Good example of how water gets in your fuel tanks

Am I right in thinking that a lot of that is from ambient vapor in the air? And when the air warms up it would be absorbed into the air again? (Either way, is that enough to be dangerous if it drips into the fuel instead?)
 
I'm sure there was more condensation frozen on the upper skin inside the tanks. Even with full tanks there will be some exposed area for the moisture to condense.
Now, will it evaporate or drip in the fuel? Don't know, but I'd think some of it will end in the fuel, just by the sloshing action of the fuel in the tank.
 
Water vapor goes through deposition (frost) directly. Then warms up, melts, drips into tank, settles below the fuel. It usually never sublimates back to gas in a confined space, the vapor pressure is above the freezing temp and no airflow in the area to wick it away.
 
My first plane was a T-Craft, tied down outdoors, back when people still did that. Always found water in the gascolator, figured that was normal... until I learned to swap the cork-and-wire fuel gauge cap with a solid cap when leaving the plane.

Hangared nowadays, I found a couple of drops of water in the sample... once in over 10 years.
 
Common in winter with planes that park outdoors. The fuel likely has some ice crystals, too. Those precipitate out at the bottom of the tank and form ice. You can’t sump ice. The solution is to add isopropyl alcohol per aircraft manufacturer’s instructions, usually 1%. One 12oz bottle per 10 gallons.
 
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AV8R_87 said:
Found this under my fuel caps during pre-flight this morning. Temps in the single digits overnight.

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This is not water getting in, but water that was already in the tank. There is air in the tank. Air has moisture. When temperature drops, the relative humidity increases, and water will condense on cold surfaces. The top skin being surrounded by air is will be colder than the fuel. so it is not surpring that water condensed on the fuel cap and then froze.
 
sarangan said:
This is not water getting in, but water that was already in the tank.
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Yep. Moisture from the air condensing and freezing in the tanks. Probably helped by the high ambient pressure swings. And probably not evaporating when the temperatures go above freezing. Good time to shake the wings and sump well.

Baked Potato said:
Is this a no-go condition? What did you do?
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Since it was cold enough for a reindeer to have a gender identity crisis, I decided none of that was going to melt and cause a problem. Performed a long run-up to ensure no ice in the fuel lines and went flying. But will sump the tanks thoroughly once things warm up.
 
You guys do know that while ice is easy to see, the same condensation occurs whenever dewpoint supports it, right? That’s why we sump tanks. It happens inside the engine, too.
 
Fuel tanks have vents. As atmospheric pressure varies, air is drawn in and pushed out the vents. This provides ventilation providing new, damp air on a continuous basis.
 
Water sits nicely on the bottom waiting to be sumped. Ice crystals float around in suspension and can clog finger screens. When you detect that loss of power, carb heat won’t help. Sometimes the crystals find their way into the carb bowl where they thaw from engine heat. A few drops of water in the float bowl can cause issues, too.
 
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