Cowl

Let’s see…when we last left off, I was about ready to start working on the spinner-cowl gap. I hung the cowl back on the airplane again and went to work tuning that gap. I changed my approach a bit, though…previously I was trying to work my way up to a 1/8” pice of aluminum with sandpaper glued on it, but I realized there was a better (more incremental) way. I already had a piece of .063” aluminum with sandpaper, and…well, I just started adding layers of packing tape on the back of it. This worked a lot better than trying to jump from one sanding “file” to another that was almost twice as thick.

However, I noticed an issue while working on this – I could see the upper edge of the lower cowl deforming inward when I was sanding in that area, which was working against actual sanding productivity. So I decided this was a good time to pause on the sanding and go ahead and lay up my joint flange between the cowl halves.

This ended up involving more prep work than I actually expected. First up, I revisited the gap between the cowl halves. I’d opened this gap up way back in the early fitting days, but over the course of various iterations and such it had closed up a bit, so I went back to my old technique of working sandpaper into the gap to open things up again. The next issue was to address alignment between the halves. There was still some extra material trial on the lower cow, remnants of the original flange that I cut off. I ended up doing several iterations of removing material there until the inside surface of the cowl halves mated up pretty reasonably. I didn’t want my flange layup to have to do any kind of big ugly jog. I finished up the prep last night by carefully taping up the mating area on the upper cowl.

This morning was the official layup day. I double-checked my tape job – don’t want to accidentally epoxy the cowl halves together – then joined the cowl and got it set up in place on the workbench. I did the usual fake prepreg trick here, wetting out six layers of glass between plastic, then squeegeeing the excess epoxy out and cutting out strips to lay up in the flange area. Then I stuck them in there, carefully stippled out any air bubbles, and left it to cure:

By the time I came back home from coffee with the neighbors, the glass was setting up nicely. I gave it another hour or so, then it was time for the big question: would the cowl halves separate? Good news, they did! The raw layup was pretty nasty-looking, but it needed to cure some more before I did any trimming and cleanup:

Later in the afternoon, I marked the edges and trimmed off the excess, sanded the edges to some reasonable standard of cleanliness, and match-drilled the pilot holes for the attach screws. Now I can cleco the halves together and make the prop spinner area nice and rigid:

Later in the evening, I hung the cowl back on the airplane and got back to work on that spinner gap. It continues to be tedious work, but the gap is looking pretty even now. The main thing I need to work out now is getting the upper and lower halves flush – my sanding approach doesn’t seem to be making this happen. I might need to work on that with the cowl off the airplane…

At some point I got tired of the spinner gap tedium, so I pivoted to working on cleaning up the lateral joint between the halves. Things don’t line up perfectly here, so I’ll be sanding this seam in order to make for a nice smooth transition. Here you can see where I’ve cleaned things up towards the forward end, whereas further aft it still needs more attention. Plenty more work to be done here, I’m afraid:

Yup, I’m back at it again. Turns out a nice late-summer cool front is good motivation to get back out in the hangar.

First I picked back up on smoothing the lateral joint between the cowl halves. This was some pretty tedious work to be sure; there was a fair amount of material to be removed in many places to get the smooth transition, as well as smooth out the rivet heads. It doesn’t help that I’m sanding glass layup and gelcoat here, both of which are a lot tougher to sand than, say, micro.

At some point, I decided to spend my breaks (read “when my arms got tired”) working on fixing up the gap between the halves. This was generally OK in the middle of the joint, but too tight towards the ends. I took a hacksaw blade and carefully worked it from the OK areas out to the less-OK areas, this opening up a nice eve gap. The trick was to go slowly so I didn’t start cutting into the hinges. I followed the hacksaw blade up with some of my heavy-duty sandpaper, which was better suited to selectively sanding the actual fiberglass instead of the hinges.

The results are kind of hard to capture on camera, but I gave it a try anyway:

Eventually there was nothing to do but get back to working on that pesky spinner gap. I’ve been gradually opening this up by using a strip of sandpaper glued to a piece of aluminum. Working it between the spinner and cowl applies a little pressure to take material off the cowl, and as the gap opened and the pressure slacked off, I’d add strips of packing tape to the aluminum, This allowed me to gradually open up the gap until things started to even up.

Here again, it was pretty tedious work, but eventually I decided I was satisfied with the gap:

Next, I pulled the upper cowl off and started working on blending all that micro into the existing cowl profile. As usual for micro, there was a lot of extra material here to sand off, but at least it was mostly easy to blend the transition. The only exceptions were where the cooling inlets join the prop spinner, making for some compound curves.

I still need to work on rounding the corners here – the spinner face is flat, the transition areas are flat, but they join at a sharp angle. I’ve also got a fair number of voids and pinholes that will need to be filled, and I think I want to add some micro on the inner portion of the spinner ring as well. But before I do any of that, I want to get that corner rounded, since there’s a good chance that’ll expose some more voids.

Quick one tonight. I worked a bit on rounding over the transition from the upper cowl surface to the spinner flange, though I didn’t put a lot of effort into making it perfect. Mostly I wanted to get in the general neighborhood just to see if I uncovered any more pinholes that needed filling. (which I didn’t)

With that done, I decided it was time for another application of micro. The main purpose was to fill the various holes that had opened up while I was sanding, but I also wanted to build up the inside edge of the upper spinner flange. When I sanded that down previously, I discovered I hadn’t really gotten the micro far enough over the transition to cover everything. So after working micro into the various voids, I smeared a bunch of it into that inner edge.

One thing I’ve learned about dealing with micro is that while it’s nigh-impossible to put it on cleanly when it’s fresh, if I just wait about half an hour for it to set a bit, I can come back out and use a gloved finger to massage it much closer to the desired final shape. This really helps to cut down on the sanding compared to my previous method of just glopping on about three times as much as I thought I needed, and ensuring that the low points were still high enough to sand off.

So that was my last act tonight; now I get to wait until tomorrow and have yet another round of sanding on this lovely modern art masterpiece:

Let’s see – looks like our last installment was when I went and did some void filling around the prop spinner. I did work on sanding that the following day, even though I didn’t write about it then. And of course, in the process I saw quite a few more voids that I neglected to fill.

So when I picked up again last night, I mixed up yet another batch of micro, and went around applying it to yet another batch of voids. Then today was, of course, sanding day again. After working over everything, I did turn up a few more pinholes, but at this point I think they’re all too small to effectively fill with micro – I’ll worry about them whenever I do a general pinhole/finish skim coat on the cowl halves.

After that, I decided I’d fit things together sufficiently to get back to working on the pin cover cutouts. A few rounds of trial-and-error, slowly massaging the cutouts, got me to the place I wanted, where the dummy covers fit nicely into place. The only thing that annoys me is that they won’t sit flush against the cowl the whole way around. Whenever I lay up the flange behind these, I’m just going to have to decide how I want them to sit and deal with the consequences…though I’m a little tempted to let the cover sit a little proud, and do a little micro buildup around them to get things sitting a little nicer. On the other hand, that sounds like a lot of work for maybe limited benefit.

Anyway, the dummy covers fit nicely now:

I also worked on setting some more paint gaps, specifically around the outside cowl corners, and where the spinner halve meet. I’m pretty satisfied with those at this point.

I think my next move is to do the layup behind the pin covers and get that flange established where it needs to be. Which means I’ll have to make a decision about how the covers sit against the cowl. It also means I’ll have to stick my entire upper body into the cowl, just to reach that inside area where the flanges will go.

Overall, I think I’m getting perilously close to being able to resume the actual cowl work steps outlines in the construction manual. I think maybe the next things will be attaching the cooling ramps, and working out the oil access door…

Today was the day I finally did it – I convinced myself to stop overanalyzing and just go ahead and get the glass work done for these pin covers. I’ve been sort of putting this off for a while, probably because there’s a sort of finality to actually mixing up fiberglass – though the reality is that you can cut/sand off pretty much anything and redo it. I’d rather avoid that, though…

I did have one epiphany since the last work session, though. At that point I was wondering about dealing with the covers not quite sitting flush with the cowl (the curvature doesn’t match 100%), and I’d had the thought to have them sit a little proud and then add micro to get the contour right.

The epiphany was to basically do the opposite – set the covers so they were flush at the highest points, and then sand off the fiberglass to get the contour I want. In one sense, it’ll be tougher – sanding an actual layup is a lot more work than sanding micro – but on the other hand, I don’t have to deal with coating the front of the covers with release agent, slapping on a ton of micro, and then dealing with the inevitable voids. The other concern could be sanding all the way through the layup, but since I’m adding material on the inside to create the flange behind the covers, that’s not a real concern.

So I got to it today. First up were a couple of prep steps – the dummy covers used for fitting needed a few coats of wax to act as a release agent, and the insides of the cowl needed cleanup. Alternating between the two tasks worked pretty well – put a coat of wax on the covers, then go to town inside the cowl with the Dremel on the flox I added a while back. Once I was happy with that, I got the cowl assembled on the work table, and paused for a bit to allow the wax to dry.

Next was taping the dummy covers in place. The holes are snug enough to grip the covers just a bit, which means the tape isn’t doing a ton of work; it’s just there to help ensure the covers don’t move while the glass work is happening. This was also my opportunity to get the flush/proud/inset positioning I wanted. This photo of a cover taped in place highlights how the ends of the cover at relatively flush, but the middle is inset. The overhead lighting really accentuates the resulting shadow:

On the inside of the cowl, the flat backs of the covers don’t match the cowl really at all, so the first step is to mix up some micro and smear it around the edges of the cover; this provides a relatively even surface to top with glass plies later on. I was a little worried about moving the covers around while doing this, but they stayed in place very nicely:

While that micro was getting tacky, I moved on to the glass portion. I’d already measured before to determine the proper size for the glass pieces, so I used that to cut some glass and do the tried-and-true prepress technique – wetting out the glass plies between two layers of plastic, squeegeeing the excess off, and cutting out the pieces I needed. Then I just got to lean way inside the cowl – again – and stick them in place. Some work with gloved fingers and a chip brush worked out air bubbled, and then it was time to sit back and wait for it all to cure:

Next up will be removing the tape, drilling the screw holes, and then I get to lean inside the cowl yet again and re-separate the halves – at the moment they’re bonded together. I’m a little nervous to see how things look with the real covers in place, but I should get that chance tomorrow, I think. Another one of those moment-of-truth situations…

OK, time to get these cowl halves split again. The portion forward of the covers was pretty easy; a hacksaw blade slips nicely into the gap, so I could cut right up to the cover. Then I went inside and used a Sharpie to mark a cut line from there back to the back edge of the cover. The good old oscillating saw let me make shallow cuts along those lines. Then I got a flat blade screwdriver into the cut and was able to drive out the covers, and finally finish the cut with the hacksaw blade as needed:

Next up is adding nutplates for those screw holes, then removing excess fiberglass. I need an opening so I can actually access the pins to split the cowl. I decided to just make this opening the entire length of the cover cutout – after all, I only really need the material to locate the nutplates, right? (more on this decision later…) After that trimming, plus the requisite cleanup with sandpaper and such, I rejoined the cowl halves for a fit check:

Then I figured I’d test-fit the final covers to see how things looked. These are a bit smaller than the dummy covers; this is intentional to leave a paint gap. Interestingly, the right cover (shown below) ended up not exactly centered in the cutout. Not entirely sure how this happened:

A different angle shows how far the cover is inset on the top side; this is expected, as I mentioned in yesterday’s post:

It’s kind of amusing the decision I made yesterday which was intended to avoid working with a bunch of micro here, because it looks like I’ll be doing that after all, thanks to that odd final fitment issue (the other side is similar, though not as bad). I think what I’ll do is first sand the area to match the contour and fix the inset issue, using the dummy covers again. I assume that this will yield an irregular gap, which I can then fix in the usual fiberglass fashion: stuff in a bunch of micro and sand, sand, sand. We’ll see.

Late-breaking update: I went back out and decided to try fitting the dummy covers in place. I had the thought that maybe somehow the screw holes and/or nutplates ended up slightly out of location, and that was what caused the real covers to look so off. If so, then when I popped the dummy covers back in place, I should see misalignment with the screw holes.

I did not, in fact, see any such misalignment, and I was able to screw the dummy covers in place just as easily as the real ones. So now I’m wondering if this is a visual effect from the covers not matching the cowl contour. I guess the upshot is that regardless, my first move is to get to work sanding those contours, and then I can decide from there what I want to do next.

When we left off last time, I was dealing with some weird gap appearances around the pin covers. First step for dealing with this was to work on sanding the cowl counters to match the dummy pin covers. I put electrical tape on them to save them from sanding – not for cosmetic reasons, since they’re throwaways, but really just because I only want to sand the cowl, not them – installed them, and went to town. At first I was trying to use a small block, but I was finding it really awkward. Instead, I decided to break out my oscillating multitool and use it with a 60-grit sanding pad. This worked out really nicely; I was able to carefully localize the sanding to just outside the covers, and ease the material off nicely. Doing this did leave a bit of a bug just outside where I was sanding, but the block I was using before worked well for cleaning up that contour.

With the dummy covers showing a nice consistent contour all around, I swapped in the real covers, expecting things to look much better, Well, they did look better, but still not like I was expecting. For example, the right-side cover still had a really prominent overhang going on in the upper rear area:

I find this mildly annoying. The idea of this pin cover kit is that you do all the fitting with the dummy covers, then swap in the real ones, which are slightly smaller and thus allow for a paint gap. The implication here would seem to be that all the contours should be the same, but my experience isn’t showing that.

Another reason for using the dummy covers is to avoid marring the real ones, but at this point I decided there wasn’t much to do but to instal the real covers and use those as a visual guide for refining the contours even more. As before, I covered them with electrical tape for protection, and went to town with the oscillating tool again. This time, of course, I was really careful working near the covers.

In the end, I got things to a point where I was satisfied with the overall fit. It’s not picture-perfect, but at some point I need to calm down here or I’m going to end up sanding this cowl on a daily basis until I die of old age.

Similarly, I’m still not 100% pleased with the fit when viewed from the side. Again, given how the dummy covers are supposed to be used for fitting, I’d expect to have a nice even gap all around, but instead things are definitely uneven. But I don’t really have any desire to go nuts here trying to make things perfect. At least not right now…who knows what dumb idea I might given a few days to mull over it

Anyway, here’s the side view:

Also shown above, but maybe less obvious, is some more fiberglass work I did here. When I originally opened up the cover backing to allow access for the pins, I took the opening all the way to the edge of the pin cover opening. The results, when the real covers were installed, were obvious openings at the forward/rear ends of the cover. I guess they might not have really been noticeable in the real world, but they were bugging me…so I decided to fill them in.

To do that, I did the usual scarf-joint dance: sanding the existing glass to a knife edge, then laying up some more small strips at the ends of the openings, with the dummy covers in place to keep things neat. Then, the following morning, I got to split the cowl halves again and do some more cleanup. Now those inner flanges extend a bit all around, and provide a nice backing for the covers:

Back to this evening, I finished things off by fitting the lower cowl back on the plane. I think my next move is to take the temporary pins I’ve been using and get them trimmed to length and formed for actual usage. The big question in my mind is what I want to do with the forward ends. These need to project past the forward extent of the hinges, and I need to be able to reach in with something like needle nose pliers to grab and extract them. Not sure if I want to just put a little 90° bend up here, or bend a little grab ring, or what. I think this calls for some research into what other people are doing.

Didn’t put in a ton of shop time today, at least partially because I’m annoyed at it still being 90+° in October. You’d think I’d be somewhat used to that after 11 Houton summers, but nope, the way it stays hot so late still bugs me every year…

Anyway, I decided to work on finalizing the cowl pins. I knew I was going to need some sort of bend at the forward ends, but I’d been thinking of a few ideas for a day or so. I did some poking around with other build sites, but didn’t really find any solid information. So today, I found some scrap Romex lying around and found that it was a good size for doing some tinkering with what shape I wanted. I settled pretty quickly on having the pin bend inboard about 30° at the forward most hinge eye, then bending a little eye shape about an inch and a half away. After mocking it with Rolex, next I did a trial bend on some extra pin material I had lying around, just so I could do a trial of actually inserting/removing the pin.

That worked out well, so I moved on to the real pins. Nothing really exciting here, though it did take a bit of trial and error to get the bend just right. I wanted the eye to be clear of the back of the pin cover, but only just barely, so I could still easily grab it with needle nose pliers. Then it took a couple iterations to trim each pin to the proper length and grind a point on the aft end to help it get through the hinge eyes.

The resulting business end:

With the pin fully inserted, it tucks into place nicely:

With that done, I had the opportunity to get a look at the cowl sort of in its final form, with the pin covers installed. At least the gaps look just fine from 10’ away:

Speaking of those pin covers and they gaps…as I sort of anticipated yesterday, the more I look at those gaps, the more they annoy me. In the midst of thinking about that today, I randomly tried adding washers behind the pin covers, and found that having them sit just a bit higher does help aesthetically. So now I’m considering adding a little material to the packing there to make this extra spacing permanent…but then there’s the question of correcting the gaps.

I’m considering opening up the edges a bit, then packing micro back there and installing the covers over it to set better gaps (and, by extension, the nearby cowl contour). The main problem there is that I’d need to find some way to tape the cover edges to establish the gap, like maybe five or six layers of electrical tape. It might work, but it also feels kind of fiddly to me. So I dunno, I’ll still be mulling that over for a bit.

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.