Baffles: Let the trimming begin!

Posted on February 9, 2025 by pclifton

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.

Posted in Firewall Forward | Hours Logged: 4.5

Baffles: fine-tuning the inlet ramps

Posted on January 3, 2025 by pclifton

The baffle journey continues! The overall theme here was to refine the interface between the inlet ramps, the forward side baffles, and the cowl inlets. As seen below, as provided, the ramps sit well below the lower portion of the inlet:

This isn’t what we want. We need those ramps to fit closely to the inlets, so they can eventually seal together. So I got to get even more practice taking the cowl on and off while tweaking the bends of both ramps. At least I was able to bend the ramps in place, instead of having to remove and reinstall them repeatedly; that at least reduced the tedium a bit. After a few iterations, I had both ramps resting gently against the bottoms of the inlets.

This led to the next tweak: since the inlets aren’t perfectly flat, we need more bending. The idea is to mark the spot where the ramps contact the inlets near the spinner, and draw a diagonal line outboard. Then the ramp gets bent along this angle, until the outboard portion of the ramp sits up nicely against the inlet as well. Unfortunately this did require taking the ramps on and off a few times (along with the cowl, of course).

The result is a nice close fit across most of the width of the inlet:

Next up, the ramps and side baffles need to be trimmed. They can’t actually overlap the inlets as seen above; if they did, then installing the cowl would require starting an inch or so forward of the final position and sliding it backwards. That can’t work once the prop is in place.

Instead, the ramps are trimmed until they stop just short of the aft edge of the inlets. This will allow the cowl to be lifted vertically into place, so it can work within the space behind the prop spinner. Eventually there will be flexible material added to the cowl, which will seal against the ramps…but that’s later:

With that trial-and-error work done, the next step was to fabricate a support bracket for the left ramp. This will prevent the forward board edge of the ramp from being pushed down by high-pressure air entering the cowl. The bracket consists of a flat plate that screws into the engine block and a thick angle to tie that plate into the ramp. Both pieces are precut, but the plate needs to be trimmed to fit. I ended up cutting off about half an inch or so to get it to clear the ramp.

Then the plate gets screwed into place, the angle is clamped to the ramp and against the plate, and the four holes get match-drilling. Here are the two pieces prior to drilling:

Then, after demurring and such, they get riveted together. The angle also needs to be drilled to the ramp. Curiously, the plan images show the angle having three prepunched holes in this spot, but my angle had none. The instructions say to only rivet the two outboard holes, and not the middle one – I think it ends up being in common with another attach angle that will be added later. So I just laid out and drilled the two outboard holes for now – I’ll figure out the middle one later.

Here’s the support angle after drilling the ramp attach holes:

The next step would be to rivet the ramp assemblies together, but I decided it was a bit late for riveting (these will require use of the rivet gun). Instead I jumped ahead to adding some bends to the forward side baffles. Previously, after finishing all that tweaking, I traced the edge of each ramp on the intersecting side baffle. These lines then are used to bend the lower flanges inboard; this bend provides some more support for the forward outboard corner of each ramp.

The instructions sort of gloss over the details here, but I had to do some trimming of both pieces to accommodate the bends. One of them I was able to do on my little bending brake, which was nice, but the other one I had to do the old manual way – clamping it with a piece of wood and beating the crap out of it with a hammer.

Once the bends were done, I remounted the side baffles on the engine; they’ll be ready to receive the ramps again once I get those assemblies riveted together:

Next session will involve some fun scratch metal working, as I address those square corners between the ramps and the side baffles.

Posted in Firewall Forward | Hours Logged: 4

Baffles: Fitting the tapered cylinder extensions

Posted on December 31, 2024 by pclifton

Not much in the way of shiny content today. Mostly I’ve been working on getting those tapered cylinder extensions fitted in place and drilled for rivets. Part of what made this fun is that for the most part, there’s just no good way to clamp the extensions to the adjacent baffles, especially with everything installed on the engine – which is what I wanted, so I could ensure the extensions laid across the cylinders properly.

The one exception to this was the #1 baffle, where I was able to get a cleco clamp through the large hole for the prop governor oil line. I wasn’t so lucky with #2, but that’s still at the front of the engine, where there’s decent access, so it wasn’t so bad. #3 and #4 were quite a bit more challenging, since I had to work around the engine mount. I ended up using some creative methods involving scrap wood and popsicle sticks to sort of hold things in place while I marked one hole at a time, then drilled it on the bench, then went back to mark the second, and so on.

Here are a couple photos of the #1 and #2 extensions in place; the extensions are the little wedge-shaped pieces just barely visible near the cylinder bases I didn’t even bother trying to get similar photos of the other two, because 1) it would have been a lot tougher to frame and 2) I was more in a “just get it done and move on” mode.

With those in place, I went back to the instructions and started…following them (a rare luxury at this stage of the build). The ensuing work was just getting the two inlet ramps baffle assemblies deburred and match-drilled as needed. There were a couple pieces to get riveted together, but for the most part everything is staying clecoed for the time being.

So those ramps are back in place, and I have the lower cowl hung again right now. The next step will be tweaking and trimming the baffle pieces in this area so they’re in the right spot relative to the cowl inlets. There’s also some fun to be had up here to get things fitting nicely to the rounded corners of those inlets…stand by for fabricating some fun conical aluminum pieces…

Posted in Firewall Forward | Hours Logged: 5

More baffle work

Posted on December 28, 2024 by pclifton

Yet another multi-way post. When we left off last time, I’d been working on trimming the baffles in an attempt to get the lower cowl in place. At that time I thought I was pretty close when I quit for the night. Turns out I was “pretty close” in the same way that I’m “pretty close” to having a flying airplane…

Basically, it took about another four or five iterations of 1) remove some material, 2) clean up the cut edges, 3) try to put the cowl in place, and 4) find the new spot where something was interfering. But eventually, I got the lower cowl attached with the baffles in place:

That got me to the point of laying the upper cowl in place just to try and get a very generic idea of what I’d be trimming and where. That line of thought also led me to go read through the instructions to try and get a high level idea of how things fit together. I was specifically interested in how the baffle ramps and the forward side baffles pieces interfaced with the cowling inlets. None of that was immediately relevant to work that needed to be done, but it’s always nice to clear up the big picture a bit.

The next time I got out to do some work, it was pretty unseasonably warm. This was a good thing, because something I needed to address before even thinking about trimming anything was adding the upper inlet ramps in the cowl. These are two fiberglass curved pieces that basically block off the hollow area inside the inlets, preventing turbulence from the air entering and keeping it smoothly moving towards those toasty cylinders. These ramps get located on either side of the upper cowl and epoxied into place. And that’s why the weather was important – fiberglass epoxy doesn’t like to kick off when it’s cold outside, but 75° and sunny works just fine.

That’s a really long introduction for the next photo, which shows the ramps clecoed in place, right after I’d gooped the mating surfaces with epoxy and a bit of flox. These will later need to be sanded, and I’ll probably add some cloth at the interface just to reinforce things a bit:

After that, it was back to sheetmetal work. I was going through the baffle instructions and trying to figure out what stuff I could do right now. Eventually I decided it’d be a good use of time to start match-drilling and deburring the forward ramp parts. The goal was to go ahead and rivet these subassemblies together, but…this got me to the point of needing to address those custom baffle pieces for the tapered Titan cylinders. Those pieces will need to be riveted in assembly with all those other parts.

As mentioned before, other builders have gone before me here, so all I had to do was download some handy PDF templates (linked here for credit to the creators, as well as to help if anyone else is reading this and needs them). After printing those out and verifying the scale of the printouts, it was time to do some arts & crafts work. First I cut out the paper templates, then taped them to a manila folder and cut out some more rigid templates (much better for tracing on aluminum):

Then I got to trace those on some aluminum sheet stock and cut them out, followed by lots of filing, sanding, and other joyous tedium:

 

Then there was the real fun, lots of bending. The flanges were pretty easy – mostly just 90° bends, which I was able to do in my trusty Harbor Freight bending brake – but getting the curve around the cylinder was a little more fun. The aluminum is a bit too thick to just sort of bend freehand, but eventually I worked out some techniques with the vise and scrap wood to get things looking pretty good. It’s helpful that I don’t need to get the curve perfect here, because these pieces will be pulled tightly in place by retaining rods when they’re done. So they just need to be relatively close:

There was one piece that was more challenging than the rest, though; the #3 baffle has this little stair-step bend in it, which is basically closing a gap between the matching rear baffle (which is vertical) and the tapered cylinder. It took a decent amount of thinking to figure out how to do this, and in the end it involved me cutting scrap wood into a properly-shaped wedge to help things out. The actual bending I had to do with hand seamers – no way to get a bending brake or anything like that in here for the second and last bend:

This is a top-down look at that piece in place, showing how that little joggle will fill the gap here:

At the end of the night, I had all four of these tapered baffle pieces bent and ready to go. I guess tomorrow I get to figure out how in the world to clamp these pieces in place so I can drill in assembly with the rest of the baffles.

Posted in Cowl, Firewall Forward | Hours Logged: 10

Lots of baffling work

Posted on December 22, 2024 by pclifton

Once again, I’m absurdly behind on writing these blog posts. Not that I’ve been hilariously productive, but I have been doing stuff. The fun part will be remembering half of this.

Basically, with the oil door done, it seemed like a good time to switch gears to the engine baffles. Some of this stuff I’d fitted before, but that was a while ago. The first order of business was starting back with the baffle pieces along the back of the engine. These were a royal pain when I was fitting them, mainly due to maneuvering the pieces that wrap around the cylinders into place. But here’s the thing – since I have a Titan engine with tapered cylinder barrels, I need to modify some of this stuff anyway. The factory baffles are design for non-tapered cylinders, and won’t sit pull tightly in place, which in turn will compromise cooling, After all, the entire objective here is to force as much air as possible through the fins on the cylinders.

The fit for this is to cut off these parts, and fabricate some new custom bits designed for the tapered cylinders. Fortunately, that last part won’t be so bad; other builders have gone before, and one person was nice enough to upload templates for making the new pieces. That portion of the program is still in the future. though; for the time being I just had to do the cutting:

Once I’d gotten all that done, I reinstalled the rear and side baffles onto the engine. This, again, was stuff I’d done before, so at least a lot of the head-scratching was behind me. The one thing I hadn’t yet figured out was how to brace the center of the rear baffle. Normally this is supported by a brace that attaches to a pair of the case through bolts, but those are the bolts that are not being used to mount the upper coil pack.

I did a ton of thinking about this, and even spent some time with cardboard trying to mock up a complex bent piece that would tie into the coil pack mount, but none of it really seemed right to me. It’s hard to design a piece that provides decent bracing, but still stays clear of the actual plug wires. Plus it’d probably have to attach via the bolts between the coil pack and the mount, which would mean modifying the spacers, and probably some other annoyances.

Bottom line, I still haven’t solved this. The idea I landed on after that night of experimentation was to just get a big block of aluminum and sandwich it between the back of the coil pack and the baffle. The would let the coil pack do the bracing work, while also spreading the load over a fairly large area. I order a big chunk of aluminum, and…it’s heavy. Maybe heavier than I want for this task.

It’s kind of tough to see in the photo below, but it’s a split between the left and right sides of the rear baffle, right behind the coil pack:

Eventually I kind of left that issue alone for a while, and instead got to looking at the baffle pieces that attach to the front of the cylinders. These are long flat pieces that lead up to the cowl inlets, and do the first part of directing the air to the cylinders. Fitting these things was quite a bit of fun – they interfered with the complex curved part of the case just behind the crank snout, and there was nothing to do except endless rounds of trial-and-error – fitting, marking interference points, filing off some more material, fitting again, and so on.

The real fun came with the right-side ramp; over in this spot is the crank sensor mount for the SDS electronic ignition, which I mounted in place ages ago. That mount, along with the guard I fabricated for the wiring harness (to protect against damage in the case of an alternator belt failure) interfered heavily with the baffle. But before I could even deal with that, I had the same fitment issues with the crankcase itself mentioned above, so I started by just removing the mount.

After handling the initial fitment issues, I came to the realization that having the prop on the plane was a real annoyance. Not just working around the blades, but having the flywheel in place would make it a royal pain to work with the sensor mount while handling those fitment issues. So I decided it was time to pull the prop off. I always knew I’d have to do this, since I neglected to install the alternator belt before hanging the prop.

The main difference is that instead of briefly pulling it off to install the belt, now it’s going to stay off for a while, probably until I’m feeling somewhat close to first engine start. That means I need to figure out storage, since I (perhaps unwisely) disposed of the crate it came in a while back. For now it’s just sitting on top of a big trash can – which actually works pretty well as a place to lay the prop down, but definitely is not OK for long-term storage. I think I’ll probably end up modifying my rolling engine cart for this purpose – I’ve got some ideas there.

In the meantime, I get to look at a prop-free airplane for the first time in quite a while:

Removing the prop was today’s first task, and after that I was freed up to get to work on that pesky sensor mount. At first I’d been intending to trim the baffle around the mount, but I was worried about air leakage, and that thought had been bothering me for a while. At some point today, it occurred to me that it’d be way smarter to modify the baffle as little as possible, and instead modify the cable guard (which was the most egregious source of interference).

So I only had to take a small notch out of the baffle for the mount, and that finally let me sort-of hold the mount in place and get an idea about how to start trimming the cable guard. Basically, I needed to shorten it from the rear, and then cut off some of the lower material on an angle to follow the inlet ramp:

That, too, was another long run of trial-and-error fitting, but eventually I had it where it fit nicely. This photo is a little more cluttered, as I have another baffle piece in place – the vertical portion behind the mount:

That vertical portion is the last major part of the baffling, which basically encapsulates the area behind the prop and none of that inlet air goes tumbling around that area instead of actually cooling the cylinders. Those pieces are temporarily held in place for the the being:

The last bit of work I did for the day was to make a first attempt at putting the lower cowl in place to see how the ramps fit to the cowl inlets. This, too, became another gradual trim party – both the ramps and the side baffles are too long as-is to allow the cowl in place. I took a couple iterations at trimming them, and got pretty close, but I never did actually get the cowl in place before it was time to quit for the day.

Maybe I can get that done tomorrow. I’m off work until January 2, so hypothetically I should be able to get some good work done. Today was a very productive day, and I feel like I’m back in that productive mindset – let’s see if I can keep that momentum going.

Posted in Firewall Forward | Hours Logged: 10

Oil door mostly done

Posted on November 19, 2024 by pclifton

Confession: the hours logged here are pretty much a wild guess. I think I’ve had five or six nights in a row where I was just about to fall asleep and remembered I hadn’t written anything up about the build. Which is to say, I’ve been doing stuff, but not really keeping up with the build log.

When we left off last time, I was about to start worrying about the latch setup for the oil door. As previously mentioned, the approach here will be to use regular old piano hinge, with a bowden cable to release them. The first step was to plan how I’d lay out the hinge halves. At first I got really hung up on wanting the edges of the eyelets on the door to line up with the edges. That was a problem because the door opening is about 1/4” narrower than the eyelets I’d want to line up. I started to think of crazy ways to handle that, before realizing that it was unnecessary.

I started by laying out the hinge on the cowl side. I cut a piece of hinge long enough to cover the opening, plus have an extra eyelet on the forward side, to act as a guide for the cable. I also spent a lot of time trying to think through how to ensure the hinge on the door would clear the cowl, and finally I decided to just line the cowl side of the hinge up with the opening and call that sufficient. That meant I could just go ahead and attach the hinge to the cowl without worrying about fitting everything beforehand.

So I laid out the rivet holes, drilled the hinge and cowl together, and got everything prepped. As usual for metal-fiberglass bonds, I mixed up some loose flox and painted the joint with it before riveting things together. Another consideration here is that due to the recess of the door flange, the part of the hinge that projects forward sits a good bit above the cowl interior. To handle that, after I’d painted on the loose flox, I thickened the mixture up and put a big blob under that forward projection, to fill that gap. The next morning, it had cured up nicely:

Next up was the hinge half on the door itself. The big consideration here was shining the hinge off of the door to get it to mesh nicely with the other half. My initial measurements indicated that some .063” aluminum would work nicely, so I cut a shim off some scrap and went ahead and riveted it to the hinge I’d cut. Things seemed to line up nicely, and I drilled the rivet holes to attach that stack to the door.

But once I was testing the door movement, the hinges wouldn’t mesh any more. Seems that I needed a little more shim action – so I ended up cutting another shim out of .032” scrap (I think), and I got to drill out the rivets in my hinge-shim stack and add the extra shim. With that in place, things lined up very nicely. After testing the door action a bunch more times, I decided it was time to permanently attach everything else – not just the latch hinge half, but also the actual hinge pieces, to the cowl and door. I wanted to do all these at once so as not to waste epoxy – even one pump of epoxy yields about five times more flox than is needed for just one of these joints.

I did take a different approach to these joints. Previously, for these metal-glass joints, I painted on the flox, clecoed things together, and riveted immediately. This was invariably a messy experience; this time, I decided to try just checking things, letting the flox cure, and then come back to do the riveting later. This worked out pretty well – though for some reason I didn’t take any pictures of any of this work…

After going back and riveting, it was time to put everything together and test the fit and action of the door. Things worked pretty well, but the one thing I noticed that bothered me was that the door didn’t quite sit flush with the cowl once I had the spring installed in the hidden hinge. It seemed that that spring – which is there to make the door pop open when it’s unlatched – was pushing up on the hinge side of the door just enough to keep it from sitting flush.

I was able to close the gap a bit simply by tweaking the hinge itself, but it still didn’t really get the job done. I suspected that the flexibility of the door itself was contributing here, and I spent a fair amount of time trying to think of ways to add some stiffeners to the inside of the door, but none of the ideas I had seemed like they’d be especially pleasant to implement.

Then I read an absurdly simple solution on another build log, where the guy simply used the piece cut out of the cowl, epoxied to the back of the door, to add stiffness. Since that piece, by definition, already has the same curve as the door it ought to work well. And here was a case where my poor shop cleaning habits worked in my favor – I still had the original piece I’d cut out of my cowl sitting on the work bench.

It was still plenty big enough for this job, so I got to work. The big fun here was to do the necessary trimming to get it to fit inside the door. I went a little above and beyond by having it extend around the edges of the hinge; probably unnecessary, but since that was the exact area where the door was popping up, I wanted to add rigidity as far in that direction as possible. So instead of just cutting a nice square-ish piece, I had to carefully fit a cutout around the hinge.

Here’s a look at the trimmed cowl piece after trimming. I’d already added some masking tape in preparation for the impending application of epoxy:

Next, I drilled the two pieces together so I could use clecos to hold them while epoxying, did a whole lot of work to rough up the mating surfaces, and also added packing tape on the cowl flanges. The last thing I wanted to do was accidentally epoxy the door to the cowl, after all.

Then it was time to make another batch of flox, paint the surfaces again, cleco everything together, and clean up all the squeeze-out. After that, I reinstalled the door on the cowl, making sure to use both the hinge pins as well as the cleco holes I drilled on the perimeter, to hold the entire assembly in the exact position I wanted it, and thus ensure that it cured with the desired shape.

Here’s a look at the assembly just before I added the perimeter clecos; the packing tape on the flange is clearly visible:

The next morning (this morning, actually) was the age-old fiberglass routine: go find out if I accidentally glued two things together that weren’t supposed to be. It’s always a bit of a relief when the parts that are supposed to separate do just that.

I revisited the setup after work; the big question mark was seeing if this stiffening actually helped the fit problem I was trying to solve, or if I’d just wasted time. I’m happy to report that it now fits up very nicely. I may still sand down the top forward corner (lower right in the photo below) just to really fine-tune things, but it looks pretty good as-is:

I also spent some time sanding off excess epoxy inside the door; it seemed like a lot more squeezed out while this was curing. I tried to make a nice semi-rounded transition between the door and the reinforcement, mainly so there aren’t annoying sharp edges here, but also just because it looks nicer. And finally, it was time for one more function check of the door. It’s a little rough popping up when the latch pin is pulled, but I think I can fine-tune that just by sanding the edges of the eyelets where they contact. For the most part, though, the thing pops up nicely:

I told someone this weekend that when the oil door was done, I was probably done with fiberglass for a while. Technically, I do still need to take care of glassing in the cooling ramps on the upper cowl, and it’s looking like I am still going to need to add a blister to clear the mixture arm, but I think I’m about ready to switch gears for a while. Plus, it’s supposed to cool off later this week, and low temperatures don’t really agree with fiberglass – if it’s cold, the epoxy won’t kick off and cure properly.

So I’m going to pull the engine baffle kit out of the bin and get back to work on that. I think it’ll be nice to get back to doing some regular old sheetmetal work.

Posted in Cowl | Hours Logged: 6

Oil door shenanigans

Posted on November 4, 2024 by pclifton

Yes, shenanigans. It’s the most appropriate word, I think.

The overall goal was to apply filler around the oil door opening so I could get a nice paint gap as well as have the door be flush with the cowl around it. The first step to this was to basically sand off the factory-molded lip around the oil door flange, so I could build it back up. Then there was the really fun part – figuring out a way to add some material to the door itself so that when I laid up the micro, I’d get a reasonably usable starting point for the gap.

First, I tried just using layers of electrical tape, kind of like I did for the cowl pin covers. Problem was, I wanted more layers than I used for the covers, and trying to lay on a bunch of tape while still keeping the edges tight, and invariably, after about three layers I’d get a wrinkle. Then I made a brief attempt to use self-fusing tape, which is thicker, but that just didn’t go well at all.

Finally, I tried using some edge molding I had laying around. This is stuff you might stick inside a lightening hole to avoid chafing, and I thought I could apply it around the door. At first, it didn’t really want to lie flat, but with some strategic electrical tape, it seemed OK:

I followed this up with another layer of electrical tape around the perimeter, and checked the fit against the sanded-out door cutout:

Then it was time to glop on the micro, reinstall the door to squeeze out the excess, and build up as needed around the perimeter:

This ended up being way more micro than I needed, so the next day I had a whole lot of sanding to do to get back down to the proper contour. As I worked that down, I could see that the edge molding apparently hadn’t been flush all around – there was one particular spot where it must have popped out a bit, and so I had an excessive gap. I went ahead and sanded everything down, then worked on fine-tuning the gap, hoping I could make it less obvious, but in the end I wasn’t happy with the result. The annoying spot is at the bottom right of this photo:

So…I sanded all that micro off and started over again. This time I made another attempt at just wrapping with electrical tape, but by being VERY careful I was able to get the whole thing done with no wrinkles. Once again, I glopped on the micro, added the door, and built up as needed:

This time, the results were better. It was a little annoying to go through thee exact same contour sanding operation again (at least I used less micro this time), but after it was all said and done, things were looking pretty decent, though I think I’ll still end up doing more fine-tuning of the gap here when I finish the cowl as a whole:

So now I suppose it’s back to the hinge and latch…

Posted in Cowl | Hours Logged: 4.5

Oil door stuff, cable planning

Posted on October 29, 2024 by pclifton

I have been working on the project – maybe not as much as I like – I just haven’t been writing about it. Picking up from where I left off last time, I got in my Aircraft Spruce shipment, and got right to work on the oil door.

To start with, I located the door in the cutout and drilled a few holes around the perimeter; this allows me to cleco the door in place while I work on other fitting-related items. First up in that department was the hidden hinge. This is pretty straightforward; the measurements given for locating the hinge half on the cowl looked good, so I drilled and checked it in place.

The half for the door required a bit more work, though. It didn’t want to sit flush against the door itself; I suspect this is due to the cowl having a bit of a conical profile here, rather than a pure cylinder. Other builders I’ve read have used shims or flox to fill the gap; I instead decided to tweak the bends on the hinge itself to get a good flush fit. Basically, I needed to close up the sort of C-profile a bit on one end to pull the flange down. Then the entire flange needed to be bent a little to get a flush fit.

After numerous iterations of this bending, things were nice and flush and so I went ahead and drilled the hinge to the door as well:

Once this is riveted in place, there will be no visible hardware for the hinge at all:

The next logical course of action would have been to work on adding filler around the door to set the paint gap, but at some point I unilaterally decided I needed a break from fiberglass, so I decided to poke around at other firewall-forward things. This led me to revisiting the throttle and mixture cable routing. Specifically, I wanted to see if I could tweak this setup to help with my potential clearance issue between the mixture rm and the lower cowl. I really don’t want to have to mold a blister down there for clearance if I don’t have to.

To make a long story short, I determined that I could position the mixture arm further back, but not with the cable mounts as provided with the Showplaces cable bracket I bought. But all I really needed was to move the cable down and sideways a bit, and add a bit of angle. Normally I’d fabricate a bracket for something like this, but the bracketry here is 4130 steel instead of aluminum, which I imagine is related to this stuff being really close to hot exhaust pipes.

So I ended up dusting off some 20-year-old neurons, relearning how to do basic CAD modeling, and designing a slightly modified cable bracket, which I then ordered from SendCutSend. I’m pretty optimistic that this will help a lot with my cowl clearance issues:

From here, I guess I need to get over my anti-fiberglass feeling and get back to work on that oil door. I think that’s the last thing I really need to do before I can move on to the engine baffles – which is the task that started me on this whole cowl odyssey…

Posted in Cowl | Hours Logged: 3

Pin covers finished, on to other cowl things

Posted on October 21, 2024 by pclifton

We rejoin the fun times from Sunday morning, where I went straight to work on all that micro I laid up around the pin covers. Unfortunately, my electrical tape trick didn’t work out perfectly – the tape ended up sliding off the edge of the pin covers in a couple spots. As a result I had no gap at all towards the aft end of both covers. The plus side is that since micro is way easier to sand than epoxy and glass, this wasn’t a huge problem. After the initial contour sanding, I went to work slipping sandpaper around the cover edges to clean up and open up the gaps as needed.

The resulting gaps aren’t what I’d call “perfect,” but this time I really am satisfied leaving it alone:

Looking at it from an oblique angle, the covers line up much more nicely with the cowl curve thanks to the contour sanding, though again the aft end of the right side cover is a little proud…oh well:

The next task will be the oil door. I pulled the upper cowl again, but before getting to the door, I finally took the time to sand the rivet line at the firewall edge. This is harder work than messing with the covers, but at least it’s not finicky. Basically I just go to town with 40-grit until the area is relatively level, then follow up with 100 grit on a soft block to smooth out the scratches.

I also went ahead and did a first round of scuffing on the perimeter of the oil door opening. The finish here was kind of crappy to begin with, especially the edges of the recess for the door, so I fully intend to reform this whole area with filler as part of the oil door fitting process. The micro needs a rough surface to adhere to, plus I want to sand the existing recess edges back to a bit of a bevel, kind of like I did with the pin cover openings. I’ll still want to do more work on that bevel, but this is a start:

For Monday’s work session, I did some more detail work. While I’d refined the paint gaps along the sides of the cowl and the cheeks, the spinner joint was still way too tight. So I joined the halves on the bench and spent about half an hour working on those until I had a nice gap in place:

Then it was on to the door itself. The door is provided as a prefab fiberglass unit, but it’s oversize and needs to be trimmed down. There are scribe lines on the door as trim guides, but upon close inspection they’re not perfectly straight, nor are they even. So while I used them as rough guides, in the end I put in my own work to properly squares up the trimmed door. Here’s the door before trimming:

My approach was to first rough cut one of the curved sides, sand it roughly straight, and then fine-tune it. For the fine-tuning, I glued sandpaper to a piece of aluminum angle; resting the door and the angle on the table made it easy to gently sand a very straight and very square edge.

One that was done, I used a square to lay out the other three cut lines, and repeated the process of rough cutting and then sanding to exact shape. Finally, I traced out radii for the rounded corners I wanted, and hand sanded those to shape. My cuts ended up a bit outside the scribe lines in some spots, so I also hit the perimeter of the door with 100-grit on a soft block to smooth things out a bit.

Here’s the trimmed door sitting in the cowl cutout:

The next question will be how I want to locate and fix the door in place on the cowl while I do the hinge and latch fitment. I might just end up drilling a few perimeter holes where I can cleco it in place, but I’ll want to think on that a bit. Food for thought while I wait for my parts from Spruce to come in.

Posted in Cowl | Hours Logged: 3.5

Cowl pin cover refinement

Posted on October 20, 2024 by pclifton

So, in a development that will probably be completely unsurprising to folks following this build, I found myself unable to leave well enough alone with those pin covers, which led to some work sessions over the past few days.

First up, as mentioned previously, I tried spacing the covers out a bit with washers. I liked the way this placed them against the cowl, so I decided to keep that spacing. As a first step, I attached each washer in place with a bit of superglue, using the screws to hold them in place while the glue dried. That gave me “permanent” spacers to start with:

I wanted to shoer up the rest of the area back there, though – with just the washers in place, the covers were able to rock around a bit, since they were now only making contact on the washers themselves. I fixed this with some good old-fashioned micro filler; I mixed up a match, smeared it around the edges of the cover recess, and then installed the dummy covers in place, which squeezed the micro to cover the entire mating surface. The next day I opened the cut lines again, cleaned off the excess, and ended up with a nice mating surface:

From there, I started fiddling with the gaps some more. At first I thought I might have found a way to clean up the gaps without using more filler – I started playing around with working sandpaper between the edges of the covers and the cowl, and carefully removing material that way. Unfortunately, I eventually decided this wasn’t going to work. First off, it would take me an absurd amount of time to open the gaps up that way, but more importantly, the largest gap was big enough that if I evened everything to match, I’d have an ugly setup all around.

So I resigned myself to using more micro filler here. I experimented a bit with using electrical tape around the covers to allow for molding the micro with a decent gap from the get-go, and it seemed to work out fairly well. Then I got the Dremel out and committed to the task by sanding a bevel all the way around the cover openings on both sides. I also rough-sanded the area around the cover to ensure the filler would adhere; since I’ll be blending a contour here, I wanted to carry the filler an inch or so away from the opening in all directions.

Sanding that bevel also meant messing up that nice micro layer I added before, but no worry, it’s going to get replaced:

Next was final-prepping the covers. The backside has a layer of clear packing tape, while the front is protected by electrical tape – this will protect the covers when I’m contour-sanding this later on. Finally, I wrapped I’ve layers of tape around the edge of each cover, then carefully trimmed off the excess on the backside. I left the excess on the front, figuring it would provide a nice surface to push the filler up against:

After that, it was pretty much repeating the previous procedure; wiping micro around the edges of the openings, then installing the taped-up covers. This time, to accommodate the contour sanding, I added more micro around the perimeter, pushed up against that extra tape. Like any good application of filler, the immediate aftermath looks awful. I’ve come to accept that this is just the way it is:

One thing I’ve learned to make the micro mess a little better is ti wait about half an hour, then use a gloved finger to pack the filler down and smooth it out a bit. This makes things a little easier for sanding, and also allows me to fine-tune the distribution of the stuff. When the filler is fresh, there comes a point where the more I try to spread it, the more it just adheres to the popsicle stick I’m using and makes things worse. But once it’s set up just a bit, I can move it around with a little more finesse.

Another item I’ve been poking at this week is the oil door, which will be the next item to address. I’ve always intended to go with a hidden hinge – a fairly common modification – but for some reason I had the idea in my head to fabricate my own instead of just buying the $40 unit from Spruce. For once, I did the smart thing here – I started drawing up a design for my own hinge, trying to figure out the geometry, then after about half an hour realized that this was a dumb thing to burn a lot of extra time on. Prefab hidden hinge it is!

The other oil door consideration is how to latch the door. The plans method is just a couple quarter-turn fasteners, which I don’t like at all. I’d been considering using Hartwell latches, or the common push-button Camlock type seen on a lot of certified aircraft. But after doing some research and poking around, I’ve decided to go with a hidden latch as well. I got the idea from this build log and I like the simplicity. It uses simple piano hinge halves, with a Bowden cable acting as the hinge pin. The cable extends to the town inlet up front, and the door is unlatched by simply pulling the cable out about 6”.

This approach means I don’t have to make careful cutouts in the door for a latch system, in addition to making things look nice and slick with no visible hardware. I also like that it’s pretty fail-safe – an oil door that gets stuck closed is a big problem, because removing the cowl requires reaching in through the oil door to pull cowl pins. Some of the other, more complex hidden-latch setups would make me concerned about a possible failure becoming a real annoyance. The cable setup should be pretty bulletproof.

Posted in Cowl, Uncategorized | Hours Logged: 4