Cowl extension cleanup

So the last two nights’ work has been doing lots and lots of sanding on that extension piece I grafted not the cowl. The basic idea here was to sand a scarf, lay up multiple layers of cloth, and then sand the overlapping area back down flush. This was, to put it lightly, quite a bit of sanding. Especially since resin and cloth makes for some pretty hard stuff that doesn’t exactly sand easily.

It also makes it more fun that this is a contoured surface, though at least it’s not a compound curve. Still, that means my normal tools for trying to sand a straight line, like a nice sanding block, are no good here. I ended up wrapping sandpaper around a deep socket – yes, you’re reading that correctly – to make a sort of round sanding block. Then I went to town with that thing, for…a lot of time. I think it was about 45 minutes in that I really wanted to go tell Past Philip that that old gap really wasn’t that bad after all…too late now, though.

Tonight, I finally got things sanded down to a relatively flush point, so I switched to a soft foam block and 60-grit paper to finish the blend between the old and new glass. The result of all that work was this:

Next up was getting started on re-trimming that extension. I basically repeated the initial trim steps – laying the cowl in place, marking a conservative initial cut line, then gradually sanding the edge to fine-tune the fit. After a couple iterations, I was able to pin the two cowl halves together again. The gap still needs some work, but I think I’m going to go with the approach of riveting all the hinge halves in place before I remove any more material:

Oh, and I’m still not done sanding here, even ignoring the gap itself. I took a wild guess that eight layers of cloth would be about the same thickness as the rest of the cowl, but that looks to have been too many layers. The new grafted edge is a decent bit thicker than the rest of the cowl, to the extent that I can’t pin the upper cowl to the firewall right now – too much misalignment. So I’m going to have to work on thinning that extension down some before I can put this whole task to bed.

In retrospect, it probably would have been smart to do some test layups to get an idea of the finished thickness of different layer counts. But, much like the whole “that gap wasn’t so bad after all,” that ship has sailed, and there’s not much to do except…more sanding…

Posted in Cowl | Hours Logged: 2

Initial pin cover fitting and other misc stuff

Worked on a few different things today, all of it looking towards getting those hinges riveted in place. First item of business was laying out and rough cutting the cowl pin covers. With both cowl halves in place and pinned together, I used the cover templates to trace the outline off each side of the cowl:

Then I super rough cut the openings with a spiral bit in the Dremel – that worked mostly OK but boy does that thing like to wander around. Next I used a rotary file bit to shape the edges and get them a little closer to the cut line. The final cut will wait until after I’ve riveted the hinges so I know everything is fixed in place:

Well, mostly. After working on the layup on the upper cowl (more on that in a moment), I went ahead and sanded the cutouts in the lower cowl to snugly fit the template covers. These cheap covers are slightly oversize compared to the actual ones; a snug fit for these templates will allow for a nice paint gap around the final covers:

OK, so about that layup on the upper cowl. I decided I didn’t like how the gap ended up between the right side of the upper cowl and the firewall, so I wanted to add some material so I could rework the gap. The basic idea here was to sand a scarf joint and lay up a bunch of layers of cloth to overhang the edge. To get the contour of the cowl right, I clecoed a piece of aluminum scrap in place on the outside and covered it with packing tape to keep the fiberglass from sticking:

Then I laid up eight layers of cloth on the inside, which should give me about the same thickness as the original cowl edge. Once this cures, I’ll have a lot of sanding to do to clean up the scarf joint here, before I even get to working on the actual edge:

Finally, while working on other stuff, I had an idea for improving the cowl alignment at the firewall. The basic issue here is that the very upper edge of the lower cowl is unsupported, along with about a 6” portion of the upper cowl in the same area. So while everything else is pulled into nice alignment the upper edge of the lower cowl sits a bit proud of the fuselage skin:

The construction manual suggests possibly drilling a hole in the firewall for the hinge pin to slide into, this providing some additional support for this area. That seems like a decent idea, but I’m not a big fan of unsealed holes in my firewall, no matter how small they are. But I realized that I might be able to add some aluminum blocks inside the firewall flange, which could in turn force the pins inboard and pull the cowl edge into alignment.

Some experimentation with scrap from my panel cutout looked promising, so I cut a couple pieces and match drilled them. I also added a taper on the forward edge of the spacers, to help guide the pins into place as they’re inserted. These pieces still need some final trimming and cleanup, but the idea seems sound:

Much better alignment with the spacer in place:

I guess the next order of business will be cleaning up that flange extension – as mentioned, lots of fun sanding in the works there. Then maybe I’ll see about riveting all these assorted hinges in place…

Posted in Cowl | Hours Logged: 3

Cowl repair/hinge prep

So…I was prepared this morning to go forward with my plan to rough-cut the pin covers, then pivot to working on the hinges. Instead, I took a brief detour. As I was considering the placement of the covers and marking the cut lines, I decided that it’d be a good idea to patch up the previous pin passthrough cuts I made. These cutouts are just a bit forward of where the new cover cutout would be, close enough that I figured I was likely to mess up the cover cutouts if I went back and patched the old cutouts later on.

So I pivoted to working on those. I sanded the perimeter to a decent taper, then laid up four strips of cloth across the inside of each cutout. I pressed the cloth just a bit into the cutout, mainly to ensure good contact with the taper I’d sanded. The basic idea was to bridge the gap with cloth, then come back later and add flox to fill things out (the latter bit was done this evening).

In the meantime, while the first layup was curing, I pulled the horizontal hinges and deburred all my rivet holes. I also countersunk the rivet holes in the lower cowl…upper cowl will wait til later, ie once the current layup/patch work has cured.

So tomorrow I’ll get to do more sanding (it never ends with fiberglass work), then I’ll probably take an initial look at the gap between the upper and lower cowl. While I don’t want to try to get it precise until the hinges are riveted, I’d at least like to get a rough fit done. In particular, right now there are a couple spots where the upper and lower cowl halves make contact and interfere a bit.

I think I’m also going to add some material back to the upper cowl and rework some of the gaps there. There’s one spot in particular where I ended up with a much larger gap than I really wanted.

Posted in Cowl | Hours Logged: 1.5

Upper cowl hinge fit

Straightforward stuff again this time. Last night I opened up a small passthrough on the upper cowl for the hinge pins, then laid out the rivet locations. Tonight I made some bracing blocks from wood, to support the aft end of the upper hinge half while drilling, then got the upper cowl in place and did the actual drilling.

I’m now trying to decide whether I want to go ahead and mark/cut the openings for the hinge pin covers, or if I should go ahead and rivet the horizontal hinges in place first. I’m kind of leaning towards the latter approach – I’ll likely want to do some sanding/shaping at the horizontal cowl joint, especially towards the front where the covers will be, and I can’t really finalize all that sanding/shaping until the hinges are permanently attached. The main reason for that is that things always fit differently with actual rivets instead of clecoes, and I don’t want to do any finish-fitting (eg setting the gap between cowl halves) with temporary fasteners in place.

On the other hand, just cutting the cover openings is pretty low impact, and would make installing/removing the pins a lot easier for the time being. The point at which I’ll want something resembling final fit is when I add the backer flange for the covers…but that can wait a little while. Maybe I’ll rough-cut the covers tomorrow and then switch gears to attaching the hinge halves.

Posted in Cowl | Hours Logged: 1.5

Lower cowl hinge fit

Just more chipping away at the cowl hinge. Last night, I worked on modifying the lower cowl-firewall hinge. In order to accommodate the new horizontal hinge location, I needed to remove one eye from the cowl half of the firewall hinges. Once those were trimmed, cleaned up, and reinstalled, I got the two lower horizontal hinge halves cut to length and those cut ends cleaned up as well. I also broke out the rivet fan and marked all of my rivet hole spots on the lower cowl.

Tonight was drilling time – just clamping each hinge half in place and doing a lot of drilling, moving clamps, adding clecoes, and so on. Once the two lower halves were drilled and flecked, I marked the upper halves and got those cut to length as well. Last order of business for the evening was to lay the upper cowl in place again and mark the area where I needed to remove some material to accommodate the hinge pins during fitment – that’ll be where I pick things up next session.

In the meantime, hey look, it’s a hinge:

Posted in Cowl | Hours Logged: 2

Cowl hinge layout

So the general to-do item right now is to redo the cowl hinges. But before I can figure out the length of the hinges and their layout, I need to decide where to locate the hinge pin covers. This has been a source of quite a bit of head-scratching and second-guessing over the past, well, six months. All that time when I wasn’t making blog posts, I was still occasionally taking a look at this issue and trying to figure out how to solve it.

These nice machined covers from Aerosport Products are intended to match the profile of the cowl, but that kind of depends on putting them in the right place. And while they have specific instructions for locating the covers on some RV models, the RV-8 is not among those. I’d previously tried using the RV-7 instructions as a starting point, but they didn’t really work due to apparent differences in the cowl design. So that left me with trying to reason the whole thing out.

To save some time, I’ll skip to the end here – I decided the best way to experiment with location and fit was to make a female mold of one of the mockup covers (these are used for fitment instead of the actual covers). So I covered the, um, cover with plastic wrap and then laid up a few plies of fiberglass over it. Once cured, I sanded the mold to shape, and now I had a way to truly visualize how the perimeter of the cover would rest against the cowl.

This still wasn’t the panacea I might have hoped for – while it gave me a good look at fitment, it also showed me that there was apparently no location where the cover would perfectly match the cowl. That at least allowed me to stop trying to think the problem into submission, and I just chose the best apparent location and moved on. Later on, I may add some micro around the covers to make them blend in better, but I’ll cross that bridge when I get there.

In the meantime, I moved on to laying out the hinge on the lower cowl. I figured out the overall length, laid out the end locations and the outer rivet holes, and marked my guide points for laying out all the other rivet lines with the rivet fan. I shifted all the holes a bit in order to try and put them in between the previous holes that I filled. This is probably overkill, but…well, I am still me, so here we are.

Drilling will need to wait until another night; first I have to remove the lower cowl again and modify the vertical hinges that attach it to the firewall. Those will now interfere with the new horizontal hinges, so I’ve got to solve that problem before I can get to actually drilling the horizontal hinges – but I have a good sense of how I want to handle the situation.

Posted in Cowl | Hours Logged: 2

Starting over with cowl hinges

What’s this, a blog post? No way!

OK yeah, I’ve coaxed myself past the “walk through the hangar and think of what I should be doing” phase and into, well, actually doing something. I’ve been tinkering from time to time with stuff relevant to the cowl, namely trying to figure out the right placement for my hinge pin covers, as well as a trial run for filling the old hinge rivet holes with flox. The latter isn’t really a complex procedure, but since I had some scrap lying around (the cutout for the oil door), I decided that trying a new technique on something other than the really expensive cowl was a good idea.

Turned out it really was pretty foolproof. Mix up epoxy, add flox (flocked cotton fiber) until I got a peanut-butter consistency, then work a bit of it into each hole. From there, I sort of worked the excess from one side of the material to the other to get good filling of the holes, while gradually scraping off excess. Worked out pretty nicely.

That was…a few weeks ago. Tonight, after doing various household chores, I talked myself out of continuing to sit on the couch and into getting those old rivet holes filled. I just had to remove some of the clecoed hinge pine, mask off some close-by holes that I didn’t want to fill, and then get to wiping flox into the holes…a whole lot of them. In addition to the rivet holes, I also filled the two holes I made in the lower cowl way back when, which I used during the fit-up process.

So now the rivet holes are filled and curing. Next I’ll knock down the area with some sandpaper, then I need to finalize the hinge pin cover locations, before hanging the cowl again and fitting and drilling the new replacement hinge halves. Eventually it’ll be back to working on all that micro I glopped around the prop spinner area, which will be lots of fun…

Posted in Cowl | Hours Logged: 1.5

Cowl shaping

Once again, we have a post here that covers several days worth of work. Most of this work was from a few days ago, but I just consistently kept forgetting to actually write this.

Fun fact: I took all of last week off work, with the intent of putting in a lot of time on the RV. It didn’t really work out that way, due to a combination of being more worn out than I expected, plus lots of other to-dos and prep work for our upcoming vacation. Still, I did put in some time, and I feel like I’m developing that habit of working on the project again. A lot of that probably comes from pushing myself past the “think everything through” stage into “just do stuff.”

The actual form “just do stuff” took was starting to throw fiberglass material at my shaping/fitment issues. The first question at hand was whether I wanted to do any shim work at the forward edges where the hinges were really pulling on the upper cowl. To evaluate this, I assembled the cowl on the workbench and moved all the hinge clecoes to the inside, so I could actually get a better look at the alignment. That also gave me the chance to deburr the hinges after all that drilling. After getting everything together, I decided that shimming wasn’t necessary.

That left the other two big fitment issues: alignment of the spinner surround and forward corners. I really don’t understand how the spinner got misaligned – somehow everything lined up nicely on the bench, but after all the trimming and hinge fitting was done, the lower cowl sat forward of the upper by about 1/8”. The choices to fix this were to either fill the holes at the firewall on the lower cowl, then re-do the trim and hinge drilling, or just work with the front of the cowl…I chose the latter. It helped that I ended up with a slightly larger gap between cowl and spinner on the upper cowl, so adding some thickness there won’t hurt my feelings.

Overall, the plan is to add about 1/16” to the upper, then sand off about 1/16” on the lower, to get the alignment I want. At first I considered adding a few layers of glass for the initial buildup, but at some point I realized that there was no reason not to just use dry micro here as a filler. I also decided to take the same approach to getting the outside corners lined up.

Before I could do any of this, I had to sand off the gelcoat in all the areas I was going to build up…boy, that stuff is tough. After putting a lot of elbow grease trying to hand-sand this, I found that the Dremel with a flap wheel makes much quicker work of it. It doesn’t leave a nice flat surface, but that doesn’t really matter when I’m going to be covering with micro anyway.

Finally, it was time to actually mix the micro and glop it on. As per usual, this stuff refuses to be coaxed into any sort of neat-looking shape on application, so I just put on more than I think I need and accept all the weird resulting protrusions:

Yesterday, I started working on sanding this stuff. First step is just knocking off the obvious peaks and high spots, and getting things somewhere in the neighborhood of the proper form. That wasn’t so bad on the corners, but the spinner area is different. My approach to sanding this to get the gap I want is to make a couple of sanding “files,” which I can slip between the spinner backplate and the cowl with the cowl installed; this allows the thickness of the “files” to easily control the final gap.

The downside to this approach is that the cowl has to be installed first, which means enough of the micro has to be sanded off for it to clear the spinner. To do this, I once again assembled the cowl halves on the bench and used the lower spinner area as a reference for the rough sanding. Then I went to install the cowl halves on the airplane, and had one of those annoying little sidebar issues…which I’ll get to in a second. For the time being, I got the cowl installed and started working on the sanding…which has been tedious, but I’m making slow, steady progress.

OK, back to that sidebar issue: I had the worst time getting the hinge pins started to join the halves. I tested this back when I was deciding if I could skip redoing the upper cowl, and things seemed to go together well…but not today. I probably spent an hour trying to get those pins in. To make a long story short, I probably need to do some shimming of the upper cowl after all.

But this also got me thinking about how I laid out those hinges. Because I wanted to not have the hinge teeth visible in the gap between cowl halves, I offset the hinges up. This means the hinge pin isn’t in line with the cowl split, but rather about 1/4” above it. This causes a couple of annoying problems: one is that maneuvering the pins in the small temporary access holes I cut is tough, but another one is that my rivet holes on the lower hinge half don’t have proper edge distance. The latter would probably be OK, since I intend to epoxy the hinges to the cowl in addition to riveting.

The other result of this decision was that I was going to make my own custom fiberglass cover plates for the hinge pins; these would be removed to access the pins and remove the cowl. At this point, I think continuing with what I’ve done is just going to add more work and time, and I need a lot less of that if I want to get this project done next year.

End result? I’m going to redo the horizontal hinges. This time I’ll put the pin in line with the split line, and I’ll just use the prefabricated cover plates. Those plates are a little pricey, but I think the reduction in custom work is well worth it. I’ll just have to fill the rivet holes I already drilled with flex and start over…that will probably be my next task once I get this spinner shaping done to my satisfaction.

Posted in Cowl | Hours Logged: 6

Upper cowl drilling, plus some black comedy

So, once again, it’s been a while. I’ve been less able to use the heat as an excuse recently, especially over the past couple days…but I’ve still been putting off this whole cowl rework. Just always seemed like it was going to be a big deal, with ample opportunity to mess the cowl up and so forth.

The thing that finally got me moving on this was that after this week, I’m taking a week off work, with the intent of getting in some good build time. I’ve got a bunch of vacation to burn before the year is out, so a staycation is in order. What I didn’t want, though, was to spend that first day of vacation doing an hour of fiberglass mold prep, and then…having to wait a day for stuff to cure. I really wanted to get working on the mold.

The first practical action for this is pretty simple: I wanted to start drilling the upper cowl to the hinge along the split line, and my intent was basically to work my way forward until I couldn’t easily pull the cowl halves into alignment. I figured this would identify the spot where I’d make the cut in the upper cowl, and that’s where I’d start working on the mold and redoing the layup.

So I started on that today, and…well, I made it pretty close to the inlets, with things pulling into alignment nicely. I started to wonder if I could go all the way forward and skip the layup, so I spent some time messing around. While it’s not really possible to pull the upper cowl in in this area, the lower cowl can actually be pulled out and into alignment without a lot of difficulty.

My last test before committing to drilling the rest of the holes was to try removing and reinstalling the hinge pins. My thinking here was that if there was excessive tension caused by the misalignment – the kind of tension that could lead to the hinges breaking in the long term – then it’d manifest in making the pin really difficult to insert. That wasn’t the case at all, though – I got the pins out and back in with no drama at all.

So I finished drilling. The halves don’t pull perfectly into alignment, as shown in the following photo, but it’s close enough that I think I can make this work with just some shimming, filling, and sanding, which is far less of a daunting proposition than completely redoing things here.

And that’s where the black comedy comes in. I have spent literal months agonizing over how best to redo these layups, how to make the molds, how to avoid making things worse, and just generally finding an excuse not to work on this…and it sort of just came together without a whole lot of effort.


Posted in Cowl | Hours Logged: 2

Upper cowl rework – making some molds

So…yeah, it’s me. Last time we were here, I made an offhand comment about the cowl not lining up properly near the front corners. I think I said something about it “maybe requiring a little work” to address. Since then, I have spent a lot of time both thinking of the best way to address this, and trying to avoid the inevitable need to cut out chunks of the cowl and completely redo the layup. It also hasn’t been difficult to talk myself out of working on the airplane with weeks on end of triple-digit heat.

This post is sort of a culmination of a bunch of small assorted work sessions over the past week or two, but with some actual consistent work over the past couple days.

The basic deal here is that I need to find a way to create a mold of the upper cowl as it needs to be shaped – then I can adapt this to the existing cowl and work out scarfing in new fiberglass to fix the areas where fitment is an issue. For while I was intending to start with pink insulation foam board from the home improvement store, carefully sculpted to the right shape. The problem with that is that it would require a lot of work to get the shape right, especially since some part of it would have to match the existing cowl. I did go so far as buying the board and starting to work on it, but that just made me even more aware of how much work would be required.

I’d also considered experimenting with two-part expanding pour foam. I’ve seen folks use this for molds as well, and it has the advantage that I can mold the inside of the cowl as a starting point, then build off of that. So I bought some of the stuff, mixed up a test batch, and…didn’t like it. It wanted to collapse after curing, and didn’t get very hard. I was ready to abandon that, when I talked to someone who said that’s definitely not how it should cure. So I decided to mix up a second test batch, and when I did I saw that one of the component bottles was a lot lower than the other. This stuff is supposed to be mixed 1:1, but apparently I somehow mixed it more like 2:1. No wonder it didn’t turn out well. Test batch #2 was much better, and I finally felt I had something I could try out.

So the next step was to prep part of the upper cowl to essentially take a cast with the foam. This just involved me spending a lot of time laying down plastic packing tape inside the cowl, covering every surface where I’d be molding to keep the foam from, uh, becoming one with the cowl. Then I carefully cut cardboard pieces to create a dam around the area I wanted to mold. Nothing here is straight, so there was a lot of fiddly work to get to this point:

Eventually there was nothing left to do except mix up a batch of foam, pour it in, and hope I’d sealed everything up decently. Then I mixed up a second batch, because I’d vastly underestimated how much I needed to fill this space. Then I mixed up a third batch, because it still wasn’t enough. The result is kinda weird looking, but that’s OK, I expect to cut off a lot of what’s seen here as part of shaping the mold:

Then came the real fun: seeing if this mass would actually turn loose of the cowl. It definitely took some muscle, but it finally broke loose. I also had to spend a bunch of time peeling off all that packing tape, which let go of the cowl in favor of sticking to the foam. I was a little worried about the foam filling in the space around the cowl inlet, but it did pretty nicely:

I did some rough trimming and then decided to leave this piece alone for the night (this was Tuesday, I think). The “outside” of the mold is a little irregular, thanks to the packing tape wrinkling on the various compound curves, but I figure once I’m done shaping this, I’ll hit it with some microballoon slurry to fill out the voids and make a nice surface:

So that was one of the two corners I needed to do this for. Tonight, I spent another hour or so going through the same process for the other corner. So at this point, I have the starter molds for both sides of the cowl. I think the next step will be drilling the upper cowl to the hinges as far as I can, then I can start thinking about the fun part of cutting some big chunks out of that upper cowl.

My current plan  isn’t to completely redo the layup in this area – I’d like to keep those corners with the really tight compound curves, and then basically splice them back into the rest of the cowl. I’m not sure how that’ll work in practice, but I’ll give it a try. The cloth I have should be fine for handling the compound curves, but I’d still rather avoid that fun if at all possible.

Posted in Cowl | Hours Logged: 3.5