Fuel Tank vent direction

[Graeme Bird]

I seem to recall seeing a thread like this but cant find it, excuse me if I am repeating.
My 20mm fuel vent pipe pops out of the bottom of my C42 at right angles to the air flow, surely its going to drag fuel vapour out of the tank isnt it?
I guess I could cut it at 45 deg facing the airflow, whats normally done? I know on my Rallye it used to face forward like a pitot pipe.

[Andrew Leak]

I think you answered your own question there! Yes you will draw off the vapour if the pipe points rearwards or at 90 degrees to airflow, mine does (rearwards) - I don't understand why your Rallye vent tube pointed forwards though, it must have pressurized the tank in flight?

[David Hardaker]

FWIW, our local Jodel D18 has a forward facing vent. Most vents I've seen face forward.
I recall that a restored Lysander finished up in the wrong place because of a fuel tank cap that wasn't vented at all (but was designed to be) That was because the gasket had become mis-aligned with the hole in the cap, causing a partial vacuum in the tank, and subsequent power loss.
Forced landing anyone ?

[Nigel Ramsay]

My Taylorcraft has a main tank with the ever reliable wire in a cork fuel gauge, gravity feed to carb, effectively a straight up vent. However, the wing tank has the traditional 90 degree bend in the vent pipe (in cap). I once made the mistake of leaving it to the refueller to replace the cap. He put it on with the vent facing backwards. On a long cross country to Cornwall, I turned on the wing tank (which drains into the main); nothing happened! I was forced into a precautionary landing at a farm strip and as soon as I landed the fuel started to flow! A little positive pressure helps either with or without a pump, but negative is a BAD thing!

I try never to change tanks over the Channel!