Dave’s RV-7A Building Log

I spent the evening working on making a nice, even paint gap between the cowl halves and between the cowl and the fuselage. The top part of cowl was pretty easy. The gap along the top worked out about perfect without touching it. I had no gap when I drilled, but the smaller hinge pin along the top lets the cowl pull away slightly.

The bottom part of the cowl was more troublesome. As I made the gap larger along the bottom, the cowl sagged more. I now have 1/4″ sag at the nose. I started with 3/32″. Some sag is good as the engine apparently settles in the engine mounts after running for a while. But 1/4″ is more than I wanted. If it ends up being a problem I can always add and sculpt some filler along the top of the cowl to match the spinner.

Vans instructions should really recommend pre-loading the hinges. There is so much slop in the hinges that the whole cowl is able to move around quite a bit. Pre-loading the hinges in just the right directions would solve that problem. For example, pull the hinge along top as far forward as possible before drilling. Maybe secure it with some tape. Along the horizontal seams, pull the bottom half of the hinge forward. The bottom hinges should be pulled back.

I think it’s easy to get obsessed trying to get the perfect gap. In reality the whole cowl moves around quite a bit with the hinge slop. I’m going to work on it a little more and then call it good enough.

Yesterday was the first meeting trying to get a new EAA chapter going on the Seattle Eastside. We had a great turn out, and everybody was enthusiastic about the idea.

Tonight I spent some time trimming the oil door. It is a little over-sized to start with. There were some scribe lines on it, but even those would make it too large to fit in the recess. I used the cut-off wheel to trim the sides. Hopefully that’s the last time I have to use that thing. It makes a huge cloud of dust. I cleaned up the sides on the stationary belt sander. Looks great.

I then clecoed all of the hinges in position and tried installing the cowls using the pins. Up to this point, I’ve just been clecoing and unclecoing to get it on/off. It was much easier than I expected. The top hinges gave me a little trouble, but pushing on just the right spot made them slide into place. Now I just need to sand the paint gaps, countersink the holes in the cowl, and attach all of the hinges. Getter closer.

I previously marked the location of the oil door in the top cowl. It’s kind of tricky. There’s no definitive edge to measure from. I sort of estimated where the down slope stopped and made some marks. I squared that up and then left about a 1/2″ flange all the way around. I drilled 1/2″ holes in the corners and connected them with the cut off wheel. A file and some sand paper cleaned it up nicely.

I deburred the rest of the cowl hinges as well. I started to look at cutting the door itself to size. There are some scribed marks, but they aren’t square. I squared them up, but then figured out that it was still too large to fit in the recess in the cowl. I inset the marks another 3/16″ on each side. I’ll cut to that line and then sand to fit from there.

What a perfect day. We slept in. Went up skiing/boarding in the afternoon during the Seahawks game, taking advantage of the very light crowds. And then came back and watched the Hawks on Tivo crush their way into the Super Bowl. I’m not a huge sports fan, but it’s cool to see them finally go to the show after so many years.

And to top it off, I spent a little bit of time deburring the cowl hinges that I drilled yesterday.

Since the exhaust was installed, I might as well install the cabin heat muff as well. It took a few minutes to figure it out, but it looks like a good system. I deburred the edges of everything a little bit first. I don’t have the hose clamps installed yet, because I’m not sure if I’ll need to adjust the position later.

I decided I might as well make some more progress on the cowl. I sanded the horizontal seams, checking the progress frequently, until they were right where I wanted them. I then finished drilling the top hinge to the cowl. The instructions have you drill just a couple of spots to start with, but I didn’t want it to move around any more. Of course, with the undersized pin installed, the thing moves around anyway.

Next, I positioned the hinge on the lower half of the cowl and laid out holes 1″ apart. I drilled all of those.

I then used the pin to attach the top half of the hinge. I re-installed the top half of the cowl and taped it exactly, exactly where I wanted it. Drill time. All of the hinges are now drilled to the fuselage and cowl.

I’m pretty happy with how it all turned out. With the blocking and duct tape removed, the cowl is right where I want it. It seems strange to obsess over the position so much when the cowl has some free play in it. I can move it around about 1/32″ due to the small top cowl pin and the slight slop in the hinges. It still looks good. I’m glad I didn’t make a paint gap yet along the top. With the blocking removed, the gap ended up being perfect without needing to sand any more.

Today ended up being much longer than I expected, but I won’t spend much time on the project tomorrow as we’re going skiing. And I’ll watch a bit of the Hawks.

I didn’t get much done tonight. Helping somebody with her book report is more important. I did sand the edges of the cowl a bit more and widened the slot for the nose gear leg. The slot is almost wide enough now. I’m just going to make a couple of small semicircles right around the leg to finalize the fit. The edges are getting very close now as well. It’s almost time to do the horizontal hinges. I made up a new sanding board as well, as my old one is fairly worn down. Fiberglass is easy to sand, but it wears down the grit pretty quick.

I started making a check list of items to do on the cowl. Working in little 1-2 hour sessions, it’s easy to forget things.

I finished up the shims I started making last time for the sides. The bottom hinges didn’t need any shims, but I used some 0.016 along the top and sides. With the side shims installed the cowl seems perfectly flush with the sides.

I attached the bottom cowl again, got it exactly into position, and drilled the holes along the bottom hinge. I then laid out and drilled holes along the sides. A trick I figured out for holding the hinge steady while drilling is to put some masking tape over the loops. That holds the hinge in position well enough for drilling.

With all of the hinges along the firewall drilled, the cowl is very stable. I removed the top cowl just to check out the clearances below the engine. The starter is pretty close to the cowl, but not too close. The Mattituck alternator looks close as well, but I won’t know for sure until I install the belt and position it correctly.

I did a bunch of little things fitting the cowl. I trimmed one loop off the bottom hinges at the outboard corners. They were keeping the corners from fitting well. I made the slot around the nose gear leg wider. I marked some lines on the bottom cowl using the bottom skin rivet lines. I then used those lines to straighten up the nose gear leg slot. I trimmed the horizontal edges of the bottom cowl to within 1/16″ of the desired line in stages. I laid out and drilled holes in the bottom of the bottom cowl for drilling to the hinges.

I think that was it. I try to get as much done for each iteration, but I still end up removing and re-installing the cowl a few times per hour. It’s not difficult to do–just repetitive. This is a stage where it definitely pays to be careful, though.

Another long day of fitting the cowl. I cut and countersunk hinge material for the sides of the fuselage.

I must be missing something, but it seems like Van’s didn’t supply enough of the larger hinge pin material. I have gobs of the thinner pin, but am about 4″ short of the thick stuff.

The bulk of today was many iterations of removing the cowl, tweaking the edges with the sanding board, putting the cowl back in place, and marking for further tweaking. I worked slowly and deliberately, but I think that paid off. The cowl now fits pretty well all the way around at the firewall. I still need to make a paint gap between the cowl and aluminum. I’ll do that before riveting on the hinges. I’m thinking 1/32″ will work fine.

I drilled a few keeper holes along the aft edge of the bottom cowl to stabilize it. I also sanded the horizontal edge of the top cowl until it was straight. I then marked a trim line on the bottom cowl.

It seemed like a long day, but the cowl is really shaping up nicely. This pic shows the final state for the day with just the horizional trim left to do. You can also see the various chunks of duct tape I’m using to hold the cowl where I want it.

Today was sort of a blur of taking the cowl off, trimming and/or sanding, and putting the cowl back on. The sanding I did around the spinner area helped cure the “over-bite,” but I needed to drill new keeper holes at the front. That improved things immensely. The old holes won’t be a problem because they get drilled out to a bigger size anyway. Here are side views from the left and right of the area behind the spinner. You can see that the recess is a little large than needed. I’ll have to fill that in later.

With the top cowl exactly in its final position, I drilled four holes at the back along the top to put keeper clecos in. That helped stabilize the position quite a bit. I then marked and trimmed the bottom of the cowl.

I followed the advice of another builder and made a longer sanding board, about 2 feet long. I glued sand paper to both sides of it with wood glue and weighted it down to dry. Contact cement would have worked better, but I didn’t have any handy. I sanded the aft, bottom edge of the cowl until it was fairly close to final and then marked and trimmed the sides of the bottom cowl.