Fuse Side Skins - Steps

Getting ever closer to finishing Section 29! Had the day off from work yesterday for my birthday (woo!) but didn't really work on the plane itself; instead I just cleaned up and organized around the shop a bit. Today, though, it's on. I started by finishing the rear air vents that Sarah had started the other day:

The L/R Rear Vent assemblies

Pretty straightforward part of the plans, just some match-drilling, deburring, and edge-finishing. I used a dremel with a small bit to smooth the inside groove of the track, shown here:

Smoothing (and slightly enlarging) the groove to smoothly fit the shaft of a AN525-10R7 screw, shown to the left.

After a quick shot of primer, they got riveted together and then put into place in the side skins, and that checks one more thing off the list that needs to be done for this chapter! Looking ahead, I needed to wait for Sarah to get home later so we could finish that one last forward fuse channel before continuing with the forward floors. So, why not skip ahead and start on mounting the steps in Section 30? I hear it's a pretty easy section, especially after the arduous and infamous Section 29. So, I grabbed the two plastic blocks used to secure the end of the step mounts and marked as shown in the plans with a silver sharpie:

Marked 3/8" from each side in the four corners for drilling

Drilled the two blocks #10 at each of the four corners

Next step was to deburr the steps themselves. I used the scotch brite wheel quite liberally around where the welds are to try and clean them up a bit... they were fairly rough-looking. A test-fit into the fuselage seemed to work well going through the main steel support bracket and into the newly-drilled plastic mounting blocks. The next thing to do is match-drill the four holes from the blocks into the baggage floor ribs, but I'll save that for later. Sarah got back home at this point and we went right into riveting the R lower forward fuse channel. This completes all the rivets for the forward side skins!

Now that the skin riveting is done, the next step will be to install the forward floor covers. This part has me a bit anxious, because the design of the RV10 is such that the forward floor covers are a permanent part of the structure-- they have to go in underneath the landing gear mounts and will basically "never" come back off again without some major work. Combined with that, there is a lot of discussion (almost as much as there is for different kinds of primers) about insulation: which one is best for soundproofing, thermal insulation, fire retardant, etc etc. You can spend months researching all this stuff and still not be happy with your decision, I believe. The biggest concern, of course, is using insulation that will not readily burn, and will not release loads of toxic smoke when exposed to flame.  I've read through all the forums, and had some good conversations at OSH with a number of builders who are very well versed on this topic, and I believe I have made an informed decision. Here's what I ended up doing.

A month or so ago I purchased a 120ft roll of 1/8" x 24" FiberFrax felt, which is a 2000deg ceramic insulation blanket and is commonly used on firewalls and other high-temperature fire-prone areas. I will be using a layer of this against the bottom skin, topped by some household-type acoustic/thermal insulation. The stuff is actually made out of recycled denim, which at first seemed a bit odd and made me a bit hesitant to use it but the more I read about it and the more I tested it (see below) the more I decided this was the right stuff for me. I also recently watched this video on the burn characteristics of different kinds of insulation:

After watching this video (although they didn't test the denim insulation in question) it kind of shot down my thoughts of using fiberglass insulation... it just melts away into a big hole! I wondered what the denim stuff would do, and I was quite happy with the results. I performed a similar test to what the guy did in the video above at 2:20.

Click here to watch the video

Mapp torch/penny burn test for UltraTouch Denim Insulation

As you can see, the insulation does carry a small flame for a few seconds after the torch is removed (slightly worse than the cellulose in the video above), but more importantly there is very little fume and it forms the same kind of char that helps to block the fire from spreading as quickly. Plus, this was at penny-melting temperatures when exposed to a direct torch flame... by the time this were to happen in the airplane it would have already burned through the firewall and a layer of fiberfrax. I hate to imagine that kind of scenario, but hey, anything is possible and you have to plan for it in your design. So, the insulation got cut and laid into place:

Layers of Fiberfrax (right) topped with UltraTouch acoustic/thermal insulation (left)

Once the insulation was laid up, I said one last goodbye to the forward floor area and clecoed the floor panels into place! That's it for tonight, first thing tomorrow I'll rivet these floor panels down and continue with finishing Section 29!