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.

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.

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.

So this is a combination post for both today and yesterday. The reality is that I spent a lot more than three and a half hours on airplane stuff, but a lot of that was doing research and stuff inside…so due to my completely arbitrary decision to only count “shop time” when I accrue hours, that’s what the number is.

The first thing I worked on yesterday was the firewall penetrations. As mentioned before, I decided to ditch the plans method of using a plastic snap bushing cooped with sealant, in favor of nicer stainless penetrations. One concern with the penetration kits I bought was that they weren’t going to work as provided, due to how close the two firewall holes sit to the outside skin. So job #1 was to modify the mount flanges for to handle this. For now, I’m only working on the two 3/4” fittings – I also have a 1/2” one that’ll get used for the alternate air cable, but I’m not going to mess with that right now. Basically, I just cut one corner off each fitting flange. That leaves me with only three screws instead of four to secure these, but since they’ll be mounted with a layer of sealant underneath, I don’t think there will be an issue with proper sealing.

The more fun part of this was figuring out if the fittings were going to work. One downside of these new fittings is that they actually don’t accommodate as much stuff as the snap bushings. The snap bushings end up being maybe 11/16” ID, but these stainless fittings call for their ID to be lined with firesleeve to provide chafing protection – which reduces the usable space quite a bit. This isn’t an issue for the port-side fitting – it will only carry two power supply wires, one 6AWG and the other 10AWG. The starboard fitting is a different matter – the wire bundle there is already a decent size, and it doesn’t yet include the SDS ignition harnesses that need to be threaded back into the fuselage.

So I spent a whole lot of time today tinkering with that particular passthrough. Through trial and error, I verified that it was not possible to pass all my wires through the 3/4” fitting with the firesleeve lining in place. Well, that’s a problem. There’s a 1” fitting just like this one, but there’s not enough room between the side skin and the firewall angle to fit that – 3/4” is as big as I can go. I considered adding a 1/2” fitting below the first one, and splitting the bundle, but due to the way the flanges are laid out, it’d have to be probably 2” away from the other one. This would also cause problems for my cable management plans inside the forward baggage area.

It eventually occurred to me that I don’t have to use firesleeve inside the fitting – just something that works for anti-chafing. There will be an outer firesleeve sheath that provides actual fire protection; the internal bit isn’t really doing anything. I did an experiment where I just wrapped the wire bundle in silicone tape, which fit just fine, and I thought I had a decent solution – but this approach might make me hate myself down the road. It’s very possible I’ll want to add wires to this bundle down the road, and trying to remove and replace that tape in situ would be, to put it mildly, difficult.

What I needed was some chafe-resistant material that I could put inside the fitting, and have it essentially stick to the fitting, not the wires. After some thinking, I had the idea of putting some sort of tubing inside the fitting. Some time spent browsing McMaster-Carr yielded exactly what I needed – some thin-wall nylon tubing. With a little fine-tuning of the tubing OD, I should be able to press-fit a section into the fitting, thus providing my chafe resistance, while still leaving plenty of space for the wire bundle. In a sense, I’m ending up with something like one of those plastic snap bushings, but inside a far more fireproof fitting.

On the other hand, that means no more mucking with the penetrations until Yet Another Parts Order comes in. What to do now? I ended up completely switching gears. The build manual suggests starting the FWF layout with the exhaust, since it’s an immovable object that’s going to be emitting tons of heat – that is, it’s a pretty big consideration for routing everything else. I’d had the upper exhaust stacks on the engine for a while, but left the lower pipes off to keep them out of the way while removing/reattaching the engine repeatedly. Now that I’m (hopefully) done with that, I might as well go ahead and put those on, and start figuring out how the hangars and other stuff work.

It definitely looks a lot more airplane-like with the full exhaust system in place…even if it’s just sort of hanging in thin air for now:

I spent the rest of the afternoon wrapping my head around the exhaust hangar setup. There’s some bracketry that I’ll need to drill bolt holes in before I can actually work with the hangars…that’ll be another day. The other packaging consideration for the exhaust is the cabin heat muff – this is a somewhat bulky device that wraps around two of the exhaust pipes. Also, it’s kind of a royal pain to assemble, which is especially annoying when considering that the spot I temporarily mounted it today isn’t going to work…so I’ve got to pull it back off again.

That’s also a job for another day. Maybe tomorrow.

Oh, another consideration – before I do anything remotely final with the exhaust hangars, I probably need to drag out the lower cowl and at least hold it in place, to get an idea of clearance between the pipes and the cowl. That’s going to be fun, since I’ve sort of been using the finish kit crate as a table…actually the shop in general is in dire need of some cleanup and organization. Maybe that needs to be tomorrow’s job, instead of more building stuff.

So…I’ve been holding off on moving forward with the battery mount, mostly out of an abundance of caution. I’d gone ahead and ordered some spacers from McMaster-Carr, and I wanted to do a real fit-up with those spacers and thus evaluate the battery placement in that position, before actually drilling the bolt holes. Those spacers came in today, so I got that final fit-up done.

The basic deal here is that I’m placing the battery box as high as it can possibly go. The placement I chose will put the top right bolt under the starter contactor – meaning that solenoid will have to be removed before that bolt can be loosened – but such is life. I could possibly have gone higher, but I’d have had to added washers between the starter contactor and the mount, and that sounded like way more of a pain to deal with down the road.

So I got that location plotted out, then went ahead and drilled the box mount holes. Next up was once again tracing around the various mount holes and laying out how to trim the mount down. I took a lesson from the last mount and didn’t go nuts with all the inside curves in an effort to shave off as much material as possible. This will make it a lot easier to finish the edges, and I think I can make up most of the weight by way of adding more lightening holes.

Before calling it a night, I rough-cut the outline on the bandsaw:

Next, I’ll get to finish the edges and round the corners, then it’ll be time to lay out the lightening holes.

In other news, the stainless flange fittings I ordered from Amazon were far too large to be useful, so no joy on making some cheap passthroughs (though at least I can return these). I looked around some more for something to press into service, but eventually decided to just cough up some $$$ for some passthrough kits that Spruce has. Even those will require some modification due to how close the passthrough holes are to the firewall edge, but I think it’ll be doable. Worst case, I can still fall back to just the snap bushings and a big blob of sealant…

Well, this update really started last night. Josie and I had things to do after work, but when we got home I decided to spend at least a little time out in the hangar. My main motivation was to figure out some hardware requirements and go ahead and get a Spruce order in. I started by re-hanging the engine, feeling good about no longer needing lots of access to the firewall.

Next I went to trial-fit the battery mount, and as soon as I had it mounted to the firewall, I realized I had a problem. Making the on-the-fly decision to locate the contactors beneath the battery was a bad idea; they interfere with the lower engine mount tube, and not in any sort of trivial sense. That nicely finished battery mount is unusable.

The good news is that I still have the unfinished first attempt, and after a little more trial fitting, I can make it work with the original layout. The one minor annoyance will be needing to remove the starter contactor to reach one of the battery box mount bolts. Not great, but also not a deal-breaker, and considering the only other option is to start from scratch again with the mount…yeah, I think this will be fine.

I gave up on getting the Spruce order together after this, though I did go ahead and order the spacers I’ll use between the mount and the firewall from McMaster-Carr. I’m pretty sure I have the right length bolts to mount this when the time comes, so it doesn’t look like anything I need from Spruce will be a blocker.

Tonight I did a bit more fitting and tinkering, but mostly I set the battery mount aside and decided to work on finalizing the pressure manifold. Here again, I ran into an issue – I need AN3-6A bolts to attach this, but…I don’t have any. They’re not even provided with the FWF kit. Something else to add to the Spruce order, I guess.

I did go ahead and get the AN fittings installed for the pressure lines, along with the plugs on the opposite sides of each fitting point, and the actual sensors. I also temporarily mounted the manifold in place, using too-short bolts and thin jam nuts. That’ll hold the thing in place until I get the right hardware”

Finally, I’ve been thinking through my passthrough fittings for the wiring and alternate air cable. Previously, I’d decided to go with the traditional Van’s approach, just running the wires through a snap bushing and covering the area with firewall sealant. That’s still my fallback plan, but I’m going to try making some DIY fittings instead. I found some stainless flange fittings on Amazon that I think I can modify to work here. If I can make these work, I’ll end up with a much more robust and gas-tight fitting. So we’ll see how that works out…

I guess in the meantime here, while I wait on parts, I might start working on the case top ignition coil mount. I can’t pull the ignition harnesses through yet, since I’m still figuring out the passthrough stuff, though. I’m sure there’s still random stuff I can work on in the meantime.

Nothing too exciting tonight. I laid out and drilled the screw holes for the remaining two eyeball fittings and fabricated the aluminum spacer necessary to make the outboard one cooperate with the adjacent firewall angle. With that done, I got the backplates mounted, and went ahead and assembled the rest of the eyeballs in place. The last part is kind of extra work – they’ll have to come apart again when the control cables get installed – but this is as good a way as any to store the remaining pieces. Better this than to go searching for a bag of stuff in a month or so…

Also, I’m equal parts annoyed and amused that each fitting ended up rotated off the vertical in the same direction and about the same amount:

I guess now there’s not much left to do but to hang the engine again and start having some real fun.

So the battery mount is set aside for a while. That left two more firewall tasks, one simple and one less so. The first was just drilling the two mount holes for the oil/fuel pressure manifold – that was easy enough. The second was finishing up the holes for the three control cable penetrations.

For these cables, I decided to go with steel eyeball-type mounts. These provide a nice sturdy seal, but also allow for some finessing of the angle at which the cable goes through firewall. The fun, though, is that each of these requires six screw holes around the perimeter, in addition to the actual passthrough hole. The eyeballs come with nice drill templates, but they assume that you’re starting from scratch – that is, you’d use the template to make the six screw holes as well as the center of the pass through, then drill them all. Well, I had two 1/2” prepunched holes, and one 1/8” one…so I couldn’t use the templates as provided.

After exercising a decent amount of brain power figuring out an approach for this, I hit upon a solution, which revolved around using the actual backer plate as a template. The first step was to open up the prepunched hole to just under 1 1/8” using a step drill, and then I could use that step drill bit to hole the backer in place, using the passthrough hole as a reference. Then I used a 5/64” drill bit to start a dimple through one screw hole, then finished that hole to 1/8”. That allowed me to put one screw in, plus the step drill for centering, and follow the same procedure for the other five screw holes.

This procedure worked out fairly well, except for one thing – using  step drill on the thin stainless steel doesn’t make for a really great hole. In fact, it tends to wrap the steel just around the hole, while also creating an enormous burr on the backside of the hole. I spent a pretty annoying amount of time reducing that burr to a manageable state, but in the end the hole still isn’t super clean.

I didn’t really like the idea of using this same approach on the other two holes, so I paused and did some research fro better ways to approach this. At some point, I realized that I had a much better tool for this – a knockout punch set I bought a while back. The only problem was figuring out where I’d put the thing…and I spent probably a solid hour hunting around the hangar (this time is not included in tonight’s logged build hours).

All that searching time paid off. One of the punches was the exact size I needed for the passthroughs, which was a nice bonus. I got the second and third holes punched, but stopped short of drilling the screw holes – I’ll leave that for another night. This photo shows how much nicer the punched holes (right and center) are compared to the drilled one (left):

There’s also one more bit of complexity, which my be visible above – the rightmost hole is really close to the firewall support angle, to the point that the punch took a small bite out of the angle. Because of this, the backer plate isn’t going to be able to sit flush against the firewall without some additional creativity. I have a plan, though – the angle piece is .063” thick, and I have plenty of .063” scrap, so I should be able to just fabricate a shim to go between the backer and the firewall; this will effectively make a full flat surface for the backer plate to rest on.

Tonight was just putting the finishing touches on this mount, or at least most of them. I wanted to get all the lightening holes cut, but I can’t “finish” finish it until I have the nutplates I’m missing, and I’m going to wait until I also know the mount bolts I need so I can combine Spruce orders.

I did spend some time thinking through the layout of the holes, and I ended up massaging the large hole behind the battery a bit, and then laying out just a few smaller holes in the area below the battery box. There wasn’t any room for useful holes anywhere else, at least while still leaving what I felt was enough material. Probably this thing is way beefier than it needs to be, but such is the nature of eyeball engineering – better safe than sorry.

Anyway, the large hole got cut with my hole cutter, but the smaller ones I did with a large step drill. The hole cutter is nice, but I don’t have quite the precise control over hole size that I get with the step drill. All that step drilling generated a pretty big pile of aluminum fuzz:

And here’s the mostly-finished mount:

So now I’ll set this aside and do the rest of the firewall stuff, which at this point is limited to the manifold mount holes and the eyeball passthroughs for the control cables. Hopefully by this weekend I’ll be hanging the engine…again…