Fitting the cowl halves together

Today I picked right back up with the fun of trying to hash out the junction between the cowl halves. After looking at some other build logs last night, I worked out a better idea for trimming the forward corners, which in turn allowed for me to make a much better attempt at nesting the spinner area.

This showed me a new problem: specifically, the material thickness in this area on the upper cowl is 1) not consistent, and 2) significantly thicker than the recessed mating area on the lower cowl. So I went to work removing material here; I sanded down the upper cowl mating area a bit, but decided to do the bulk of the removing on the upper cowl. So far, I’ve been through three or four iterations of removing material, smoothing the area out, and trial-fitting the halves together.

Things still aren’t fitting perfectly, but they’re a lot better. I can slide the junction almost all the way together:

But the junction still isn’t quite flush, as a picture from inside the spinner opening shows:

I’ve already surrendered to the fact that this mating area isn’t going to fit snugly at first – there’s just no way I’m going to accurately sand this stuff down to a precise fit. My goal is just to get it to a point where it nests properly, and then I figure I’ll cover one side with tape and mold release, then apply some epoxy-flox mixture and clamp it back together again to fill the gaps.

Similarly, the front corners aren’t exactly meeting beautifully. Maybe they’ll end up looking better once I’m really fitting the halves together, but I’m preparing myself for the possibility of needing to do some significant reshaping there to get things looking good.

Posted in Cowl | Hours Logged: 1

More upper cowl trimming, starting on lower half

OK, so…first order of business today was revisiting the aft flange of the upper cowl. As mentioned yesterday, while I did a lot of fine-tuning of the fit to the fuselage, I still wasn’t completely happy about it. So I spent even more time carefully sanding the flange to further tweak the fit. The good news was that things were close enough that I no longer needed to remove the cowl to sand it. With the spacer between the cowl and the prop spinner, the back of the cowl was pressed snug against the fuselage. That meant that I could wiggle the joint around to figure out where there was contact, then lift that area enough to sand it a bit with some 80 grit glued to a popsicle stick. By doing this, well, a bunch of times, I eventually got things looking really tight:

Since I was finally happy with the fit, it was time to move on to drilling the upper cowl to the hinge halves that retain it. To do this, the holes get laid out and initially drilled in the cowl, then later drilled in assembly with the hinges. As suggested in the construction manual, I laid out the rivets about 1” apart, after marking the ends of the hinge pieces on the cowl. A little work with the rivet fan and I had my holes taken care of:

I also took this opportunity to rough-cut the opening for the oil door; this opening also serves to allow access to the upper cowl hinge pines, so I needed it open for the upcoming work. I didn’t open this up all the way to the plans dimensions; I’m probably going to do something custom with the hinge and latch for this, so I’m leaving extra material for potentially working that out later.

Then the cowl went back onto the fuselage, and I very carefully got it positioned, then started drilling. My approach to managing the gap between the cowl and fuselage is to use that spinner spacer to hold the claw snug against the fuse, then I just manually held the hinge half in the rearmost position while drilling. The intent here was to use the bit of slop in the hinges to allow for moving the cowl forward for final fitting later on. About the only issue here was that while I could easily manipulate the hinge on the right side of the plane – thanks to that oil door opening – the left side was way more difficult. The end result is that I don’t have quite as much room to move the cowl forward on the left side, but I’ll still be able to do even more sanding on that later on to finalize the gap.

Anyway, at the end of all that I had the cowl fully checked to the hinge half: 

And with the cowl off, we can see those newly fitted hinge halves:

There was still more work to be done on these hinges, though; the cowl isn’t as thick as the material stickup in the fuselage, so there’s some shimming needed here to get a nice flush line between the cowl and the fuselage. The plans call for just doing a blanket .032” shim, but I noticed that the gap was more pronounced around the edges of the cowl, and less so in the middle. So I did some trial-and-error with some aluminum scraps; this resulted in using those .032” shims on the outside edges, but then closer to the middle .025” shims made for a better fit.

Once all that was laid up, I got to do the work of cutting the shims, drilling them in assembly with the hinge halves, and finally fitting everything back to the cowl. Once that was done, the cowl went back on – again – to verify that things lined up as expected. The fit still isn’t 100% perfect, but if I want to fine-tune this down the road, I should be able to do it just by adding a bit of micro to the cowl and sanding to fit.

OK, next up – it was time for the rest of the trimming on the upper cowl. With everything else in place, I could use some layout marks I already had just behind the spinner – marking the correct cut point to get things nice and symmetrical with the lower cowl – and lay out the cut lone for the bottom edge of the cowl. My approach for this was to use a laser level to first verify that my reference marks were appropriately level, and then to carry those marks around each side of the cowl.

I started with the fuselage in the level flight attitude – this would have given me a cowl split line parallel to the longerons – but that resulted in the level line dropping off the bottom edge of the cowl at the aft end. So I had to gradually lower the tail until the cut line carried the full length of the cowl. It’ll end up being a degree or two off from the longeron line, but I kind of doubt anyone will notice…

Then I got to go and carefully make Sharpie marks along the level line, along both sides of the cowl… while also making sure not to, you know, lase myself in the eyes:

Then, as with the last trim, I used masking tape to lay out the cut lines all the way around:

Which was followed by rough-trimming, sanding the cut lines close to the masking tape lines, and finally using a long sanding board to finish the entire cut line nice and straight. This was surprisingly not really a ton of work; unlike the aft cut line, which had to be carefully fitted to another part, in this case I’m creating the layout line, so there’s not so much trial-and-error. (That’ll come later when I trim the lower cowl to fit…)

OK, enough of the upper cowl…now it’s time for the real fun, the lower cowl. The lower half mostly butts against the upper cowl, except for the spinner area. Here, the lower cowl has an inset flange that need to fit snugly into the upper cowl…but that there’s no way to test-fit this intersection as provided, because the extra material the outboard cowl edges interferes:

So the strategy here is to carefully and gradually trim the forward outer portion of the lower cowl to hash out this nesting area. The marker line in the previous picture follows the edge of the flange, so that’s hypothetically where I’ll want to trim things here. Thing is, I don’t want to trim any further back than I have to, since I can’t know how what the overlap of the two halves will look until I can fit them together…aka not until I get the front to nest. It’s a sort-of maddening chicken-egg type problem.

The approach so far has been to slowly and conservatively remove material in this area, while repeatedly trial-fitting the halves. Eventually I should be able to creep up on a decent trial fit, but I’m not there yet. I got this far before deciding it was time to call it a night:

So this is where I’ll be picking up next time. I’ll probably need to rethink my localized trimming here to creep up on the fitment…that’s something to mull over for a while. As tedious as some of this is, though, it’s still pretty neat to see the cowl profile coming together.

Posted in Cowl | Hours Logged: 7

Upper cowl: first trim

Once again, this is a multi-day report; I actually started on this stuff yesterday afternoon. I’d actually put the upper cowl on and off a couple times over the preceding week, as I was thinking through my next move for the fitting process. I also swung by Home Depot this past Thursday to pick up a 2’x2’ piece of 1/4” plywood, to make a spacer between the cowl and prop spinner. That work got done yesterday – first, making a hole in the middle of the sheet to match the prop hub, then splitting the sheet into two pieces. The idea was that I could rest it on top of the hub for fitting.

Next up, it was time to start messing with the cowl itself. Before doing anything, I needed to get the fuselage into a level attitude, which meant finding the right combination of boxes and scrap lumber to raise the tail to the proper height. The good news here is that it’s a lot easier to lift the tail with the engine hanging out front – that’s really good since I’ve now put the tail on and off the boxes several times.

Anyway, with the fuselage leveled both front-back and side-side, I got my laser level set up to give me a horizontal reference line. This was mainly so I could similarly level the cowl side-side while doing the other positioning. Then I got to mess around with my adjustable supports up front to get the nose of the cowl where I wanted it relative to the spinner, as well as maintaining the side-side level I wanted. Then I checked, double-checked, triple-checked, and so on, until I was really satisfied that I had the location I wanted. Once that was done, I used the tape line I laid out on the fuselage, measuring 2” forward, and laid out the cut line for the back end of the cowl:

Next, I broke out the masking tape and laid a stripe along the marks to create a continuous reference line for the cut:

Then it was time to take a deep breath and make that first cut. I wanted to creep up on the final size, so I worked to make the cut about 1/8” or so shy of the actual cut line. Getting the final fit was always going to require a lot of iterative sanding, so no real reason to try and get super close on the first pass:

Now, the real fun part here is that before I could get to the iterative sanding, I first needed to install the hinge halves that will support the back of the upper cowl. Prior to trimming, it was resting on the fuselage, but now it would need to butt against the fuselage, and thus rest on the hinges. So starting this morning, I cut all the hinge pieces I’ll need around the cowl, then set about fitting the upper hinges to the firewall. This is kind of fun since the hinge needs to be bent to roughly the same profile as the fuselage before fitting, and then there’s just a lot of drilling in assembly. Then I cut the pins for these pieces, and pinned the other hinge halves in place.

Also, I forgot to take any pictures of this, I guess because I was so excited to lay the cowl in place and see how it looked.

Anyway, this got me into the fun iterative part. All told, this cowl probably went on and off the airplane fifteen or twenty times today. Lay it in place, evaluate the fit, figure out where the interference was, take it off, sand that area, lay it in place again…and so on. I was pleased to see that I started with only about a 3/16” gap from cowl to spinner, meaning that I had plenty of leeway to fine-tune the fit while getting the gap right. Eventually I worked up to fitting the plywood spacer between cowl and spinner while doing the fit-ups, and eventually I had a fit that I (mostly) liked at the firewall:

Up front, I’ve got a nice even gap between the cowl and spinner:

I think I’m still going to tweak that fit at the back a bit more tomorrow; there are a couple spots I’m still not completely happy with. Once that’s done, the next step will be to lay out the rivet holes on the cowl, then use those to drill through the cowl into the hinge and cleco everything together. That, in turn, will make the upper cowl stable enough that I can mark the horizontal trim lines along the bottom, and make those cuts. At least those won’t require a bunch of fitting, since they just need to be straight – the lower cowl will eventually get trimmed to match those cut lines.

The one thing that’s bothering me is that the hinge halves for the upper cowl have some slop in the fit. The plans specify undersize hinge pins for those, which are necessary in order to fit the curve of the upper fuselage. But that also means that the hinges don’t fit tight…and that means that it’s going to be hard to get the gap I want between the upper cowl and the forward upper skin. I don’t want a contact fit here; there will eventually be paint in that gap, and if it’s too tight the paint will get chipped removing and reinstalling the cowl.

My best guess for handling this is to allow the lower cowl – which will attach with full-size hinge pins – to do the primary locating work. It’ll be fixed in place, and the upper cowl will be fixed to it via the horizontal hinges that will join the halves. Maybe the best approach is to get the upper cowl fitting tightly to the fuse, drill the hinges such that the cowl can be pulled forward to establish the right gap, and then get everything fixed in place when I add the lower cowl.

We’ll see how this all works out over the next week or so, I suppose.

Posted in Cowl | Hours Logged: 6

More cowl fitting prep work

So, as implied by the title, today was all about getting set up for the joy of cowl fitting. I started this off last night by pulling out the line material that will be used to attach the cowl halves. This was in line with the first step of cowl fitting, per the instructions, being to cut and install the the hinge halves on the firewall. However, I ended up putting those back and delaying for later, mainly because I can’t really follow the instructions to the letter here. The main hangup is that I don’t (and won’t) have the forward upper skin riveted in place, which in turn precludes having those hinges riveted, since all these items are riveted in assembly.

Instead I moved on to a more fun problem, something I’ve been mulling over for the past few days. Briefly, the cowling halves are provided slightly long, and need to be cut to length in order to fit snugly against the firewall. The basic procedure for this is to lay out a line 2” aft of the firewall flange, lay the cowl on top so it overlaps the forward fuselage, and after doing all the fitting and positioning, measuring back 2” forward from that line lays out the initial cut line.

First problem: The firewall isn’t held in position unless that forward upper skin is installed. That’s not necessarily a show-stopper; I can cleco it in place, measure back from the firewall to mark the line, and then remove the checks so the cowl rests on the skin. But that leads to…

…the second problem, which is the right upper portion of the firewall. The left side is held securely in position by the skin, but the right side has a giant open spot where the forward baggage door will go. As provided, the skin didn’t have this piece cut out, but…I cut it out some time ago so I could match-drill that skin to the underlying structure. In retrospect, I wish I hadn’t done that. If that piece wasn’t cut out, then this skin would hold the right side of the firewall securely as well.

Anyway, it’s water under the bridge, and I’m left with this setup. You might be able to imagine how that portion of the firewall has a lot of freedom of movement here:

To solve this problem, I decided to temporarily add the baggage door to the party. Actually fitting this piece is a whole procedure that apparently gives lots of builders fits, but all I needed it to do was serve as a sort of filler piece to position the firewall. In practice, the top of the door attaches to the forward upper skin and underlying structure with a length of piano hinge; for this purpose, I cut a piece of .063” to sit in place of that hinge and attach the door. That piece of scrap was first drilled to the hinge attach structure, then I worked on putting the door in place on the fuselage before drilling the door to the scrap piece.

While doing this, I reviewed the baggage door instructions for inspiration. It turns out that that procedure calls for a nontrivial usage of duct tape, which I took inspiration for. In order to hold the door in the right position for drilling, I added strips of duct tape on the forward side, which also served to pull the firewall into proper position. Between that, and some more strips of tape to hold the bottom edge of the door in place, I finally got the brace drilled, which fixed the door in place pretty well:

Next, I worked between the clecos to place the 2” guide line off the firewall flange, then added another strip of duct tape to really ensure the firewall wasn’t going to move. Finally, after going all the way around the firewall and making marks for the guide line, I put down a strip of masking tape all the way around, which will be my actual reference when it’s time to mark the cowling:

So that takes care of allowing the back end of the cowl to be positioned and marked – the next task is to allow for positioning the front end. If we just lay the cowl atop the engine, the front edge sits on the crank pulley and is far too low. So I created a couple of adjustable plungers which allow for carefully raising the front. These were made using scraps from my first instrument panel cut; each piece attaches to a baffle attach point on a cylinder, and then has a 1/4-20 tapped hole for a long bolt. The bolts are topped with rubber vacuum line caps so as not to damage the inside of the cowl. I also added jam nuts on each bolt, to ensure I could prevent the bolts from moving, as well as taking some load off the threads in the admittedly thin brackets:

 

Finally, it was time for a trial fit of the cowl to see how all this worked out. Mostly I wanted to make sure that those bolts up front were long enough to raise the cowl to the level needed…or if I was going to need to buy some longer ones. So while this is in no way a careful fitting, I did take the time to roughly align the cowl with the prop spinner:

In this position, I still have a little bit of bolt length left, so it looks like I’m in good shape here. For the final fitting, I’ll need a way to precisely space the cowl off the spinner backplate, as well as a way to establish that the cowl is level from left to right. Really, I just generally need to review the fitting instructions, so I have an idea of the big picture of what I’m doing. It’s probably not surprising that I want to quadruple-check everything I’m doing before I reach the point of actually trimming the cowl…

Posted in Cowl | Hours Logged: 5.5

More coil mount work, getting ready for cowl fitting

Tonight I picked up where I left off with the coil pack mount. Since the first piece from last night fit up nicely, I used it as a pattern for making its mirror-image mate. Drilling the two bolts holes and roughing out the cuts went pretty quickly, but it took a little more work than that. Turns out the case casting is slightly different on the left side, and I needed to remove a little more material to get it to fit nice and flush on the case.

Once I got both pieces bolted in place, it was time to set the coil pack on top and evaluate the fit. One concern I had after last night was whether these two pieces of angle would actually provide a large enough mount pad for the coil pack. After the test fit, I think this is going to be fine, though there’s not a lot of extra space. I could make this a little better by adding some washers or spacers between the brackets and the case, but doing that would make this a lot more annoying to install or remove. I’ll have to evaluate the actual edge distance on these bolts to make a decision here.

The other thing to evaluate here is the clearance between the coil pack and the cowl. In an attempt to get a first approximation of this, I once again draped the cowl over the top of the engine and firewall. I found that the cowl would rest on the coil before it contacted the flywheel, which isn’t necessarily a bad thing. After all, the cowling isn’t supposed to contact the flywheel, but the unanswered question here was what the right position for the cowl nose ought to be. Both the vertical and longitudinal positions here can make a good bit of difference in clearance with the coil pack.

So I decided that this was a good time to do some of the prep work for fitting the cowl. The nose of the cowl gets its position set relative to the prop spinner backplate, so that backplate needs to be in place for this. In the case of a CS prop like what I have, the backplate attaches to the prop itself, which means that I need the prop in place to fit the cowl. So I got to work breaking out the prop and spinner, installing the backplate, and finally actually hanging the prop.

Installing the prop is a bit of a slog, though that slog is balanced out by, well, by the fact that I’m installing the prop, which is sort of a cool milestone. The thing is that the six prop bolts are captive inside the prop hub, and the arrangement means that each bolt can be turned about one flat at a time with a wrench. Additionally, the bolts need to be tightened gradually and equally, to pull the prop squarely onto the crank flange. What this means is that I did a lot of walking from one side of the prop to the other and back. All told I think I spent 40 minutes tightening those bolts.

I haven’t done a real recheck of clearance with the coil – I also need to rig up something at the front of the engine to support the cowl nose at the proper height – but I did lay it back on top just to help get some “hey, it looks even more like an airplane” photos:

Fun fact: you may notice some mud dauber nests on the prop blades. At least those are easy to clean off, right now they’re making my nice carbon fiber blades look not as good as they’re supposed to.

So there we are. I need to get some hardware to rig the from cowl support, and also install the forward top skin, but I’m in a decent spot to start thinking about laying out the first big trim cut on the upper cowl.

Posted in Cowl, Firewall Forward | Hours Logged: 2

Cabin heat feed, ignition mount start

This is another two-day post; yesterday I was mostly busy working on Helio stuff, but I did get some time in the shop in the evening. The first thing I was working on was making the hole in the right rear baffle that will feed air to the exhaust heat muff, and thence into the cabin. I used the provided flange part to outline the required hole, and marked the center. Unfortunately, because of the bends in the baffle here, I couldn’t use my trusty hole cutter, but I was able to use the largest of my knockout punch set to make a starting hole that was only about 1/8” undersize. Then I just opened the hole up to my outline with a Dremel cutting bit.

Next I clamped the flange in place and drilled the four rivet holes, followed by some fine-tuning of the hole. At this point I was ready to rivet the piece in place…or so I thought. There’s a provide piece of metal screen that’s to be trapped between the flange and the baffle, I guess to prevent debris (like insects) from entering the cabin in-flight. The plans call for tank sealant to be used in between the flange and baffle, I assume to keep the joint well-sealed. I was planning on using some good old RTV, but…turns out I don’t have any. I think now I remember that the last time I needed RTV, I had to poke a hole in the side of my tube because it was so dried up.

So I just set this aside for now, and moved on to starting on the real fun fabrication work: the case top mount for the ignition coil pack. I busted out the angle I bought for this purpose, did a bunch of measuring, marking, and laying out, and got to work. After drilling the two bolt holes, I outlined the material I needed to remove from the vertical flange. This is necessary both to ensure the mount fits well against the case, as well as to provide an aperture for the fuel injector line to go through. After all, the whole reason for this custom mount is to work around that line.

After all that layout work was the usual dance of drilling holes, rough cutting with the bandsaw, refining the shape with a cutter in the Dremel, and straightening things up with the file. Then it was time for the big event: a test fit on the engine. It lines up nicely and provides good space underneath for the injector line, so it looks like it’ll achieve its purpose:

 

Of course this is only one of the two mount pieces; I’ll need to make essentially a mirror image that will go on the other side of the case. There will also be more trimming to be done – these pieces are intentionally oversize, and once I get the location of the coil pack right, I should be able to remove a good bit more material. I’ve also got to think of how I’ll adapt a brace on the backside of this piece for the rear baffles.

But hey, things are going well so far. I’m thinking that from here, I’ll finish the coil mount, get the coil in place, then set the baffles aside and start working on fitting the cowl. That way I’ll get my look at whether the cowl properly clears the coil pack – it’s still possible I might have to relocate the coil elsewhere, though I sure hope not.

Posted in Firewall Forward | Hours Logged: 2.5

Baffles #2

Today was a day of lots of trial and error. As mentioned previously, the right rear baffle piece didn’t fit the engine as well as its left rear companion. Last night I put in a little bit of time to get ahead of this – I traced the baffle piece on cardboard and cut that out, to use as a starting point for the trimming. It only took a few iterations of trimming the cardboard to get a shape that seemed like a pretty good fit.

Today I traced that new shape on the baffle and did some trimming, before going for the first trial fit on the engine. Much closer to fitting, but not quite – I guess the flexibility of the cardboard hid some remaining fitment issues. The basic frame of reference I was using here was a screw attach hole for this piece, which is located near the top right engine mount. My goal was to get this piece to where I could install that screw and pull the baffle snug against the engine.

This ended up requiring something like five or six iterations…just lots of fitting, marking interference points, removing, trimming, deburring (this piece rubs on everything while weaseling it into place), then doing it all over again. But finally I had it in a state where I could actually mount it and mate it to the adjacent piece that attaches to the cylinder head.

The next step was to evaluate how both of these pieces fit against the center brace. This is a little triangular piece that attaches to the top of the engine, and then to the baffling, to hold it in place. Getting this piece in required removing two case bolts, along with a mount for one of the injector lines. Notably, I won’t be actually using this brace, since I’ll be putting a coil pack in this same spot, but the brace is still useful for getting the baffle location right. And once I get that right, I can use that original brace to fab up an equivalent piece, which will end up being part of the coil pack mount.

Anyway, adding that brace to the mix set off another few rounds of trimming. In this case, the left rear piece did end up needing some work after all – it couldn’t quite scoot far enough aft to accommodate the brace. Fortunately, that only required maybe two iterations. The right rear piece took quite a bit more before I was finally satisfied with its positioning.

I figured the smart direction to go from here was to look at the coil pack mount. I still have some concerns about interference with the pack and the upper cowl, so the first step was just holding the pack roughly in place to see how it looked. The good news was that the rear edge sits well below the baffling, which implies that that area should be fine. However, it’s not clear exactly how the cowl will slope down from the baffle area to the front of the engine. I did a rough check by laying a yardstick from the baffle to the flywheel, which seemed encouraging but not particularly satisfying.

So I decided this was as good a time as any to drag the cowling halves out of their crate and see what things looked like. Hey, it’d have the side benefit of briefly making this thing look even more airplane-y, right?

Unfortunately, this ended up sort of derailing the day, as it turned out. After extracting the cowl halves, I tried draping the upper cowl over everything. I knew it probably wasn’t going to fit perfectly, but I just wanted some sort of rough idea. Thing was, it just wouldn’t drape properly. It would either rest on the flywheel and the baffles, or the baffles and the firewall flange. The baffles themselves seemed way too high. A closer look revealed that it was mostly the outboard corners of those baffles.

At this point I took a step back and observed, for the first time, just how different the top contour of the baffles were compared to the firewall:

I also had a moment of clarity regarding the part numbers for these pieces. Everything had been either CB-7xx or CB-10xx. It’s worth noting that for kit part numbers, the first number generally designates the model – so -8 parts might be W-8xx or F-8xx or whatever. The logical conclusion was that these were parts originally specified for an RV-7 or RV-10. Uh, did I get the wrong parts?

Digging up the FWF packing list showed that yes, I really did receive a kit for an RV-8. So I went looking for RV-8 build logs, and found one with lots of good baffle pictures, which…looked just like mine. And the builder made note of how they’d need substantial trimming to fit an -8. Well hey, there’s something I didn’t realize before…

Further digging showed that while Van’s does have an -8-specific baffle kit for an angle-valve IO-360, there’s no such thing for a parallel-valve like mine. Well, there’s something fun to look forward to.

The other thing I learned from this research is that I’m jumping the gun on some work again. I was thinking that the baffles needed to be in place before the cowl was fitted, but it seems that it’s the other way around. Which probably means that I’ll be switching gears to that task pretty soon. In the meantime I’m going to continue working on the baffles, since I already have all the parts pulled out and spread on the work table – I guess I’ll get as much done as I can right now, then put it all aside to work on the cowl instead.

Boy howdy, there’s sure a lot of jumping around and false starting on this FWF stuff.

Posted in Firewall Forward | Hours Logged: 4.5

Chafe-proof firewall penetration

We were out and about tonight, so only limited time to do shop stuff, but my shipment from McMaster came in and I couldn’t resist having a go at my penetration solution. I ended up ordering slightly different tubing than what I originally expected to line this. At first I was looking at some nylon 6/6 tubing that was only 1/32” thick, but the minimum length was 5’. Instead, after some poking around, I realized that double that wall thickness would still give me a larger OD than the snap bushing I was using previously. So instead I ended up ordering some 3/4” OD, 1/16” wall thickness Delrin tubing – and I only had to order a foot, In addition to cutting down on wastage, this also reducing the shipping cost a lot.

The fun thing here is that the stainless penetration is a little less than 3/4” OD, not including the bit of taper on the forward end. So I needed to turn down the Delrin to get the press fit I wanted. Though I should say that “turning down” implies a lot more precision than what I did, which was to figure a way to chuck a short piece of tubing with the drill and then gradually sand down the OD while repeatedly checking the fit in the penetration. Once I had the fit I wanted, I cut off excess tubing length on the backside, carefully sanded and rounded both ends of the Delrin, and finally pressed it into the stainless tube.

The resulting piece is just long enough to protrude about 1/8” on both ends of the fitting:

 

And a test fit confirms that it’ll accommodate all the wires needed here with room to spare:

I do think I’m going to remove the insert and add some glue before reinserting it, just to be extremely sure that it’s not going to slide out. Probably overkill, but…that might as well be the name of this project at this point.

Posted in Firewall Forward | Hours Logged: .5

Baffles!

In my continuing quest to find something FWF to work on that didn’t have infinite dependencies, I drug out all the baffle components after work today. A nice touch here is that the instructions for the baffling come in the style of the newer kits – these combined instruction and drawing pages. So instead of constantly referring from a big page of text to a drawing, each page of the instructions has smaller, more focused drawings for reference. However, I kind of found myself uncomfortable with the very prescriptive nature of these instructions, and so I found myself skipping steps in short order.

The first step was just separating some angle/brace type pieces and doing some trimming on them. This was where I started skipping steps – in some cases the trimming of pieces was pretty obvious, in others it seemed less clear. I decided that I wanted to see these pieces in assembly with their neighbors to better understand the trimming, so I set them aside and moved on.

From there, we jumped to working on the left rear baffle components. This sent me in a new direction of uncertainty, though. The first bits were easy – just fitting and riveting a couple of reinforcements where the side baffle piece will be screwed into a cylinder head. The next bit involves fitting the oil cooler, though…and despite the drawings showing a pre-existing hole in the left rear baffle for this, my piece had no such hole. Some research indicated that it’s up to the builder to figure out this location. It also turns out that RV-8 builders quite frequently have clearance issues between the oil cooler and the cowling. Oh, and almost everyone adds extra reinforcement in this area, as it’s a common location for cracking from vibration.

The end result of all that is that I’m skipping the part where I fit the oil cooler for now. Presumably there’s plenty to do with the baffling before I get to that requirement…I guess we’ll see. In the meantime, as part of my goal to comprehend how the baffling comes together, I decided to temporarily fit most of the left-side baffling in place on the engine:

It’s nice to see that despite abundant uncertainty, this stuff all fits like a glove. Unfortunately, I wasn’t so lucky with the right baffling, which I tried stuffing in place as well. The right rear piece doesn’t seem to be shaped properly to fit against the engine, so it looks like I’ll have to do some strategic trimming there.

Basically, tonight once again involved a nontrivial amount of head-scratching, but I think I’m starting to wrap my brain around how all this stuff fits together. Hopefully I can at least make some good progress in getting this stuff together, even if I have to keep deferring things.

Posted in Firewall Forward | Hours Logged: 1

Mostly just FWF head-scratching

So yeah, not exactly a super productive evening. The sort of infinite recursion of dependencies is not playing well with my inherent tendency to overthink everything. I started out tonight thinking I’d hash out the exhaust hanger setup, but that didn’t go too well. There’s a whole debate around how best to secure the exhaust on these planes. Most people us a hanger setup that consists of two pieces of tubing, with the ends flattened and drilled for bolts, and joined together with a short piece of rubber tubing to provide some flexibility. Vetterman suggests securing one end to the exhaust and the other to an engine mount tube, but this seems to frequently lead to cracked hangers. So folks instead suggest securing the other end of the hanger to the engine itself, but the ones provided with the exhaust are too short for this.

That doesn’t even get into the other question of where on the exhaust pipes to secure the hangers. To figure this out on the #1 and 3 cylinders, I have to look at where to put the cabin heat muff. That probably needs to go as far forward as possible, but the next question is how the scat tubing for the heat muff inlet is routed. That got me pulling parts of the baffling out, which made me realize that’ll I need to rework a brace for the baffles due to both the case-top ignition coil mount and the injector tubes, as well as worrying about whether the case-top coil might hit the cowl.

This is a really long and drawn-out way to say that I’m not going to work not he exhaust right now. The baffling seems like the most pertinent thing to get going on, so I’m going to switch gears to that. In the meantime, I decided to switch to shop cleanup for the rest of the night. My big work table is a disaster, and there’s a bunch of crap piled on top of the finish kit crate. I want to be able to spread some stuff out on the table, and also pull the cowling halves out so I have them on hand for rough fitment checks.

Things sure aren’t spic-and-span as of yet, but I made good progress. I suppose I’ll keep going on that tomorrow, though I’ll have some electrical stuff coming in, so I might also fab up some more cables – there’s some stuff I can do there that’s not dependent on 40 other things…I think.

Posted in Firewall Forward | Hours Logged: .5