Dave’s RV-7A Building Log

After enjoying a smoke-free beer at the Roanoke with Steve-o (Washington’s smoking ban is awesome), I didn’t do too much on the plane.

I decided to check the paint gap on the cowl all around one last time. In the process of doing that, I realized I screwed up the side hinges. I attached them one rivet too far down. I double-checked yesterday when I was riveting them on, but apparently still messed it up. The only real problem is that there is one less hinge loop at the top to support the corners of the cowl. I’m trying to decide whether to drill them out and re-attach, or just leave them as is.

After carefully looking at all of the gaps and testing them with a strip of .020, I sanded just a tiny bit more along the horizontal seams. It should be ready to go now. I had Julie document the special occasion.

I’ve also been looking at the Milspec camloc group buy. Those things sure are tempting. I’ve installed/removed the cowl a couple of times now using the hinge pins. The hinges along the horizontal seams are easy to install. The others, especially along the top and bottom, are not easy. With the 30% group buy discount, I could do the firewall for about $200 including tools. Hmm…

I decided to go with the tried-and-true 74″ blended airfoil Hartzell propeller, C2YR-1BF/F7496. I mailed the order form to Vans today.

I put some high-temp RTV between the firewall and side skin and riveted on the side hinges. It was a little difficult to get the RTV in there. I used a popsicle stick to open up the gap, and a strip of scrap aluminum as a putty knife. Worked really well. The only hinges left to attach to the firewall are along the top. Those will wait until the forward top skin is ready to attach, which is after all the wiring is done–way down the road.

There was a suggestion on the forum about using extruded hinges for the cowl. They are a bit more expensive, but I guess they are less prone to cracking. I’m not sure if I’m going to stop progress and order some of them or not. Some people have had trouble with hinge loops breaking off. A couple of suggestions I’ve read are to make sure the hinges are not pre-loaded and to deburr the corners between the hinge loops. Decisions, decisions.

We went out to the beach for the weekend, but we returned fairly early on Sunday. I managed to do a few things, basically getting over the hump on the cowl.

I countersunk the top and bottom cowl halves in preparation for riveting. I also worked on the paint gap a bit more. It’s now as good as it’s going to get. The sag at the front didn’t get any worse than 1/4″. I’m ready to rivet on the hinges.

Sorry there haven’t been many pictures lately, but sanding the paint gap is just a monotonous task. I’ll have some good pictures of the cowl once the hinges are on.

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 sanded the cowl a little bit, but quickly decided to do something else. Cowl boredom is setting in.

I pulled out the exhaust pipes. Considering all of the tricky bends and twists, these things fit amazingly. I just put them together, installed the gaskets and put the nuts on the studs. A couple of spots have very limited access. I didn’t tighten down the nuts yet. Getting a wrench on a couple of them is going to be impossible.