November « 2007 « Matt's RV-7 Project

Archive for November, 2007

Firewall passthrough

Sunday, November 4th, 2007

I used my Greenlee punch to put a 1 1/8" hole in the upper starboard corner of the firewall:

…through which I then installed a firewall passthrough fitting from SafeAir. Read this article from Bob Nuckolls for the background on why you'd want to bring wires through the firewall in this way. I also squirted some Biotherm firestop sealant between the fitting and the firewall, the better to keep fumes out.

The fitting has a nice radius on the aft side, so it won't chafe my wires. I'm planning to bring all the heavy electrical wires through here, and possibly the Lightspeed ignition wires as well if the routing works out. The small-signal stuff will all go through a separate passthrough, to prevent inductively coupling noise from the power/ignition wires into the sensor leads.

There's a different and somewhat similar stainless firewall penetration kit sold by EPM-AV (whose site is unreachable at the time of this writing) which I actually bought before I decided to use the SafeAir kit instead. Here you can see that the EPM fitting is made of rolled and welded stainless sheet, instead of being a one-piece spun part like SafeAir has.

Call me crazy, but I just don't like the idea of having sharp edges near my wires. Add to this the fact that the SafeAir kit is more complete, uses a hole size that I already have a punch for, and is slightly cheaper, and I know which one is my favorite.

Posted in Firewall Forward |

Finished fuel pump plumbing

Sunday, November 4th, 2007

I ordered my fuel valve with built-in banjo fittings, with the idea that they would make it easier to route the fuel plumbing within the confines of the selector valve enclosure. Sure enough, it was very helpful to be able to make small adjustments to the angle of of the input lines. After I got everything lined up, I tightened the banjo fittings and safety-wired them in place. Banjo fittings will only pass fuel when the silver nut thing is rotated to a certain orientation relative to the flare fitting, so you don't want them to move around on their own.

Since the edges of the fuel pump mounting plate will be slightly visible where the carpet meets the spar, I decided to paint it to match the rest of the interior. This of course involved removing all the components, which I was going to do anyway. I also put a fresh coat of paint on the selector valve mounting plate, since it was a little bit dinged up. While the paint was drying, I blew out all the fuel lines and inspected the flares for FOD. Finally, I put everything back together and tightened each and every fitting.

I put fuel lube on the threads of the flare fittings, but not on the actual flare itself. You never put anything on the flare since the mating surfaces are designed to seal themselves mechanically, but I like to use something on the threads purely for anti-seize purposes. I also put a dab of torque seal on each fitting to remind myself that I did in fact tighten them, and also to be able to look for loose fittings during annual inspections.

I made a little cover for the selector valve shaft out of some dowel scrap, to keep it from poking me in the ribs when I'm crawling around inside the fuselage. I elected not to put the selector handle on just yet, since it's equally rib-pokey.

Posted in Fuselage |