On my RV-6A I have two fuel configurations one for races less than 500 miles and one for cruising which has 4 tanks. At the end of the season (last race Nov. 22) I removed the racing tips and installed the tip tanks and stock tips with the lights etc. (increases the wing span by 3 feet). After the change I fueled up all tanks and flew to Pine Bluff for an operational check of the entire system. Everything worked fine and each tank was used for approximately one half hour verifying the valves, fuel lines and tanks. When I returned to Drake Field in Fayetteville, Arkansas. I refilled all tanks. The fuel consumption was just over 10 gallons/hour which is normal under the conditions I was running it under.
Eleven days later the Avionics shop said that my repaired altimeter was back so I delivered the plane to them. When I started the engine three EI fuel gauge gross fuel level indicater lights were top end of the series green and the left tip tank was bottom of the series red and the digital display read "2". When I got to the shop I removed the cap and looked in the tank and saw fuel at a low level in the tank. I was sure I filled it but I did give that a lot of thought.
When I got back to the hangar I looked at the floor I saw what looked like old fluid marks In the locations that indicated a leak had occurred but not a big stream puddling leak. I looked at the under side of the wing at the inboard edge of the tip tank and I saw a single small sub-drip formation of blue fluid. At this point there was no question that there was a leak on the inboard side of the tank. When I removed the tip and the tank (involving around 100 screws, three large nuts on threaded internal support shafts, 17 wire terminations) I saw that the inboard wall/rib of the tank was dry and showed no leakage stains from any penetration or seam. I put my finger under the flexible hose fitting and it came back with a wet blue fluid (fuel). I remembered when I reattached the hose to the tank flare fitting I had the wrench on the hose coupling nut but I had a little trouble keeping it off of the fitting nipple wrench flats which are the same size (11/16") and I probably turned it when I was tightening the coupling nut on the tank fitting. The problem is that this is the loosening direction for the hose fitting assembly (nipple out of the collar threads) on the end of the hose itself.
OK now I knew where the leak was and my plan was to tighten the assembly with two wrenches, add fuel and test for leaks. I did that and it leaked significantly more fuel at the hose fitting than when the tank contained very little fuel. It was obvious to me that if you break that seal between the hose rubber and the fitting nipple you cannot easily fix it by retightening the fitting assembly.
I brought the hose home cut off part of the service loop to get a new termination surface where the cutter/wedge ring could do its work to spread the rubber and seal against the nipple, etc. Even clamping the hose in a vise and holding the collar both rotationally and longitudinally to tighten the assembly on the hose and prevent hose pushout per the instructions in the Aircraft Spruce catalog, this is an awkward task. The fittings are Aeroquip 816 and the hose is steel jacketed "601". I have not been able to leak test this hose yet.
Hope this warning makes someone else a little more careful. Had I taken off knowing the last time I put the plane away I had filled all of the tanks and if I didn't have the EI gauges with the indicater lights and the individual digital readout for each tank I would have had one empty tank. It is common for 4 tank installations like mine to run the outboard tanks into the inboard tanks with no gauge for the outboard tanks.
Bob Axsom
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