Bill:" Is it because the suction affecting the right tank, through the cracked flange, is more than the fuel pump's suction can overcome?"
Hartmut: I think the suction of the pump was good enough as long as there was something to suck. When your left tank showed empty, the tank and the tanks interconnecting fuel lines where empty. The only remaining fuel was slowly pulled over into the right tank and held there due to the suction. Now not much was left for the pump to get. It received maybe a mix of air and fuel, thus showing only a slow sinking float. However. Question now is ho are you going to repair this crack? In our wing tanks the fittings are riveted from inside as is the filler neck. One needs to disassemble the whole tank to replace that neck. Maybe you can get away with stop drilling the crack and then sealing it with pro-seal... Hartmut To: [email protected] From: [email protected] Date: Mon, 14 Sep 2009 19:12:41 +0000 Subject: [ercoupe-tech] Fuel Siphoning Issue First, the particulars about my plane: 415-C, S/N 4313 9 gallon aluminum wing tanks, vented caps Skyport Rain-pruf nose tank guage, vented fuel pump is less than one year old, and has about 15 hours on it. Bear with me for the background. Went flying yesterday and my passenger noticed fuel siphoning around the cap on the right wing tank, about 15 minutes after takeoff. (The wing tanks were about 3/4 full, and the fuel level was the same on each side before takeoff.) I did a 180 to return to the airport and, as we were on our way there, I noticed that the gauge in the left wing tank had dropped to "0". Then, a few minutes later, the nose tank float gauge (a Skyport Rain-pruf version) started dropping: not drastically, but definitely noticeable. Shortly before we got back to the airport, the siphoning had stopped, but the left tank gauge still read "0". After we landed and were taxiing in, the nose tank float gauge gradually returned to the "Full" mark on the glass tube. We parked on the ramp and started investigating the problem. We noticed that the fuel levels in the wing tanks had stabilized and were again equal (but down to about 1/2 full after the flight and the fuel siphoning). I thought I had a cap-sealing problem on the right tank. Not so: the problem was the tank filler neck flange, which was cracked about a third of the way around its circumference. The fuel was siphoning in the small area between the outer edge of the cap gasket and the upper skin of the tanks. In flight, it looks like it's coming out from under the gasket. The crack isn't visible from the top: you need a mirror in the fuel filler hole, and a flashlight. OK, so that's the story. But I'm puzzled. I understand that the fuel will siphon because there is a pressure differential between the tanks, as a result of the crack. Low-pressure area and all that. But what I don't understand is, Why would the nose tank level drop? After all, there was still plenty of fuel in the right tank ("pulled" over there from the left tank by the pressure differential.) Is it because the suction affecting the right tank, through the cracked flange, is more than the fuel pump's suction can overcome? Thanks for listening! Bill T. _________________________________________________________________ Share your memories online with anyone you want. http://www.microsoft.com/middleeast/windows/windowslive/products/photos-share.aspx?tab=1
