Dave’s RV-7A Building Log

I spent the morning helping my friend Steve put a new VHF antenna at the top of his mast. It was great to work outside in the sun for a change.

After an afternoon bike ride with the family and dog, I spent a little time positioning the oil cooler reinforcement. This is about as high up as I could get it without risking some interference with the baffle seal. A tiny bit of the top corner had to be removed. It looks like only the bottom 1/4 of the cooler will be blocked by the cylinder. That seems about typical from other installations I’ve seen. I drilled a few holes with the reinforcement positioned on the baffle.

I then took it off and drilled the rest of the holes on the bench where I had better access. I cleaned up all of the holes on the angle parts and managed to give them a quick shot of primer before it got too cold outside. The next task will be to make a big hole in the back baffle.

The final thing to do on the baffle trimming was the front bulkheads. In the post I read, it was suggested to leave these off to make it easier to mark the other baffles. I’m not sure that was really necessary. It was easy to mark and trim them, though. The access to the front bulkheads is really good.

With the trimming finally done, I could complete a few other tasks. I fabricated the angles that reinforce the back left corner of the baffles where the oil cooler mounts. My first attempt at the diagonal angle didn’t go up high enough, so I made another. I’ve gotten pretty good at quickly whipping up various aluminum parts. The band saw and deburring wheel are my friends.

The reinforcements needed at this corner is not exactly clear from the plans. The oil cooler drawing shows the spacer, but not the angle. The baffle drawing shows the angle but not the spacer. I put both in, as I figured it couldn’t hurt. The spacer is definitely needed otherwise the two sides of the baffle don’t meet correctly.

I also started to contemplate the location of the oil cooler. I want it as high as possible, but I don’t want it to interfere with the cowl or baffle seal.

I did a tiny bit more baffle trimming. There were a couple spots on the left side that still didn’t have a finger width of space.

I used the band saw to trim the right side baffles. I put the top cowl back on and noticed the gap is still not quite large enough on the left side and it got larger than I was shotting for on the right side, about 9/16″. I guess the cowl wasn’t sitting completely level. I put the bottom half of the cowl on just to make sure the top cowl was correctly positioned, and it was. While I had the bottom cowl on, I marked the left cowl inlet where I need to do a little more trimming. The position of the filter dictates the amount that the left floor extends forward. In order to get a 3/8″ gap, I’ll need to trim the inlet a little more.

I did a bit more trimming on the left side baffles, and called it quits for the night. Hopefully the trimming is about done.

I received the first draft of my panel drawing from Ross at Experimental Air. It’s looking great. One thing I didn’t account for in my mock-up is the fact that most of the instruments take up more room than just their face plate. For example, the avionics stack need a strip on the left and right for the supports. That’s a good example of why it’s helpful to have someone like Ross do the layout for you.

I also got the price tag from John Stark on the avionics that will go into that panel. He’s got great prices, but ouch! Time to cut a big check.

I finally went down to Sears and picked up a strap wrench to tighten the timing gears on the P-mags. The torque for the AN6 nut is 160 in-lb, but I could only get it up around 120 in-lb. That should be good enough. There’s a key that keeps the gear from turning anyway.

I next turned to the final baffle trimming. I used the band saw and Scotchbrite wheel to do the final trimming on the left side and back baffles. Since I have to remove the baffle to do this trimming, it’s taking a little longer.

I started the process of trimming the baffles to the top cowl. The trick with the 1″ aluminum circle and a cut-off sharpie works excellent. I put the side and rear baffles (and later the front floors) onto the engine. I placed the top cowl on top and made sure it was centered. There was about an inch gap in the back and front.

This picture shows how the aluminum circle is used. Ideally, the disk should be flat against the baffle.

Reaching in and around the engine, I was able to use the circle to mark a trim line all the way around. On the left side of the engine, it seems to be easier to mark the inboard side of the baffles. The right side is the opposite. I guess it’s the way the engine is positioned relative to the cowl.

I used tin snips to make a rough cut at the trim line. I was able to accomplish this without removing the baffles for the most part. Lather, rinse, repeat.

It took about 3 rounds of that before the cowl was sitting down into its normal position. The baffles were nearly perfectly trimmed right up to the cowl.

I then marked the final trim line all the way around the baffles. The 1″ circle makes the line 1/2″ below the cowl. The instructions say this is the maximum amount, but I’ve heard from other builders that 3/8″ can be a bit too small. They’ve seen the baffles rubbing on the cowl. I don’t want that.

I’m going to think about the final trim a bit more and do the trimming probably on the band saw tomorrow.

I really thought that trimming the baffles to the cowl was going to be a major ordeal. So far, it’s turned out to be fairly easy. All I have left on the baffles is the final trimming, mounting the oil cooler, installing the oil cooler stiffeners, riveting all the parts together, painting, and installing the seal fabric. Well, I guess I still have a ways to go.

I didn’t have much time to work on the plane. The furnace has been acting up. I had to spend an hour tinkering with it. The problem ended up being a clogged up orifice in the pilot light line.

I made a 1″ diameter washer out of aluminum with a tiny hole in the middle. I read a trick on the Matronics list that involved this washer and a Sharpie in order to mark the baffles for trimming to the cowl. It sounded so cool that I had to try it. I’ll see how it works tomorrow.

I put both halves of the cowl on and clamped a block to the crankcase flange that will hold up the top cowl at just the right height. I want to be able to install and remove just the top cowl during the trimming.

The alternator air door flange set up well overnight. I’m using the “fast” hardener, and it’s still taking a while to set up. I moved the part inside to keep it warm, which I think helped. I drilled out the holes again that got filled up with epoxy and used a deburring tool to clean up the dimples.

Overnight I thought about how to attach the pop rivets. In other locations where pop rivets are used in fiberglass, they are backed up with a washer. In this location, you don’t want any chance of the washer getting loose and falling into the air intake of the engine. I hate to think of what a washer would do to the inside of the engine. I had some left over #4 washers I ordered a while back, which is the perfect size for 1/8″ pop rivets. I decided to use the washers, but epoxy them in place. I used some JB Weld under the washers, pulled the pop rivets, and then added a little more JB Weld over the top and around the edges. The washers aren’t going anywhere and the pop rivets won’t pull through the epoxy. (Sorry for the fuzzy pics.)

I then attached the door and gave it a try. Works excellent. This is something that will stay closed 99.9% of the time. The only time it gets opened is if the air filter gets clogged up for some reason.

After lunch, it warmed up enough to do a priming session. It’s been a long time since I’ve done any priming. I actually like it, because I know the next step is final assembly!

I was hoping this weekend to get the baffles to the point of trimming them to the cowl. I got pretty close. I feel anyway that I’m over the major hump with these crazy baffles. I spent a ton of time going part by part, doing any last trimming and drilling. A few things have to wait until after the baffles are trimmed to the cowls, like the oil cooler.

This appears to be a common problem. With everything screwed down, this one flange just wasn’t sitting right. Cranking it down would have tweaked everything around it to the point of not fitting.

I ended up cutting off the flange and using a short chunk of .063 x 3/4 x 3/4 angle. I also made the stiffener for the back right side wall from the same angle stock.

I bent the back bulkhead bracket some more. It was about 3/8″ short of where it needed to be. I then drilled the back bulkheads to it.

I also drilled the two back left bulkheads to each other and did some final filing around the engine.

I have a bunch of riveting to do now, but the baffles are basically ready for trimming to the cowl after a lot of hours on them this weekend. Yeah!!

I riveted the nut plate onto the flange and enlarged the hole in the FAB for it. I mixed up some epoxy with flox to fill under the flange. I mixed it up to the consistency of paste per the instructions. I clecoed the flange in place and noticed it wasn’t sitting very level with respect to the FAB. I used a side cleco clamp and a small block of wood at the nut plate end of the flange. Then I noticed that the flange appeared to be bowed. The best approach is to just clamp the flange in two maybe three spots so that it’s sitting flat and square to the FAB.

I also did some trimming on the baffle floors. I think it’s the FAB instructions that say to bend down the forward lip of the baffle floor. Seems like a good idea. The flange will provide more rigidity to the middle of the floor.

I also cleaned a batch of baffle and alternator parts for priming. The weather is supposed to be good tomorrow.

Sorry for the lack of pictures lately. I’ve just been in a zone of getting these baffles hammered out. I won’t be done a day too soon with these miserable things.

I worked some more on the alternate air door. I finished off the hole in the FAB pretty easily. I positioned the flange, drilled the holes, dimpled the flange, and countersunk the fiberglass. The fiberglass was a bit thin on one side. It wouldn’t hold a cleco after being countersunk. I’ll have to do something about that. I also bent over the little tab at the top. It forms a slot to hold the door. One end of the slot is crimped to form a stop. I was skeptical, but I tried rotating the door into the slot and it seem like it’ll work pretty good.