CHAPTER 63 – Plumbing Fuel and Brakes

So I discovered that it would be easier to do the forward plumbing if I removed the fuel tanks.  As it turned out, this was a good idea because it prompted me to pressure test them again.  But first, the plumbing.  I had pre-marked the locations long ago, so it was mostly a matter of drilling the location and routing the tube.  The brakes used a bulkhead fitting and the first thing I did was route the line from the fitting down the leg and to the brake.  You can see the loop at the brake that allows the unit to move in and out in operation, and the electrical tape that holds the line to the leg; there’s a piece of split tubing spacing the line slightly away from the leg.  The first picture also shows the main fuel line and the snap plug (just behind the tank mount bracket) for the fuel vent line.

Skipping to the fourth picture, you can see how the fuel lines were routed.  The plans were vague about the fuel control mount and the parts didn’t match either the RV-6A drawings or the RV-7 preview plans, but I made it work out.  I left a little gape between the console and the seat pans that I will fill with leftover rubber channel from the wing fairings.  I blocked one inlet, leaving two at 90 degrees and the bottom connection for the output side.  I also turned the handle so it would read correctly using the handle as the pointer (I’ll probably file off the little pointer to avoid confusion).

Continuing with the brakes, I mounted the reservoir using washers to space it from the firewall (due to the top angle) and plumbed the nylon lines and flexible hoses.  I had removed the battery box to make the hole for the nose gear bolt; now I replaced it so I could route the right aluminum brake line over the box.  It will be held by clamps secured by the battery box bolts and also by a clamp and bolt at the lower longeron; similarly, the left side also has a clamp at the lower longeron. The vent lines were also routed as per the plans though I secured them at the top longeron with a clamp and bolt and ran them inboard of the bulkhead flanges to keep them from interfering with the rudder cables.  I then placed the tanks on the wings to measure and fabricate the fuel fittings and also the tank bracket slot and nutplate fitting.

While I had the tanks off, I decided to pressure test them again and found that I had leaks in both of them.  In the right tank, it was just a pinhole leak and I also found that I had failed to tighten the screws after removing the bulkhead to check the fuel pickup attachment (there was an AD regarding rotation of this fitting).  The left side turned out to have a large leak on the outboard end where the leading edge of the rib met the skin.  Proseal fixed the leaks, once I had tightened the screws on the sender bulkhead.  I mentioned the method I had used a long time ago, but this time I have pictures.  The pump is a beer keg pump with the connection end clamped to aluminum tube and a flare fitting that goes to the vent fitting.  The fuel pickup fitting has a balloon placed over it and tightly wrapped with a rubber band (I also use a little Fuel Lube).  The filler caps are taped over (they are not perfectly airtight).  Air is pumped in until the balloon inflates; it prevents you from over inflating the tank and bulging the skins.  When the balloon stays up overnight, the tank is leak free.

I used the same method to test my pitot system from the wing/fuselage connection out to the tube (check out the last two pictures).  It turned out I had forgotten to tighten one of the connections within the mount and it took a lot of swearing and blind work with the wrenches before I finally got the balloon to stay up.  Seriously, it took about two hours to verify four connections (counting the one at the pump), but I had just seen a friend go through this on a nearly completed system during IFR certification and I think it’s better to do it now than while you are paying someone big bucks to certify your system.