MPPalmer(at)aol.com
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 Posted: Wed Feb 11, 2009 10:39 am Post subject: Case closed on "the case of the missing fuel" |
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Hi All:
If I don't take ten minutes to write this now, I'll probably never get around to it.
A few months ago, I posted on this list server that we were mysteriously losing fuel in our Glasair. That, after 12 years of the Fuel Totalizer always being an accurate predictor of how much fuel remained in the tank, something suddenly changed and we were ending up short of fuel. Once, in flight!
I did two things to the plane that solved the problem. Not a great experiment, because I don't know which variable changed things. (One, the other, or both?)
I blew out the vent lines like I never have before. I disconnected the "cross" fitting in the middle rear of the wing (where the two wing tip vents connect in the GII and GIII vent topology). With the tanks 3/4 full (to keep air from one side of the wing from leaking to the other side), I blew air into each wing tip, one at a time. That not only blew air out the middle vent, but it also siphoned fuel along the way. A bit of a mess, but a good purge of any solid blockage.
Then, when I reconnected the fittings to the cross, I made a longer outboard vent tube. That's the one that sticks out the belly pan. Our old vent tube had slowly eroded (exhaust gas?) and was only about a two inch stub. I had noticed some staining around it, but hard to know if fuel. (We painted the bottom half of the plane a deep red and it's difficult to see 100LL blue stain on the red.) Now the vent tube protrudes four inches, as it used to.
One of those two things (or both) solved the problem. It's been a few months now, but the Totalizer is once again a reliable indicator of how much fuel remains in the tank.
I'm thinking it was the short vent line that was the culprit. I theorize that it had eroded to the point we weren't getting positive pressure in it anymore (it's in the dead air of the cowl scoop) and was actually in a lowish pressure area, siphoning fuel outboard in flight when the tanks were full.
Thanks for all the suggestions. I'm glad it wasn't a leak in the wing.
Mike Palmer <><
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