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Fuel coming from header tank vent.
Fuel coming out of header tank vent…..
I have this vent that comes out at the left wing. It is routed to a 2 quart header tank at the firewall.
The vent is normally covered with a cover. The builder drilled two small holes in the wing skin to account for atmospheric pressure since it is covered.
Pretty much every flight, fuel or at least some white frosty vapor is on my wing skin from this vent.
I seem to be using anywhere from 7-8 gallons an hour. My engine is a 0-200 with about 24 hours on it since a complete overhaul. Just had it inspected 12 hours ago.
This is Bill Bears build. He seemed to be fairly active on here. I’d sure like to talk with any of you that may have known him and this build.
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IMG_3959.jpeg, 2 MB
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Replies to This Discussion
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Permalink Reply by Matt Pope
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Yikes, it sounds like you're losing almost half your fuel out the vent. The simplest fix would be to extend the vent upward and bend it so the opening faces into the slipstream, just like the fuel cap vents. Right now it's sitting there in the low pressure region over the wing at right angles to the slipstream - the perfect setup for a vacuum to suck fuel out of the header tank.
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Permalink Reply by Matthew Bradbury
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I don’t understand how that happens though since it has a cover. Shouldn’t there be zero airflow flow over the top of the vent? Maybe those two holes that are drilled in front and behind it are allowing the air to come in there?
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On second look at the pictures, I see that the vent hose itself was covered during flight and you removed the cover for the picture, but still, that just means the actual vent is those two holes, not the end of the tubing. Venting it to holes in the wing skin will create a vacuum during flight because fast moving air is at lower pressure than the fuel in the tank. It's the same physics that makes a carburettor work - when air flows faster, its pressure drops, which sucks fuel into the engine.
With the vent barely above the level of the wing tanks, it would only require a small pressure differential to suck fuel out.
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Permalink Reply by Cristian Ernesto de Azevedo
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The tube above the fuel tank cap creates positive pressure in the tank.
The vent positioned above the wing profile creates negative pressure.
These two factors cause fuel to leak out of the vent. Sorry for my poor English.
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