Fuel Tank Vents?

[SuperFly]

I am thinking of putting a small pipe bung in the top along the inboard edge of my fuel tanks to put in vents. Rather that have the vent in the cap which will cause fuel drain issues when the wings are full and folded. If the vent were at the inboard edge, it would be at the highest point while folded. My plan is to weld in a pipe bung, then weld the vent tube into an aluminum pipe bushing to thread into the bung. This way, is allows the tank cover to be installed with out having to mess around with the vent, and more importantly, it allows the vent to be easily removed for cleaning if a wasp were to make a mud nest in the vent.
I plan to be a regular wing folder, as I am going to fly this out of my front yard. It seems like it should work just fine. Any reasons I am missing that this may be a bad idea?

[danerazz]

If when the wings are NOT folded the fuel level is above the fuel vent hole in the tank, any heat expansion of the fuel will cause spillage. A port on the outboard AND inboard points of the the tank, then a vent tube running to the opposite and same side wing tips respectively (so they cross during routing) would work in pretty much all circumstances. I have thought about this a lot, and will probably just put the vents in the caps. If you wanted to add your inboard vents, then have caps on them when not folded and caps on the standard vents when folded that would alleviate the tank draining when folded thing.

Also, if you ran a vent inboard and outboard, then ran the line from the outboard port TO THE INBOARD PORT then BACK TO THE SAME WING WINGTIP (or at least outboard of the tank) you could avoid crossing the fuselage with vent. The vent to vent loop is necessary to break a siphon action.

[User GDS]

Something else to consider, when the wings are full of fuel they are heavy, so even if they don't leak fuel, when you're folding them they'll be a handful, I'd avoid it. I don't fold the wings for storage, but for performance reasons I don't carry the weight of full fuel; usually end up landing with about 7 gallons fuel on board. If you end up having to fold them when they are pretty full, a piece of tubing over the vent will stop the leaking. You can either clamp off the tubing or run it into an empty fuel container.

[Gil T]

Keep in mind you are going to have a great deal of weight added to the tail wheel if you have a successful method of keeping the tanks full with the wings folded. This means that you don't want to have to maneuver the airplane much if at all. That's a lot of stress on the tail wheel and I know that with a minimum amount of fuel it is still a job that must be done carefully. I have to fold my wings anytime I use the airplane. This just means that I have about 7 or 7 and a half gallons in them. It's possible to design a venting system that will work with fuel tanks but for me the KISS system works best. Good preflight planning, and accurate method of fueling (I have a fuel delivery system with a digital quantity indicator) and at the end of the day have about seven gallons left. If not, defuel as needed. Good luck.

Gil T

[SuperFly]

Yep, I had not considered the fuel dumping with expansion when the wings are not folded. Thats exactly why I posted the question. I knew a fresh set of eyes would expose the flaw in my plan. Thanks guys. I also had not thought much about the extra weight on the tailwheel, though that is something that I am going to have to deal with regardless. Id like to say that I will be able to plan the remaining fuel in the tanks when I put it away. But realistically, thats not gonna happen.

Perhaps I'll put a bit taller vent tubes on the caps, and make up risers to slip on the vent tubes if I do have to fold with an unusually higher amount of fuel than ideal.

Thanks again guys.

[danerazz]

Remember, the fuel in the tanks doesn't have to be higher than the OUTLET of the vent tube to spill, just has to cover the tank port then expand a little. If the expansion causes a positive pressure it will still leak, so a longer vent tube may not help.

[Familyflyer]

Just a thought. Build a dolly stand to set the tail on it high enought to keep the wings/ nose attitude level. A stand with big caster wheels that will roll on gravel. The wings will be easier to fold and the fuel will remain as normal no matter the level. I know that it pretty high, but even if you could get half way up with the tail, it would likely help. It would have to have a pretty big base to be stable though.

[SheepdogRD]

Just a thought. Build a dolly stand to set the tail on it high enought to keep the wings/ nose attitude level. A stand with big caster wheels that will roll on gravel. The wings will be easier to fold and the fuel will remain as normal no matter the level. I know that it pretty high, but even if you could get half way up with the tail, it would likely help. It would have to have a pretty big base to be stable though.

There's good information about tailwheel dollies in this recent thread: http://www.wingsforum.com/viewtopic.php?f=218&t=23034. Trilander Ted pointed out that his tailwheel dolly system -- which is on pavement -- works well because he triangulated the dolly with the main gear, so it's stable.

Here's where levyland wound up with his SS tailwheel transporter: http://www.wingsforum.com/viewtopic.php?f=218&t=23107.

[levyland]

I posted this on an earlier forum but the SS DOES NOT require a separate fuel vent from the supplied venting gas caps. I am routinely folding my wings with full fuel and there is NO ISSUE with spilling fuel. I believe it has to due with how much higher the wing is SS is, and the angle of the fuselage than the Highlander. There are several issues as it relates to ground handling with the wing folded and the aft loaded weight that I address here http://www.wingsforum.com/viewtopic.php?f=218&t=23107. Essentially 180 LBS of moment on the tail wheel tire and strut is too much and needs to be blocked when being stored. I attached pictures of how I addressed that. Now that I have been folding for a while I would recommend buying an inexpensive floor jack and making wooden uprights so it would be easier to jack it up. Also my tail wheel transporter works like a charm on concrete. If you were operating off concrete you would need larger tube type tires. How that helps Cheers John