I ordered my fuel site gages from Vance Atkinson in 1998. It's September 2010 now and I'm just getting around to installing them. It seems that everyone orders them around Chapter 5 so they can carve the site gage depressions correctly. (Reference Chapter 5, Step 3, Contouring the Insides.) Then they go back into the box until after the strakes are built. I waited even longer than that. I waited until the entire airframe was completely built so that the beatin' and bangin' of buildin' didn't scratch or tear up the site gages. I followed Vance's installation instructions to the letter except for one item.
I installed the gages while the plane was upside down on jacks. This way, I could stand up inside the plane instead of having to crouch and contort into the rear seats. So, please note --> All of the following pictures are upside down because the plane is upside down.
1. Mark the Pieces
The fuel site gages come in two pieces -- the white bases that get floxed to fuselage and the clear bubbles that get floxed over the bases. When you receive the gages from Vance, the bubbles are matched to their bases. It's a great idea to mark which bubble goes with which base and to mark which end of the bubble goes with which end of the base. If you get the parts mixed up or flip a bubble 180 degrees by mistake, it may be possible that bubbles may not line up exactly with the bases or the two tiny fill and vent holes drilled into the bases.
2. Determine Precisely Where the Bottoms of the Fuel Tanks Are
Before you flox the base plates to the fuselage, you must know where the bottom of the fuel tank (the inside skin) is located. Each base plate has two small holes drilled into it. The bottom hole allows fuel to flow in and out of the site gage. The top hole allows the air to vent in and out. To get the most accurate fuel level reading when it matters the most (like when you're about to run out of gas from that tank), the base must be positioned with the bottom hole as close to the bottom of the fuel tank as you dare. Don't place it too high or the gage will indicate empty before the fuel tank is empty. Don't place it too low or the hole you drill later in Step 4 will miss the tank completely. The gage will not work properly if the bottom hole is not exposed to the fuel tank. I highly recommend that you place a mark on the depression just after you've installed the strake bottom and before you flox on the strake top. Simply place a bright light in the fuel tank and point it at the depression. You will clearly see where the inside strake skin crosses the depression area. If you forget to do this in Chapter 21, all hope is not lost. You can still shine a light through the gas cap opening (NO FUEL, please!) and get the same results. You can see my mark and the two base holes in the picture in the next step.
3. Flox the Base onto the Fuselage Depression
The first step is to flox the white base to the fuselage. Before doing anything, I used masking tape and covered the area in the middle of the base that's seen once the bubble is installed. The tape keeps that area pristine and free of scratches and flox smears. Per Vance's instructions I sanded a 3/8th inch border on the front and back sides of the bases. I spread the flox bead around the back side of the base and pressed the base into the fuselage depression. I made sure the bottom hole was located properly to my strake mark. Vance recommends using dabs of bondo to hold the base in place while the flox cures. I used duct tape instead -- one strip to keep the base from sliding down and a second strip to hold the base to the fuselage. Whatever you do, DO NOT BEND the base by pressing it into the fuselage!! Let the flox fill the gaps. The base must remain as flat as possible to avoid gaps when the bubble gets floxed to the base.
4. Drill the Fill and Vent Holes into the Strakes
I removed the duct tape and masking tape after the flox had cured. Per Vance's instructions, I took a 1/16th inch drill bit and drilled through the fill and vent holes into the fuel tank. I held a vacuum cleaner hose near the drill bit to suck up debris as the holes were being drilled. It feels totally wrong to purposely drill into the fuel tanks. Do not forget to drill these holes. If you don't the gages will not work.
5. Flox the Bubble onto the Base
The bubbles are floxed onto the bases first, then secured later with 2 plies of BID. I made a template to match the outline of the bubble. I covered the outside of the bubble with masking tape to protect it from scratches and flox smears. But like I've done in other installations with the canopy, I put on five layers of tape and trimmed away the extra. The thickness forms a hard edge that helps later when positioning the 2 plies of BID. I sanded a 3/8th inch border on the front and back sides of the bubble. I spread the flox bead around the back side of the bubble. I took one last look at the inside of the bubble and carefully, so very carefully wiped away any dust, debris, and fingerprints. I also verified that the base was just as clean and pristine. I pressed the bubble onto the base and made sure the fill and vent holes were not covered by the bubble or by flox. You want to use as much flox as you can to ensure a great seal between the bubble and the base. However, you don't want to use too much either. You don't want the flox to ooze into the bubble or into the holes. The squeeze is easy to monitor as you press the bubble onto the base because you're staring at the flox. :-) If it looks like the flox will ooze into the bubble, you can back out by removing the bubble and trying again. I used strips of duct tape to hold the bubble in place while the flox cured.
5. Apply 2-BID Layups over the Bubble
I removed the duct tape after the flox had cured. Per Vance's instruction, I spread more wet flox around the perimeter to ensure I had good seals around the base and bubble. I like to use masking tape to avoid smearing flox where it doesn't belong. I wet out 2 plies of BID onto plastic and used the template to mark the opening where the glass bubble would be. I used the sharpest scissors I had to get a very sharp edge and to keep fibers from unraveling. I trimmed the overlay to size. I also used the template to cut out a peel ply overlay. I positioned the 2-BID overlay over the glass bubble and onto the surrounding flox and fuselage surfaces. I used the tip of the paint brush to carefully butt the 2-BID overlay against the masking tape that was covering the bubble. This always works like a charm. I finished by applying the peel ply overlay.
6. The Finished Product
Here's the finished fuel site gage. I should say "almost finished" because I will apply some micro to the BID and cosmetically treat those areas.