Upper cowl hinge refinement

Previously, I mentioned wanting to work on the hinges for the upper cowl before moving on to drilling the side hinges. To recap, the reason for tapering the hinge eyes is to improve the fit where the cowling curves are the tightest – and more specifically, to make it easier/possible to put the cowl in place from directly above. None of this would be necessary if the cowl could be slid in place from a forward position, but that’s not going to be possible once the side hinges are in place.

So tonight I went to work on those hinge eyes with a file. Overall, it wasn’t as tedious as I was expecting, though it still wasn’t exactly a lot of fun. One thing I realized as I did this is that the end goal here isn’t for the cowl to drop right in place from above – that’s just not going to be possible with the way the sides wrap around and down. Instead, I think it’s fine if I can drop the middle (ie not so curved) portion of the cowl in place, and then work the sides into proper mating just by manipulating each side a bit. This still gets me the real goal, which is to be able to get the cowl in place without having to slide it forward/back.

In the end it took just a couple tries to taper the pertinent eyes, and then I was able to get the cowl to pop in place like I wanted. One more little thing out of the way…

With the upper cowl dropped into place yet again, I took a bit of time to look over the alignment on the sides, and I think I’m going to have another item to cover before I can drill those hinge halves. You see, near the front corners of the cowl, where the upper and lower don’t line up perfectly, that misalignment may make it tough or impossible to get the upper cowl to nest properly with the hinge halves. I didn’t spend a ton of time really evaluating the fit, but it may be that I have to address the alignment of those corners – via adding layup material and/or carving out the inside material some – before I can do the drilling.

Working on the cowl is really an interesting love/hate thing. On the plus side, seeing the airplane with the cowl on it is motivating, because it’s really starting to look like an airplane! On the other hand, fitting this thing is turning into one of those multivariate problems where each little thing you need to do is affected by four other things, with all sorts of cascading effects.

But hey, progress is still happening, even if there’s a lot of rethinking on the fly going on…and in the end, the motivation is definitely beating out the fitting challenges.

Posted in Cowl | Hours Logged: 1.5

Lower cowl hinge drilling

So while I’m still not 100% sure what I’m going to do for my cowl pin covers, I’ve decided that figuring that out doesn’t need to stop me from moving forward on getting the hinges in place. So a couple nights ago, I measured the hinge locations for the fourth or fifth time, and then cut my hinge stock to make the two pieces. ThenI did some marking on the cowl for the rivet locations, and figured out how I wanted to lay out the rivet lines.

Tonight I actually broke out the rivet fan to mark the rivet lines, clamped the lower hinge halves in place and drilled the ~70 rivet holes for those to mount. Now that that’s done, I get to figure out how to handle drilling the upper cowl hinges. Before I can do that, I’m going to have to go back and bevel the hinge halves that connect the upper cowl to the firewall. Right now, the upper cowl has to be slid in place from the front, but that’s not going to work once the side hinges are drilled – it’ll have to drop in place. I’ve been putting this work off for a little while.

Another fun question is how I’m going to brace the back of the hinge against the upper cowling. At the front, I should be able to reach through the air inlets and get to the back of the hinge, but once I get to where the cylinders are, that’s probably not going to work any more. Maybe if I work front-to-back, I can count on each location being held in place by the preceding cleco? Not sure how I feel about that, even using a wood block to back the lower hinge, the drill bit wanted to push it away in a few spots. I’m not sure I’ll have any choice, though…if I try and do this with the cowl halves off the plane, I lose a lot of control of proper alignment between the two.

I’ll probably just have to sort of grin and bear it in the end…

Posted in Cowl | Hours Logged: 1.5

Lower cowl sanding and head-scratching

Hello, my name is Philip, and I suffer from analysis paralysis. That’s the main theme for this weekend.

After getting the lower cowl shimmed to my liking, it was time to start fine-tuning the joint between the cowl halves. A ratchet strap around the middle of the cowl helped pull things together to make the gap slightly more reasonable, but not perfect by a long shot. One bit of good news here is that some research indicated that it was best to wait on fine-tuning gaps until the hinges were riveted in place. The reasoning is that clecos aren’t perfect, and some shifting around is likely when the rivets get set. So instead of spending a bunch of time carefully sanding the joint, instead I just focus on rough-sanding it to where I could pull the cowl halves together for a reasonable tight gap with no rubbing or interference.

That led to the more fun and open-ended consideration of laying out the hinges at the joint. This seems deceptively simple, but there are a lot of interrelated issues here that all sort of come into pay at once. The first issue concerns the misalignment I have at the forward edges of the cowl. I have a few different options for addressing this. The first and easiest would be to just slap some micro on the upper cowl to build it up, then contour sand to match the lower cowl. The main concern with that approach is that the inside portion of the cowl there won’t line up at all, which could be a concern for dealing with how I want to cover the hinge pin access points.

What I’ve been wanting to do is to make some nice custom flush covers here – an approach I liked ever since seeing this RV-9 build log. However, to do what that builder did, I’ll need the inside portion of the cowl halves to line up, since it requires laying up an inside flange for the pin cover to mate with. If I want to do it that way, I think what I’ll have to do is lay up actual glass cloth to build up the upper cowl areas, then contour sand that on the outside, then sand the inside of the upper cowl to get the inner surfaces to match.

That’s quite a bit more work, but as of this morning I was still intending to go that route. But as I spent time today trying to work through the process of drawing up my pin cover shape, and laying that shape out against the cowl, and looking at how it would interface with the pins…I’ve come to like it less and less. I’m starting to lean towards a modified version of those pin covers, where the cover only mates with the upper cowl, instead of bridging across both halves.

Because of how I’ll be laying out the hinges, the access hole for them will sit entirely on the upper cowl, so really I only need to cover a hole up there. And if I can only have the cover attach to the upper, cowl, then I remove the need for the inside edges to have similar contours, which would make my life a little easier. I still think I’ll want to build up the upper cowl with actual glass instead of micro, and I’ll still carve some material out of the inside, but all I’ll have to do is get a vaguely uniform thickness up there.

So that’s my working idea for now. I think I need to let the idea bake in my head a little before I commit to it, but I do feel like this approach gives me a more definite path forward – which is something I need. I’ve got to find a way to get my brain past thinking 40-some steps in the future, and instead just be able to, say, go ahead and mark/drill the hinge halves to the lower cowl.

I guess we’ll see how I feel about this idea come tomorrow morning – a good night’s sleep seems to often help with clarity on stuff like this.

Posted in Cowl | Hours Logged: 2

Lower cowl shimming, again

Short night tonight, but I went ahead and made a second set of shims for the lower cowl using some .025” scrap. This took a little more time than last night, since I wasn’t starting with some nice 1/2” strip stock, but no big deal…just a little more cutting and smoothing. I was happy to see that with the new shims, the cowl sits much more even with the fuselage. You can still feel a little ridge there in some spots, but that’s not worth running down.

Since I was finally happy with the lower cowl fitment, I decided it was time to put the upper cowl on and see how the gap looked. At first it was a little concerning, as there was already a decent gap, especially around halfway between the firewall and prop…more gap than I really wanted. A little manipulating of the cowl halves fixed that, though – this seems to b the result of the cowl sides bulging a little at rest, whereas they were being pulled in tight with a ratchet strap when I did the cutting.

So the good news is that the gap should work out fine…the bad news is that this means I need to find some way to pinch the cowl sides while I’m working on finalizing the lower cowl cut to get the gap where I want it. I guess I’ll get to tinker with that next time out.

It is kinda cool to see the cowl halves mating fairly nicely, with no overlap any more. And the gap issues I’m seeing now don’t even show up in this photo:

Posted in Cowl | Hours Logged: 1

Lower cowl trimming and shimming

Once again, this is a post covering a few days. I’ve been trying to be productive on the weekends, but it sure is tough after, oh, about 11 AM or so. Anyway, on Sunday I got the upper cowl in place, snugged everything up, and marked the cut line on the lower cowl. Then I made the cuts on both sides and rough-sanded the cut line just to straighten it.

Another thing I wanted to do before really working on the split line was to shim the lower cowl attach to get a nice fit with the fuselage. My rationale here is that adding the shims will probably shift the upper cut edge around, even if it’s just a tiny bit. So before removing the lower cowl for the trim, I took a look at the join along the bottom and sides. The bottom looks pretty good, but on the sides, the cowl sits a little below flush. A bit of probing with calipers indicated that some .020” stock would work for a shim.

Tonight I made the shims, drilled them in assembly with the hinges, and reinstalled them. That was pretty straightforward, but I was a little surprised to see that the cowl still isn’t sitting flush. I’m suspecting that I may have messed up when measuring this. I think tomorrow I might try making a new pair of shims from .025” stock and see if I can get a better fit out of those.

Once I’m satisfied with the shim situation, I’ll be ready to start working on refining that cut line on the lower cowl.

Posted in Cowl | Hours Logged: 2.5

Lower cowl fine-tuning and hinge drilling

So this is another sort of carryover post; some of this work I did over the weekend, plus a bit more tonight. Basically, I finally talked myself into sitting down and sanding on the aft edge of the lower cowl. I didn’t go to the trouble of getting the gap exactly right like I did with the upper cowl, though. My reasoning is that things are still going to be somewhat in flux until I have the cowl join line and hinge in place; I don’t want to spend a bunch of time on this edge and then have it distort a bit when I bring everything together. So I just sanded until the cowl was able to slip in place and not overlap the fuselage.

With that done, it was time to work on the attachment hardware. I started by drilling pilot holes for the future screw holes on then bottom flange; for now these are just #40 holes with clecos in them, but later they’ll get upsized for screws. Next, I laid out the rivet holes for the hinges along the sides of the cowl, and then went to town getting those drilled and clecoed.

Once I had that finished up, I was able to remove the top cowl and, for the first time, see the lower cowl supporting itself on the fuselage:

It’s worth noting that all this time I’ve been fitting, I’ve been putting the cowl on backwards. Normally, the lower cowl goes on first, followed by the upper cowl, but since the upper cowl gets fitted first, things have to go in reverse order. The good news here is that now putting the lower cowl on/off should be easier, since I don’t have to figure out ways to hang it from the upper cowl or prop spinner.

Anyway, next on the docket will be replacing the upper cowl and using it to mark the horizontal cut line where the halves join, then I’ll get to make yet another Big Cut and spend a bunch of time sanding.

Posted in Cowl | Hours Logged: 2.5

Control cable planning

Today, in my continuing effort to avoid sanding fiberglass, I decided to take a stab at routing and so forth for the engine control cables. The idea wasn’t to end up with them final-installed with the throttle quadrant in place, but i did want to verify that the cables Van’s had supplied with my FWF kit would work with my nonstandard fuel injection and sump setup.

The cables are identical in design, but different lengths – there are two 55” cables and one 60” one. Despite looking all through my plans, construction manual, and other materials, I couldn’t find anything specifying which cable was for what. But it’s not really hard to figure out – for example, the prop governor is mounted on the back of the engine, close to the firewall, so clearly that’s where one of the shorter cables should be used. And the mixture arm is further forward and right than the throttle, so logically it should require a longer cable than the throttle.

In order to test all this, I routed the cables through the firewall and the left gear tower, and simply secured them to back side of the gear tower. This places them close enough to where they’ll eventually be affixed to the quadrant to allow for fitting – there might be an inch or so of variance, but that shouldn’t be enough to make the fit-up invalid.

Meanwhile, I got the required cable bracket attached to the prop governor, and routed one of the 55” cables over to it and temporarily added the nuts to secure the cable. This application, as expected, worked just fine. Honestly the 55” cable is a bit long, and I briefly considered replacing it with a short one, but considering this is the cable Van’s specs here, I don’t think there’s any reason to second-guess things. The extra length my be a good thing to help keep the bend radii in the cable larger.

Well, that was easy…time to start looking at the throttle and mixture cables. Before doing that, I needed to test-fit the cable bracket I bought from Showplanes. This piece is CNC cut to mount to the Superior cold air sump, and provides several sets of holed for attaching cable brackets. I still need to order the right bolts to attach this, so for now I’m just using some 1/4-20 screws from the cylinder baffles to secure the bracket for test-fitting.

The example photos on the Showplanes site show the cables routing above the bracket – that is, between it and the sump – but that seems way too cramped to me. It’s definitely too cramped to use the cable brackets that I also got from Showplanes. I thought about maybe using washers to space the bracket down a bit for more space, but the real critical concern here is clearance with the exhaust. The #1 pipe is really close here, to the point that even the attach bolt is going to be a tight squeeze. Moving this entire assembly down by even 1/8” just isn’t going to happen:

That got me to trying the throttle cable routing; this uses the rightmost set of holes in the above photo. For this spot, putting the cable bracket on the bottom of the mount bracket works fine. and it lines up nicely with the throttle arm. The only downside is that the 55” cable is too short – but the 60” cable works perfectly. I was able to fully mock this up, with the rod end on the cable, a bolt through the throttle arm, and of course I had to go reach in the cockpit, move the end of the cable, and make the throttle arm move.

So the next question was – could I also use the 60” cable for the mixture. Since I only had one 60” cable on hand, that meant I had to detach the throttle stuff and try routing that same cable to the mixture arm. But before anything, there was the issue of the exhaust clearance. The mixture bracket is further left and forward, and none of the mount hole options clear the exhaust.

To make a long story short, after a lot of thinking and trying a lot of different stuff, I hit on the idea of mounting the cable bracket from below the mount plate, but with the actual bracket posting up. This allows the cable to route between the plate and sump, and to sit low enough to clear the sump. Doing it this way did require me to grind some material off the cable bracket, and also to open up the holes on the mount plate, but in the end I got a setup that allowed the cable to properly align with the mixture arm:

The only problem, as seen above, is that the cable doesn’t reach the mixture arm. A longer cable also won’t help here, because that would require the cable bracket o be further forward, which isn’t possible with this positioning. Instead, I’m going to add a 3” extension to the end of the cable to get the reach I need…which is something else to throw on my Aircraft Spruce order list.

Posted in Firewall Forward | Hours Logged: 5

Injector line reroute

So, I’m pretty happy tonight – I worked out a problem that’s been nagging at me for a while. Previously I’ve mentioned how one of the injector lines interfered with the case top mount for the SDS coil pack, and a while back I took a crack at making a custom mount out of some angle. While the mount itself turned out OK, I discovered while fitting the top cowl that the mount was too tall, causing the coil pack to contact the cowl.

I’ve been rolling around ways to address this for a while. I’d initially thought about making a new custom mount that sat lower, but since the whole idea of that mount was to let the injector line pass below it, there wasn’t really any room to make much of a difference. This week I got back to brainstorming how to handle this, and eventually I decided I only had two real options: either relocate the injector line, or put the coil pack somewhere else. Mocking the coil pack up on the other magneto pad wasn’t encouraging; between the oil pressure sender line and the CS prop oil line, it’s pretty tight back there.

So I went on a research journey on the topic of these injector lines, starting with the intent to buy the materials needed to make a new line. It turns out that these lines can be bought prefabricated, in whatever length you need, and they’re hand-bent to the required routing. That indicated to me that simply massaging the routing of the line I had was a reasonable way to approach this, so I started down that road.

The good news is that this line had enough slack in it to allow for the rerouting I had in mind. A little more bend at the flow divider allowed the line to cross the case a couple inches further forward, in front of the SDS case top mount. I was able to reuse the previous retention mount on the side of the coil mount, thus securing the line just past the case split. Further over, the adel clamps already in place on the pushrod tube still worked just fine.

With the coil pack loosely in place on the mount, we can see the routing. The main area of concern while I was doing this was the spot in this photo – the clearance between that bend and the coil pack mount. I was able to get about an inch of clearance without violating the minimum bend radius specs for this line:

From the other side, we can see how the nice billet mount was reused to secure the line:

This was very satisfying, but it left one more question: supporting the rear baffle. Normally, there’s a brace that goes from the case top to the baffle, but the coil pack mount precludes using that. I’d been planning on figuring some way to brace from my custom mount to the baffle, but hadn’t really worked it out. Since I had the coil pack mocked up in place, I decided to put in the baffles to see how things looked. It turns out that the baffles are close enough to the coil pack that this will be an easy problem to solve – I can just use a small piece of angle to tie the baffle into this mount screw on the coil pack.

I still need to go back and permanently mount all this stuff – for example, the coil pack mount bolts are only hand-tight right now. They’ll need lock washers and torquing as well. I suppose I can go ahead and bolt the coil pack itself in place as well; that way I can double-check the cowl clearance next time I put the top cowl on.

I’m somewhat tempted to quit working on cowl fitting for the time being, and get back to general FWF cable routing and so forth. The whole reason I started on the cowl was to allow working on the baffles, which I guess I’ll still need to resume before I can finish off all the FWF stuff. I think I’m just trying to avoid that whole fiberglass + sweat situation, but there’s not going to be any way around that for probably another four months or so.

Posted in Firewall Forward | Hours Logged: 1

Injection servo mount fix

This was another of my FWF tasks that I’ve been putting off for a while. I discovered some time ago that as provided, the FM150 fuel injection servo interfered with the bottom cowl. I also determined that if I removed the 1/2” spacer between the sump and the servo, the clearance issue went away. Some research indicated that the only reason that spacer is there is because Superior provides really long studs with their cold air sump. That is, it’s just there to accommodate the mount hardware.

Well, as part of a Spruce order I put together last week, I figured out what studs I needed here and got those added to the order. That just left the fun of removing the old ones and installing the new ones. Removing these was a lot more fun than the alternator ones from a few days ago – these were really tight, to the point that my first attempt to remove one using two nuts and some heat failed miserably

I was on the brink of ordering a special stud removal tool, but I decided to give it one more try, this time being more generous with the heat. Turns out that about a 30-second blast with a Mapp gas torch puts enough heat in to break the stud loose, so I was back in business. Most of the fun came from figuring out how to orient the torch to heat the stud without destroying anything else in the area, like the rubber intake boots visible in this photo of the stud-less sump:

This led to a surprisingly long and tortuous discovery session. You see, at a glance, it looked like the studs I ordered were too short to fully engage the sump while also providing enough length for the servo and the mount nuts. I actually came pretty close to ordering another set of studs that were 1/4” longer…oh, and those studs were $18 each.

What made this fun was that I didn’t want to just install a new stud without knowing it was right – so I ended up measuring, re-measuring, reading up on proper thread engagement, and so on. Eventually I decided that these studs would work, to the point that I was confident installing one. But it was also critical that I thread the studs in to a very specific depth, so I ended up using a washer stack on each stud to give me a nice precise stopping point during installation.

After all that worrying, the first stud I installed gave me the chance to verify I had good engagement with the servo, and then the other three went in in about ten minutes. Finally, I got the servo back in place, torqued all the mount nuts, and reinstalled the fuel lines. After being temporarily mounted with a lot of stacked washers for a while, this servo is finally back in place for real:

I guess I can’t really put off cowl trimming any more now. That’s going to be a lot of fun, seeing as how it looks like we’re going to have near-triple-digit high temperatures for the foreseeable future. Sweat and fiberglass dust are not a very enjoyable combination…

Posted in Firewall Forward | Hours Logged: 1

Standby alternator install

So, in sort of an attempt to get some momentum going on this project, I’m pausing on the cowl stuff for a bit, just to get some more fun stuff done. This was somewhat enabled by receiving some parts that I’ve been waiting on for almost a year. Way back when I was trying to get all my accessories mounted before hanging the engine, I discovered that the 90° oil filter interferes with the B&C vacuum pad alternator I’d bought. So at the same time I was ordering a different oil adapter from B&C to work around my engine mount, I also ordered a drive extension kit from them. The extension kit was backordered, but that was OK…I wasn’t in any huge hurry, and worst case the airplane could fly just fine without the standby alt.

Of course, that backorder period was a good bit longer than expected, but it matched up fine with my work ethic (or lack thereof). In any case, last week I got an email from B&C that the parts were finally in, and they showed up here a couple days later. Finally, something relatively simple and fun to do!

The kit consists of a few different parts: first, a longer shear coupling that’s installed on the alternator spline drive, a spacer for the mount pad, and the most fun part: four longer mount studs. So Job #1, after removing the existing blanking plate, was to remove the old studs. In a pattern well-known to any DIY mechanic, the first three studs came off with relative ease, but the last one was a real bear, and required some torching to remove. Really fun trying to heat the stud without scorching anything else nearby…

After that, it went well…new studs went in easily with the provided stud installation tool, then I just had to stack everything together. There’s a gasket, then an adapter with a gear to the accessory drive inside and the splined socket outside, then another gasket, then the spacer, then another gasket, and finally the alternator.

That said, this isn’t 100% done yet. I unwisely used the same mount nuts for the stud removal, and a couple of them got rounded while working on that one stubborn stud. I went ahead and used them to mount the alternator, but I’m going to replace them with new nuts at some point. Oh, and did I mention that I just placed an Aircraft Spruce order today? No matter how hard I try to combine Spruce orders to save on shipping, it seems my efforts are doomed to failure…

Anyway, here’s a shiny new alternator on my shiny new engine:

Posted in Firewall Forward | Hours Logged: 1.5