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MPPalmer(at)aol.com
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 Posted: Tue Jul 08, 2008 12:08 am Post subject: The report (so far) on the "Case of the missing fuel" |
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Just got back from the hanger. (It's past midnight. Too hot to work in the hangar during the day in Phoenix.) Here's what I've done so far.
I ran the electric fuel pump off the header tank for about 15 minutes. I rotated the prop thru (backward) slowly, two rotations, listening for any change in pump frequency. I figured, by rotating the prop, I would be moving the diaphragm on the fuel pump through its various positions on the cam. If I found a place where the diaphragm was leaking, I would hear it. Also, I would be able to see the fuel level change on the header tank. (We have a sight gage.) So far, nothing. No leak at the fuel pump overflow. No fuel smell in the oil. No change in header fuel level.
I'll plan to do the test again tomorrow, maybe more exhaustively by clocking the prop at 8 points twice, and letting it sit there for a minute or two.
I disconnected the vents at the center section of the fuse. So far, no obstructions. But, to be totally thorough, I'm gonna have to pull the wing tips and disconnect the center section runners and blow them down from there. (That should be a lot of fun.)
We have a carburetor. I'm hard pressed to imagine we could be blowing a few gallons out of it, but I suppose if the needle valve sticks in flight, it could happen. You would think I would notice the mixture going super rich in flight and/or massive staining on the cowl (plus fumes in the cockpit) if the float stuck, but I'll pull the cowl and look around. It was recently overhauled and shouldn't be sticking, but ...
I can't believe that 100LL has changed, but since I'm running out of ideas, has anyone heard if 100LL is evaporating more than it used to?
Has anyone ever had a Flowscan transducer miss pulses? Ours is located downstream of the electric fuel pump, so it should be getting semi-filtered fuel. But it's 13 years old, with almost 3000 hours on it. Maybe the ball has worn out and fuel slips by uncounted?
We had a 5 angle valve job done on the cylinders a year ago... I suppose we could simply be burning more gas with an errant transducer not reporting it. But then we should have noticed the discrepancy in fuel used starting last year and it doesn't seem this has been a problem until the past few months.
I haven't yet broached the idea of fuel leaking in the wing.... can you lose a few gallons that way without smelling it in the fuselage?
Mike Palmer <><
**************
Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.
(http://autos.aol.com/used?ncid=aolaut00050000000007) [quote][b]
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bobf(at)feldtman.com
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| Posted: Tue Jul 08, 2008 2:48 am Post subject: The report (so far) on the "Case of the missing fuel" |
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leaking in the wing you will smell it. my right fuel tank vent tubing came off (broke) at the coupling and fuel was sloshing out the vent when taxiing and the tank was topped off full. the smell was very evident. fixed easily by identifying the problem (thanks to this list and suggestion to look) - bobf
glastar
On 7/8/08, MPPalmer(at)aol.com (MPPalmer(at)aol.com) <MPPalmer(at)aol.com (MPPalmer(at)aol.com)> wrote:[quote] Just got back from the hanger. (It's past midnight. Too hot to work in the hangar during the day in Phoenix.) Here's what I've done so far.
I ran the electric fuel pump off the header tank for about 15 minutes. I rotated the prop thru (backward) slowly, two rotations, listening for any change in pump frequency. I figured, by rotating the prop, I would be moving the diaphragm on the fuel pump through its various positions on the cam. If I found a place where the diaphragm was leaking, I would hear it. Also, I would be able to see the fuel level change on the header tank. (We have a sight gage.) So far, nothing. No leak at the fuel pump overflow. No fuel smell in the oil. No change in header fuel level.
I'll plan to do the test again tomorrow, maybe more exhaustively by clocking the prop at 8 points twice, and letting it sit there for a minute or two.
I disconnected the vents at the center section of the fuse. So far, no obstructions. But, to be totally thorough, I'm gonna have to pull the wing tips and disconnect the center section runners and blow them down from there. (That should be a lot of fun.)
We have a carburetor. I'm hard pressed to imagine we could be blowing a few gallons out of it, but I suppose if the needle valve sticks in flight, it could happen. You would think I would notice the mixture going super rich in flight and/or massive staining on the cowl (plus fumes in the cockpit) if the float stuck, but I'll pull the cowl and look around. It was recently overhauled and shouldn't be sticking, but ...
I can't believe that 100LL has changed, but since I'm running out of ideas, has anyone heard if 100LL is evaporating more than it used to?
Has anyone ever had a Flowscan transducer miss pulses? Ours is located downstream of the electric fuel pump, so it should be getting semi-filtered fuel. But it's 13 years old, with almost 3000 hours on it. Maybe the ball has worn out and fuel slips by uncounted?
We had a 5 angle valve job done on the cylinders a year ago... I suppose we could simply be burning more gas with an errant transducer not reporting it. But then we should have noticed the discrepancy in fuel used starting last year and it doesn't seem this has been a problem until the past few months.
I haven't yet broached the idea of fuel leaking in the wing.... can you lose a few gallons that way without smelling it in the fuselage?
Mike Palmer <><
**************
Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.
(http://autos.aol.com/used?ncid=aolaut00050000000007) [b]
| | - The Matronics Glasair-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Glasair-List |
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douglas.dodson(at)pobox.c
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| Posted: Tue Jul 08, 2008 5:44 am Post subject: The report (so far) on the "Case of the missing fuel" |
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Mike,
You only mention in this last message that the fuel computer was in error. Have you confirmed the fuel loss with direct measurements of the fuel quantity?
You can accurately measure your fuel burn rate by filling one tank, climbing up to a cruise altitude on another tank, switching to the full tank and fly with a properly leaned mixture at a fixed power setting for an hour. Land on the other tank then re-fill. You can do the same thing but don’t use one tank or the other to see if fuel is leaving one tank or the other in flight.
- Doug
--
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Craymondw(at)aol.com
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| Posted: Tue Jul 08, 2008 6:25 am Post subject: The report (so far) on the "Case of the missing fuel" |
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A Glasair 2 owner in Fort Walton Beach Fla. developed a leak in his spar. He found it by noticing blue dye around a tie down hole. He didn't smell fumes because the fuel never got past the wing rib. I would try a fuel tank pressure test to see if it holds pressure.
Also, I once had a float needle not seal.
Gas prices getting you down? Search AOL Autos for fuel-efficient used cars.
| | - The Matronics Glasair-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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