[mcencula]

While researching some other NACA papers, I ran across NACA-TN-394, The prevention of ice formation on gasoline tank vents. Interestingly enough, the paper makes recommendations which are contrary to the design recommended for RVs.

1. Larger tubes are better for the prevention of ice formation blocking the tubes. I believe this thinking could logically be extended to conclude that a screen over the inlet is far more prone to icing over than an open tube.
2. If you use a tube which projects 90 degrees into the airstream which has the end cut at 45 degrees, it's better for the prevention of ice formation to orient the tube so the open end is facing downstream rather than upstream.
3. The ideal design is a large tube (they recommended 3/4") shaped as an L with the open end pointed downstream. It resulted in a very acceptable tank pressure and was immune to icing.

Note that I'm not making any recommendations that anyone go changing anything based on this post; however, I found it quite an interesting read.

 

[terrye]

Interesting NACA TN 394 reference. I see this was published in 1931. NACA did some further research in the late 1940s on submerged fuel vents in icing conditions contained in the following papers

NACA TN 1789
NACA RM E8A27B
NACA RM E8B05A
NACA RM E8C05

See http://www.vansairforce.com/community/showthread.php?t=54167&highlight=fuel+vent&page=6

Post #57

I did some further research on fuel vents and wrote an article for Kitplanes. This should be published in the next few months.

I concluded that many aircraft use a forward facing or 45 degree cut tube vent. Those that are approved for known ice have a heater element wrapped around these type of vents. Other aircraft that are approved for known ice use one of three varieties of submerged vents. Some aircraft have both a heated 45 degree vent and a submerged vent teed together.

 

[rvbuilder2002]

While researching some other NACA papers, I ran across NACA-TN-394, The prevention of ice formation on gasoline tank vents. Interestingly enough, the paper makes recommendations which are contrary to the design recommended for RVs.

Not all that surprising since RV's are specifically promoted by Van's as not designed for IFR (obviously the reason they are also supplied with a pitot tube that would be supseptable to ice buid-up).