I think everyone knows to not rely on fuel gauges as the sole source of your true fuel state. In GA aircraft that can't be more true. GA fuel gauges are notoriously worthless. I have always dipped my tanks with a dowel I personally calibrated. So, I began the process of emptying the tanks in my Luscombe so I could refill in increments and calibrate a dip stick. Nowhere is it written in the 5 page ? operating handbook ( certified in the late 1930s ) in what attitude the fuel gauges are calibrated. I assumed it is level flight. But it is on the deck with the tail dragging is where you decide whether or not to fly. So how off are the 1940s mechanical fuel gages on the deck versus level flight? Frustratingly, very. The right tank was bouncing on empty in flight and solidly on empty on the deck. A condition I had planned to facilitate so I could drain the tank. But then saintly Mrs Wink decided we should fly the other day. Not wanting to put more gas in the tank I intended to drain, I thought I'd put some insurance in the left tank for a 30-60 minute flight. Left tank was reading less than 1/4 tank on the deck. 12.5 gal tank, I am guessing there is about 3 gal in the tank. Cruise is about 4.5-5 gph. Pattern work and you are over 6 gph. So I decided to put 6 gal in the left tank giving me a known metered amount of 6 gal and probably about 9 gal in the 12.5 gal tank. At 5 gal dispensed and at nearly full flow rate I get major spill over. Stinky ugly mess! The filler is too narrow to see in and you can't hear or feel the tank filling up like I could my C-170. I now know that the fuel gauges, on the deck, read approximately 3 gallons low. That is a 25% error, but fortunately resulting in more gas on hand than indicated. Needless to say I am very eager to drain and stick the tanks. Many more contemporary planes have commercially available dip sticks, but for the most accurate results, make your own for your aircraft.
Right tank gauge. Has run quite a while on the deck in this condition. Don't know how much will drain out.
