Dave’s RV-7A Building Log

As I’ve been working on the FAB, I’ve noticed some cracking developing, especially in the corners. The FAB doesn’t seem weakened at all. It just has some hairline cracks running through it. I discussed the issue with my friend Steve who has some experience working with epoxy and fiberglass (enough that he’s developed an acute epoxy sensitivity). We decided that the part isn’t structural, the fibers of the glass are still intact and doing their job, and if problems do develop I can take care of them. I might do a skim coat over the whole thing when I’m finished messing with it, but I’m not going to sweat it right now.

Following the instructions, I pop-riveted the flanges to the filtered airbox using #4 washers as a backer. That worked great. I mounted the FAB back onto the engine and drilled the pilot holes in the flanges to the left baffle floor. The aft flange doesn’t overlap the baffle support angle (2R I think) very much. I located the holes to divide the overlap, but there isn’t much edge distance on the flange or the angle. I might have to re-fab the angle and attach an extra plate to the flange. We’ll see.

I also marked the cutout for the filter on the floor. The bottom edge overlaps the filter, but the other three edges need to clear the filter so it can be installed from the top. I got close to the line with the drum sander in the drill press. I finish it up with a file tomorrow.

I made some great headway on the Filtered Airbox. I didn’t like the marks and holes I made yesterday for trimming and drilling the FAB flange. I more carefully positioned it all today and made new marks. And then cut the extra off the flanges.

And then drilled the holes that mount the FAB to the fuel servo.

And mounted it on the engine. Looks sweet.

I also marked and cut a rough hole in the left baffle floor with a jig saw. It will get enlarged later. I went through several more iterations of sanding the top of the FAB with the belt sander in order to get the funky double Z channels to fit. The instructions call for a 3/8″ gap between the FAB and the floor, but I needed more like 7/16″. That turned out to be the width of my short ruler. That made a handy way to determine if I had enough clearance. When it was finally perfect, I drilled the channels to the FAB.

I deburred and dimpled the channels and then countersunk the inside of the FAB.

Working on fiberglass reminds me of the sailboat my parents had when I was a teenager. Ah, the smell of fiberglass (not). It’s not too bad working with the stuff, though. It’s just a little annoying having a white dust cover everything in the garage. And my arms itch.

The FAB instructions are great. It’s nice being able to go step by step, marking things off as I go.

Today was too sunny to spend inside, but I did do a little work on the FAB (filtered airbox). I tapered one end of the plug so it would fit into the fuel servo better. That allowed me to more precisely position the FAB. I made a bunch of marks for cutting and drilling and then removed it.

I also received some different springs for the oil door from McMaster. I used two springs this time, so they certainly spring the door open better. However, they are a little larger diameter and are binding up a bit.

I’m pretty worn out on fitting the baffles. It’s a lot of install, mark for trimming, remove, cut down, repeat. I expect (hope) that I have less than 10 more hours of it. And then it’s time to trim the baffle tops down for the cowl.

For a little diversity, I pulled out the FAB airbox to check the fit again. I made a 2-3/8″ plug that is used to sort of line up the box with the fuel servo intake. The plug doesn’t really fit into the servo, but it does provide some indication of when the airbox is centered. I clamped it in place with the airbox tight up against the left baffle floor. The top of the airbox needs some trimming in order to follow the contour of the floor. You don’t want to trim too much, because the airbox will swing up and thus change the contour cutting needed. I almost cut too much the first time. After a few iterations of trimming, it is fitting amazingly well. With the airbox set down 3/8″ of an inch (to allow space for the attachment brackets), there’s 1/4″ clearance (twice the required amount) to the starter and solenoid.

There’s also just enough of the baffle floor left on the outboard edge for the airbox attachment bracket. It all seems to be working out well. I was really expecting that the airbox would need some major surgery. So far it’s working out quite well.

I did some more trimming on the front bulkheads to provide the proper clearance around the crankcase, and then drilled the brackets to the bulkheads.

The “c-locs” and tools arrived from Milspec. Looks like a quality product. The kit includes 30 of each of the c-loc parts plus a couple extra snap rings. I imagine those things can go flying if you’re not careful.

I determined the final location of the front bulkheads and drilled the brackets to the floors. I used some blocks of wood to make sure the bulkheads were parallel to the ring gear. I was able to drill the brackets on the diagonals pretty easily.

I marked the locations of the brackets and then carefully removed the ring gear for better drilling access.

I still need to tweak the height of the bulkheads and the fit to the floors a bit more. I also trimmed the bracket that holds the bulkheads to the front of the engine case. The bracket turned out pretty good.

This month ended up being the lowest number of hours I’ve spent on the project in quite some time. A week of skiing will do that. It’s also not as fun working out in the garage when it’s cold.

Worked on fitting the front bulkheads. It’s not clear where they should be located. There are notes on the diagram that they need to be at least 1/2″ from the start ring gear and that they should be parallel to the gear. I located them as far back as possible to provide enough room for the brackets that attach the bulkheads to the floors.

I wasn’t sure how to locate them relative to the cowl inlets, but there really isn’t much choice. They should be inboard of the cowl inlet and yet 1/2″ from the starter ring gear. Mine will end up lining up with the inboard edge of the inlet. I trimmed a tiny bit off one side to provide clearance to the inlet.

With the rough location determined, I made the brackets pretty much as they are laid out in the plans. A couple of them were a little bit shorter. I made them from the .032 angle provided in the baffle kit. I wasn’t sure whether that angle was for the brackets or the right wall stiffener. The other choice was to make them from the .040 sheet, but that would have been pretty hard to bend.

I haven’t been able to find many pictures of the baffles on other builder sites. I can see why, as the baffles are just tedious and confusing. I haven’t been taking many pictures either. I’ll be glad when the baffles and cowl are done.

Today I’m offically an airplane builder. After nearly 2.5 years of working on the plane nearly every day, I finally drilled a hole in my finger. It’s certainly a dubious milestone in the project.

I finally had the energy today for some serious work on the baffles. I tweaked the support for the right front floor and shaped the tab to cover the prop govenor oil line slot. I suppose if one cut the slot just right, the tab wouldn’t be necessary. Here are two views from below and one from above.

One thing I just don’t get about the baffles is how the sides are supposed to seal against the sides of the cowl inlet. Even if I pull the sides in tight, it seems like there’s still going to be a big hole there. I’d especially like to keep the left floor as wide as possible for the engine intake filter.

I cut up some thick paper to simulate the seal material. Along the sides, the material pushes against the cowl. Along the cowl inlet bottom, the seal kind of bridges the gap from the cowl to the baffle floor. I guess the two overlap enough to make a decent seal. The instructions say to center the sides in the “slot” of the cowl. I guess this is what they are talking about.

I shaped the angles that attach the right floor to the right side baffle and drilled them in place. The drawings and instructions are a bit contradictory on how to deal with the aft part of the junction. I just kind of faked it as best I could. It all feels solid. The aft-most side rivet goes through the bolt reinforcement. The drawings kind of indicate using one of the existing holes in the reinforcement, but I couldn’t make that work. I just drilled a new hole.

I also riveted together the bracket and tab contraption and added some nut plates for #8 screws. It also feels quite solid. I figured out which rubber grommet I need from Spruce to seal the gap around the oil line.

I pulled out the front bulkheads and spent a little time trying to figure them out, but I’m done for the day.

Spent more time on the right front baffle floor fit. I made a little tab to secure the slot of the prop governor line.

We’re back from skiing/boarding at Mt. Bachelor. Great place. We had great weather, great snow, and the view from the mountain was incredible.

I spent a little time just getting back into the swing of things. I messed around with the right front baffle floor.