Matt's RV-7 Project

Finally, I have the baffles all built and the rubber seals all fabricated. Nothing left to do next except attach them together. I started with the upper piece on the forward crankcase baffles… this one gets attached with screws instead of rivets, since it spans two separate baffle pieces and might someday need to be removed:

A view from the other side… I may replace these nuts with all-metal locknuts later, after my next parts order:

To keep air from leaking between the aluminum baffles and the rubber seal strips, I put down a thick bead of black RTV before I started riveting. This also means that I didn't get any pictures of the process, since my hands were too filthy to hold the camera.

Fast-forward a couple hours… my hands are all black with glue, and all the rubber pieces are attached to the baffles with large-head blind rivets. I cleaned up all the squeezed-out RTV and made sure there was an adequate bead all along the top seam.

One hole on either side gets a screw and nut instead of a rivet, so I can peel back the associated rubber strip to install or remove the metal seal tabs.

While I was in sticky-finger mode I dabbed some orange RTV in the gaps and tooling holes around the top of the oil cooler area. Don't ask me why I used two colors of glue.

Here's the finished product. The next step after this is "go all around the engine and seal every little gap between the engine and baffles with RTV", but I'm not going to do that just yet. There is an AD out on my ECI cylinders that I'll have to deal with first, which unfortunately means everything will have to come apart one more time before it's all said and done.

Finally, done with the baffles! I collected a ton of scrap cuttings of rubber seal material from around the garage – and this is probably only about half of what I generated, not counting what's already gone into the trash.

Oh, and tonight's beer is an excellent spring seasonal from a brewery just down the road from my airplane factory.

On either side of the lower cowl, you're supposed to attach a piece of rubber baffle seal material to bridge the gap between the cowl air intake lip and the metal baffles. These are the only two rubber pieces that are attached to the cowl instead of the baffles themselves. I first made some aluminum backing strips to fasten the rubber to the cowl. Note the special shape of the nearest one, which is necessary to preserve proper edge distance on the left inlet (the one that's mostly taken up by the air filter).

Once again the angle drill is worth its weight in… something heavy and expensive. You can see in this photo that I drilled an extra hole on the inboard end of each attach strip, so I could put a screw on the "upright" portion. I found that helped the rubber seal stay in place a little better when installing the cowl.

Here's what one of these seal strips looks like when being test-fitted. Since the bottom cowl is installed from below, these strips have to pass up and over the metal baffles as you raise the cowl, which can be awkward. You want to start with an oversized piece and gradually cut it down until you find the balance point between too hard to install and not enough overlap with the metal baffles. I ended up with about 1/2" of overlap, which is similar to other RV's I've seen. These strips have also been a pain in the rear on every other RV I've ever taken the cowl off of, so I think I must have them sized about right.

I added a countersunk screw at the outboard corner on each side, the better to keep the rubber seals from folding up when installing the cowl. This was only possible thanks to the extended attach flanges I laid up a while back. The screw and tinnerman washer are hidden beneath the upper cowl when it's installed.

Here's how it looks at the inboard end:

The cowl seal overlaps and sits on top of the "ears" on the crankcase baffles (exaggerated here for clarity). You can sort of see the upper leg of the metal attach strip here too:

That's the last of the rubber baffle seals to be fitted! Everything from here onwards is assembly, at least as far as the baffles are concerned.

The plans tell you to permanently attach the mounting strips to the rubber seals with Pliobond. What they don't tell you is that this stuff is also the most evil, nasty, noxious, horrible-smelling gunk on the planet. Worse than Proseal even. I had to vacate the garage while it cured so I wouldn't get gassed.

The result, a couple days later:

I countersunk the cowl for #6 tinnerman washers and attached the seal strips with screws and nuts:

The baffles on the forward part of the crankcase, just behind the prop hub, are deceptively difficult to get shaped correctly. So, it should come as no surprise that the associated rubber seal strips are also hard to get just right. After much trial and error, I ended up making the seals out of nine separate pieces of material in order to get them to lay against the upper cowl without wrinkling. Also, pay particular attention to the "ears" at the front:

Those ears have nothing to do with directing airflow – instead, they are there so you can tuck the rubber seals inside the inner face of the spinner opening on the bottom cowl, to prevent the oncoming air from peeling them back and trying to turn them inside out. I'd seen this before on other RV's but never really comprehended what I was looking at until I was deep into the baffle process.

Here's what it looks like with the top cowl on:

I had an especially hard time figuring out how these seals were supposed to go, so I'll try to help out the next guy by posting a few more detail photos of this area. When you get to this part of the build, you'll know what you're looking at.

Segmenting helps the rubber follow the shape of the top cowl:

Adjacent pieces overlap from front to back to keep the air from getting underneath:

Tabs and carefully-cut angles help go around corners: