I read Ken Krueger's (excellent) article about fuel system design in the recent issue of KitPlanes magazine last night. (Thank you, Ken!) The part about fuel vent lines not having a low spot that can trap moisture caught my attention.
Pretty sure my RV-7A has (standard design) vent lines with a low spot that could trap condensation and possibly freeze, creating a fuel starvation situation. It's getting to be the cold half of the year here in the upper Midwest, and I'm wondering how likely this condition is. (Not talking here about icing of the vent at the exterior of the aircraft, as one would encounter in flight in icing conditions.)
The fuel vent will (slowly) pass something less than 20 gallons of air every time the tank is emptied. Not convinced that that would clear accumulating moisture. Pretty sure a quick blast of air from the air hose would blow any accumulating moisture into the tank, if the cap were removed. It wouldn't take very much moisture to freeze an ice plug across the 1/4 inch vent line.
The low spot in the vent line is in the nominally heated cockpit, but I'm not comforted. The engine has to suck quite a bit of fuel before it makes much heat.
Any simple, reliable way to test vents as part of preflight on cold days?
One could make a temporary clear plastic hose vent line to see how much moisture accumulates in the vent line. ...maybe without even removing the aluminum vent line, just patch in a parallel temporary clear vent line to visually observe ....??
Does this sound like an issue to anyone else? Can anyone say with confidence that this is a non-issue?
- Roger
Pretty sure my RV-7A has (standard design) vent lines with a low spot that could trap condensation and possibly freeze, creating a fuel starvation situation. It's getting to be the cold half of the year here in the upper Midwest, and I'm wondering how likely this condition is. (Not talking here about icing of the vent at the exterior of the aircraft, as one would encounter in flight in icing conditions.)
The fuel vent will (slowly) pass something less than 20 gallons of air every time the tank is emptied. Not convinced that that would clear accumulating moisture. Pretty sure a quick blast of air from the air hose would blow any accumulating moisture into the tank, if the cap were removed. It wouldn't take very much moisture to freeze an ice plug across the 1/4 inch vent line.
The low spot in the vent line is in the nominally heated cockpit, but I'm not comforted. The engine has to suck quite a bit of fuel before it makes much heat.
Any simple, reliable way to test vents as part of preflight on cold days?
One could make a temporary clear plastic hose vent line to see how much moisture accumulates in the vent line. ...maybe without even removing the aluminum vent line, just patch in a parallel temporary clear vent line to visually observe ....??
Does this sound like an issue to anyone else? Can anyone say with confidence that this is a non-issue?
- Roger
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