fuel cap with directional vent

[joea]

I have a fuel cap for my main (fuselage) tank that has a curved vent on it. Doubt that its stock (know its not) and thus have a question.

This vent is curved to either face into the wind while flying or face aft. I have asked several people their opinion as to which direction it should face and still get differing ideas.

Some say that it should face forwards to get positive pressure in the fuel tank. Others say that if its facing forward that it could get a bug in it, stopping the venting of the tank.

Ideas?

[Jody Wittmeyer]

Forward would be my choice. Face it backwards and the tendency would be to act as a siphon, not allowing air into the tube and acting like a plugged vent. Murphy is always out there, but that is a mighty small hole for a bug to hit at 90 mph.

[Mnflyer]

Hi Joe I'm with Jody, facing aft can cause fuel to siphon out of the I've had it happen when the tank is topped off doubt it would happen with say 3/4 or 1/2 a tank. The chances of a bug blocking the vent are far more likely to happen on the ground when they can crawl around looking for a nice place to rest .

[Nathan K. Hammond]

Worse than fuel siphonning out (which will only happen at full tank or when going inverted.... JOE ) with the hole pointed aft, you could create a negative tank pressure. And that could create a problem as fuel levels get low.

nkh

[Ron Babos]

joea: Since the cap is not stock, ) I thought you US guys were by the book) it should face forward. If you don't like the bug thing, drill a small 1/32 hole just above the cap that also faces forward. Not likely bugs will close both prior to takeoff.
Ron

[Paul Agaliotis]

Joe,
I dont think it matters in your case. The Chief does not depend on a positive presure only a vent. The Waco has a tube and it is to be installed with the vent facing aft.
Paul

[Dusty]

Put a wing tank cap on facing aft and try to get it to drain sometime.

Do Wacos have a fuel pump? I don't see how negative pressure in a gravity-feed fuel tank could be a good thing.

[Paul Agaliotis]

No fuel pump on the Waco. Vent aft, must not be any negitive presure there.
Paul

[Captgrumps]

The vent tube faces forward, if you have one--most light airplanes take care of that with a vented cap--no tube...Joe, someone must have thought they had a better idea. Have had many airplanes with vent tubes facing forward and never had a "Bug" problem--just don't fly in icing conditions.
WACO's have gravity feed fuel systems unless someone has made a mod. As do older Stinsons, Travelairs, Stearmans and etc. Atleast they came that way.

Doug