Getting this hole drilled was fun; I resorted to putting a short threaded bit for the angle drill into the pilot hole, and spinning it by hand – a lot – until I had a decent little pit created in the receptacle floor. With the rail removed, I then (just barely) had enough room to get in there with the angle drill and make the hole.

This brought me to getting the holes to final size for the #6 attach screws. I discovered while doing this that, for some reason, I have a #28 drill bit for this (which is a good snug fit for a #6), but my countersink bit has a #27 pilot. Which means I had absolutely no way of drilling the screw hole and then countersinking it. To solve this problem, I countersunk the holes while they were still #30, using that bit, and only then opened them up to final size. Sorta roundabout, but it got the job done.

Finally it was time to go crawl back in the tail again. With Josie holding the screws from outside, I installed the nuts and washers from inside, and also opened that forward most hole to #28 from inside – which apparently was an operation that needed to be photographed:

After that, I got the frame installed once again, and tested canopy movement. Strangely, the slide block seems to bind up just a little bit – not enough to prevent movement, but it seems to drag a bit. Something to look at later on, I guess.

I’d intended to clamp the side rails in place, but discovered that I’m not entirely sure how to do that. Probably not a difficult problem, but it made a good excuse to call it a night. In the meantime, here’s a look at the installed rail:

Posted in Canopy | Hours Logged: 2

Canopy slide block do-over

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.

Posted in Canopy | Hours Logged: 1.5

Firewall planning

So not a ton to talk about tonight really. Initially I’d figured on threading those CPI2 harnesses back through the firewall and getting the pertinent harness bundles laced for hopefully the final time…but then I got to thinking about whether that was a good idea. The whole reason I had to wait until I pulled the rest of the harness through the firewall is that the engine side of the CPI2 harnesses are already terminated, meaning they have to be threaded through bulkheads from the engine compartment. Thing is, that firewall passthrough may not be the only place I need to thread them. For example, one of the ignition coils will be mounted on top of the engine case, which means that harness will presumably have to pass through the baffles.

Now, that might not be a huge deal down the line – the coil connector plugs can probably be depinned if necessary, I’d just have to identify the connectors and get the right tool. But the crank sensor is a different matter – the wire connections aren’t detachable there. I’m not 100% sure whether or not those wires will need to pass through baffles, but in the end it seemed that the better choice here was to wait on these bundles. I might well end up with a chicken/egg type setup here, though…if I wait until I’m doing the engine baffles, that’ll mean I’ve fitted the cowl, which almost surely would require that the forward upper skin be riveted in…and once that’s done, finishing up the harness bundles will be a lot less fun. But still, I have little to lose by waiting; there’s nothing at stake right now other than me wanting this task done.

So instead I turned to the firewall layout. Some low-hanging fruit here was to go ahead and mount the brake fluid reservoir and cabin heat control box, both of which already have prepunched holes in the firewall. Getting the brake reservoir in place also required riveting a couple nutplates, which I guess were skipped way back when I first did the firewall. The heater box I just clecoed in place for now; it’ll need to be sealed when I final-mount it, and even though that’s still just using a couple bolts, I figure I’ll wait on that.

From that point forward, I was kind of on my own. The one thing that I figured I’d definitely lay out was the manifold block that’ll be used for the fuel and oil pressure sensors. The FWF drawings provided specify a location for that block, and while I don’t necessarily have to abide by that, I see no reason not to. Rather than actually mount it – I’m definitely not ready to commit to anything like that – I just drew an outline of the block and marked the two hose attach locations.

It’s not much, but it’s a start:

The next thing I tried to tinker with was the location of the battery box; since this is a relatively large item and accessibility is a concern, it seems like something to work out early. The FWF plans call for putting it on the right side of the firewall, about halfway up; I’m sure I’ll end up on that side of the firewall, but I’m less enthusiastic about the vertical location. The big question is how to tie the box into the firewall angles; they’re not exactly conveniently located for this. I suspect I’ll probably end up needing to add another angle on the back of the firewall to accommodate this, but the main takeaway is that this requires some thought. Something else to mull over a bit, I suppose.

Of course, somewhere near the end of the night I remember that I could also have been working on stretching the engine mount to better fit the firewall mount holes. Maybe I’ll work on that next; I’m sure I’ll want to install and remove it a few times while working out some of this firewall layout stuff.

Posted in Firewall Forward | Hours Logged: 1.5

Finishing with the engine mount, doing some wire routing

As I headed out into the hangar to get to work this evening, it occurred to me that I hadn’t had a single super bright idea about how to stretch out this engine mount to get the second pair of holes drilled. All that random thinking about making a jig with threaded rod and so forth hadn’t gone anywhere concrete. So I ended up just trying to stare at things and work out a solution, and eventually I got to something.

Basically, there are two ways to approach this: either I need something inside the mount exerting outward force to spread things, or I need something pulling down on the bottom of the mount. The latter seemed impossible since I had nothing to pull against, but finally I realized that if I stopped thinking in terms of using something like a ratchet strap, there were other ways to approach this. What if I could just hang weights off the bottom of the mount and try to work with the positioning that way?

And that’s how I ended up with this amusing Rube Goldberg setup:

We’ve got a 30-pound kettlebell hanging on the center of the mount, using an S-hook normally reserved for hanging up a caliper while working on the car brakes, plus another 30 pounds of dumbbells lashed together with some spare paracord and hung from the corner with more spare paracord. The only real issue with the hanging-weight idea is that you don’t have a lot of fine control over how much the mount stretches, and that’s where the big clamp comes in. Hanging the weights as shown here got the hole just a tiny bit above where it needed to go, so with the clamp in place, I could carefully apply that last bit of force to get it all lined up nicely.

The only remaining issue was how to pull the mount snug against the firewall while doing this; as it sat, the mount face wanted to sit about 1/4” off the firewall. I initially tried using a ratchet strap secured to a long piece of lumber going through the center section, but the strap would have been bearing on the edges of the forward side skins and the firewall flange, and surely would have bent something if I’d started cranking down. Then I had another epiphany – the other lower hole could be used for this. I just had to run a 3/16” bolt through the hole and the mount, add a large washer so it’d bear against the mount hole, and tighten the whole thing down.

That pulled both lower holes up nice and snug, and once I had the lower right hole drilled and bolted, the other was already lined up nicely and didn’t even need any drama to get it set up. The only concern here is how annoying it’ll be to attach this mount unless I permanently stretch it, so I’ll probably have a go at that at some point, but not tonight.

Instead I decided to continue thinking about FWF type stuff. One item I’ve been putting off for a while is drilling the 3/4” hole down the right side of the aircraft for all the engine sensor wires and such to pass through. That seemed like a nice digestible project for tonight, so I got to it. I’d been thinking that laying the hole out properly would be a challenge, but once I got down to it it wasn’t tough at all. The only hiccup I had was that the unibit drifted a bit as I was opening the hole, and got into the edge of one of the firewall angles, so I had to then go in with the dremel and sanding drum to smooth things out.

Once that was done, I installed the snap bushing and had the fun of feeding the wire bundle through from inside, and now I’ve reached the milestone of having random wires sticking out through the firewall:

Assuming I don’t get that replacement canopy block in sometime soon, I think I might start marking up the firewall for component locations, just to sort of spitball ideas. The FWF plans include some suggested layouts that I’ll likely start with, but I’ll have to consider some other items not shown there that I’m adding – like the battery-bus fuse block and E-bus relay. Those are pretty small but they still need homes, and routing of wiring is also a concern.

The other item I could work on now would be feeding the CPI2 FWF harnesses back through the firewall and finishing up the lacing of the relevant harnesses in the cabin. Those had to wait until now, as they’re already terminated no the engine side and so can’t be fed through in the other direction. It’d be kinda nice to finish up those harnesses inside, I suppose. We’ll see.

Posted in Electrical, Firewall Forward | Hours Logged: 2

Fitting the engine mount

Well, I’m still paused on the canopy front until I get in the replacement slide block from last week’s shenanigans, but in then meantime I get to kick off a whole new category with the first bit of firewall forward work. Most of the weekend has been spent working on other stuff around the house, but I wanted to keep making progress on something and so I decided to see about fitting the engine mount to the airplane.

The firewall and the structural bits behind it came with an existing pilot hole at each corner, and I drilled those holes out to 3/16” quite some time ago to allow for the fuselage rotisserie mount. The final bolt holes are 3/8”, but final-drilling those requires some attention, since individual engine mounts can vary even though they’re welded up in a jig.

So the first step is to do a rough evaluation of fit out of the box. To do this, I installed a couple of long AN3 bolts in the upper two holes and used those to loosely hang the mount in place. Doing this allowed me to establish a good starting point, as I could verify that the width of the two upper mount points were at (or very nearly) the same width as the two pilot holes. That meant I didn’t need to do anything dramatic to get those first two holes drilled…well, almost. The construction manual calls for drilling the holes using the engine mount as a guide, which I imagine helps ensure that the holes through the fuselage structure are in line with the actual mount sleeves. So the most interesting part of all of this was figuring out how to “clamp” the mount against the firewall. I probably should have gotten a photo of the final setup, which involved some ratchet straps going from a piece of lumber across the mount to the setback support in the cabin…

In any case, the upper two holes are now drilled and bolted in place. This gives me a nice base to work off of for the other two holes at the bottom: 

However, things down here are a bit less simple; the engine mount holes are a good 3/8” or so above the pilot holes in the firewall. I figured this out by putting flashlights inside the fuselage, pointed at the pilot holes; with that light sources inside, I can easily spot the pilot holes from outside, even if I’m looking through the engine mount itself. Note the pilot hole at the bottom of the engine mount hole, mostly occluded by the mount itself:

So in order to get these drilled, I’m going to need to rig something up to precisely stretch the engine mount. I made a first rough attempt at this tonight, which didn’t work so well. I figured since both lower holes are high, I’d see about trying to push both down, so I flipped one of my large hand clamps to make it into a spreader, and put it between the upper and lower center of the mount. I was able to move the lower holes by maybe 1/4” or so, but still nowhere near into alignment.

I’m not entirely sure yet how I’m going to work this problem, but so far I’ve had some vague ideas involving threaded rods, nut, and bearing blocks, but the hard part would be getting any of that stuff braced in the right place on the mount. Normally I’d prefer pulling for something like this, but I don’t really have anything to pull against…unless I were to put concrete anchors in the floor just for this one operation, and I don’t really want to do that.

So anyway, something to mull over. I’m sure it’s a solvable problem, I’ve just got to work it out.

Posted in Firewall Forward | Hours Logged: 1.5

More canopy fitting

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.

Posted in Canopy | Hours Logged: 2

Canopy frame straightening

Let me start by summing up this evening’s work: that was kind of frightening but ultimately successful.

I shared my thoughts from the last session on the forums and got some good information. Most notably, my suspicion about the anchor pin/block nesting was confirmed: the pin should be going all the way into the block, not just a little bit. That should settle my large gap issues up front…well, once I get the hole enlarged. The hole is currently 1/4”, and the next largest drill bit I have is 9/32. Checking the different drill bit diameters with my calipers, the larger one seemed like it’d be a looser fit on the pin than I liked. To verify this (well, to convince myself not to just drill the block with what I had), I drilled a 9/32” hole in a piece of hardwood I had lying around – which I figured was about the closest delrin analog I had – and test-fit it to the anchor pin. Sure enough, it had a bit of slop that I didn’t really like. On the one hand, it’s probably not super important that this be a really snug fit, but on the other hand, it’ll never be as snug as it is when I first fit things, so I’d rather go for a precise fit out of the gate. So I guess I’ll be hunting up some weird drill bit sizes. Since the pin already goes in, just really snugly, I probably only need to remove a really tiny amount of material.

Anyway, the other item of discussion was the frame misalignment. Here, no one said anything good or bad about my intent to bend the frame, which is pretty much tacit approval on the Internet. That is to say, people are really good about pointing out problems with ideas like this. So my main goal tonight (and what I actually did first, before the block stuff discussed above) was to do the bending.

I’d been thinking offhand about how to do this for a day or two, and had a pretty decent idea how to proceed. Basically, I needed to lock the forward part of the frame and then pull sideways on the back end. So I made my big table into a jig of sorts. A piece of scrap 2×8 screwed to one end of the table served as my clamp point for the forward end, with another piece of scrap used to actually clamp the frame. I drew reference marks to center the frame on the table, then drew a centerline back where the anchor pin was. I’d hoped to find that the pin was obviously off-center, which would make me feel a little better about the whole thing, but that wasn’t the case…it was pretty much dead-on, definitely not out by the ~1/2” I’d seen while fitting on the fuselage.

Here’s a look at the whole setup on the table. I’d originally intended to hand a plumb bob from the anchor pin, but I couldn’t find mine. I decided that a combination square would work just as well, so that’s what’s seen here. It’s also worth noting that, in the end, I added more clamps to restrain the front end, because it took a lot more force than I expected for this operation:

Back to the whole “not off centerline” thing: that really made me stop and think, just to make sure I wasn’t doing something horribly wrong. Eventually I reasoned that the practical fitment on the fuselage was more important than the centerline. I’d checked the thing on the fuselage multiple times, it definitely wasn’t right, and in the end it needed to fit the plane, not some marks on a table. So I drew a second line 1/2” from my centerline, to use as a reference, and got to work:

At first, I tried just doing the bending just by pulling in the frame. After all, the manual talks about correcting the bow with “carefully controlled muscle power,” and in any case starting small is a good plan. But it was clear before long that this wasn’t good enough – I got the pin to move a tiny bit, but nowhere near what was needed. OK, time to get some mechanical advantage involved, in the form of a ratchet strap. The fun part was figuring out how to rig this. I ended up finding a large eyebolt lying around, which I installed on the bottom shelf of the table, so I could take the strap over the edge and anchor it down there.

The other consideration was some way to keep tabs on how much I was moving the frame – it was highly unlikely I’d get this right on the first pull, so I needed some way to repeatably pull to where I’d stopped on a previous attempt, and then go a bit further. To handle this, I just laid a piece of thin scrap wood along the left side of the frame. As the frame was pulled sideways, it’d move the scrap wood, and that’d serve as a sort of max-deflection indicator.

Finally, it was time to start pulling. I put what seemed like a decent amount of force on the frame, then released…and the pin had barely moved. The deflection indicator came in handy here, since I could just increment my pulling by a couple teeth on the ratchet each time. All in all, it took probably five or six iterations to creep up on the deflection I needed.

The scary part was that I was putting a lot of force into the system in the end. At first this concerned me because I was sort of necessarily standing right in line with the strap – if it broke I’d probably get a nice welt, but if that eye bolt came loos somehow I’d probably be in a world of hurt. So I tried standing off to the side as much as I could, but then on the last pull I noticed how putting all that force on a single point was noticeably changing the curve of the right-side frame bow. Oh boy, if I ruin this thing it’s gonna be really expensive to get a replacement. After releasing that pull, I sighted down from the back of the frame…whew, seems to have sprung back OK.

Time to do the real check, with the frame back on the fuselage. Before removing it, I clamped blocks on the table to ensure I could put it back in the exact same place if I needed to bend more. Then it was time for another deep breath as I carried it over to the fuselage, slid the rollers back in, and closed everything up…

…and it fits beautifully. Not quite perfect – with the anchor pin centered, the right-side gap is still maybe 1/32” of an inch, but I’m very sure I can live with that.

That was enough fun for one night. I suppose next I’ll worry about the anchor block, then refine the center slide rail, and then see what other bending I need to do while I still have this jig setup in place. I know I need to bend the aft end of the frame down a decent amount, and I may want to spread the forward bow a bit to match the fuselage sides.




Posted in Canopy | Hours Logged: 2

More canopy frame head scratching

So the title sort of sums up tonight’s short work session, though I feel like I’ve got an idea of how to move forward with the fitting. I’m still going to let that idea marinate a bit before I try doing anything about it (plus I’m gonna run it by the Van’s forum people). Even better, tomorrow I’m flying a Young Eagles event and I see that one of the other pilots is bringing the RV-8 he built. Hopefully he shows up so I can pin him in a corner and pepper him with questions. You know, in a friendly sort of way…

Anyway, out of the assorted issues I outlined before, I felt like the first one to really consider was the large gap between the canopy and windscreen frames. As mentioned before (I think), the limiting factor on forward movement of the frame is an anchor pin at the aft end, which fits into a plastic block that rests against the back of the bulkhead just behind the back seat. One thought I had was to remove some material from that block to allow the frame to go further forward, but it seemed like I’d need to remove a ton of material. To help visualize how things might need to change, I decided to get the anchor block out of the picture entirely and see what kind of gap I could get with the anchor pin actually contacting the bulkhead – that is, as far forward as it could physically go if I went completely bananas on shaving down the block.

This seemed promising at first – looking at the gap on the left side (from where I was working), it was almost nonexistent. Using drill bits as crude feels gauges, the gap was about 1/16”, probably tighter than I’d want in real life. But then I noticed the gap on the right side was a good bit larger. I double-checked at the aft end to see if the anchor pin was centered, and it was. Hmm, seems like this frame is a little crooked. I was eventually able to get an equal gap up front, but only by shifting the aft anchor point as far right as it could go in the socket:

So it seems clear that I’ll need to bend the frame a bit to get both an even gap up front and a centered slide out back. That’s not too awfully surprising, it’s known that these frames almost always need some tweaking to get a final fit, though I wasn’t expecting a sort of twist like this.

But back to that gap up front – with the anchor pin touching the bulkhead and shifted as seen above, the gap was a nice consistent 3/16” all around, which seems like a reasonable number…until you remember that this is without the anchor block in place. At this point I started to get a twinge in the back of my mind, as usually happens when I’m getting subconsciously close to some sort of epiphany. The epiphany completed when I took another look at the anchor block and noticed that the hole for the pin went all the way through it – this wasn’t obvious until I removed the part sticker on the front side. All this time I’d been assuming that the intent was for the pin to barely engage the block, but now I think that’s not the case.

The pin itself looks to just be some rod stock that’s tapered to a point:

When engaging it with the block as provided, it slides into the block essentially until it gets to the end of the tapered area and stops:

Notably, at this point the engagement isn’t very positive. I didn’t think much about that before, but I was assuming the whole time that the hole in the block was similarly tapered to match the end of the pin. But it turns out that the pin can be inserted further, though it’s a pretty tight fit. It can, in fact, be inserted until it’s nearly sticking out of the front end of the block:

So that all homes in on a path forward to handle the gap issue: if the pin is able to freely drop that far into the block, the whole frame goes further forward and I no longer have the massive gap up front. And instead of shaving material off that block while trying to keep it square, I’d just need to open up that hole in the block a bit. Currently it’s a nice slip fit with a 1/4” drill bit, so I imagine the anchor pin is also 1/4” OD rod, and would slip in there nicely if not for the additional thickness of the powder coating. Probably I can just get in there with the next size up of numeric drill bit and remove a tiny bit of material, maybe still leaving the origin ID towards the front end to keep the tip of the pin from contacting the bulkhead and doing damage over time.

This, again, is an idea I’m going to run by the forums, and maybe by that -8 builder if I see him tomorrow morning.

As a final note, there’s going to be more frame bending to do in addition to trying to square the thing up. While looking over the manual section that talks about “massaging” the frame, it also mentioned “possibly” needing to bend the aft most portion of the frame for proper clearance from the slide rail. A glance at the plans says the appropriate gap is 3/4 – 5/8”. Yeah, I’m going to need to do some bending there, as my gap is currently way larger than that:

And that’s without even getting to possibly needing to expand the lower forward part of the frame for proper alignment with the fuselage sides. The alignment there doesn’t look too bad offhand, but I’m going to want to add some aluminum strips as per the manual to really properly evaluate things. Bottom line, I see a lot of trial-and-error application of force in my future.

Posted in Canopy | Hours Logged: 1