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.