Gas tank vent or not?

[Bitshifter]

I am almost finished the center section and am ready to start the fuel tank. I have researched the plans and the archives here and I can't seem to find any information on venting the tank. The plans call for an un-vented cap but don't show any provision for a vent. Is this correct or am I missing something? I have noticed in pictures that some have installed a curved vent on the cap and some on the tank. I am currently planning on installing an un-vented cap, off set to the left side of the tank, and a vent at the center. Does anybody know why the plans call out for an un-vented tank or did I miss something? If I did please point me in the proper direction.
Thanks
Ed, Hatz Classic #154

http://www.edwinwhite.com/hatz.html

[JBMoore]

All I can say is you need a vent.

Jeff Moore

[dougm]

Agreed. You need a vent.

You're right that the plans call for an unvented fuel cap, but in my mind, that has to be a mistake as nothing else on the plans allow for a vent. Besides, any Hatz I've seen has a vented fuel cap including Billy Dawson who built the first Classic (pic below) and the photos supplied by Makelan on their CD.

Not the best pic, but you can see the vented cap...

[alvinsager]

Hi,
I am thinking that the unvented cap is a better choice in which to weld a tube for a vent. I have used that arrangement for 20+ years on my Cygnet wit no problems. Sisler recommended soldering a fine screen over the end of the tube. I did so after swaging the end larger to have more area. Brass screen soldered easily and has lasted. My vent does not arc down to act as a rainwater trap and even though I never found water in my tank in 20 years of being tied down outside, I think that would be a good idea.
Al

[dougm]

I plan on buying something like this:
http://www.aircraftspruce.com/catalog/a ... cap180.php

[M Lightsey]

I used a forward facing tube in the cap similar to the picture above. Works fine, but if you fill the tank when it's cool and the plane sits in the sun and warms up, guess what? It pukes out the vent tube and runs off the center section right into the cockpit.

For future installations, I'll install a separate vent fitting and run a line to somewhere on the bottom.

One upside of the curved vent tubes however is that if you're fueling and put the cap on your engine eyebrow (no chain), get distracted and forget to reinstall the cap, it'll hook itself to the cowling and happily ride from Washington, Iowa to Iowa City, Iowa without falling off.

I doubt a smooth unvented cap could have done that.....

Mark