The World's Most Reliable Fuel Gauge
by Ted Teach
Ever since I first started the restoration of N4122, I have been awed by
the simplicity of Al Mooney’s airplane. Not all of it, i.e. the
retractable landing gear, the trim system etc., but such as utility wheels,
brakes, tires, the gear warning system, structure (no engine mount) and the fuel
gage. I would be surprised if you other “Miters” haven’t also
bragged about the “world's most reliable fuel gauge” as I have.
Last spring (2006) I flew the Mite to Pilot Country Airport, near Lakeland, visited a friend for several days, and drove back and forth the 40 some miles to Sun & Fun. As I was leaving to returning home, some one was looking at the Mite, commented on the simple fuel gage, and again I gave my standard “world’s most reliable fuel gage” comment. You know, how can it fail? A piece of plastic tube pushed over two opposing barbed fittings, and then surrounded by a metal trough.
I departed for home with a full fuel tank and climbed out moderately to about 1000 ft., leveled off and began to smell gasoline fumes. I thought first I had not replaced the fuel cap and somehow fuel was blowing out and getting into the fuselage. I then decided to investigate further when I noticed my back getting wet. Was I sweating this out or what? My back became wetter and I decided to turn back to land. I lowered the nose and then realized my back was soaking wet with gasoline. I turned off the electrical system, then the mags and made a dead stick landing downwind and coasted back to the pumps.
I found that the plastic tube had shrunk over time and when it “let go” the top end had pulled completely off the upper fitting and was actually over ½ inch from the end of the fitting. Apparently, the total shrinkage was more than 1 inch. I installed another hardware tube to get me home and then installed tubing made for such applications.
It could have been much worse. It could have happened later in the flight with no near place to land. The tube could have pulled away at the bottom end of the gauge and the whole tank could have emptied into the cabin. It could have caught fire from static or come spark from the electrical system: I was lucky.
I suggest all Miters check the fuel gauge plastic tube material to be assured it is not tending to foreshorten, and if so replace it with tubing made for fuel.
Futher notes: Ted says the tubing he used came from Aircraft Spruce. Their catalog shows a tubing suitable for gasoline in experimental aircraft (it's not certified). The best replacement tubing seems to be Lexan, 1/4" diameter, about 2 feet in length. It is stiffer that other plastics but stronger. Cut it a little long because you can bend it so it will slip into the little metal fitting (elbow) coming out of the tank. You can use little rubber O-rings underneath the brass nuts to make a good, tight seal.