So today had a bit of an absurd theme going on. My intent going in was to install the engine control cables temporarily so I could have then in place around the engine as I worked through routing the assorted wires and stuff. What I wanted to do was to actually rig the cables to the throttle quadrant, with the hopes that I might not have to remove it later on. For various reasons, that didn’t happen.

Farce #1 came after I retrieved the throttle quadrant and cleaned it off. The next thing I needed was the cable anchor bracket, which, well, anchors the ends of the cables. I spent a full hour looking for that thing, doing the circuit around the shop (shelves? nope. big work table? nope other tables? nope. in the fuselage? nope) and gradually moving more and more stuff around, until…I found it sitting IN PLAIN SIGHT in the fuselage.

sigh

Well, at least I found it…I was getting to the point of considering just fabricating a new one, glad I didn’t have to do that. This, however, led directly into farce #2. The control cables attach to the quadrant levers with clevises and pins. I just had to find those clevises, because surely they came with the kit, right? Well, I dug through all the hardware bags I had and found nothing like that. Then I did my usual next step when I’m looking for hardware – I pulled out the kit pick lists and went through those. Sometimes this helps me know the bag number and maybe figure out where that bag might be stashed.

Well, long story short, I didn’t find any of the proper clevises in any of the pick lists. Apparently they’re not included with the kit after all, and I need to figure out the right parts and make yet another Aircraft Spruce order.

sigh again

I almost gave up on the whole thing right there, but after sitting (and yes, stewing) a bit, I realized that I was overly focused on rigging the cables to the levers. While it’d be nice to get that done, it wasn’t necessary. Just having them mounted to the cable anchor would be enough to see what the routing would look like. Any adjustments at the anchor to fit up with the levers wouldn’t make any real difference in the routing.

So I went ahead and installed the cables that way, knowing the entire time that I’d definitely be removing them again. That’s OK, it’s not like there’s anything else on the plane that hasn’t been installed repeatedly…

So here we are with the cable routing. Center cable is for the prop governor, and routes over to behind the engine. The other two are throttle and mixture, and they go under the sump to the injector servo. The eyeball fittings ensure that everything is locked down just as it would be for the real installation:

And just for fun, we can look at the cables routing through the fuselage from the firewall to the gear tower. It’s going to be a little snug in here once the scat tubing for the cabin air vent is installed:

Not pictured here: I also went back to planning the main power distribution stuff. As part of this, I modified the cable between the master and started contactors; I’d fabricated that some time ago, but I didn’t care for the routing, especially how it would interact with the other stuff I’m planning. I’m actually still thinking of replacing that cable with a copper bus bar. That would be a much more compact option, but the potential problem is that given the way the contactors are mounted, it might make maintenance difficult. The flexible cable is much easier to install here than a rigid bus bar would be. If I do the bus bar, the end result will probably be that one of the contactors will have to be removed in order to free up the bar. Which isn’t really that bad, I suppose…if I need to remove the bar, chances are it’s because I’m replacing a contactor. Anyway, more food for thought…

So…what I’ve really been wanting to work on has been the firewall passthroughs for electrical stuff. Specifically, I wanted to get the fitting installed on the right side of the firewall so I could pull the wiring bundle through and start working on routing the ignition wiring back into the cabin.

When I looked at the fittings I bought, and read the instructions, I saw they specified #6 stainless screws for attachment, or stainless pop rivets. Given how tight things are inside the cabin where these fittings would attach, I really wanted to go the rivet route, and so I spent way too much time trying to find any 9/64” stainless pop rivets, to no avail. I also considered sizing up to 5/32” – a much more common size – but all the rivets I could find had too much grip length.

So I resigned myself to the screws. Before ordering from Spruce, I worked up a few other parts I needed, in a vain attempt to save on shipping. Critically, when it came time to place the order, I wasn’t sure the right screw length. But I thought to myself, “these are only going through two thin pieces of stainless, the shortest length is probably right.”

You can probably guess where this is headed. I got the attach holes for the fitting drilled into the firewall, grabbed one of my new screws, and…oh my, that’s way too short. The screws aren’t even long enough to get full engagement from a lock nut with no material in between, much less my two pieces of stainless and a washer.

Welp, time to move on to something else until I can grit my teeth and either order from Spruce again or just buy some hardware screws locally. Fortunately, I had another task I’d been thinking on – how to brace the baffles at the back of the engine. I’ve mentioned this a bit before – the baffle kit comes with a brace that attaches to the case bolts and holds the baffles in place, but I can’t use that because my ignition coil pack will be mounted there.

I’d ginned up a few possible ideas, none of which I liked much, but then a couple weeks ago I saw a photo with a brilliant solution. Instead of bracing from the front, using the case bolts, this person was bracing from the rear, using the top two bolts on the accessory case. The brace itself looked relatively simple to fabricate, and I’ve got some scrap .063 stock lying around that would be perfect for this.

The main challenge for fabricating and fitting this would be the work space – on the back of the engine, near the engine mount, and up at about my shoulder level with the plane on the gear. Visible here – with that annoying mount in the foreground – are the two bolts that will anchor the brace:

The first fun part if figuring out the spacing of those bolt holes, since obviously the brace has to be drilled to match them. Trying to measure this with all the stuff around was going to be a real pain, but after some more thinking, I came up with an idea: a simple shop-made measuring tool. I cut a couple strips of scrap, drilled 1/4” holes in one end of each, and a 1/8” hole in the other end. A cleco through the smaller hole acted as a pivot, and a third 1/8” hole in one piece anchored a final piece of stock. That final piece made a sort of “A” shape, allowing the tongs to be fixed in a relative position.

Then I just bolted the ends to the case, clamped my crossbar in place, and I had a template for those two holes:

Easy to measure this over on the bench, and…very nice of Lycoming to make the bolt hole spacing exactly three inches:

Using that measurement, I started working on a cardboard template. First step was to just locate the bolt holes and lay out the surrounding shape to clear the accessory case, then I did a trial fit to make sure that my bolt hole spacing and the surrounding shape would work out. Seems good to me:

That was the end of the night’s work. Next will be the more-fun task of roughly locating the two bends I’ll need to get this piece touching the baffle, and then will come the real fun of starting to replicate this thing in aluminum and getting it to fit right.

This post starts eerily last the last one…in the day or two after that last session, I spent an hour or two working on finishing the trimming of the rear side baffles. Never wrote anything up about it, since I’d probably be doing more the next day…or the next…or…well, you get the idea. Also, I apparently didn’t take a single picture while working on those baffles. Huh.

Anyway, here we are today, where I picked up on the task of trimming the rear baffles, which runs along the aft side of the engine. I’d previously drawn a first hack a trim line, way back when I put paper clips on the entire assembly, but I decided to fine-tune that a bit before making my first cuts. Since I had the rear side baffles done, I could use those to mark where the intersecting pieces should be cut at the corners. Basically I marked those junction points and sort of made a freehand hack at tweaking the trim lines. I was, of course, pretty conservative while doing this – as ever, it’s a lot harder to put material back than to take it off.

That first trim was, indeed, very conservative – I still wasn’t able to get the upper cowl all the way seated. Things were much batter after the second trim – I was able to get the cowl in place and the pins installed. A peek through the oil door shows all those paper clips:

After marking yet another trim line, then doing all the trimming/filing/deburring/etc, I reinstalled everything for one more test fit. Now we can see how the baffles have the specified 3/8” clearance to the cowl – this clearance will later be taken up by the rubber seal material:

So that takes care of most of the baffle trimming. Wait, that’s not all? Afraid not. There will be another vertical baffle section just behind the prop hub, which will also need to go through this whole paper clip exercise too. And once that’s done, I’ll probably paper clip the entire perimeter and do one final clearance check all around, just for good measure.

I don’t think I’m going to do that right now, though. I think it’s time to finally remove that forward upper skin…along with what I’m sure will be some really stubborn duct tape adhesive residue. That stuff’s been on there for a couple summers now, and there’s no way it’s going to come off without some liberal application of acetone. But once that’s off, I can resume work on electrical systems, which I’m kind of looking forward to as a change from fiberglass and baffle fiddling.

So…as I start typing this, it looks like I missed documenting some work a couple weeks ago. There was some time spent fabricating a conical gusset to close out the square corner I mentioned at the end of my previous post, but I guess I didn’t take any pictures. I’ll have to try and sneak them into a later post, I guess.

After doing that work, I almost let myself get distracted by the air intake snorkel, which has to meet up with the left inlet ramp…but then I remembered the main reason I’m in here, which is to get the baffles trimmed so I can work on FWF wiring. And so I moved on to working on that trimming work.

The basic deal is that the upper portion of the baffles need to be trimmed to provide 3/8-1/2” of clearance with the upper cowl. Later, rubberized seal material will be riveted in place, which will, well, seal against the cowl. This is a somewhat annoying task in any case, and more annoying in my case since I don’t have an RV-8-specific baffle kit. My baffles are intended for a side-by-side aircraft, which means there’s even more trimming to do than in a normal case.

Anyway, there’s a pretty universal approach to this trimming task, which involves putting a bazillion paper clips across the top of the baffles, then laying the cowl in place, then using the disturbed paper clips to see the contour of the cowl and work on trimming the baffles to fit. The pictures I’ve seen have people doing the entirety of the baffles at once, but this seemed overcomplicated to me, especially for the initial trim.

So I started with just the forward side baffles. These need the most trimming of anything; they need to match the curve of the upper inlet ramps, which means 1) removing a lot of material and 2) matching a surface that’s way more curved than the rest of the cowl.

Here’s a pic looking in the front of the cowl from my first fitting attempt. You can see that the top of the baffle is straight, unlike the curved ramp, and as a result only a small area of the paper clips have been pushed down. You might also notice the huge amount of open space to the right, between the cowl halves, The upper cowl is nowhere close to sitting in place:

After a couple iterations of trimming those forward side baffles, I decided that having hacked out most of that curved ramp area would make it OK to try fitting the whole thing. So I installed all the baffles and then put paper clips all the way around. In case you’re wondering, there are 190 of them. Yes, I counted:

The really fun part is that 15 minutes after taking that picture, I removed all those clips again, after marking the first conservative cut line all around… Also, because the cowl was back to not being anywhere near sitting in the right place, and especially because that made it hard to get the orientation right, I knew these cuts wouldn’t get me far.

So after this iteration, I went back to doing a sort of piecemeal fitting, starting with getting those forward side baffles trimmed to the proper length (as opposed to “kinda close” like before). Below you can (hopefully) see the little hash marks I made at each paper clip location; this is the beginning of laying out the cut line:

A nice little game of “connect the dots” results in a trim line:

I think it was after cutting to that line – or maybe there was one more iteration, I can hardly keep track – I was finally able to get the upper cowl in place. Peeking in the inlet, we can see that there’s still more trimming to do; the gap at the very front of the inlet is good, but where it curves up, it’s still too close:

I did decide that this was the right time to add the rear side baffles into the mix. The left rear side baffle shows the contrast between the trimmed and untrimmed state:

I did go ahead and get the initial trim done on those rear side baffles, but that was when I called it a night. I’d done enough repeated installation and removal of paper clips for one day.

Next up I’ll get those rear side baffles trimmed to where the cowl will sit in place, then I’ll move on to the rear baffles…and after that I guess I’ll do paper clips all around again so I can get the final trim done.