Wednesday, November 3, 2010

The upper firewall

The RV-12 has a somewhat abnormal (at least in my experience) firewall. Rather than being one flat piece, it has a shelf in the middle of it. The engine mounts will be offset to account for that, which is pretty odd too. I'm not sure if all Rotax 912 powered airplanes exhibit the same (or something similar) trait or not. If they were, it would imply that it is a requirement based on the shape of the engine. In any event, there are two vertical firewall surfaces and the task of the day was to install the second.

As with just about everything else in the fuselage kit, the firewall wears nutplates like Charlie Allnut wore leeches when he was pulling the African Queen through the river. Nothing gets done without adding more of the parasitic little buggers. In the case of the upper firewall, there were eight to be installed, and they required those odd little blind rivets that have caused me so much trouble in the past.

The problem that I've had with those rivets is that the mandrel will break off in the rivet puller roughly twenty percent of the time. I used to have to get out the Dremel tool and a cutting disk to cut the mandrel off as close to flush with the top of the rivet as possible, and then file away the rest manually with a small file. And we all know how I feel about doing manually. Anyway, I just recently learned a better, easier way: I can just tap the mandrel back through the rivet in the other direction. They come out easy-peasy that way. Which, I firmly believe, is why I was able to pull sixteen of those little buggers without breaking a single one.


The upper firewall has a lower flange that slides underneath the horizontal shelf. You have to put some sealant between the layers before you install it; I think it's intended to make an air-tight seal to keep engine compartment fumes from leaking into the cockpit. The lower firewall had the same thing at the flange where it meets the shelf, and I remember it as being a messy job that resulted in a bunch of my clecos being covered in goopy, sticky sealant. This time around, I ran a thin bead of sealant back on the flange back behind the row of rivet holes so the clecos wouldn't get any goop on them. I think I got just as good of a seal, but with much less mess.

This is an antenna shelf. I really like this idea. The antennas for the Garmin 396 in my RV-6 sit on the glare shield under the canopy. Fiberglass is transparent to these antennas, so there's no reason that they need to sit out in the open like that. On the RV-12, both the GPS and XM (XM satellite service is required for receiving NEXRAD radar data) antennas will live out here with the engine.

It looks more like an airplane every time I touch it these days!

A couple more cowl hinges needed to be installed. These are from the sets that I cut to fit last week.

There were two more nutplates to go. They sit on the top of the shelf. The rivets were those little blind rivets that no longer bother me all that much. The had to be installed from underneath the shelf, though, which was actually a spot of bother.

Naturally, I broke two of them. And, being under the shelf, it was hard to get the mandrels pushed out.

It's always something with those little bastards.

With the firewall essentially done, Van's wants me to seal it around the perimeter with "firewall sealant." Nothing matching that description came with the kit, and no part number is provided. It's for things like this that I donate more than the requested amount for the web site every year. A few minutes of research there was enough to find out that other builders had contacted Van's to get an idea of what was supposed to be used.

The answer was that I needed something called Flamemaster CS1900. No problemo, available at Van's for the princely sum of $42 for a 3.5 ounce tube, including shipping. The "includes shipping" thing is nice; normally it's frustratingly impossible to know what they're going to end up charging for that. Google is my friend, though. I found it here for $16.99 for a 6 oz. tube. Shipping (which their site was able to tell me right up front) was $8.95.

There are a few parts that I can prep while waiting for the sealant, and there's still a recalcitrant autopilot to work on, so the four day delay isn't quite as bad as it might have been. I hate to miss a whole weekend of work while waiting for it, though. I think this is why they tell you to read ahead in the plans....

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